Welch Allyn Means ECG Physicians Manual for CP Series Electrocardiographs User Manual
Welch Allyn
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PO Box 220
Skaneateles Falls, NY
13153-0220 USA
© 2013, DIR: 80011564, Ver: E
www.welchallyn.com
MEANS ECG Physicians’ Manual
for Welch Allyn CP Series
Electrocardiographs
MEANS Physicians Manual
Caution
Federal US law restricts sale of the device identified in this manual to, or on the order of, a
licensed physician.
The information contained in this manual is subject to change without notice. No part of this manual
may be photocopied, reproduced, or translated into another language without the prior written
consent of Welch Allyn.
About this manual
This manual documents the logic behind the diagnostic criteria provided by the Welch Allyn
CP series interpretive resting ECG system. It is provided as a supplement to the
electrocardiographs user's manual for those interested in or requiring knowledge of specific details
of the system's algorithms. Please refer to the electrocardiographs general user's manual for
information about use, installation and configuration, as well as applicable precautions and
warnings.
The algorithms employed in our system are collectively known as the Modular ECG Analysis
System, MEANS. MEANS was developed by the Department of Medical Informatics at the Erasmus
University of Rotterdam in the Netherlands. Portions of this manual are copyright 1999 by the
Department of Medical Informatics, Faculty of Medicine and Health Sciences, Erasmus University
Rotterdam, P.O. Box 1738, 3000 DR Rotterdam, the Netherlands.
The initial sections of this manual provide an overview of the general signal processing methodology
involved, followed by detailed descriptions of the contour and rhythm analysis statement logic, and
an index to all statements. The final section provides an analysis of the performance of MEANS.
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Contents
1 INTRODUCTION ................................................................................................................................... 4
1.1 Signal conditioning ............................................................................................................................... 4
1.2 Pattern recognition ............................................................................................................................... 5
1.3 Parameter extraction ............................................................................................................................ 5
1.4 Diagnostic classification ....................................................................................................................... 6
1.5 Outline of the manual ........................................................................................................................... 6
1.6 References ........................................................................................................................................... 7
2 CONTOUR ANALYSIS .......................................................................................................................... 8
2.1 Contour parameters ............................................................................................................................. 8
2.2 Dextrocardia and arm electrodes reversal.......................................................................................... 10
2.3 Wolf-Parkinson-White syndrome (WPW) ........................................................................................... 10
2.4 Left Bundle Branch Block (LBBB) ...................................................................................................... 11
2.5 Right Bundle Branch Block (RBBB).................................................................................................... 12
2.6 Incomplete Right Bundle Branch Block (IRBBB) ................................................................................ 13
2.7 Intraventricular conduction delay (IVCD) ............................................................................................ 13
2.8 Atrial overload .................................................................................................................................... 14
2.9 Atrial abnormalities ............................................................................................................................. 14
2.10 Axis deviations and fascicular blocks ................................................................................................. 15
2.11 Low QRS voltage ................................................................................................................................ 16
2.12 QT abnormalities ................................................................................................................................ 16
2.13 Left ventricular hypertrophy (LVH) ...................................................................................................... 17
2.14 Right ventricular hypertrophy.............................................................................................................. 18
2.15 Infarction ............................................................................................................................................. 19
2.16 Pulmonary disease ............................................................................................................................. 25
2.17 ST elevation ....................................................................................................................................... 25
2.18 ST and T abnormalities ...................................................................................................................... 26
2.19 Repolarization .................................................................................................................................... 27
2.20 Miscellaneous ..................................................................................................................................... 28
2.21 Interaction of statements .................................................................................................................... 29
2.22 Combination of statements ................................................................................................................. 31
3 RHYTHM ANALYSIS ........................................................................................................................... 32
3.1 Introduction ......................................................................................................................................... 32
3.2 Rhythm parameters ............................................................................................................................ 33
3.3 Decision tree ...................................................................................................................................... 34
3.4 Group 1: Rhythms with artificial pacemaker spikes ............................................................................ 37
3.5 Group 2: Non-dominant QRS complexes ........................................................................................... 37
3.6 Group 3: Rhythms with atrial flutter or tachycardia ............................................................................. 43
3.7 Group 4: Regular rhythms with P/QRS 0.15 .................................................................................... 44
3.8 Group 5: Regular rhythms with 0.15<P/QRS1.0 and PR range > 60 ms .......................................... 45
3.9 Group 6: Regular rhythms with P/QRS > 1.0 and PR range 30 ms ................................................. 46
3.10 Group 7: Regular rhythms with P/QRS > 1.0 and PR range > 30 ms................................................. 47
3.11 Group 8: Irregular rhythms with P/QRS 0.15 ................................................................................... 48
3.12 Group 9: Rhythms with paroxysmal acceleration or deceleration of ventricular rate ......................... 48
3.13 Group 10: Irregular rhythms with 0.15 < P/QRS 0.9 and PR range 30 ms ................................... 49
3.14 Group 11: Irregular rhythms with 0.15 < P/QRS 0.9 and PR range > 30 ms ................................... 50
3.15 Group 12: Irregular rhythms with 0.9 < P/QRS 1.2 and PR range > 30 ms ..................................... 51
3.16 Group 13: Irregular rhythms with P/QRS > 1.2 and PR range > 30 ms .............................................. 51
3.17 Group 14: Irregular rhythms with P/QRS > 1.0 and PR range 30 ms .............................................. 52
3.18 Group 15: Rhythms with constant PR interval .................................................................................... 53
4 STATEMENT INDEX ........................................................................................................................... 55
5 THE PERFORMANCE OF MEANS ..................................................................................................... 60
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1 Introduction
Computers and humans interpret ECG signals in fundamentally different ways. The principal
difference is in the manner in which a computer “looks at” the signal. To be interpretable, a
continuous (analog) signal must be converted into numbers, i.e., digitized. The signals are
measured at short intervals, and the measured values (the samples) are stored as digital
numbers. On this set of numbers the analysis must take place. The sampling must be dense
enough to ensure sufficient fidelity in rendering the original analog signal. Current standards
for ECG recording recommend a sampling rate of 500 Hz or higher.
After collection of the data, the processing follows a number of successive stages:
Signal conditioning
Pattern recognition
Parameter extraction
Diagnostic classification
Each of these steps must be performed correctly to ensure a satisfactory final result. If, for
instance, the signals are not correctly cured of disturbances this may result in a faulty
waveform recognition. The diagnostic classification is then likely to come out wrong. The
successive steps will now be discussed more extensively.
1.1 Signal conditioning
The ECG signal can be disturbed in several ways:
Continuous noise of a single frequency, sometimes with higher harmonics, due to 50 or
60 Hz AC mains interference.
Drift: more or less gradual baseline shifts, e.g., caused by respiration.
Bursts of noise of mixed frequencies and various amplitudes due to electrical signals from
active muscles.
Sudden baseline jumps due to changes in electrode-skin impedance.
Spikes: isolated, large amplitude variations of short duration.
Amplitude saturation of the signal.
To correct these disturbances, several techniques have been used. Mains interference is
suppressed by an adaptive filter that estimates the coming noise estimates and subtracts the
estimates from the encountered signal. Baseline shift is corrected by simply connecting the
onsets of successive QRS complexes by straight lines and determining the signal amplitudes
with respect to these line segments. Beat selection and averaging (see below) help to reduce
disturbances of muscle noise. If a disturbance is detected that may affect the diagnostic
classification, the program issues a warning.
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1.2 Pattern recognition
This part deals with the analysis of the various waveforms. First of all, the QRS complexes
must be detected. No other waves or artifacts should be labeled as such. The intervals
between QRS complexes are measured and stored. After all QRS complexes have been
detected, they are typified, i.e., a comparison is performed that gives rise to classes of similar
QRS complexes.
Often there is only one type of QRS complex. If there are more, the “ordinary,”
“representative” or “dominant” one is established; the others are “extraordinary” or “non-
dominant”. Mostly, the number of dominant complexes in a recording is larger than that of the
non-dominant ones. In special cases this may not be true. In bigeminy their number may be
equal to that of the non-dominant complexes, or be one less or one more, depending on when
the recording starts and stops. If runs of tachycardia occur, the unusual complexes in a
recording may even outnumber the dominant ones.
The second step is to search for atrial activity. Both P waves and flutter waves can be
detected, when present. PP and PR intervals are also measured and stored for use in the
rhythm analysis.
The third step is to mutually compare the ST-T segments of the dominant complexes. For the
calculation of the averaged complex, only complexes are selected that have not only similar
QRS, but also similar ST-T. In this way complexes that are disturbed by spikes or sudden
baseline jumps are discarded.
For the morphological analysis, the selected dominant P-QRS-T complexes are averaged into
one complex. The main advantage of averaging is to improve the signal-to-noise ratio. Noise
is random and, in the averaging, the positive and negative oscillations will cancel out. An
additional advantage is that the analysis now has to be performed only once, i.e., on a single
representative complex. It may occur that in the averaged complex a P wave appears which
was not consistently detectable in the rhythm analysis, or vice versa.
The final step in the pattern recognition process is the determination of the zero level in the
representative P-QRS-T complex and the identification of the points of onset and offset of P,
QRS, and T. The zero level is determined for the averaged complex per lead in an interval
preceding the onset of the QRS complex. Onsets and offsets however are determined
simultaneously over all leads together.
1.3 Parameter extraction
After the onset and end points of P, QRS and T waves have been established, the relevant
parameters can be measured to provide the input for the diagnostic logic. Besides amplitudes
and durations, other measurements such as surface areas under the signal are derived. Most
measurements are made on the averaged complex in each lead separately (e.g., R
amplitude, Q duration), but some are derived taking all leads into account (e.g., overall QRS
duration, PR interval). These durations are generally longer than one would measure by hand
in individual leads or lead groups since the first onset in any lead and the last offset are taken
into account.
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1.4 Diagnostic classification
The diagnostic logic operates on the parameters and produces both a rhythm classification
and a contour or morphology classification. The criteria used by the computer may differ from
the criteria used in the ECG textbooks. The basic reason is that a human observer is
inaccurate but flexible and creative, a computer precise and obedient but rigid in its operation.
There are several specific reasons why ECG criteria in the program may differ from the
conventional ones. First, there is no uniformity of criteria in the literature. Then, criteria may
be based on inaccurate measurement by eye. Also, ECG measurements may be “falsified” for
the ease of the reader: axis calculations are generally made from the amplitudes of QRS
complexes rather than from the surface areas under the QRS tracings as prescribed by
theory. Further, criteria are sometimes not quantitatively defined (How flat must a flat ST-T
be? How slurred is a slurred QRS upstroke?) or their measurement is not unequivocally
prescribed. For the computer program to work, a quantitative definition must somehow be
decided upon. Moreover, conventional criteria may have been based on measurements
produced by technically outdated instrumentation. The amplitudes of R waves have been
consistently underestimated, especially in children, due to filtering effects by too low
frequency response of the electrocardiographs. Finally, a human interpreter may deviate from
strict criteria as he sees fit: sometimes criteria have been made to meet a priori expectations.
In one respect, the computer is inferior to the human observer: although the computer can
measure very accurately, its powers of pattern recognition are inferior. For instance, it will
have great trouble in detecting a P wave buried in a ST segment which is easily seen by the
human eye.
1.5 Outline of the manual
The following of this manual consists of two main parts. One part describes the diagnostic
criteria that are employed in the contour classification of the Modular ECG Analysis System
(MEANS), the other describes the criteria used in the rhythm classification of MEANS. Each
part contains a brief introductory section, a description of the measurements that are used in
the diagnostic logic, and a comprehensive list of statements and corresponding diagnostic
criteria. Related statements have been grouped in sections, e.g., all statements related to
intraventricular conduction delay, left ventricular hypertrophy, etc. Finally, an index of the
statements that can be generated by the program is provided on page 55.
A general format is used to specify the diagnostic criteria. The statement is given first,
followed by one or more conditions that must be fulfilled for the statement to be issued by the
program. Multiple conditions are combined with the use of logical “and” and “or” connectives,
binding the (combinations of) conditions that have the same level of indentation. For example:
Say: “probable inferior infarct”
if: Q duration 40 ms and 0.2 Q/R ratio < 0.3 in aVF
or 30 Q duration < 40 ms and Q/R ratio 0.3 in aVF
or Q duration in aVF 20 ms
and Q duration 50 ms and Q amplitude > 300 µV in III
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1.6 References
In several publications, the program structure and signal analysis part of MEANS have been
described. One publication, which also provides many references for further reading, is:
Van Bemmel JH, Kors JA, Van Herpen G. Methodology of the modular ECG analysis
system MEANS. Methods Inf Med 1990;29:346-53.
The measurement and classification parts of MEANS have extensively been evaluated, both
by the developers themselves and by independent observers. A major evaluation study in the
field of automated electrocardiography has been the project Common Standards for
Quantitative Electrocardiology (CSE), in which about 15 ECG computer programs from all
over the world have participated. The CSE study consisted of two parts, one pertaining to the
measurement part of the ECG programs, the other to the diagnostic classification part. Two
key references are:
Willems JL, Arnaud P, Van Bemmel JH, Bourdillon PJ, Degani R, Denis B, et al. A
reference database for multi-lead electrocardiographic computer measurement programs.
J Am Coll Cardiol 1987;10:1313-21.
Willems JL, Abreu-Lima C, Arnaud P, Van Bemmel JH, Brohet C, Degani R, et al. The
diagnostic performance of computer programs for the interpretation of
electrocardiograms. N Engl J Med 1991;325:1767-73.
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Name
Description
Heart rate
Ventricular rate (in beats per minute, BPM)
P axis
Axis of the P wave (in degrees, from –180 to 180)
P duration
Duration of the P wave (in ms)
PR interval
Duration of the PR interval (in ms)
QRS axis
Axis of the QRS complex (in degrees, from 180 to 180)
QRS duration
Duration of the QRS complex (in ms)
Corrected QT interval
QT interval corrected for heart rate according to Bazett’s formula:
QTc = QT * (HR/60) (in ms)
Hodges’ formula:
QTc = QT + 1.75 × (HR-60)
Note: The CP 50, CP 100 and CP 200, and the CP 150 and
CP 250 devices support either the Bazett or Hodges QTc
calculation on the printout. MEANS always uses the Bazett
calculation in its interpretive output statements.
2 Contour analysis
2.1 Contour parameters
All parameters that are used in the diagnostic criteria of the contour classification are
measured in the representative P-QRS-T complex. The lead-independent, overall parameters
are presented in Table 1.
Table 1. Lead-independent parameters for the contour classification.
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Name
Description
Delta wave
Slurring of the initial part of the QRS complex.
Negative J amplitude
Amplitude of a negative J point (in µV).
Positive J amplitude
Amplitude of a positive J point (in µV).
Negative P amplitude
Amplitude of the negative deflection of the P wave (in µV).
Positive P amplitude
Amplitude of the positive deflection of the P wave (in µV).
P notch
Notch in the positive deflection of the P wave.
Q amplitude
Maximum amplitude of the Q wave (in µV).
Q duration
Duration of the Q wave (in ms).
negative QRS
amplitude
Amplitude of the largest negative deflection of the QRS
complex (in µV).
positive QRS
amplitude
Amplitude of the largest positive deflection of the QRS
complex (in µV).
top-top QRS amplitude
Amplitude of largest positive plus largest negative deflections
of the QRS complex (in µV).
QRS area
Area under the positive deflections of the QRS complex
minus area under the negative deflections of the QRS
complex (in mVms).
Q/R ratio
Ratio of the maximum amplitudes of the Q and R waves.
QS pattern
QRS complex consisting of a Q wave only.
R amplitude
Maximum amplitude of the R wave (in µV).
R duration
Duration of the R wave (in ms).
R notch
Notch in the positive deflection of the QRS complex.
R amplitude
Maximum amplitude of the R wave (in µV).
R/S ratio
Ratio of the maximum amplitudes of the R and S waves.
S amplitude
Maximum amplitude of the S wave (in µV).
S duration
Duration of the S wave (in ms).
S amplitude
Maximum amplitude of the S wave (in µV).
ST slope
Slope of the ST segment (in µV/100 ms).
Negative T amplitude
Amplitude of the negative deflection of the T wave (in µV).
Positive T amplitude
Amplitude of the positive deflection of the T wave (in µV).
The parameters that are computed for each lead separately, are shown in Table 2. All
amplitudes are taken as absolute values.
Table 2. Lead-dependent parameters for the contour classification.
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2.2 Dextrocardia and arm electrodes reversal
Skip tests
if: QRS area in I > 0
or top-top QRS amplitude in I 150 µV
or positive T wave in I
or 100 P axis 100
Say: “dextrocardia”
if: top-top QRS amplitude in V6 500 µV
Say: “arm electrodes interchanged”
if: top-top QRS amplitude in V6 > 500 µV
If either test passed, no further contour analysis is performed.
2.3 Wolf-Parkinson-White syndrome (WPW)
The presence of delta waves is a necessary condition for the diagnosis of WPW. The length
of the PR interval is another obvious parameter to use. However, it is not a necessary
criterion, for if the accessory pathway is slowly conducting, the PR interval could be normal.
Moreover, WPW can occur in the absence of P waves, for example in the presence of atrial
fibrillation. For this reason this criterion has not been used to construct the diagnosis of WPW,
but has only to distinguish between LBBB and WPW type B in case both diagnoses have
been made (see section LBBB).
Say: “WPW”
if: delta waves in at least 2 extremity leads
and delta waves in at least 2 precordial leads
and QRS duration > 100 ms
If test WPW passed, only a test for LBBB is performed.
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2.4 Left Bundle Branch Block (LBBB)
The primary condition for the diagnosis of a complete block is prolonged QRS duration. In the
program the limit is 130 ms. The normal initial QRS activity to the right and anterior is smaller
than normal or absent. Soon after the beginning of QRS the electrical forces turn posteriorly,
and somewhat to the left and mostly horizontally. The predominantly posterior activity
produces generally deep S waves in V1 and V2 while the R waves in V5 and V6 tend to
remain low. Therefore, the program requires r waves in V1 and V2 to be minor (they even
may be lacking, and in V5 and V6 q’s must be reciprocally absent). This is expressed by the
requirement of a net negative area and R/S ratio of less than 1/3 in V1. The R waves in V5
and V6 will have a delayed intrinsicoid deflection. Septal infarction should not be diagnosed in
the presence of LBBB. Finally, if LBBB and WPW both come into consideration the case is
decided by the duration of the PR interval.
Skip tests
if: Q wave in any of I, V5, V6
or QRS duration 130 ms
Say: “LBBB”
if: QRS area in V1 < 100 mVms
and S amplitude in V6 1000 µV
or 100 QRS area in V1 < 40 mVms
and negative QRS amplitude > 3 times positive QRS amplitude in V1
and QRS area > 0 in V6
and intrinsicoid deflection at 50 ms in V5 or V6
Say: “possible LBBB”
if: QRS area in V1 < 100 mVms
and S amplitude in V6 > 1000 µV
or 100 QRS area in V1 < 40 mVms
and negative QRS amplitude > 3 times positive QRS amplitude in V1
and QRS area > 0 in V6
and intrinsicoid deflection at < 50 ms in V5 and V6
or QRS area 0 in V6
and intrinsicoid deflection at 50 ms in V5 or V6
if: test LBBB passed
and test WPW passed
and QRS area in V1 5 mVms
and 0 QRS axis 90
then:
Say: “possible LBBB”
“possible WPW”
if: PR interval > 140 ms
suppress: “LBBB”
if: PR interval 140 ms
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2.5 Right Bundle Branch Block (RBBB)
The ECG abnormality in RBBB consists of a late, protracted QRS activity to the right and
anterior with concomitant overall increase of QRS duration ( 130 ms). The program therefore
looks for a late R, an R or a broad notched R wave in V1 or V2, all with delayed intrinsicoid
deflection, and reciprocal broad S waves in the lateral leads.
The QRS axis has a certain influence on the S duration in lead I. Lead I, although horizontal
in geometrical space, is tilted upward on the left side in electrical space. In left axis deviation,
this will result in a projected S wave which is less deep and of shorter duration than the S
wave in V5 or V6 leads that are tilted downwards on the left. This aspect has been taken into
account for the criteria on the S duration. In the presence of RBBB, a diagnosis of RVH may
also be entertained if the R wave in V1 is tall.
Skip tests
if: QRS duration < 130 ms
or S amplitude in V1 100 µV
Say: “RBBB”
if: S duration 50 ms in I, V5, V6
and intrinsicoid deflection at 55 ms in V1 or V2
or S duration 30 ms in V5 or V6
and S duration in I 20 ms and QRS axis < 45
or S duration in I 30 ms and QRS axis 45
and R wave or R notch in V1 or V2
or Q wave and intrinsicoid deflection at 50 ms in V1
if: test RBBB passed
and Q amplitude > 100 µV in V1 and V2
then:
Say: “septal infarct”
if: Q duration 30 ms in V1 or V2
Say: “probable septal infarct”
if: Q duration 20 ms in V1 or V2
Suppress “RBBB”
if: Q amplitude in V2 100 µV
or R amplitude in V2 < 200 µV
or intrinsicoid deflection in V2 at < 50 ms
if: test RBBB passed
then:
Say: “posterior infarct”
if: positive QRS amplitude in V1 1500 µV
and positive T amplitude in V1 700 µV
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2.6 Incomplete Right Bundle Branch Block (IRBBB)
For IRBBB, comparable conditions apply the same as RBBB, but QRS duration is less
increased (between 110 and 130 ms) and the intrinsicoid deflection time is shorter.
Skip tests
if: QRS duration 130 ms
or QRS duration 110 ms
or S amplitude in V1 100 µV
Say: “incomplete RBBB”
if: R amplitude 300 µV in V1 or V2
or R in V1
and positive P wave in V1
or S duration 40 ms in I, V5, V6
and intrinsicoid deflection at 45 ms in V1 or V2
2.7 Intraventricular conduction delay (IVCD)
Only in the absence of diagnosable RBBB, LBBB or WPW will a statement of intraventricular
conduction delay be made. The delay can be classified in different grades of severity.
Say: “slight intraventricular conduction delay
if: 112 ms QRS duration < 126 ms
Say: “moderate intraventricular conduction delay”
if: 126 ms QRS duration < 140 ms
Say: “marked intraventricular conduction delay”
if: 140 ms QRS duration < 180 ms
Say: “very marked intraventricular conduction delay”
if: QRS duration 180 ms
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2.8 Atrial overload
The diagnosis of right or left atrial overload (RAO and LAO) will be considered in the
presence of a normal P axis. Otherwise an unusual P axis will be reported.
In LAO the P wave is characterized by a broad negative terminal part in lead V1 and an
increase of overall duration. In RAO a tall P wave in lead II and aVF and/or in V1 and V2 is
expected. In diagnosing RAO an adjustment has been built in for heart rate: in tachycardia the
amplitude of the P wave has to be slightly higher to qualify for the diagnosis, than with normal
heart rate. The reason for this adjustment is the superposition of the P on the preceding U
wave or T wave occurring at higher heart rates. Above 130 BPM no attempt is made to
diagnose RAO.
Skip tests
if: P axis 30
or P axis > 100
Say: “left atrial overload”
if: negative P amplitude in V1 180 µV
and P duration > 135 ms
or LVH test passed
Say: “right atrial overload”
if: heart rate < 100 BPM
and positive P amplitude 275 µV in V1 or V2
or positive P amplitude in II + positive P amplitude in aVF 525 µV
or 100 heart rate < 130 BPM
and positive P amplitude 300 µV in V1 or V2
or positive P amplitude in II + positive P amplitude in aVF 575 µV
2.9 Atrial abnormalities
Say: “unusual P axis”
if: P axis 30
or P axis > 100
Say: “intra-atrial conduction delay”
if: P duration > 135 ms
and negative P amplitude in V1 180 µV
Say: “high P voltage”
if: test RAO did not pass
and positive P amplitude 275 µV in any lead
and heart rate < 100 BPM
or positive P amplitude 300 µV in any lead
and 100 heart rate < 130 BPM
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2.10 Axis deviations and fascicular blocks
Axis deviations are distinguished in vertical, right, marked right and extreme right inferior on
the one hand and horizontal, left, marked left and extreme right superior on the other hand.
Besides a complete LBBB it is also possible to find a left anterior or posterior fascicular block
(LAFB or LPFB). These statements will always be tested in combination with an axis
deviation. (LPFB can only be diagnosed in conjunction with RBBB.)
In the presence of inferior infarction no statement of left axis deviation is given, it being due to
initial negativity in the inferior leads. In the presence of LBBB the axis tends to deviate to the
left. Therefore the threshold for stating left axis deviation is increased. Moreover, the
diagnosis of complete LBBB takes precedence over that of left anterior fascicular block.
Say: “vertical axis”
if: 80 < QRS axis 100
Say: “right axis deviation”
if: 100 < QRS axis 120
Say: “marked right axis deviation”
if: 120 < QRS axis 150
Say: “extreme right inferior axis deviation”
if: 150 < QRS axis 180
Say: “consistent with LPFB”
if: 120 < QRS axis 180
and RBBB
Say: “horizontal axis”
if: 30 QRS axis < 10
if: test LBBB did not pass
then:
Say: “left axis deviation”
if: 60 QRS axis < 30
Say: “marked left axis deviation”
if: 120 QRS axis < 60
Say: “extreme right superior axis deviation”
if: 180 QRS axis < 120
Say: “consistent with LAFB”
if: 120 QRS axis < 45
and S amplitude in III > 500 µV
and S amplitude in III < S amplitude in II
if: test LBBB passed
then:
Say: “left axis deviation”
if: 120 QRS axis < 45
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2.11 Low QRS voltage
Say: “low QRS voltage in extremity leads”
if: top-top QRS amplitude 500 µV in all extremity leads
Say: “low QRS voltage in precordial leads”
if: top-top QRS amplitude 1000 µV in all precordial leads
Say: “low QRS voltage”
if: both previous tests passed
2.12 QT abnormalities
The QT interval is measured from the beginning of the Q wave until the end of the T wave. In
the case of intraventricular conduction delay, the excess QRS duration (>106 ms) is
subtracted from the measured QT. A correction is made for the heart rate, using Bazett’s
equation: corrected QT interval = QT interval * (heart rate/60). The corrected QT interval
renders the QT interval for a standard heart rate of 60 beats per minute. The upper limit of
470 ms is increased to 500 ms in case of infarct.
Skip tests
if: WPWB and QRS duration < 126 ms
or heart rate 110 BPM
Say: “short QT interval, consider hypercalcaemia”
if: corrected QT interval < 330 ms
Say: “long QT interval, consider hypocalcaemia or quinidine-like drug”
if: corrected QT interval 470 ms
and no infarct test passed
or corrected QT interval 500 ms
and any infarct test passed
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2.13 Left ventricular hypertrophy (LVH)
The diagnosis of LVH rests on three types of parameters: voltage, shape, and repolarization.
For each parameter, points are accumulated according to its degree of abnormality. The
higher the score, the higher the overall grading of the LVH. The following gradations are
distinguished, in which severity and probability go together: “consider”, “possible”, “probable”,
“definite”, “pronounced”, and “very pronounced”.
The voltage is determined in both the horizontal and frontal planes, but only the plane with the
highest score will be used in the classification. For the horizontal plane the voltages are
measured in leads V1, V5 and V6. In the frontal plane leads I and II are used. If the voltage in
either plane does not meet the criteria, no further analysis for diagnosing LVH will be done.
In both planes an adjustment has been made for age. At age 35 no correction is applied, at
age 90 a maximal correction of about 6 mm in the precordial measurement and of 3 mm in
the frontal plane is added to the measured voltage. For people younger than 35 years the
adjusted voltage will be lower than the calculated voltage, for older people the opposite
applies.
The shape of the QRS complex is determined in that plane where the highest voltage score is
reached. The main parameters on which the shape score is based are the intrinsicoid
deflection and the sequence of small r waves in the right and tall R waves in the left precordial
leads.
In the category repolarization the program tests for the presence and degree of ST
depression and T negativity in the leads I, II, aVL, aVF, V5, and V6. Strain scores in the
frontal and horizontal planes are determined using the ST slope and the J- and T-wave
amplitudes.
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2.14 Right ventricular hypertrophy
The diagnosis RVH is not subdivided in such an elaborate way as LVH is. A distinction
between probable and definite can be made.
Presence of left or right atrial overload helps to make the diagnosis of RVH, because it
provides circumstantial evidence. In the presence of RBBB, IRBBB or posterior infarction, the
program may issue a statement that RVH is still to be considered. A more definite statement
of RVH is ruled out, to prevent too much over-diagnosing.
Skip tests
if: QRS duration 160 ms
or QRS axis 0
or test RBBB passed
or test LBBB passed
Say: “RVH”
if: R/S ratio 1 in V1 and Q/R ratio 1 in V1
and positive QRS amplitude in V1 500 µV
and positive T amplitude < negative T amplitude in V1 and V2
or positive QRS amplitude < S amplitude in V5 or V6
or QRS axis 100
and LAO or RAO
or QRS axis 120
and R amplitude < S amplitude in II
and S amplitude in aVF 200 µV
and S duration in aVF < 40 ms
and tests for high-lateral, lateral, and inferior infarcts did not pass
Say: “probable RVH”
if: Q/R ratio 1 and R/S ratio 1 in V1
and positive QRS amplitude in V1 1500 µV
and positive T amplitude in V1 < 700 µV
or Q/R ratio 1/2 and R/S ratio 2 in V1
and positive QRS amplitude in V1 300 µV
and positive T amplitude < negative T amplitude in V1
or positive QRS amplitude < S amplitude in V5 or V6
or QRS axis 80
and positive T amplitude < negative T amplitude in V1 and V2
and positive QRS amplitude < S amplitude in V5 or V6
and S amplitude in aVF 200 µV
and S duration in aVF < 40 ms
and test for lateral infarct did not pass
or QRS axis 100
and LAO or RAO
Say: “consider RVH”
if: test RBBB passed
and QRS axis -45
and positive T amplitude < negative T amplitude in V2
or test IRBBB passed
and positive QRS amplitude in V1 500 µV
and positive QRS amplitude > negative QRS amplitude in V1
or test posterior infarct passed
and QRS axis > 100
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2.15 Infarction
This section of the program classifies an infarction according to location and estimates the
probability of its presence. The diagnosis of infarction is largely based on the presence and
duration of Q waves, Q/R ratios, and QS patterns. T and ST abnormalities are used in
statements on the age of the infarct (see section Repolarization).
The location of the infarction is determined by the leads in which the abnormalities are found.
The program distinguishes six locations: septal (lead V1, V2), anterior (V3, V4), lateral (V5,
V6), high lateral (I, aVL), inferior (aVF, III), and posterior (V1, V2). Lead II may be involved in
inferior infarction as well as in lateral infarction. Combined and more extensive infarcts will
generate infarct statements for more than one location (see section Combination of
statements).
Four degrees of probability are distinguished: “definite”, “probable”, “possible”, or “consider”.
Criteria on which a diagnosis of infarction has been made can also lead to other diagnoses,
like LBBB, RBBB, LVH and RVH. The choice between these possible diagnoses is based on
exclusion logic in the program, and in some situations, probabilities are adapted or criteria are
tightened.
Inferior infarction
An abnormal Q wave must be found in aVF and either II or III to even consider the diagnosis
of inferior infarction. As a rule the Q wave in aVF is shallower and shorter than that in III. Its
threshold to qualify as an infarct Q can therefore be lower.
Inferior infarction may produce a left (i.e., superior) axis deviation if one only considers the
ratio of upward and downward forces. In inferior myocardial infarction, however, this ratio is
shifted due to initial negativity (Q in aVF) whereas in ordinary left axis deviation it is
associated with deepening of the S wave in aVF.
Skip tests
if: Q amplitude + R amplitude in aVF < 200 µV
or Q amplitude in aVF 100 µV
or Q amplitude in II 70 µV
and Q amplitude in aVF 70 µV
or Q amplitude in III 100 µV
Say: “inferior infarct”
if: Q duration 40 ms and Q/R ratio 0.3 in aVF
Say: “probable inferior infarct”
if: Q duration 40 ms and 0.2 Q/R ratio < 0.3 in aVF
or 30 Q duration < 40 ms and Q/R ratio 0.3 in aVF
or Q duration in aVF 20 ms
and Q duration 50 ms and Q amplitude > 300 µV in III
Say: “possible inferior infarct”
if: 30 Q duration < 40 ms and 0.2 Q/R ratio < 0.3 in aVF
or 20 Q duration < 30 ms and Q/R ratio 0.3 in aVF
and Q duration in III 40 ms
or Q duration in aVF 20 ms
and 40 Q duration < 50 ms and Q amplitude > 300 µV in III
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