HP M1700 Physician guide
Hewlett-Packard Interpretive Cardiograph
Physician's Guide
ABCDE
HP Part No. M1700-92908
Printed in USA September 1994
Edition 4
E0994
Notice
The information in this documentmaychange without
notice.
Hewlett-Packard makes no warrantyofany kind with
regard to this material, including, but not limited to,
the implied warranties of merchantability and tness
for a particular purpose. Hewlett-Packard shall not be
liable for errors herein or for incidental or consequential
damages in connection with the furnishing, performance
or use of this material.
This document contains or refers to proprietary
information which is protected by copyright. All
rights are reserved. Copying or other repro duction
of this document without prior written permission of
Hewlett-Packard Company is prohibited.
c
Copyright 1990, 1991, 1992, 1993, 1994
Hewlett-Packard Company.
Printing History
May 1990 Edition 1
September 1990 Edition 2
January 1992 Edition 3
September 1994 Edition 4
iii
About This Guide
This guide explains how the clinical ECG reports
are analyzed by an Hewlett-Packard interpretive
cardiograph. It also shows howanHPinterpretive
cardiograph ensures reliable results.
Note
Computerized ECG analysis should always be reviewed
by a qualied physician.
iv
Who Should Read
This Guide?
Information Resource
This guide is intended for physicians who read or review
ECGs produced by a Hewlett-Packard interpretive
cardiograph. It also maybeofinterest to other
healthcare professionals who want to know more about
HP's interpretive cardiographs. The following table
shows where you can nd additional information on
related topics.
How to congure the cardiograph. The
cardiograph.
Description of ECL (the programming
language in which the interpretive
ECL Programmers Reference Manual
Hewlett-Packard
criteria is written).
Complete ECL program listing of all
criteria statements.
Operating instructions and guidelines for
the Hewlett-Packard ECG Management
System.
Note
This book discusses several functions that may not b e
Interpretive Criteria Listing
Hewlett-Packard
ECG Management System manuals, or contact
your Hewlett-Packard customer support
representative.
available on your HP interpretive cardiograph, suchas
oppy-disk storage, mo dem data transmission, extended
measurement report, signal averaged ECG, internal
congurations, alternate patient lead sets or patient lead
congurations. Refer to the
your cardiograph for a guide to the functions available
on your cardiograph.
User's Reference Guide
User's Guide
provided with your
. Order from
. Order from
supplied with
v
Documentation
Map
Documentation Map
If you want to: Use this manual:
Verify that all equipmentis
included
Packing List
Record ECGs
Enter patientID
Make copies of ECGs
Store ECGs
1
Transmit or receive ECGs
Troubleshoot problems
Maintain the cardiograph
Set up the cardiograph
Install battery
Install software
1
Load paper
Congure the cardiograph
Prepare patient
Maintain the cardiograph
Install and use the mo dem
Order supplies
Use lters
Operating Guide
1
User's Reference Guide
1
Understand analysis
1
Note: your cardiograph may not be equipp ed for this function.
Physician's Guide
vi
Contents
1. Why Use an Interpretive Cardiograph?
What You Can Exp ect of the HP ECG
Analysis Program . . . . . . . . . 1-2
2. How Computerized ECG Interpretation has
Developed
3. Understanding Simultaneous 12-Lead Acquisition
Digitizing the ECG . . . . . . . . . . 3-3
Reducing Artifact . . . . . . . . . . 3-5
Common Mode Rejection . . . . . . 3-5
Using Filters . . . . . . . . . . . . . 3-6
Frequency Response Filters . . . . . 3-7
AC Filter . . . . . . . . . . . . . 3-8
Baseline Wander Filter . . . . . . . 3-8
Artifact Filter . . . . . . . . . . . 3-10
Monitoring ECG Quality . . . . . . . 3-10
4. The HP ECG Analysis Program
Understanding the HP ECG Analysis
Program . . . . . . . . . . . . . 4-2
How the HP Interpretive Cardiograph
Measures ECGs . . . . . . . . . . 4-3
Waveform Recognition . . . . . . . 4-4
Comprehensive Measurements . . . . 4-4
Group Measurements . . . . . . . . 4-4
Lead Measurements . . . . . . . . . 4-5
Atrial Rhythm Analysis . . . . . . . 4-5
Global Measurements . . . . . . . . 4-6
Axis Measurements . . . . . . . . . 4-6
Contents-1
The ECG Criteria Language (ECL) . . . 4-7
Categories . . . . . . . . . . . . . 4-7
Sentences . . . . . . . . . . . . . 4-7
Overall Severity . . . . . . . . . . 4-9
Further Information . . . . . . . . . . 4-9
5. The HP Adult ECG Criteria Program
Understanding the HP Adult ECG Criteria
Program . . . . . . . . . . . . . 5-2
Pediatric Age Disclaimer . . . . . . 5-4
Calibration Notice if Not Standard . . 5-4
Technical Quality Statements . . . . 5-5
Electronic Pacemaker . . . . . . . . 5-5
Basic Cardiac Rhythm . . . . . . . 5-5
Premature Beats (Short R-R) . . . . 5-6
Pauses (Long R-R) . . . . . . . . . 5-6
Miscellaneous Arrhythmias . . . . . 5-7
AV Conduction (PR Interval) . . . . 5-8
QRS Axis . . . . . . . . . . . . . 5-9
Ventricular Conduction Delays . . . . 5-10
RightAtrial Enlargement . . . . . . 5-11
RightVentricular Hypertrophy. . . . 5-11
Prominent R or R
0
in V1 . . . . . 5-11
Prominent Q or S in I or V6 . . . . 5-12
RightAtrial Enlargement . . . . . 5-12
Right Axis Deviation in the Frontal
Plane . . . . . . . . . . . . 5-12
ST{T Changes Characteristic of RVH 5-12
Left Atrial Enlargement. . . . . . . 5-12
Left Ventricular Hypertrophy . . . . 5-13
High Voltage in QRS Components . 5-13
Left Axis Deviation in the Frontal
Plane . . . . . . . . . . . . 5-14
Left Atrial Enlargement. . . . . . 5-14
ST{T Changes Characteristic of LVH 5-14
A Prolonged QRS Duration or
Ventricular Activation Time . . 5-14
Chronic Pulmonary Disease . . . . . 5-15
Contents-2
Inferior Infarct . . . . . . . . . . . 5-15
Posterior Infarct . . . . . . . . . . 5-16
Lateral Infarct . . . . . . . . . . . 5-17
Anteroseptal and Anterior Infarct . . . 5-17
Anterolateral and ExtensiveAnterior
Infarct . . . . . . . . . . . . . 5-18
Apical Infarct . . . . . . . . . . . 5-19
Tall T Waves . . . . . . . . . . . . 5-19
Drug and Electrolyte Eects . . . . . 5-19
TWave Abnormalities . . . . . . . 5-19
Ischemia . . . . . . . . . . . . . . 5-21
ST Segment Depression . . . . . . . 5-21
Subendocardial Injury . . . . . . . . 5-22
Combined ST and T Abnormalities . . 5-23
Injury and Ischemia . . . . . . . . . 5-23
ST Segment Elevation . . . . . . . . 5-23
Severity . . . . . . . . . . . . . . 5-24
6. The HP Pediatric ECG Criteria Program
Understanding the H-P Pediatric ECG
Criteria Program . . . . . . . . . 6-2
Pediatric ECG Interpretation . . . . 6-4
Calibration Notice if Not Standard . . 6-4
Technical Quality Statements . . . . 6-4
Electronic Pacemaker . . . . . . . . 6-5
Dextrocardia . . . . . . . . . . . . 6-5
Basic Cardiac Rhythm . . . . . . . 6-5
Sinus Rhythms . . . . . . . . . . . 6-5
Atrial Premature Complex . . . . . . 6-6
Ventricular Premature Complex . . . 6-7
PR Interval . . . . . . . . . . . . 6-7
Wol-Parkinson-White Syndrome . . . 6-7
Ventricular Conduction Delay . . . . 6-7
Right Bundle Branch Block . . . . . 6-7
Left Bundle Branch Blo ck . . . . . . 6-8
RightAtrial Enlargement . . . . . . 6-8
RVH: QRS Voltage Criteria . . . . . 6-8
Right Axis Deviation . . . . . . . . 6-9
Contents-3
RVH: T Wave Criteria . . . . . . . 6-9
RightVentricular Hypertrophy. . . . 6-9
Left Atrial Enlargement. . . . . . . 6-10
LVH: QRS Voltage Criteria . . . . . 6-10
Left Axis Deviation . . . . . . . . . 6-10
LVH: ST Segment and T Wave Criteria 6-11
Left Ventricular Hypertrophy . . . . 6-11
Biventricular Hypertrophy. . . . . . 6-11
Anterior ST Elevation . . . . . . . . 6-11
Inferior ST Elevation . . . . . . . . 6-12
Anterolateral ST Elevation . . . . . . 6-12
Anterior ST Depression . . . . . . . 6-12
Inferior ST Depression . . . . . . . 6-12
Anterolateral ST Depression . . . . . 6-12
Anterior T Wave Changes . . . . . . 6-13
Inferior T Wave Changes . . . . . . 6-13
Anterolateral T Wave Changes . . . . 6-13
Anatomical Diagnoses . . . . . . . . 6-14
Severity.. . . . . . . . . . . . . 6-14
7. Reading the Printed Rep ort
Auto Interpretive Reports . . . . . . . 7-2
Patient Information . . . . . . . . . 7-3
Basic Measurements . . . . . . . . 7-4
Interpretive Information . . . . . . . 7-5
Calibration Pulse . . . . . . . . . . 7-6
Rhythm Strip . . . . . . . . . . . 7-6
Settings . . . . . . . . . . . . . . 7-7
Auto Rep ort Formats . . . . . . . . 7-8
Extended Measurements Report . . . . 7-10
Manual Reports . . . . . . . . . . . 7-11
Cardiograph Settings . . . . . . . . 7-12
Manual Report Formats . . . . . . . 7-13
Contents-4
8. Managing Your ECGs
PageWriter Communications . . . . . . 8-3
ECG Management Systems . . . . . . 8-4
Clinical Rewards . . . . . . . . . . 8-5
CurrentTrends . . . . . . . . . . . 8-6
A. Questions and Answers
B. PatientIDCodeTables
C. The Extended Measurements Rep ort
Morphology Analysis . . . . . . . . . C-3
Individual Lead Measurements . . . . C-3
Cal Factors . . . . . . . . . . . . C-8
Frontal/Horizontal . . . . . . . . . C-9
Analysis Statement Co des . . . . . . C-10
Rhythm Analysis . . . . . . . . . . . C-10
Group Measurements . . . . . . . . C-10
Group Flags . . . . . . . . . . . . C-13
Global Rhythm Parameters . . . . . C-14
Rhythm Grouping of Beats . . . . . C-16
D. Understanding the M1754A Signal-Averaging
Process
Introduction . . . . . . . . . . . . . D-1
M1754A ECG Signal Averaging . . . . D-3
Signal Acquisition . . . . . . . . . D-3
SAECG Technique . . . . . . . . D-3
Lead System . . . . . . . . . . . D-3
SAECG Signal Path . . . . . . . D-4
Signal Amplication . . . . . . D-5
Signal Digitization . . . . . . . D-5
Signal Conditioning . . . . . . . D-5
Template Selection . . . . . . . . . D-6
Signal Averaging . . . . . . . . . . D-7
Beat Rejection . . . . . . . . . . D-8
Noise Reduction . . . . . . . . . D-10
Filtering . . . . . . . . . . . . . . D-11
Contents-5
Measurements . . . . . . . . . . . D-13
QRS Duration . . . . . . . . . . D-13
Terminal RMS Voltage . . . . . . D-14
Low Amplitude Signal Duration . . D-15
Total RMS Voltage . . . . . . . . D-17
Understanding the M1754A ECG
Signal-Averaging Rep ort . . . . . . D-18
Patient Information . . . . . . . . . D-19
Report Settings . . . . . . . . . . D-20
Individual Lead and Vector
Measurements . . . . . . . . . . D-20
Unltered Leads . . . . . . . . . . D-21
Absolute Filtered Leads . . . . . . . D-21
Vector Magnitude . . . . . . . . . D-21
Bibliography. . . . . . . . . . . . . D-22
Glossary
Index
Contents-6
Figures
3-1. Ten Seconds of 12 Leads on an Auto 3x4
Report. . . . . . . . . . . . . . 3-1
3-2. Ten Seconds of 12 Leads on an Auto 6x2
Report. . . . . . . . . . . . . . 3-2
3-3. Digitizing the ECG. . . . . . . . . . 3-3
3-4. The Filter Box on the ECG Report. . . 3-7
4-1. The HP ECG Analysis Pro cess. . . . 4-1
4-2. ECG Morphology Measurements. . . . 4-3
7-1. A Typical Interpretive Report. . . . . 7-2
7-2. An Auto 3x4 Report. (3x4) . . . . . 7-8
7-3. An Auto 3x4 Report with a Rh
ythm
Strip. (3x4, 1R) . . . . . . . . . 7-8
7-4. An Auto 3x4 Report with 3 Rh
ythm
Strips. (3x4, 3R) . . . . . . . . 7-9
7-5. An Auto 6x2 Report. (6x2) . . . . . 7-9
7-6. An Extended Measurements Report
(Morphology). . . . . . . . . . . 7-10
7-7. An Extended Measurements Report
(Rhythm). . . . . . . . . . . . 7-11
7-8. A Manual 3-Lead Format. . . . . . . 7-13
7-9. A Manual 6-Lead Format. . . . . . . 7-14
7-10. A Manual 12-Lead Format. . . . . . 7-14
8-1. Managing ECGs. . . . . . . . . . . 8-2
A-1. A Cabrera Report. (6x2) . . . . . . A-5
A-2. Frontal Plane Lead Axes. . . . . . . A-5
C-1. An Extended Measurements Report.
(Morphology) . . . . . . . . . . C-2
C-2. ECG Morphology Measurements. . . . C-3
C-3. An Extended Measurements Report.
(Rhythm) . . . . . . . . . . . C-10
Contents-7
D-1. The Signal-Averaging Process. . . . . D-4
D-2. The Noise Reduction Curve. . . . . . D-10
D-3. The Vector Magnitude Waveform. . . D-12
D-4. QRS Duration. . . . . . . . . . . . D-13
D-5. Terminal RMS Voltage. . . . . . . . D-15
D-6. Low Amplitude Signal Duration. . . . D-16
D-7. The RMS Voltage. . . . . . . . . . D-17
D-8. The SAECG Rep ort. . . . . . . . . D-18
Contents-8
Tables
5-1. Calibration . . . . . . . . . . . . 5-4
5-2. Borderline and Abnormally Prolonged
PR Intervals (ms) . . . . . . . . 5-8
5-3. T Wave Abnormality Lo calization . . 5-20
5-4. ST Segment Depression Localization . 5-22
5-5. ST Segment Elevation Lo calization . . 5-24
6-1. Calibration . . . . . . . . . . . . 6-4
6-2. Age vs. Ventricular Rate for Sinus
Rhythms . . . . . . . . . . . . 6-6
7-1. Basic Measurements . . . . . . . . 7-4
7-2. Calibration Signals . . . . . . . . . 7-6
B-1. Patient ID Fields . . . . . . . . . . B-2
B-2. Medication and Diagnosis Codes . . . B-3
B-3. Race Co des . . . . . . . . . . . . B-4
B-4. Severity Co des . . . . . . . . . . . B-4
D-1. Rep ort Settings . . . . . . . . . . D-20
D-2. Individual Lead and Vector
Measurements . . . . . . . . . . D-20
Contents-9
Why Use an Interpretive Cardiograph?
While a computer-interpreted ECG rep ort is not a
substitute for overreading by a qualied physician,
computerized interpretation is a very useful tool in
improving physician and sta productivity. The
program's basic measurements and interpretation can
help the physician save time when overreading reports.
The HP ECG Analysis program is highly eectiveat
screening normal ECGs. ECGs requiring comment
already have the initial computerized commentary on
them, so the physician has a head start on the nal
interpretation.
The HP ECG Analysis Program makes quick and
consistent measurements of the ECG. It makes detailed
measurements over the entire ECG, providing more data
for a more accurate interpretation. The program can
help identify problem areas for the physician. This saves
time for the physician or editing technician who may
only need to add, delete or mo dify a few statements.
1
Those who read ECGs infrequently may nd the
interpreted rep orts to be useful training to ols. They can
refer to reasons asso ciated with each statement for the
rationale for why a particular condition was suggested.
Why Use an Interpretive Cardiograph? 1-1
What You Can
Expect of the HP
ECG Analysis
Program
The HP ECG Analysis Program provides an analysis of
the amplitudes, durations and morphologies of the ECG
waveform. The ECG waveform analysis is based upon
standards of interpretation of these parameters as well as
upon calculations of the electrical axis and relationship
between leads.
Just as cardiologists may disagree on interpretations,
occasionally there is some disagreementbetween an
interpretation given by the computer program and that
made by a cardiologist. The interpreted ECG is a tool to
assist the physician in making a clinical diagnosis. It is
best used in conjunction with the physician's knowledge
of the patient, the results of the physical examination,
the ECG tracing, and other ndings.
1-2 Why Use an Interpretive Cardiograph?
How Computerized ECG Interpretation has
Developed
Development of computer-assisted ECG analysis began
in the 1960s. Initially only used in research facilities,
computer interpretation has developed into an accepted
tool for physicians.
Hewlett-Packard entered the computerized ECG analysis
eld in 1968 when it obtained and oered sev
existing analysis programs. In 1975 Hewlett-Packard
introduced one of the rst commercially available
systems to provide long-term ECG storage. ECGs were
stored, retrieved and managed on this rst HP 5600C
ECG Management system. The system analyzed ECGs
using the existing analysis programs. Hewlett-Packard
was able to identify some unique contributions it could
make to the eld of ECG analysis, which resulted in
the 1978 introduction of the ECG Criteria Language
(ECL). ECL enabled HP to write the Hewlett-Packard
Adult Criteria program, which replaced all of the earlier
programs.
2
eral
In 1980 Hewlett-Packard intro duced the HP 4700
PageWriter cardiograph, which digitally acquired ECGs.
In 1983 it became p ossible to transmit ECGs digitally
over phone lines to the HP 5600C ECG Managemen
system.
How Computerized ECG Interpretation has Developed 2-1
t
Computerized ECG interpretation b ecame available
on the cardiograph in 1983 when Hewlett-Packard
introduced the HP 4760AI PageWriter Intelligent
cardiograph. The proven ECG analysis program from
the HP 5600C was implemented on the HP 4760AI
cardiograph. Hewlett-Packard's Pediatric Criteria
program was also introduced in 1983 for b oth the HP
ECG Management system and the cardiograph.
Your HP interpretive cardiograph continues the tradition
of improving the p erformance of the analysis program.
The ECG Measurement program has been enhanced and
is now in its seventh revision. Simultaneous twelve-lead
acquisition allows detection of waveform onsets and
osets more accurately. The additional waveform
information helps to dene each beat's components
better in the measurements section of the analysis. This
increased denition produces more consistent results
overall.
The Criteria program continues to evolve. Since its
initial release, the program has undergone several
changes. The current release is the eighth revision of
the Adult analysis criteria and the fourth revision of
the Pediatric analysis criteria. Suggestions made byan
advisory group of respected electro cardiographers are
evaluated regularly for inclusion in subsequent releases.
2-2 How Computerized ECG Interpretation has Developed
Understanding Simultaneous 12-Lead Acquisition
Computer-assisted ECG analysis begins with acquiring
high quality, accurate ECG waveforms. Your HP
interpretive cardiograph simultaneously acquires up to
16 ECG leads (depending on the mo del) and analyzes 12
leads. Although the printed recording doesn't show it,
the Hewlett-Packard ECG Analysis Program uses the
full ten second recording in each lead. Figure 3-1 shows
how the Auto 3x4 format displays consecutive 2.5 second
segments of 12 leads, three leads at a time. Figure 3-2
shows how the Auto 6x2 format displays consecutive5
second segments of 12 leads, six leads at a time.
3
Figure TLD34 here.
Figure 3-1. Ten Seconds of 12 Leads on an Auto 3x4 Report.
Understanding Simultaneous 12-Lead Acquisition 3-1
Figure TLD62 here.
Figure 3-2. Ten Seconds of 12 Leads on an Auto 6x2 Report.
Besides the conventional 12 leads, your cardiograph may
have the capability to use one of the following sets of
supplemental leads:
pediatric leads V4R, V3R, V7
or Frank leads X, Y, Z
or research leads VX1, VX2, VX3, VX4
The p ediatric leads may b e used for conrming certain
right-sided interpretations in pediatric and, o ccasionally,
in adult applications. The research leads provide four
additional V-type leads that may be placed at your
discretion and recorded simultaneously with the standard
12 leads. Because their lo cation is not preassigned as
with the pediatric leads, they are simply labeled VX1
through VX4. The Frank leads, X, Y, and Z,
3-2 Understanding Simultaneous 12-Lead Acquisition
capture a three-dimensional, orthogonal view of the
heart's electrical activity. If they are available on your
cardiograph, any of these supplemental leads can be
displayed as rhythm strips with the conventional 12-lead
ECG. Regardless of which supplemental set of leads you
choose, all ECG waveforms are acquired simultaneously.
Digitizing the ECG
The continuous, analog ECG signal at the bo dy surface
is digitized at the input to the cardiograph. On some
cardiographs the signals are digitized internally,on
others, they are digitized by the patient module (as
shown in Figure 3-3). The ECG waveform data is
captured at a sample rate that signicantly exceeds the
250 samples per second at 5V resolution requirements
of the Hewlett-Packard Analysis Program. It is also fast
enough to accurately detect pacemaker pulses.
A/D Conversion
Patient Mo dule
Cardiograph
Figure 3-3. Digitizing the ECG.
Understanding Simultaneous 12-Lead Acquisition 3-3
As the ECG is converted to digital form, it is digitally
ltered. Not only is this approach more exible, it
provides superior results when compared to analog
ltering. The HP cardiograph's digital signal processing
ensures the most accurate reproduction of the patient's
ECG waveforms.
The American Heart Association's 1989
Recommendations for standardization and specications
in automated electrocardiography: bandwidth and digital
signal processing,
for adult ECGs to 125 Hz and for infant ECGs to
150 Hz. These recommendations are met by the data
acquisition scheme in all HP interpretive cardiographs.
The HP interpretive cardiograph's input circuitry has
a dynamic range that meets or exceeds current AAMI
standards.
extended the recommended bandwidth
3-4 Understanding Simultaneous 12-Lead Acquisition
Reducing Artifact
Electrical interference, patient respiration, patient
movement and muscle tremors can add noise and artifact
to the ECG signal. Poor quality electro des or inadequate
patient preparation can also degrade the ECG signal.
Your HP interpretive cardiograph has b een carefully
designed to substantially reduce artifact and accurately
record the ECG signal.
Common Mode
Rejection
Some of the noise sources that interfere with the ECG
signal are common to each electrode attached to the
patient. To the extent that they have an identical eect
on the ECG signal in each lead, they are removed
from the ECG by the cardiograph's input circuitry as
the signal is acquired and digitized. The amountof
reduction of these
common mode
signals is referred to as
the common mode rejection ratio. The common mo de
rejection ratio of your HP interpretive cardiograph's
input circuitry meets or exceeds current AAMI
standards.
The eects of ACinterference on the ECG are twofold,
common mode and dierential mode. The interference
which is common to all electrodes (common mo de) is
removed in the HP interpretive cardiograph's input
circuitry.Even though this circuitry greatly reduces
common mode noise, go od ECG technique is still
important. In the case of dierential mode, the magnetic
elds associated with electrical p ower interact with
the lead wires. This induces electrical signals which
appear as high frequency noise on the ECG. Ho
wmuch
distortion there is depends on the size of the loop
created by the lead wire and its orientation. A go od way
to prevent this distortion is to align the lead wires with
the patient's bo dy.
Understanding Simultaneous 12-Lead Acquisition 3-5
Using Filters
Computerized signal processing in the HP interpretive
cardiograph removes noise and artifact while minimizing
distortion of the ECG waveform. A sophisticated set of
digital lters can be selected by the op erator (or during
conguration) to optimize the ECG waveform. Digital
lters have the advantage over traditional analog lters
in their abilit y to be nely tuned to selected frequencies.
Unlike analog lters, digital lters are very stable over
time and temperature, meaning that ECGs taken under
various conditions will receive the same high quality
ltering.
With the exception of the AC lter, whichisvery
selective, there is always some tradeo in ltering
between delity and clarit y of the ECG trace. The more
ltering applied to the signal, the greater the possibility
of removing details of the ECG signal with noise of the
same frequency.
There are a variety of noise sources which can potentially
degrade the repro duction of the ECG signal. Sev
types of lters can be used in y
cardiograph to counteract them and reduce the artifact
in the ECG. In the lower right-hand corner of the HP
interpretive ECG report is a bo
about the ltering options used on each ECG. Note that
your PageWriter mayor may not have all of these lters.
our HP interpretive
x containing information
eral
3-6 Understanding Simultaneous 12-Lead Acquisition
Insert artwork here.
Figure 3-4. The Filter Box on the ECG Report.
Frequency Response
Filters
These lters suppress frequencies at the high and lo
ends of the ECG signal spectrum. The a
frequency response lter 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 (American Heart Asso ciation's 1989
Recommendations for standardization and specications
in automated electrocardiography: bandwidth and digital
signal processing
records and analyzes all ECGs with frequencies up
to 150 Hz. The 40 and 100 Hz lters only aect the
printed report. They result in a smoother-lo oking ECG
waveform, at the expense of eliminating some of the ne
detail in the signal. Small deections, notches, and slurs
may b e distorted or may disapp ear altogether if one of
these lters is selected for the Auto frequency response.
). Your HP interpretive cardiograph
vailable high
w
Understanding Simultaneous 12-Lead Acquisition 3-7
The available low frequency response lter settings are
0.05, 0.15, and 0.5 Hz. The 0.5 Hz lter is also the
baseline wander lter. The low frequency response lter
settings aect analyzed and printed ECGs.
The frequency response of the ECG is indicated in the
ECG rep ort's lter box.
AC Filter
Baseline Wander
Filter
The AC lter adaptively detects the ACinterference in
the ECG signal and very selectively removes it without
aecting the ECG. This lter aects analyzed and
printed ECGs.
The AC lter removes interference created by the
magnetic elds associated with electrical power
interacting with the lead wires. The frequency of the
ACinterference is very stable at 60 or 50 Hz, so the A
C
lter can remove the AC noise and leave the ECG signal
intact.
The line power, or AC, lter is indicated in the second
position of the ECG report lter bo
"(your cardiograph may also report the congured
\
line frequency 50 or 60). If the lter bo
xby the symbol
x does not
contain this symbol, the AC lter was not used for the
ECG.
Baseline wander is the term used to describe the slow
(typically 0.1{0.2 Hz) drifting of the ECG baseline up or
down during the ECG recording. Baseline wander may
result from patient respiration or from other sources.
Severe baseline wander can make it dicult to determine
the true wave shap es in the ECG.
3-8 Understanding Simultaneous 12-Lead Acquisition
Early analog attempts to suppress the eects of baseline
wander resulted in \smearing" the QRS complex
into the ST segment. In 1975, the American Heart
Association addressed this problem by recommending
that frequencies as low as 0.05 Hz be preserved in the
ECG signal to prevent the then common ST segment
distortion. (American Heart Association's 1975
Recommendations for standardization of leads and of
specications for instruments in electrocardiography and
vectorcardiography.
)
Since the advent of digital ECG acquisition in the
1980's, eective baseline wander suppression techniques
that do not distort the ST segmenthave been a part
of Hewlett-Packard's cardiographs. While the lower
frequency limit of 0.15 Hz, whichwe recommend for
normal use, eliminates baseline wander from most ECGs,
you may occasionally need extra suppression. The
4
Filter
5
key on the key panel can b e congured to allow the
operator to turn on the baseline wander lter when
needed. The baseline wander lter suppresses frequencies
below 0.5 Hz. It aects analyzed and prin
ted ECGs.
The baseline wander lter is represented by a \W" in the
ECG report's lter box.
Note
Because of the continuous recording of the ECG in
Manual mo de, a dierent 0.5 Hz (baseline wander)
lter that may distort the ST segmentmust be used.
Therefore, do not attempt to interpret the contour
aspects of Manual ECGs at this setting. If contour
analysis is important in Manual mode, use the 0.05 Hz
Manual frequency response setting which minimizes the
ST segment distortion. Regardless of the low frequency
setting in Manual mo de, the rhythm characteristics of
the ECG are accurately recorded.
Understanding Simultaneous 12-Lead Acquisition 3-9
Artifact Filter
The Artifact lter removes skeletal muscle artifact. This
source of noise is the most dicult to eliminate because
it has the same frequencies as the ECG signals. The
Artifact lter, while eliminating skeletal muscle artifact,
also removes low amplitude, high frequency components
from the ECG.
Specically, the lter removes up to 50V of signals
in the frequency range from 5 Hz to 150 Hz which can
aect P waves as well as the entire QRS-T complex. Use
the Artifact lter only as a last resort for ECGs which
would otherwise b e unreadable due to signican
t levels
of muscle artifact. The Artifact lter only aects ECG
data on the printed ECG report and not ECG data that
is analyzed.
Monitoring ECG
Quality
The letter \F" in the far left position in the lter bo
x
indicates that the Artifact Filter was applied to this
ECG.
The HP interpretive cardiograph monitors ECG trace
quality throughout the lead attachment, ECG acquisition
and analysis process to ensure that you receive the
highest possible quality ECG trace. There are four
possible ways that trace quality problems are indicated,
depending on howyour cardiograph is equipped:
on the patient mo dule display during electro de
attachment
on the preview screen before recording the ECG
on the keyboard display during analysis
in the analysis statements on the printed report
3-10 Understanding Simultaneous 12-Lead Acquisition
Loading...