Philips 12-Lead Algorithm User manual

The Philips 12-Lead Algorithm

Physician’s Guide

Notice

About This Edition

Publication number M5000-91000

Edition 1

2003 Koninklijke Philips Electronics N.V. All rights are reserved.

Permission is granted to copy and distribute this document for educational purposes.

Warranty

Philips Medical Systems makes no warranty of any kind with regard to this material, including, but not limited to, the implied warranties or merchantability and fitness for a particular purpose.

Philips Medical Systems shall not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing, performance, or use of this material.

CAUTION

In the U.S., Federal Law restricts this product to sale on or by the order of a physician. Use of accessories other than those recommended by Philips may compromise product performance.

THIS PRODUCT NOT INTENDED FOR HOME USE.

Medical Device Directive

This algorithm is a software component used in many Philips Medical Systems medical devices. Consult the documentation supplied with your product for information about Medical Device Directive and other medical regulations.

Authorized EU-representative:

Philips Medizinsysteme Böblingen GmbH Hewlett Packard Str. 2 71034 Böblingen Germany

About This Guide

This Physician Guide explains how ECG signals are analyzed by the Philips 12Lead Algorithm.

NOTE No automated analysis is completely reliable. Computerized ECG analysis

should always be reviewed by a qualified physician.

Who Should Read This Guide?

This guide is intended for physicians who overread ECGs interpreted by the Philips 12-Lead Algorithm. It also may be of interest to other health care professionals who want to know more about ECG interpretation.

NOTE This Physician Guide describes features that may not be available on all Philips

Medical Systems equipment. Refer to the documentation supplied with your particular product to learn more about available features.

ii Philips 12-Lead Algorithm Physician Guide

About This Guide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

Who Should Read This Guide? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ii

The Philips 12-Lead Algorithm

Introduction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

The Philips 12-Lead Algorithm Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-2

Quality Monitor. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Reducing Artifact . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Common Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Differential Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-3

Using Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

Artifact Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-4

AC Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Frequency Response Filters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Baseline Wander Filter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-5

Waveform Recognition and Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6

Waveform Recognition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-6

Comprehensive Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Group Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Lead Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Atrial Rhythm Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Global Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-7

Axis Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8

Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8

Overall Severity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-8

Adult and Pediatric Rhythm Analysis

Cardiac Rhythm Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

Paced Rhythm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

Basic Cardiac Rhythm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-2

Ventricular Preexcitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

Premature Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-3

Pauses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Miscellaneous Arrhythmias. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Atrioventricular Conduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-4

Philips 12-Lead Algorithm Physician Guide iii

Table of Contents

Adult Morphology Analysis

Adult Morphology Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-1

Dextrocardia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2

Right Atrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2

Left Atrial Abnormality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2

Biatrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2

QRS Axis Deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-2

Ventricular Conduction Delays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3

Right Ventricular Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-3

Left Ventricular Hypertrophy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-4

Low Voltage and Chronic Obstructive Pulmonary Disease Pattern. . . . . . . . . . . . . . . . .3-5

Inferior Myocardial Infarction. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-5

Lateral Myocardial Infarction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-5

Anteroseptal and Anterior Myocardial Infarction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-6

Anterolateral and Extensive Anterior Myocardial Infarct . . . . . . . . . . . . . . . . . . . . . . . . .3-6

Posterior Myocardial Infarction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-6

ST Depression and Myocardial Ischemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-7

T Wave Abnormalities and Myocardial Ischemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-7

Repolarization Abnormalities and Myocardial Ischemia . . . . . . . . . . . . . . . . . . . . . . . . . .3-8

ST Elevation, Myocardial Injury, Pericarditis, and Early Repolarization . . . . . . . . . . . . . .3-8

Tall T Waves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3-8

QT Abnormalities, Electrolyte Disturbance, and Drug Effects . . . . . . . . . . . . . . . . . . . . .3-9

Pediatric Morphology Analysis

Pediatric Morphology Categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-1

Dextrocardia. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2

Right Atrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2

Left Atrial Abnormality. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2

Biatrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-2

QRS Axis Deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-3

Ventricular Conduction Delays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-6

Right Ventricular Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-7

Left Septal Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-7

Left Ventricular Hypertrophy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-7

Biventricular Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-8

Low Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-8

Q Wave Abnormality and Myocardial Infarct . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-9

ST Depression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-9

T Wave Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-9

Repolarization Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-9

ST Elevation, Pericarditis, and Early Repolarization . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-9

Tall T Waves. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-10

QT Abnormality and Electrolyte Disturbance. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-10

Congenital Heart Defects. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4-10

iv Philips 12-Lead Algorithm Physician Guide

Table of Contents

Reading the Printed ECG Report

Interpretive, Reason, and Severity Statements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-2

Severity Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

Basic Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-3

Patient ID Clinical Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-4

Patient ID Clinical Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-5

Patient ID Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-7

Patient ID Ethnicity Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-8

Institution Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-9

Configurable Clinical Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-10

ECG Order Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-11

Physician Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

Report Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-12

Calibration Information. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-13

Time Separator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15

Pacing Detection Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-15

Algorithm Version Number . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-17

Speed and Sensitivity Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

Device Identification Number. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-18

12-Lead ECG Report Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-19

Extended Measurements Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-26

Morphology Analysis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-27

Morphology Lead Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-28

Derived Transverse QRS Vector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-31

Frontal/Horizontal Plane Axis Parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

Global Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

Analysis Statement Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-32

Rhythm Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-33

Group Measurements. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-34

Group Flags. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-35

Global Rhythm Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-36

Rhythm Grouping of Beats . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-37

Ectopic Rhythm. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-37

Pacemaker. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-38

Rhythm Report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-40

Disclose Report. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5-43

Appendix A. Normal Measurement Values

Appendix B. Interpretive Statements (by Category)

Appendix C. Interpretive Statements (Alphabetical)

Philips 12-Lead Algorithm Physician Guide v

Introduction

Development of computer-assisted ECG analysis began in the 1960s. Initially used in research facilities, computer interpretation has developed into an accepted tool for physicians. Development of the adult ECG Criteria Program began in 1971 as a combined effort between engineers and a worldwide panel of cardiologists. At the core of ECG analysis is the ECG Criteria Language (ECL). ECL is a computer programming language that was developed specifically for the definition of electrocardiographic criteria, and was first introduced in

1978. The primary objective of ECL is to provide a method for ECG criteria to be expressed in a form meaningful to both a cardiologist and to computers. ECL describes ECG criteria using consistent terminology selected from a broad base of cardiologists as well as electrocardiography texts.

The Philips 12-Lead Algorithm provides an analysis of the amplitudes, durations, and morphologies of the ECG waveforms and the associated rhythm. ECG waveform analysis is based on standard criteria for interpretation of these parameters, calculations of the electrical axis, and the relationship between leads.

The Philips 12-Lead Algorithm

The algorithm is highly age and gender specific. Patient age and gender are used throughout the program to define normal limits for heart rate, axis deviation, time intervals, and voltage values for interpretation accuracy in tachycardia, bradycardia, prolongation or shortening of PR and QT intervals, hypertrophy, early repolarization, and myocardial infarct.

Adult criteria apply if the patient age entered is 16 years old or older, or if no age is specified. Pediatric criteria apply if the patient age entered is younger than 16 years of age.

A computer-interpreted ECG report is not intended to be a substitute for interpretation by a qualified physician. The interpreted ECG is a tool to assist the physician in making a clinical diagnosis in conjunction with the physician’s knowledge of the patient, the results of the physical examination, and other findings. The algorithm helps to identify problem areas for the physician and saves time for the physician or editing technician who may only need to add, delete, or modify a few statements.

1-1

The Philips 12-Lead Algorithm The Philips 12-Lead Algorithm Process

The Philips 12-Lead Algorithm Process

The Philips 12-Lead Algorithm produces precise and consistent ECG measurements that are used to provide interpretive statements. The process begins with the simultaneous acquisition of the twelve conventional leads and follows four steps to produce the interpreted ECG report.

1 Quality Monitor – examines the technical quality of each ECG lead

2Waveform Recognition – locates and identifies the various waveform components

3Measurement – measures each component of the waveform and performs basic rhythm

analysis, producing a comprehensive set of measurements

4 Interpretation – uses extended measurements and Patient ID information (age, gender) to

select interpretive statements from the program

Figure 1-1 The Philips 12-Lead Algorithm Analysis Process

ECG Patient Data Quality Monitor Feedback to Operator

Extended Measurements Criteria

Philips 12-Lead Algorithm

Interpretive Report

Overreader

1-2 Philips 12-Lead Algorithm Physician Guide

Quality Monitor The Philips 12-Lead Algorithm

Quality Monitor

Computer-assisted ECG analysis begins by obtaining accurate ECG waveforms through simultaneously acquiring and analyzing 12 ECG leads.The analog ECG signal at the body surface is digitized by the Patient Module. The ECG waveform data is captured at a sample rate of 4 Mhz and reduced to 500 samples per second with 5 will accurately detect pacemaker pulses.

Philips Medical Systems equipment monitors ECG trace quality from the time of lead attachment, to ECG acquisition, and throughout the analysis process. This ensures the highest possible quality ECG trace. This also enables the correction of problems before the ECG trace is printed.

During analysis, the trace quality is analyzed to ensure good ECG measurements. The ECG is also analyzed for muscle artifact, AC noise, baseline wander, and leads-off. Any noise problems not corrected by the operator are described in the interpretive statements on the ECG report.

If noise conditions are severe, a report may not be printed. If noise conditions are significant enough to prevent ECG analysis, the ECG may be printed without interpretation. The operator must then correct the noise problem and retake the ECG.

µV resolution. This sampling rate

Modifying lead placement and improving patient preparation helps to eliminate most noise quality problems.

Reducing Artifact

Electrical interference, patient respiration, patient movement, and muscle tremors may add noise and artifact to the ECG signal. Poor quality electrodes or inadequate patient preparation may also degrade the ECG signal.

The two types of AC interference in the ECG signal are common mode and differential mode.

Common Mode

Some noise sources that interfere with the ECG signal affect all of the electrodes attached to the patient. These common noise sources are removed from the ECG by input circuitry as the signal is acquired and digitized. The amount by which these common mode signals are reduced is referred to as the common mode rejection ratio. The common mode rejection ratio for Philips Medical Systems input circuitry meets or exceeds current AAMI and IEC standards.

Differential Mode

The magnetic fields associated with electrical power interact with the lead wires. These fields induce electrical signals that appear as high frequency noise on the ECG. The amount of distortion differs from lead to lead, depending on the size of any loop created by the lead wire and on its orientation. A good way to prevent distortion is to align all the lead wires with the patient’s body along the head-to-foot axis.

1-3

The Philips 12-Lead Algorithm Quality Monitor

Using Filters

A variety of noise sources may degrade the reproduction of the ECG signal. A sophisticated set of digital filters may be selected by the operator (or during system configuration) to optimize the displayed or printed ECG waveform.

With the exception of the AC filter (which is highly selective) there is trade off between fidelity and clarity of the ECG trace when a filter is applied. The more filtering applied, the greater the possibility of removing ECG signal details.

In the lower right corner of the ECG report is a box that displays information about the filtering options used on the ECG.

NOTE While all filters affect displayed and printed ECGs, the Philips 12-Lead Algorithm always receives and

analyzes unfiltered data.

Figure 1-2 Example of the Filter Box on the ECG Report

Artifact Filter

The artifact filter removes skeletal muscle artifact. This noise source is the most difficult to eliminate because it has the same frequencies as ECG signals. The artifact filter eliminates skeletal muscle artifact, but also reduces all high frequency components of the ECG.

The filter removes up to 50 affect P waves and the entire QRS-T complex. Use the artifact filter only for ECGs that would be unreadable due to significant levels of muscle artifact.

1-4 Philips 12-Lead Algorithm Physician Guide

µV of signals in the 5 Hz to 150 Hz frequency range. This may

Filter Box

Quality Monitor The Philips 12-Lead Algorithm

AC Filter

The AC filter removes interference created by the magnetic fields associated with electrical power interacting with the lead wires. The frequency of the AC interference is stable at 60 or 50 Hz, so the AC filter removes the AC noise and leaves the ECG signal intact. The line frequency of 60 or 50 Hz is selected during system configuration.

If the filter box does not contain the AC filter symbol, the AC filter was not used for the ECG.

Frequency Response Filters

These filters suppress frequencies at the high and low ends of the ECG signal spectrum. The available low frequency response filter settings are 40, 100, and 150 Hz. In 1989, the American Heart Association recommended that frequencies up to 125 Hz be recorded for adult ECGs and that frequencies up to 150 Hz be recorded for pediatric ECGs.

Changing the low frequency filter to 40 or 100 Hz results in a smoother-looking ECG waveform while eliminating some fine detail in the signal. Small deflections, notches, and slurs may be distorted or may disappear if one of these filters is applied.

The high frequency response filter settings are 0.05, 0.15, and 0.5 Hz.

NOTE With the baseline wander filter on, the high frequency response filter is automatically set to 0.5. It is

recommended that the 0.05 high frequency response filter setting be used for all other ECGs. See “Baseline Wander Filter” below for more information.

The frequency response of the printed ECG is indicated in the ECG report filter box. The algorithm uses 0.05 to 150 Hz bandwidth for maximum fidelity.

Baseline Wander Filter

Baseline wander is the slow (typically 0.1 - 0.2 Hz) drifting of the ECG baseline up or down during ECG recording. Baseline wander may result from patient respiration or from other sources. Severe baseline wander may make it difficult to determine the true wave shapes in the ECG.

Effective baseline wander suppression techniques do not distort the ST segment. While the highest frequency response limit of 0.05 Hz (recommended for normal use) eliminates baseline wander from most ECGs, additional suppression may be required. Turning on the baseline wander filter suppresses all frequencies above 0.5.

1. Bailey JJ, Berson AS, Garson A, Horan LG, Macfarlane PW, Mortara DW, Zywietz C: Recommendations for Standardization and Specifications in Automated Electrocardiography: Bandwidth and Digital Signal Processing. Circulation, 81:730-739 (1990).

1-5

The Philips 12-Lead Algorithm Waveform Recognition and Measurements

NOTE A 0.5 Hz baseline wander filter that may distort the ST segment is used during continuous ECG

recording in Rhythm mode. Do not attempt to interpret the contour aspects of Rhythm ECGs at this setting. If contour analysis is important in Rhythm mode, use the 0.05 Hz Rhythm high-pass frequency response setting that minimizes the ST segment distortion. Rhythm characteristics of the ECG are accurately recorded regardless of the low-pass frequency setting in Rhythm mode.

Waveform Recognition and Measurements

The Philips 12-Lead Algorithm calculates measurements for all the waveforms on an ECG report. Every beat in each lead is measured individually, allowing the natural variation among beats to contribute to the representative measurements. In the algorithm, all of the representative group, lead, and global measurements are calculated from the comprehensive set of measurements for each beat. The algorithm can use any combination of these three types of measurements (group, lead, global) thereby enhancing the flexibility and power of its interpretive capabilities.

Figure 1-3 ECG Morphology Measurements

Waveform Recognition

The first step of the measurement program involves waveform recognition and beat detection. A pacing spike detector is run on all leads if the ECG pacemaker setting is Pacer spikes are removed and the resulting waves are analyzed with a boundary indicator derived from all leads over the ten-second analysis period. After the approximate QRS complex and pacemaker spike locations are known, another boundary indicator waveform that

1-6 Philips 12-Lead Algorithm Physician Guide

On or Unknown.

Waveform Recognition and Measurements The Philips 12-Lead Algorithm

enhances P and T wave detection is derived. Approximate P wave, QRS complex, and T wave regions are then determined for each beat in the ECG.

Comprehensive Measurements

After the approximate waveform locations are known, they are further refined to determine precise onsets and offsets for each waveform. Once the onsets and offsets are determined, the amplitude, duration, area, and shape are calculated for every P wave, QRS complex, ST segment, and T wave in each lead. Waveform irregularities such as notches, slurs, delta waves, and pacemaker spikes are also noted for every beat.

Group Measurements

Each beat in the ECG is classified into one of five rhythm groups based on rate and morphology parameters. Each group has beats with similar R-R intervals, durations, and shapes. All ventricular paced beats are grouped together, regardless of other parameters.

 Group 1 measurements represent the type of beat that is predominant.

 Groups 2 through 5 represent other beat types whose measurements are averaged together.

The group into which each beat is classified is noted under the heading

OF BEATS

in the Rhythm Analysis section of the Extended Measurements report. See

“Extended Measurements Report” on page 5-26.

Lead Measurements

Measurements for each of the 12 leads are calculated from the Group 1 beats. Only if all beats in the ECG are ventricular paced will the measurements be for paced beats. If an ECG contains both paced and non-paced beats, only the non-paced beats will be measured.

The lead measurements are averaged representatives of the dominant waveform present in each lead and are reported in the Morphology Analysis section of the Extended Measurements Report.

Atrial Rhythm Analysis

Atrial rhythm is determined by examining leads V1, aVF, II, and III in succession until the algorithm can determine the number of P waves per QRS complex. If the determination fails, no atrial rhythm parameters are calculated.

Global Measurements

The global measurements for the ECG (including the frontal and horizontal plane axis measurements) are reported to the right of the lead measurements in the Morphology Analysis section of the Extended Measurements Report. See “Extended Measurements Report” on page 5-26 for more information.

RHYTHM GROUPING

These interval, duration, and segment measurements are the measurements of the representative beat in each lead from Group 1. The global rate reported is the mean ventricular rate over the entire ECG unless the algorithm determines that one of the group mean ventricular rates is more representative of the underlying rhythm.

1-7

The Philips 12-Lead Algorithm Interpretation

Axis Measurements

Although it is convenient to use waveform amplitudes when making axis measurements manually, using the areas of the waveforms yields more accurate results. Philips Medical Systems equipment uses the waveform areas from the lead measurements in calculating the P, QRS, and T axes. The sum of the ST onset, and middle and end amplitudes are used in calculating the ST axis.

The frontal plane axis measurements use the limb leads and nine lead pairs (all at least 60 apart) to estimate the axes. The horizontal plane axis measurements are calculated from leads V1-V6 in a similar manner.

The resulting estimates are examined to ensure that they converge to a single result. They are averaged to form the representative axis measurement.

Interpretation

Within a diagnostic category, the criteria for interpretive statements become more and more restrictive from beginning to end. Criteria met for any given interpretive statement in a diagnostic category automatically suppresses any previous statement (in that category) that had been selected.

Each category may only be represented on the final report by one statement. This statement is the last one encountered whose medical criteria were true based on the measurements, earlier decisions, and Patient ID information (age, gender).

Overall Severity

Each interpretive statement selected for the ECG report has an associated severity. Severities that are more abnormal override lesser severities. The severities of all selected interpretive statements are combined to determine the overall severity of the ECG. This severity is printed on each page of the ECG report.

Table 1-1 Overall ECG Severity

Severity Code

No Severity NS

Normal ECG NO

Otherwise Normal ECG ON

Borderline ECG BO

Abnormal ECG AB

Defective ECG DE

1-8 Philips 12-Lead Algorithm Physician Guide

Adult and Pediatric Rhythm Analysis

The interpretive statements generated by the Philips 12-Lead Algorithm are based on the full range of ECG wavelet measurements and include wavelet durations, other parameters.

All of the interpretive statements are grouped into diagnostic categories. In each diagnostic category, more clinically significant findings override more benign ones. For instance, in the category of Ventricular Conduction Delays, the statement Left Bundle Branch Block (LBBB) overrides Borderline Intraventricular Conduction Delay and Incomplete Left Bundle Branch Block. In addition, the presence of LBBB also suppresses a statement from a previous category such as Left Axis Deviation and bypasses tests for ventricular hypertrophy, most infarcts, ST deviations, and abnormal T waves. These suppression and bypass conditions generally are not addressed in the descriptions of the diagnostic categories.

The diagnostic categories are divided into two sections: cardiac rhythm and morphology. Each diagnostic category includes a set of interpretive statements with variations in severity and probability. Detailed cardiac rhythm criteria are described in the following section. Detailed morphology detection criteria are described in Chapter 3, “Adult Morphology Analysis” and Chapter 4, “Pediatric Morphology Analysis.”

amplitudes, areas, and

ECG analysis begins with rhythm analysis with the first interpretive statement describing the basic rhythm of the ECG, or the paced rhythm of the ECG.

A second interpretive statement may be appended to describe additional rhythm abnormalities, including premature complexes, pauses, atrioventricular conduction abnormalities, and miscellaneous arrhythmias.

Cardiac Rhythm Categories

 Paced Rhythm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 2-2)

 Basic Cardiac Rhythm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 2-2)

 Ventricular Preexcitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 2-3)

 Premature Complexes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 2-3)

 Pauses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 2-4)

 Miscellaneous Arrhythmias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 2-4)

 Atrioventricular Conduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 2-4)

2-1

Adult and Pediatric Rhythm Analysis Cardiac Rhythm Categories

Paced Rhythm

Paced rhythm interpretation concentrates on the apparent rhythm, not on the underlying pacemaker mode (which may not be apparent from the observed rhythm). Atrial, ventricular, dual AV sequential, and atrial-sensed ventricular-paced pacing rhythms may be described.

The term

PACED RHYTHM is used when all beats fit a characteristic paced pattern.

Paced complexes are described when pacing is intermittent and non-paced complexes are also detected. Such complexes may include ectopic atrial or ventricular premature complexes, or episodes of sinus rhythm. Intermittently paced rhythms are not further analyzed for rhythm patterns during the non-paced periods.

Demand behavior with pulse inhibition in one or both chambers may be detected.

Noise spikes in technically poor tracings may mimic pacer spikes. If these are suspected, a statement of pacemaker-like artifact is generated.

When the ECG record is obtained with a magnet in place, the pacemaker spikes occur at a fixed rate and may be asynchronous with the underlying rhythm. This phenomenon is declared as a failure to sense and/or capture and the presence of a magnet is questioned.

An attempt is made to diagnose atrial fibrillation in the presence of ventricular pacing. No other atrial rhythm diagnosis is performed.

QRS complexes that are not ventricular paced (non-paced or atrial paced complexes) and that are not classified as ventricular ectopic beats will be measured and used for further morphology interpretation. No further interpretation is considered for ECGs with continuous ventricular or AV dual pacing.

Basic Cardiac Rhythm

When no pacing spikes are found, one interpretive statement describes the basic cardiac rhythm and is based on the interrelationship of the atrial rate, ventricular rate, P wave axis, QRS duration, and other measurements. Possible statements include those related to:

 Sinus, atrial, supraventricular, junctional, and ventricular rhythms

 Tachycardia, bradycardia, and varying rate

 Complete AV block

 AV dissociation

 Atrial fibrillation

 Atrial flutter

A normal P axis measurement (-30

º to 120º in the frontal plane) is assumed to indicate a sinus

origin of the P wave. An abnormal P axis signifies an atrial or a junctional origin.

Tachycardia is generally defined as a rate of 100 bpm or higher in adults; bradycardia is

slower than 50 bpm. This is different from the value of 60 cited by many ECG texts

. The operator may reset the default criteria from 50 bpm to 60 bpm (if available). Consult the Philips Medical Systems product documentation for more information.

1. Surawicz B, Uhley H, Borun R, Laks, M, et al. Task Force 1: Standardization of Terminology and

Interpretation. Amer J Cardio 41:130-145 (1978).

2-2 Philips 12-Lead Algorithm Physician Guide

Cardiac Rhythm Categories Adult and Pediatric Rhythm Analysis

Heart rates slower than the normal range are considered bradycardia and those higher are considered tachycardia as shown in Appendix A (pediatric values only).

An interpretive statement of complete AV block is generated when the ventricular rate is low (< 45 bpm) and the atrial rhythm is asynchronous with the ventricular rhythm. Additional categories of complete AV block include wide QRS complexes and atrial fibrillation.

AV dissociation is detected by looking for a normal ventricular rate with considerable variation of the apparent PR intervals. While describing the ECG rhythm strip, the algorithm does not define the underlying rhythm (which may be complete heart block or a junctional rhythm). An attempt is made to diagnose the underlying rhythm, complete heart block or junctional rhythm, rather than AV dissociation.

The criteria for atrial fibrillation are rather complex. Fine fibrillation is diagnosed with missing P waves in most leads and marked variation in the ventricular rate. Coarse fibrillation is diagnosed from multiple shapes of P waves with a rapid apparent atrial rate and variation in the ventricular rate.

An interpretive statement of atrial flutter is generated when the atrial rate falls between 220-

340. An attempt is made to describe the degree of block with flutter.

Ventricular Preexcitation

Ventricular preexcitation is recognized based on the occurrence of delta waves in multiple leads and a mean QRS duration greater than 100 ms.

A short PR (PR segment <55 ms or PR interval <120 ms) reduces the number the leads with delta waves required to detect this condition.

Leftward or rightward initial QRS axis deviation criteria are added to determine whether a left or right accessory pathway is present. The rest of the algorithm program is bypassed if ventricular preexcitation criteria are met.

Premature Complexes

Premature complexes are recognized when the preceding R-R interval is shorter than the average R-R interval of a background ventricular rate that is basically regular. A reduction in R-R interval of 15% (typical) or greater is considered significant.

Premature complexes with normal QRS duration (QRSd) are considered to be atrial or junctional in origin, depending on the presence or absence of a P wave. Those with longer than normal QRSd are considered to be either ventricular in origin or to be aberrant supraventricular in origin.

Atrial premature complexes (APC, multiple APC) are generally recognized by their early appearance, normal QRS duration, and atypical P-wave morphology. More than one APC is diagnosed as multiple APCs.

Ventricular premature complexes (VPC, multiple VPC) are generally recognized by an early appearance, wider than normal QRS duration, a compensatory pause, and a different polarity than normal beats. Interpolated VPCs have ventricular morphologic characteristics without compensatory pauses. Multiple VPCs are diagnosed when more than one VPC is detected.

2-3

Adult and Pediatric Rhythm Analysis Cardiac Rhythm Categories

Junctional premature contractions (JPC) have the same characteristics as APCs, but without a P-wave being detected. No attempt is made to detect retrograde P waves with JPCs.

Ventricular or supraventricular bigeminy is diagnosed when ventricular (V) or supraventricular (A) premature beats alternate with normal (N) beats.There must be at least two consecutive occurrences of the pattern (NV or NA) to generate an interpretive statement of bigeminy.

Ventricular trigeminy is diagnosed when two consecutive occurrences of the pattern NNV are detected.

Two adjacent VPCs are diagnosed as a pair. The characteristics are primarily morphological since compensatory pauses are not usually seen.

A run of VPCs is diagnosed when three or more adjacent VPCs are seen.

Pauses

Long R-R intervals are significant if they are more than 140% (typical) of the average R-R in a background ventricular rate that is basically regular. They are considered to indicate either a sinus arrest or an intermittent AV block.

The presence or absence of a P wave, as well as the duration of the QRS, indicate the origin of an escape beat. Atrial and supraventricular escapes show a P wave and a normal QRS duration (QRSd). Junctional escapes show no P wave, but a normal QRSd. A prolonged QRSd indicates a ventricular origin of the escape beat, although aberration cannot be excluded.

Different grades of second degree AV block are indicated on the basis of more P waves than QRS complexes.

A statement indicating Mobitz I (Wenckebach) AV block depends on progressively longer PR intervals preceding the long R-R interval.

Miscellaneous Arrhythmias

This category includes arrhythmias that are not covered in the preceding sections.

Statements relating to interpolated beats depend on recognizing that consecutive R-R intervals are approximately one-half the average R-R of a background ventricular rate that is basically regular.

Aberrant complexes are recognized when the R-R interval is only slightly decreased but the QRSd is prolonged, as if it were of ventricular origin.

Atrioventricular Conduction

Statements in this category are based on the measurement of a prolonged PR interval.

2-4 Philips 12-Lead Algorithm Physician Guide

Cardiac Rhythm Categories Adult and Pediatric Rhythm Analysis

The PR interval varies slightly according to age and heart rate, as shown in the following table.

Table 2-2 Borderline and Abnormally Prolonged PR Intervals (ms)

Heart Rate (bpm)

Left Value = PR Interval Upper Limit (Borderline) Right Value = PR Interval Upper Limit (1st degree AV Block)

Age (years)

less than 50 51-90 91-120 over 120

16-60 210-220 200-210 195-205 190-200

over 60 200-230 210-220 205-215 200-210

2-5

Adult Morphology Analysis

The morphology interpretation starts by testing for dextrocardia. Morphology abnormalities are examined in anatomical order from right to left and from atria to ventricles. The interpretive criteria are described (by diagnostic category) in the following section.

Adult Morphology Categories

 Dextrocardia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-2)

 Right Atrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-2)

 Left Atrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-2)

 Biatrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-2)

 QRS Axis Deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-2)

 Ventricular Conduction Delays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-3)

 Right Ventricular Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-3)

 Left Ventricular Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-4)

 Low Voltage and Chronic Obstructive Pulmonary Disease Pattern . . . . . . . . . .(page 3-5)

 Inferior Myocardial Infarction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-5)

 Lateral Myocardial Infarction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-5)

 Anteroseptal and Anterior Myocardial Infarction . . . . . . . . . . . . . . . . . . . . . . . .(page 3-6)

 Anterolateral and Extensive Anterior Myocardial Infarct . . . . . . . . . . . . . . . . . .(page 3-6)

 Posterior Myocardial Infarction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-6)

 ST Depression and Myocardial Ischemia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-7)

 T Wave Abnormalities and Myocardial Ischemia . . . . . . . . . . . . . . . . . . . . . . . .(page 3-7)

 Repolarization Abnormalities and Myocardial Ischemia . . . . . . . . . . . . . . . . . .(page 3-8)

 ST Elevation, Myocardial Injury, Pericarditis, and Early Repolarization . . . . . .(page 3-8)

 Tall T Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 3-8)

 QT Abnormalities, Electrolyte Disturbance, and Drug Effects . . . . . . . . . . . . . .(page 3-9)

3-1

Adult Morphology Analysis Adult Morphology Categories

Dextrocardia

Dextrocardia is suggested if the P wave and the QRS axes are abnormal in the frontal plane (deviated rightward), if the horizontal plane QRS is directed rightward, and if small QRS complexes are present in V5 and V6. The rest of the morphology interpretation is bypassed if dextrocardia criteria are met.

Right Atrial Abnormality

Large P waves are considered suggestive of right atrial abnormality (RAA). The minimum duration considered significant is 60 ms, the minimum voltage considered significant is 0.24 mV (typical).

Greater than normal P wave duration and amplitude in limb leads produce a statement of consider right atrial abnormality. Additional conditions such as a biphasic P wave in Lead V1 indicate probable RAA. Larger P waves lead to more definitive interpretive statements regarding the likelihood of RAA.

Left Atrial Abnormality

Left atrial abnormalities (LAA) are detected from large P waves on limb leads and a biphasic P in Lead V1, and the durations and the amplitudes of the initial and terminal portions of a biphasic P wave.

A duration greater than 110 ms combined with amplitudes over 0.10 mV in limb leads is considered significant, though not necessarily abnormal unless present in multiple leads. A notched P wave adds to the significance of the other values. Lead V1 is specifically examined for duration, amplitude, and area of the negative component of the P wave. Although duration of over 30 ms and amplitudes over 0.09 mV can be considered significant, the area of this negative component must be greater than 0.60 Ashman units to be considered LAA. An Ashman unit is the area of 1 square millimeter at normal speed (25 mm/sec) and normal sensitivity (10 mm/mV). An Ashman unit equals 40 ms x 0.1 mV.

Biatrial Abnormality

Biatrial abnormality (BAA) combines right and left atrial abnormalities. Associated LAA is diagnosed when a P amplitude greater than 0.1 mV in V1 co-exists with RAA. Associated RAA is considered when LAA statements are combined with a significant P wave greater than 10 ms in duration and greater than 0.07 mV in amplitude, and an R wave greater than 1.0 mV in Lead V6. BAA is considered if RAA and LAA statements with high severity were previously generated.

QRS Axis Deviation

Interpretive statements based on frontal QRS axis measurements describe left and right deviation as well as superior, horizontal, and vertical directions.

The mean QRS axis (mean vector of the electric force) is calculated in the frontal and horizontal planes. The normal frontal axis range varies with age and gender. The frontal QRS axis in young male patients tends to the right. The frontal QRS axis in older patients tends to the left.

3-2 Philips 12-Lead Algorithm Physician Guide

Adult Morphology Categories Adult Morphology Analysis

A frontal QRS axis between -30º and 90º is considered normal, subject to modification by age and gender. Frontal QRS axis measurements counterclockwise from -30 deviated to the left, and those clockwise from 90

º are considered to be deviated to the right.

º are considered to be

Ventricular Conduction Delays

A QRS duration (QRSd) greater than 100 ms is common to all of the interpretive statements in this category except for isolated left anterior fascicular block (LAFB) and left posterior fascicular block (LPFB), which do not cause a prolonged QRS.

LAFB interpretations are associated with leftward deviation of the mean frontal QRS axis between -40 deviation of the mean frontal QRS axis between 120

Other than the fascicular blocks, a definitive block interpretation requires that the QRSd exceed 120 ms. A QRSd between 110 and 120 ms is non-specific intraventricular conduction delay, and between 100 and 110ms is considered borderline intraventricular conduction delay.

Right bundle branch block (RBBB) interpretations are always associated with the terminal portion of the QRS being directed to the right (dominant negative Q, S forces in Leads I, aVL, and V6, and positive forces in Lead V1). A QRSd between 110-120 ms is considered incomplete RBBB.

º and 240º counterclockwise. LPFB interpretations are associated with rightward

º and 210º clockwise.

Left bundle branch block (LBBB) interpretations are always associated with the terminal portion of the QRS being directed to the left dominant positive (R, R') forces in Leads I, aVL, and V6, and negative forces (Q, S) in Lead V1. A QRSd between 110-120 ms is considered incomplete LBBB.

Right Ventricular Hypertrophy

Right ventricular hypertrophy (RVH) is detected on the basis of several findings:

 Presence of a prominent R or R' in Lead V1

 Presence of a prominent Q, S, or S' in either Lead I or V6

 Right atrial abnormality

 Right axis deviation in the frontal plane

 Repolarization abnormalities typical of RVH

An R in V1 that is more than 75% the size of the Q or S is significant, and is considered to be prominent. An R' larger than 20 ms and 0.30 mV in V1 is significant. A QRS in V1 with a positive component larger than the negative component is highly significant.

Repolarization abnormalities typical of RVH are determined by an examination of Leads II, aVF, V1, V2, and V3 for the presence of depressed ST segments and inverted T waves as typical of the right ventricular strain pattern.

The statements to be printed regarding RVH are determined by combinations of the above findings. One voltage criterion generates a consider RVH statement. Two voltage criteria or one voltage plus repolarization abnormality generates a probable RVH statement. Definitive RVH statements result when multiple findings are present.

3-3

Adult Morphology Analysis Adult Morphology Categories

A Q, S, or S' larger than 40 ms and 0.20 mV in either Lead I or V6 is significant and is considered to be prominent. A QRS with a negative component larger than the positive component is highly significant.

Left Ventricular Hypertrophy

Left ventricular hypertrophy (LVH) is detected on the basis of several findings:

 Prominent R or R' in V5 or V6

 R in Lead I plus S in Lead III

 Sokolow-Lyon Voltage (R in V5/V6 plus S in V1)

 Cornell Voltage (R in aVL plus S in V3)

 Cornell Product (R in aVL plus S in V3) multiplied by QRSd

 Left axis deviation in the frontal plane

 Left atrial abnormality

 Prolonged QRS duration or ventricular activation time (VAT)

 Repolarization abnormality typical of LVH

Voltage values for the QRS complexes that are considered excessively high vary with patient age and gender. Because higher voltages are normal for young patients, age is considered when evaluating LVH. The younger the patient, the more stringent are the requirements for an LVH statement. Females have lower voltage values than males

. Voltage limits also vary with

the leads involved and whether the deflection is positive or negative.

In frontal leads the minimum value considered excessive is a positive deflection of more than

1.20 mV in Lead aVL. Precordial Leads V1 and V2 are examined for negative deflections (Q or S) and V5 and V6 are examined for positive deflections (R or R'). These values are considered individually; any value greater than 2.50 mV is considered significant.

The negative values in V1, V2 and the positive values in V5, V6 are added together. Any total for Q or S in V1 plus R or R' in V5 or V6 that exceeds 3.50 mV is significant. A total of Q or S in V2 plus R or R' in V5 or V6 must exceed 4.0 mV to be significant.

Higher voltages contribute to qualifying statements regarding LVH. Cornell Voltage criteria are used for LVH detection. This limit is an R amplitude in Lead aVL plus S amplitude in Lead V3 greater than or equal to 2.8 mV in males and 2.0 mV in females. LVH voltage criteria combine with additional features determined in previous categories such as left axis deviation, presence of LAA, QRS duration greater than 95 ms, and ventricular activation time (VAT) greater than 55 ms.

LVH with secondary repolarization abnormalities is determined separately and results in more definite statements regarding the likelihood of LVH. Secondary repolarization abnormalities are determined by examining Leads I, aVL, V4, V5, and V6 for the presence of ST depression and inverted T wave as a typical left ventricular strain pattern.

3-4 Philips 12-Lead Algorithm Physician Guide

Adult Morphology Categories Adult Morphology Analysis

Low Voltage and Chronic Obstructive Pulmonary Disease Pattern

All leads are examined for QRS peak-to-peak voltage.

Frontal leads: if no lead has a value exceeding 0.60 mV, the ECG is considered borderline low voltage. If no value exceeds 0.50 mV, the ECG is considered definite low voltage, an abnormal finding.

Precordial leads: if no lead has a value exceeding 1.00 mV, the ECG is considered definite low voltage, an abnormal finding.

Combinations of low voltage statements, rightward deviation of the frontal P and QRS axes, and right atrial enlargement may generate statements suggesting the likelihood of chronic pulmonary disease.

Inferior Myocardial Infarction

Leads II, III, and aVF are examined for Q wave presence and size, the ratio of Q to R, the presence of T wave changes (flattened or inverted), and the presence of an elevated or depressed ST segment.

As the Q waves become larger or appear in more leads and the R waves become less prominent, the interpretive statements are more significant. For inferior Q waves to be considered significant, at least one of them must be longer than 25 ms in duration and greater than one-sixth the amplitude of the associated R. For any infarct statement to qualify, at least one Q wave must be longer than 35 ms and greater than one-fifth the amplitude of the R wave.

A leftward direction of the axis of the initial portion of the QRS adds to the likelihood of an inferior infarct statement. T wave and ST changes are used to estimate the age of the infarct. Deeper T wave inversion and larger ST segment deviations generate statements indicating more recent infarction. Gender and age influence the detection of inferior infarct. Males and younger patients are more likely to have normal Q waves in the inferior leads.

Lateral Myocardial Infarction

Leads I, aVL, V5, and V6 are examined for Q wave presence and size, the ratio of Q to R, the presence of T wave changes (flattened or inverted), and the presence of an elevated or depressed ST segment.

For lateral Q waves to be considered significant, at least one must be longer than 35 ms and greater than 0.10 mV in amplitude. It must also have an amplitude that is at least 20% as large as that of the R wave. As the Q waves become larger or show in more leads and the R waves become less prominent, the interpretive statements become more significant.

T wave and ST changes are used to estimate the age of the infarct. Deeper T wave inversion and larger ST segment deviations generate statements indicating more recent infarction.

Gender and age influence the detection of lateral infarct. Males and younger patients are more likely to have normal Q waves in the lateral leads.

3-5

Adult Morphology Analysis Adult Morphology Categories

Anteroseptal and Anterior Myocardial Infarction

Leads V1, V2, V3, and V4 are examined for the presence of Q wave, Q wave area, the relative and absolute sizes of the R and S waves, whether the QRS area is negative or positive, the presence of T wave changes (flattened or inverted), and the presence of elevated or depressed ST segments. Positive findings in V1 and V2 tend to be reported as anteroseptal infarcts, while abnormalities in V2, V3, and V4 tend to be reported as anterior infarcts.

For any anteroseptal or anterior Q wave to be considered significant, it must be longer than 30 ms in duration and over 0.07 mV in amplitude. As the Q waves become larger or show in more leads and the QRS progression from negative to positive becomes shifted more laterally, the interpretive statements become more definitive for infarction in the anterior region.

T wave and ST changes are used to estimate the age of the infarct. Deeper T wave inversion and greater ST elevations generate statements indicating more recent infarction.

Anterolateral and Extensive Anterior Myocardial Infarct

Leads V2, V3, V4, V5, and V6 are examined for Q wave presence and size, the relative and absolute sizes of the R and S, whether the QRS area in V3 is negative or positive, the presence of T wave changes (flattened or inverted), and the presence of elevated or depressed ST segments.

For any anterolateral Q wave to be considered significant, it must be longer than 30 ms (typical) in duration and over 0.07 mV in amplitude. As the Q waves become larger or show in more leads, the interpretive statements become more definitive for infarction.

Positive findings in all six precordial leads generate statements describing extensive anterior infarction.

Gender and age influence the detection of anterolateral infarct. Males and younger patients are more likely to have normal Q waves in the anterolateral leads.

Q, ST changes, and T wave are used to estimate the age of the infarct. Deeper T wave inversion and greater ST elevations generate statements indicating more recent infarction.

Posterior Myocardial Infarction

Leads V1, V2, and V3 are examined for the relative and absolute sizes of the R and S waves, an absent or insignificant Q wave, ST depression, and a positive T wave.

A prominent R, in the presence of an insignificant Q, and an upright T may generate a statement suggesting the likelihood of a posterior infarct (PMI). ST depression in V1-V3, and upward T or T' are detected for acute posterior infarct. Combined inferior and posterior MI is called inferoposterior MI, and combined acute inferior MI and acute posterior MI is called acute inferoposterior MI.

Indications of LVH or RVH decrease the likelihood of a PMI statement. Gender and age influence the detection of a posterior infarct. Males and younger patients are more likely to have prominent R waves in V1 and V2.

3-6 Philips 12-Lead Algorithm Physician Guide

Adult Morphology Categories Adult Morphology Analysis

ST Depression and Myocardial Ischemia

All leads are examined for negative values in the ST segment. The values examined include the following points in the ST segment:

 The onset of the ST segment (the J point)

 The point midway between the onset and the end of the ST segment

 80 ms past the J point

 The end of the ST segment (the beginning of the T wave)

Besides negative values in the ST segment, other features are examined:

 The slope of the ST segment in degrees

 The shape of the ST segment (straight, concave up, or concave down).

The smallest negative ST deflection that is considered significant is 0.03 mV

As the negativity of the ST segment increases, more severe statements are generated. Minor depression of the segment produces statements with a severity code of

(ON) or NORMAL (NO). Increasing depression produces statements progressing through from BORDERLINE to ABNORMAL.

OTHERWISE NORMAL

Whenever possible, the location of ST abnormalities is indicated as part of the interpretive statement. The localization generally fits the description that follows.

Table 3-1 Location of Infarcts and Lead Group of ST-T Abnormalities

Lead Groups (Location) I IIIIIaVRaVLaVFV1V2V3V4V5V6

Anterior XXXX

AnterolateralX X X XXXXX

Lateral X X X X

Inferior X X X

ST depression is associated with rapid heart rate. A statement is generated indicating ST depression, probably rate related, if the mean heart rate is greater than 190 minus (age in years) bpm.

A concurrent statement regarding RVH, LVH, LBBB, RBBB, any new infarct, or any statement associated with drug therapy or electrolyte imbalance impacts this category by tending to suppress ST depression statements. This is more likely for the less severe ST depression statements than for the more severe ones.

T Wave Abnormalities and Myocardial Ischemia

All leads are examined for T wave amplitude, the relative amplitude of the T and the QRS, and whether the T is negative or positive. The frontal axis of the T wave and its relation to the frontal QRS axis is also measured.

3-7

Adult Morphology Analysis Adult Morphology Categories

Reduced T wave amplitude (both absolute and relative to the QRS), and negative T waves are considered to be abnormal findings. Minimal changes in one or a few leads produce less severe statements. As the changes become more prominent in magnitude and the number of affected leads increases, the statements become more severe.

A frontal T axis that is not between -10 may result in a statement indicating nonspecific T wave abnormalities. Whenever possible, the lead group of T wave abnormalities is indicated as part of the interpretive statement.

A concurrent statement regarding RVH, LVH, LBBB, RBBB, any infarct, or any statement associated with drug therapy or electrolyte imbalance impacts this category by tending to suppress T wave statements. This is more likely for the less severe T wave statements than for the more severe ones.

º and 100º or a QRS-T angle that is greater than 90º

Repolarization Abnormalities and Myocardial Ischemia

This category includes statements indicating the presence of both ST segment and T wave abnormalities. None of these statements involve any new examination of measurements.

All statements in this category are determined by the combination of statements in the T Wave Abnormalities and ST Depression categories. The severity of the statements in this category depends on the severity of the qualifying ST and T wave abnormalities.

ST Elevation, Myocardial Injury, Pericarditis, and Early Repolarization

ST segment elevation is based on examination of all lead groups for positive values of the ST onset (J point), the deflection at 80 msec after onset, and the slope of the ST segment (in degrees).

The smallest positive ST displacement considered significant is 0.05 mV (0.5 mm). When ST elevation is small (0.05 mV to approximately 0.10 mV, that is, less than 1 mm), the statements are considered to be of elevation greater than 1 mm is generally classified as

A specific lead group always follows a statement of borderline or abnormal ST elevation. Abnormal ST elevation in a specific lead group is described as consider, probable, or definite myocardial injury. If ST elevation is widespread on all anterior, lateral, and inferior lead groups, either pericarditis or probable early repolarization is suggested.

Tall T Waves

All leads are examined for the presence of positive T waves with amplitudes that exceed

1.20 mV, or for positive T waves that exceed 0.50 mV and are also more than half the size of the peak-to-peak QRS voltage.

The presence of such T waves generates statements alerting to the possibility of metabolic, electrolyte, or ischemic abnormalities.

OTHERWISE NORMAL (ON) or BORDERLINE (BO) severity. ST

ABNORMAL (AB).

3-8 Philips 12-Lead Algorithm Physician Guide

Adult Morphology Categories Adult Morphology Analysis

QT Abnormalities, Electrolyte Disturbance, and Drug Effects

Measurements of QT interval, as corrected for heart rate, and measurements associated with ST segment depression and T wave changes are examined for values characteristic of the effects of digitalis and abnormal calcium and potassium levels.

A QT interval corrected for heart rate (QTc) that is shorter than 340 ms is considered to be a short QT interval with a severity code as

QTc greater than 465 ms is considered as borderline prolonged QTc. An additional 20 ms qualifies the condition as prolonged QTc. Presence of RVH, LVH, and VCD suppresses statements of a prolonged QTc.

If the QTc is shorter than 310 ms, a statement of short QTc suggesting hypercalcemia is generated.

A significantly prolonged QTc interval greater than 520 ms is considered to be due to hypocalcemia.

A significantly prolonged QTc interval ( > 520 ms), combined with ST segment depression and a positive T wave in multiple leads, is considered to be due to hypokalemia.

The presence of an Rx code indicating use of digitalis favors interpretive statements that the findings are compatible with the effects of this drug. A combination of a short QTc and repolarization abnormality is considered to be due to digitalis effect.

OTHERWISE NORMAL (ON).

3-9

Pediatric Morphology Analysis

The pediatric Philips 12-Lead Algorithm is intended for use on ECGs of patients from birth up to 16 years of age. Age is an important factor in the pediatric algorithm since normal limits in heart rate, axis deviation, and waveform amplitudes are highly age dependent. Specification of age is highly recommended to improve overall ECG interpretation quality. If an age is not entered or is invalid, the interpretation is based on a default adult age, and a special statement noting this assumption is printed on the report.

Specific age limits of ECG features are adopted in the pediatric algorithm. information, see Appendix A, “Normal Measurement Values.”

The interpretive statements are described (by diagnostic category) in the following section.

Pediatric Morphology Categories

 Dextrocardia . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-2)

For more

 Right Atrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-2)

 Left Atrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-2)

 Biatrial Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-2)

 QRS Axis Deviation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-3)

 Ventricular Conduction Delays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-6)

 Right Ventricular Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-7)

 Left Septal Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-7)

 Left Ventricular Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-7)

 Biventricular Hypertrophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-8)

 Low Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-8)

 Q Wave Abnormality and Myocardial Infarct . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-9)

 ST Depression . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-9)

 T Wave Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-9)

 Repolarization Abnormality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-9)

1. Davignon A, Rautuharju P, Boiselle E, et al.: Normal ECG Standards for Infants and Children. Ped Cardiol

1:123-131 (1979/80).

4-1

Pediatric Morphology Analysis Dextrocardia

 ST Elevation, Pericarditis and Early Repolarization . . . . . . . . . . . . . . . . . . . . . .(page 4-9)

 Tall T Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . (page 4-10)

 QT Abnormality and Electrolyte Disturbance . . . . . . . . . . . . . . . . . . . . . . . . . (page 4-10)

 Congenital Heart Defects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .(page 4-10)