Download Evaluation of R Wave Amplitude Changes versus ST

Evaluation of R Wave Amplitude Changes
versus ST-Segment Depression in Stress Testing
PETER E. BONORIS, M.D., PAUL S. GREENBERG, M.D.,
GEORGE W. CHRISTISON, MARK J. CASTELLANET, M.D., AND M. H. ELLESTAD, M.D.
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SUMMARY Exercise ECGs and coronary angiograms were
reviewed in 266 patients (81 normals and 185 with significant coronary artery disease). Thirty-three false positive and 96 false negative
ST responses to stress testing were purposely chosen to determine if
the R wave could reduce the number of false ST responses. R wave
amplitude changes were measured in the control and in the immediate
postexercise period. An increase or no change in R wave was taken as
evidence of an abnormal response, while a decrease in the R wave was
a normal response. The sensitivity by ST segment was 48% and the
specificity was 59%. These values were low because of the large
number of false positive and negative ST responses in the study. It
was our purpose to determine if these lowered values could be
significantly improved by the R wave. Using R wave criteria, the sensitivity was 63% (P < 0.01) while the specificity was 79% (P < 0.01).
The sensitivity and specificity of stress testing can be significantly improved using R wave changes.
EXERCISE STRESS TESTING is undoubtedly one of the
most common noninvasive methods for detecting coronary
artery disease. However, it is known that stress testing fails
to accurately distinguish all cases and because of this some
criticism has been directed at the test.' Sensitivity and
specificity is dependent on the prevalence of disease in most
studies. It has been shown that as the specificity increases
the sensitivity decreases, the values also being dependent on
the degree of ST depression used to denote disease.
McConahay,' using the double Master's test for ST depression of . 0.75 mm, reported a sensitivity of 42% and
specificity of 91%, but when he used ST . 1 mm, the sensitivity was 35% and the specificity 100%. Mason et al.,3
using a near-maximal exercise test for ST depression > 0.75
mm, reported a sensitivity of 84% and a specificity of 83%,
and when they used ST depression of > 1 mm found the sensitivity to be 78% and the specificity 89%.
This study was undertaken to test two new criteria for exercise ECG evaluation.
to 69
(mean 49.2). In the CAD group were 63 males with
ages ranging from 37 to 72 (mean 55.8) and 15 females
whose ages ranged from 40 to 70 (mean 56.6). The DMI
group constituted 53 males with ages from 29 to 66 (mean
51.3), and eight females with ages from 40 to 74 (mean 53.6).
The AMI group consisted of 39 males 39 to 74 years of age
(mean 53.4) and seven females whose ages ranged from 27 to
64 with a mean of 53.2.
Another group of 53 apparently healthy subjects, 39 males
and 14 females, underwent maximal treadmill stress testing
for screening evaluation. Their ages ranged from 19 to 38
with a mean of 30. Their history and physical examination
revealed no evidence or symptoms of heart disease. These
patients were volunteers, with no known risk factors for coronary artery disease, in a Long Beach Heart Association
study of risk factors and had not undergone angiography.4
Patients with hypertension, cardiomyopathy, conduction
defects, valvular diseases or who had been taking digitalis in
the last two weeks, or beta-blockers, diuretics or nitrates
within 48 hours were excluded.
The interval between the treadmill stress test and coronary angiography ranged from the same day to 4 months
with an average of one week.
Materials and Methods
A retrospective study was done reviewing the records of
266 nonconsecutive patients with a treadmill stress test
(TST) and a coronary angiogram in a two-year period from
1974 to 1976. Thirty-three false positive and ninety-six false
negative ST responses to treadmill stress testing were purposely chosen sequentially from a computer printout of
patients in our files who satisfied the restrictions cited.
The 266 patients were analyzed in four groups as follows:
normal patients, patients with coronary artery disease
(CAD) without previous myocardial infarction, patients
with previous transmural diaphragmatic infarction (DMI),
and patients with previous transmural anterior infarction
(AMI). Criteria for previous infarction were Q waves of 0.04
sec or more in leads III, aVF, or in V2-V6.
In the normal group were 51 males whose ages ranged
from 25 to 72 (mean 48.6) and 30 females with ages from 31
Treadmill Stress Test
Patients underwent a progressive maximal treadmill
stress test (TST) according to the Ellestad protocol5 I using
the maximal predicted heart rate as a target end point.
Three leads (CM,, a vertical bipolar lead, and a unipolar V1
lead) were monitored continuously and recorded in the sitting position (control) and in the standing position immediately after exercise. The mean difference between the
R-wave sitting and standing was 0.5 mm. The R wave control measurement was taken in the sitting position for comparison with ST changes which we routinely measure sitting
for the control value. The CM, lead was used for all
measurements. ST depression > 1 mm below the resting
level 60 msec from the J point if horizontal or downsloping
and > 1.5 mm of depression at 80 msec if upsloping, in the
immediate postexercise period, was defined as positive
(ischemic). R wave amplitude was measured from the
isoelectric line to the peak of the R wave in mm for an
average of 12 consecutive beats. The average value was used
in the study so the respiratory variation, if any, was
From the Division of Clinical Physiology, Section of Cardiology and the
Memorial Hospital Medical Center, Long Beach, California.
Supported in part by funds from the Long Beach Heart Association and
Memorial and Children's Medical Center Foundation.
Address for reprints: M. H. Ellestad, M.D., Department of Clinical
Physiology, Memorial Hospital Medical Center, 2801 Atlantic Avenue, Long
Beach, California 90801.
Received September 12, 1977; revision accepted December 23, 1977.
904
EXERCISE STRESS TESTING/Bonoris et al.
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minimized. An increase in R wave amplitude or no change
immediately after exercise was defined as evidence of abnormality, while a decrease in the amplitude was defined as
evidence of a normal response. In a previous study,7 we
noted that R wave increase correlated with coronary disease
while a decrease correlated with no or minimal disease. As
the normal patient exercises, tachycardia and catecholamine
release result in a reduced left ventricular volume and by the
Brody effect a decrease in R wave, while the patient with
coronary disease, as exercise progresses and ischemia
develops, increases his left ventricular volume and R wave
increases.
An index (ARST) was formed from the algebraic summation of the R wave and ST-segment changes. ST depression
was taken as a positive value. The R wave was taken as
positive if there was an increase and negative if a decrease
(fig. 1). An index of 0 or a positive value was taken to represent abnormality, while a negative index was taken as
evidence of a normal response.
Treadmill stress tests were evaluated in each group using
three criteria: ST depression, change in R wave amplitude,
and the index (,ARST). Specificity and sensitivity for each
criteria were determined and compared each with the other
criteria. Specificity and sensitivity in each criteria were compared to determine if the index or the R wave changes could
significantly reduce the number of false positive and negative
responses by ST criteria. The numbers of false positive and
negative responses were purposely large numbers and
therefore resulted in a low sensitivity and specificity.
However, it was our purpose to see if these lowered values
could be improved by the R wave or index.
905
Heart Catheterization
Left and right heart catheterization and coronary
angiography were performed using the Sones or Judkins
technique. Coronary angiography was performed on 35 mm
film with multiple views. Left ventricular angiography was
performed in the RAO position. Occlusion of 70% or more
of luminal diameter in one or more coronary arteries was
defined as significant, while normal coronary angiograms
were defined as no occlusion or less than 30% cross sectional
narrowing. Patients with obstruction of 31% to 69% were arbitrarily excluded from the study. Coronary arteries were
divided into branches according to the reporting system of
the American Heart Association.8 The coronary anatomy
was examined by two independent observers without
knowledge of the treadmill stress test and any discrepancies
were resolved by a third observer.
Results
Angiographically Normal Group
Treadmill Stress Test
The ST segments were normal in 48 (59%) and positive in
33 (4 1 %) of the 81 patients with normal coronary anatomy.
The high incidence of false positives was due to patient selection as noted previously. The R wave increased in 14 (17%)
by 3.6 mm ± 0.9 SEM. Three (4%) showed no change and 64
(79%) showed a decrease of 3.45 + 0.25 mm (fig. 2). These
differences in the R wave amplitude were significant
lo0
*
*
R INCREASE
R DECREASE
R NO CHANGE
64
80,
70L
46
60[
I~-
z
'a
50*
I
40
30
20
1C
0/I
,'0
_ _ f _ __
AR -1
_
_ ~~ST =+2_
-
-_ARST
FIGURE
1.
=
_
1 I
_ 1
1
Ir
+1
Schematic representation
of calculation of the index
(ARST), in two cases with STdepression and R wave increased and
decreased.
25
14
II
NORMAL
I
CAD
DMI
AMI
FIGURE 2. R wave amplitude changes in the normal and in the
disease groups. Decrease in R wave amplitude is seen primarily in
normal patients. In the A MI group the percentage of the patients
with a decrease in R wave amplitude is higher than that with increase. Numbers on the top of the bars represent the number of
patients.
906
CIRCULATION
(P < 0.01). The index (ARST) was negative in 57 (70%) and
in 24 (30%) of the patients was 0 or positive. Thus, of the 81
patients with normal coronary anatomy, 59% had a negative
test and 41% were false positives by ST criteria. Evaluation
by changes in R wave amplitude revealed 64 (79%) had a
true negative test and 17 (21%) had a false positive one. By
using ARST as a criterion, 57 (70%) had a negative index
(true negative test) and 24 (30%) had an index of 0 or a
positive value (false positive test) (fig. 3 and 4).
The R wave was more specific than the ST segment
(P < 0.01) or index (P < 0.05) in detecting normal subjects.
The index, although not significantly different from the ST,
still gave better results.
Ventricular Function
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Although all patients had normal coronary arteries, it is
very interesting that eleven (65%) of the seventeen with increased or no change in R wave amplitude had segmental
abnormalities in the left ventriculogram and five of them had
significant ST-segment depression.
CAD Group
Treadmill Stress Test
There were 78 patients in this group. Of these, 44 (57%)
were true positives by ST criteria and the remaining 34
(43%) were negatives. The R wave increased in 46 (59%) by
+ 2.98 ± 0.41 mm, remained the same in 7 (9%), and
decreased in 25 (32%) by - 2.83 ± 0.33 mm (fig. 2). All
these differences were significant (P < 0.01).
The index was 0 or positive in 59 (76%) patients and
negative in 19 (24%). Thus, the sensitivity by ST-was 57%,
by R 68%, and by ZXRST 76% (fig. 3).
Severity of Disease
Of the 46 patients with an increase in R wave amplitude,
10 (22%) had single vessel disease, 17 (37%) had two vessel
disease and 19 (41%) had three vessel disease. Of the 25
patients with a decrease in R wave amplitude, 10 (40%) had
single vessel disease, 10 (40%) had two vessel disease and five
(20%) had three vessel disease. Out of seven patients with no
change in the R wave, five (71%) had two vessel disease, and
two (29%) had three vessels with significant cross-sectional
narrowing (table 1).
Diaphragmatic Myocardial Infarction Group
Treadmill Stress Test
Of the 61 patients with previous diaphragmatic infarction, 29 (48%) were classified as having a positive exercise
ECG and 32 (52%) as having a negative test using STsegment depression as the criterion. The R wave increased in
32 (53%) patients by + 4.58 ± 0.65 mm and decreased in 22
E ST
I.-
ER
90,
n ST
90
8
7
VOL 57, No 5, MAY 1978
ER
O ARST
Li ARST
80
70
50
60
C,,
I.-
+
LU
I--
20
1{
0
1
2Z
3
4
I~-
C*
50
LU
E 40
24
30
20
10
I-
7
0
TN
70/^
-
CAD
NORMAL
AMI
DMI
FIGURE 3. Sensitivity and specificity by the three criteria in normal and diseased groups. The ability of R wave changes or the
Index (ARST) to detect disease is significantly higher than that of
ST alone.
FP
TP
FN
OVERALL DISEASED
FIGURE 4. True negative (TN), false positive (FP), true positive
NORMAL
(TP), and false negative (FN) by three criteria in the normal and in
the overall diseased group. The sensitivity was higher by R and increased more by ARST. The R wave was more specific than the
ARST, which was more sensitive. The ST was significantly less sensitive and specific when compared to the other two criteria.
EXERCISE STRESS TESTING/Bonoris et al.
907
TABLE 1. Correlation Between R Wave Amplitude Changes and Diseased Vessels
Vessels
CAD
N = 78
DMI
Patients
1
2
3
1
2
3
4
or more
T
46 (59)
25 (32)
7 (9)
32 (53)
22 (36)
7 (11)
15 (33)
22 (48)
9 (19)
93 (50)
69 (37)
23 (13)
10 (22)
10 (40)
17 (37)
10 (40)
5 (71)
19 (41)
5 (20)
2 (29)
9 (19)
7 (28)
6 (13)
4 (16)
1 (14)
20 (44)
6 (24)
3 (43)
3 (9)
7 (32)
5 (16)
5 (23)
3 (43)
2 (13)
5 (23)
1 (11)
15 (16)
24 (35)
2 (8)
36 (39)
27 (39)
13 (57)
16 (50)
5 (23)
4 (57)
7 (47)
8 (36)
2 (22)
42 (45)
18 (26)
8 (35)
3 (9)
5 (23)
2 (13)
7 (32)
2 (22)
13 (40)
10 (45)
3 (43)
6 (40)
7 (32)
5 (56)
11 (24)
8 (32)
3 (43)
8 (25)
8 (36)
1 (14)
2 (13)
3 (14)
4 (45)
21 (23)
19 (28)
8 (35)
16 (50)
4 (18)
3 (43)
9 (60)
10 (45)
2 (22)
45 (48)
20 (29)
8 (35)
l
T
N = 61
l
AMI
N = 46
l
Overall
disease
l
N = 185
Branches
R wave
changes
T
T
2 (13)
4 (18)
2 (22)
14 (15)
16 (23)
2 (8)
13 (14)
14 (290)
5 (22)
Numbers in parentheses represent percentages.
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(36%) by - 2.28 ± 0.31 mm (P < 0.01). In seven patients
(I %) the R wave did not change (fig. 2). The index (ARST)
was 0 or positive in 41 (67%) patients and negative in the
remaining 20 (33%) of the 61 patients. Thus, the sensitivity
in patients with diaphragmatic infarction was 48% by ST
criteria, 64% by R, and 67% by ARST. The false negative
responders were 52% using the ST, and 36% using the R
wave amplitude. The index in this group was again more
sensitive with a false negative incidence of 33% (fig. 3).
Severity of Disease
Of the 32 patients with an increase in R wave amplitude,
three (9%) had single vessel disease, 13 (40%) had two diseased vessels, and 16 (50%) had three vessel disease. Of the
22 with a decrease in R wave amplitude, seven (32%) had
single vessel disease, 10 (45%) had two vessel disease and five
(23%) had three diseased vessels. Out of seven with no
change in R wave, three (43%) had two and four (57%) had
three vessel disease (table 1).
Anterior Myocardial Infarction Group
Treadmill Stress Test
In this group, 46 patients with a previous anterior
myocardial infarction were studied. Of these, 16 (35%) were
found to have a positive exercise ECG, and 30 (65%) were
false negative using ST criteria. The R wave increased in 15
(33%) by + 2.73 ± 0.49 mm, showed no change in nine
(19%), and decreased by - 2.59 ± 0.31 mm in 22 (48%)
(P < 0.01), (fig. 2). Thus, with R wave changes as the
criteria, 24 patients (52%) were found to have a positive exercise ECG and 22 (48%) were false negative. The index was
0 or positive in 27 (59%) and negative in 19 (4 1%) of the 46
patients (fig. 3).
Severity of Disease
The distribution of the diseased vessels in this group was
as follows: Of the 15 with increase in R wave, two (13%) had
single vessel disease, six (40%) had two and seven (47%) had
three vessels with significant disease. Of the 22 with decrease
in R wave, seven (32%) had single vessel disease, seven (32%)
had two, and eight (36%) had three vessel disease. Finally, of
the nine patients with no changes in the R wave, two (22%)
had single, five (56%) had two, and two (22%) had three
vessels with significant obstruction (table 1).
All Patients with Coronary Artery Disease
This group included all 185 patients with coronary artery
disease with or without a previous infarction. Of these, 89
(48%) had a true positive and 96 (52%) a false negative exercise ECG according to the ST pattern. Using the R wave
amplitude changes, 116 (63%) were true positives (P < 0.01)
and 69 (37%) were false negatives. The sensitivity increased
when the index (AvRST) was used for the interpretation.
Thus, 127 (69%) of the 185 patients were classified correctly
(P < 0.01) and only 58 (31%) patients were found to have a
false negative exercise ECG (fig. 4). The index was more sensitive than ST and R (P < 0.01).
Severity of Disease
Of the 93 patients with increase in R wave, 15 (16%) had
single vessel disease, 32 (34%) had two, and 42 (45%) had
three diseased vessels. Of the 69 with a decrease in R wave,
24 (35%) had single vessel disease, 27 (39%) had two, and 18
(26%) had three significantly occluded vessels. Out of 23
with no change in R wave, two (9%) had one, 13 (56%) had
two, and eight (35%) had three vessel disease (table 1).
False Positive and False Negative Group
In order to test our data, the 33 false positives and the 96
false negative patients by ST-segment criteria were analyzed
separately. All of these patients had been interpreted 100%
incorrectly by ST alone. Using the R wave amplitude
changes, there were a total of 17 false positive responses. Of
the 33 false positive ST responses, 23 (70%) were correctly
identified by the R wave. The R wave reduced the 96 false
negative ST responses by 47 (51%). The index (ARST) was
more sensitive but somewhat less specific. There were 24
false positive responses and 58 false negative responses by
using the index (fig. 5).
The breakdown in males and females, and the sensitivity
VOL 57, No 5, MAY 1978
CIRCULATION
908
RST
RST
33
100
90
70
(3%) had
60
z
versus
no
change.
Correlation Between ST and R Wave Amplitude
In the normal group, 70% of the 33 patients with ST
depression (false positives) had a decrease in R wave
amplitude immediately after exercise, while the percentage
of R wave decrease in the true negatives was 86%. In the
overall diseased group, the correlation was as follows: 75%
of the 89 patients with ST depression had increased R wave
amplitude and in 25% it was decreased (table 3).
501
40
30
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20
Discussion
The most extensively studied parameter of exercise ECG
is ST depression, which has been found to be fairly well correlated with the presence of coronary artery disease on
angiography as well as with coronary events in a long term
follow-up study.9"- McConahay,' Mason,3 Kassebaum,"
Bailey," and Lewis et al.14 report sensitivities from 78 to
50% and specificities in the range of 80 to 90%, all higher
than in our series. Our reported sensitivity of 48% and
specificity of 59% were low because of the large numbers of
false positive and negative responses which we purposely included to determine if the R wave changes or index could
reduce these false responses by ST criteria and therefore
enhance the sensitivity and specificity of the treadmill stress
10
~o
FP
FN
FIGURE 5. The percentage of false negative (FN) and false
positive (FP) tests by the three criteria. All the patients in this group
were classified incorrectly by ST segment changes. The R wave and
the index were more sensitive and specific, so the number of false
responders was minimized.
and specificity for all groups and all three criteria,
in table 2.
are
shown
test.
Statistical Analysis
The fact that CM, may explore primarily the anterior wall
be a cause for a false negative exercise ECG in patients
with previous anterior infarction and disease in the vessels
nourishing the anterior wall only. Had we used ischemic
changes in the other leads recorded, we would expect a 5 to
10% increase in sensitivity.
The sensitivity, measured by ST-segment depression and
the presence of false negative responders, depends on the
severity of the disease" 1", 15 patients with single vessel disease are commonly false negatives. Our data support this
The three criteria were analyzed in patients with and
without coronary artery disease, using the McNemar test.
The results are as follows:
Normal patients:
R versus ST X2 = 9.4 (P < 0.01)
R versus RST X' = 5.1 (P < 0.05)
RST versus ST X2 = 2.1 N.S.
Overall diseased group:
R versus ST X2 = 11.3 (P < 0.01)
can
so
TABLE 2. Specificity and Sensitivity in Males and Females by ST, R, and ARST
Normal (N = 81)
CAD (N = 78)
DM1 (N = 61)
Males
Females
Males
Females
Males
Females
(N 51) (N = 30) (N = 63) (N = 15) (N = 53)
(N = 8)
=
ST
R
ARST
ST X2 = 22.9 (P < 0.01)
R X2 = 8.1 (P < 0.01)
Young Healthy Group
Of the 53 young asymptomatic healthy subjects who did
not have angiograms and were evaluated for screening only,
48 (90%) had a decrease in the R wave amplitude immediately after exercise, four (7%) had an increase, and one
80
EU
versus
FP
TN
FP
TN
FN
TP
FN
TP
FN
TP
FN
TP
23
28
10
20
26
37
8
7
25
28
7
1
AMI (N 46)
Overall disease (N = 185)
Males
Females
Males
Females
(N = 39)
(N = 7)
(N = 155)
(N = 30)
FN
TP FN
TP FN TP FN TP
=
26
13
4
3
77
78
19
11
(45) (55) (33) (67) (41) (59) (53) (47) (45) (55) (88) (12) (67) (33) (57) (43) (50) (50) (63) (37)
12 39
5 25 18 45
7
8 18 35
4
4 18 21
4
3 54 101 15 15
(23) (77) (17) (83) (29) (71) (47) (53) (34) (66) (50) (50) (46) (54) (57) (43) (35) (65) (50) (50)
16 35
8 22 15 48
4 11 17 36
3
5 17 22
2
5 49 106
9 21
(31) (69) (27) (73) (24) (76) (27) (73) (32) (68) (37) (63) (44) (56) (28) (72) (32) (68) (30) (70)
Numbers in parentheses represent percentages.
EXERCISE STRESS TESTING/Bonoris et al.
909
TABLE 3. Correlation Between ST and R
Normal
Overall dis.
AMI
DMI
CAD
*
**
STp
STn
N = 48
N = 44
N = 34
N = 29
N = 32
N = 16
N = 30
N = 89
N = 96
N 10
7
34
19
25
14
8
16
67
49
or-% 30
N 23
14
41
77
10
56
15
86
4
44
18
50
8
53
14
75
22
51
%70
86
23
44
14
56
50
47
25
49
RWA
T
l
N = 33
ST,
ST.
STp
STn
STp
ST.
STp
STn
47
*Significant (ischemic) ST depression.
**ST with no depression.
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concept, but the changes in the R wave consistently correlate
better with the angiograms than does the ST-segment
depression.
The number of false positive patients, based on ST
segments, in this study was 33 (41%) of 81 with normal coronary arteries. We believe the inclusion of a large group of
known false positives provides the opportunity to rigorously
test the R wave criteria. Analysis of changes in the R wave
amplitude make it possible to increase the specificity from
59% to 79%, and the sensitivity as follows: in the CAD group
from 57% to 68%, in the DMI group from 48% to 64%, and
in the AMI group from 35% to 52%, and finally in all
patients with coronary artery disease from 48% to 63%.
Using the index (ARST), the specificity was 70%, which is
somewhat lower than by R wave but higher than found using
the ST segment. The sensitivity was 76%, 67%, and 59% for
CAD, DMI, and AMI, respectively, and 69% for the overall
diseased group.
As table 3 shows, 25% of the patients with ST depression
had a decreased R wave amplitude, which according to our
criteria should represent a negative stress test. On the other
hand, 51% of the patients with no ST depression but with
disease (false negatives) had an increase in R wave
amplitude, a finding which would suggest disease. Fourteen
percent of the normals without ST depression had an increase in R wave, while 25% of the patients with coronary
disease and ST depression had a decrease in R wave. These
discrepancies can be reduced by the index (ARST), but eventually the combination of these findings with other coexisting signs and symptoms will play the most important
role.4 Prospective studies are needed to resolve these
differences before R wave criteria can be clinically im-
plemented.
Mechanism of R Wave Change
Brody"6 postulated that the intracavitary blood mass influences the QRS complex. This has been documented by
others in experiments with animals, by mathematical
calculations, and by experimental models.'7-22 It would
appear that under the sympathetic drive of exercise both
systolic and diastolic volume progressively decrease even
though stroke volume is maintained. The failure of the
ischemic ventricle to decrease its volume during strenuous
exercise"-" seems to be responsible for the absence of the
usual reduction of the R wave amplitude. In a previous
study, an increase in R wave correlated with more severe disease and more severe segmental abnormalities in the left
ventriculogram.7 Consequently, in this study an increase or
no change in R wave was taken to indicate coronary disease
while a decrease in R wave was taken as a normal response
to exercise stress testing. This tends to be supported in our
young normal subjects in whom 90% had the expected reduction in the R wave.
Although current evaluation of an exercise ECG is usually
primarily based upon the ST-segment changes, other factors
can affect the interpretation. These include angina during
the test, presence of angina in the history, premature ventricular contractions or other arrhythmias during the test, duration of the test, hypotensive response to exercise, maximal
systolic blood pressure, resting ECG, time of onset of the ST
depression, heart rate response to exercise,26-3 and others.
Ellestad4 showed that using multivariate analysis, these findings and symptoms increase the percentage of correct interpretation. The addition of these two new criteria may also be
useful in the above method. The ability to identify 79% of
those with normal coronary arteries is especially encouraging in view of the large group of false positives included in this patient sample. By using R wave amplitude
changes and the index (ARST), the specificity increased by
20% and 1 1%, respectively. The sensitivity increased in the
overall diseased group by 15% and 21%.
The preliminary studies are encouraging, but it remains to
be demonstrated how much these criteria will improve the
predictive power of the exercise stress test when they are
applied to other patient cohorts.
Although statistically significantly better than STsegment depression alone, the R wave and index criteria still
leave a considerable number of false positive and false
negative responders.
Acknowledgments
The authors thank Larry J. Leamy, Ph.D. for the statistical analysis, and
Mrs. Fritzie Cohn for secretarial assistance.
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Vectorcardiographic Quantification
of Infarct Size in Baboons
SAMUEL A. WICKLINE,
AND
J. JUDSON MCNAMARA, M.D.
SUMMARY A vectorcardiographic method has been developed for
determining the absolute size of myocardial infarcts in baboons
resulting from coronary artery ligation. Spatial area (mvolt * msec)
and voltage (mvolt) difference-vectors were obtained for 8 animals by
measuring the voltage loss and temporal deviation from pre- to postligation McFee scalar leads. The difference vectors were then correlated with the absolute infarct volumes, which were derived by
histological assessment 10 days after ligation. Absolute lesion sizes
ranged from approximately 2 cc to 14 cc, involving 10-30% of ventricular muscle mass. The correlation coefficient, r, for the area
deviation index was 0.98 (SEE = ± 0.24 cc); and for the voltage deviation index, r was 0.92 (SEE = 0.51 cc). These results demonstrate
that the severity of infarction can be accurately determined if
prepathological vectorcardiograms are available.
NONINVASIVE QUANTIFICATION of absolute infarct
size using electrophysiological data would be of considerable
benefit in the management of patients with acute infarctions
and in the assessment of experimental therapeutic interventions. Although epicardial QRS and ST-complex changes
during infarction have been correlated with subjacent myocardial necrosis,'-' the invasiveness of the recording technique precludes its eventual clinical implementation. Recent
investigations of infarcts using extensive body surface maps
indicate that surface potential recordings also contain a sub-
stantial amount of potentially quantifiable information.4
These studies suggest that necrosis in specific ventricular
wall segments will produce characteristic alterations in maps
of body surface potential. By subtracting postinfarction and
control thoracic potentials point-for-point, a voltage
difference map that represents the original electrical contribution of the necrotic segment to the control map can be
derived.4 This method of "difference mapping" appears
promising, but body surface recording in general is too
cumbersome and extenuating to be clinically practicable at
present.
From the Department of Surgery and Physiology, John A. Burns School of
Medicine, University of Hawaii, Queen's Medical Center, Honolulu, Hawaii.
Supported by NIH Grant HL1457-03A1.
Address for reprints: J. Judson McNamara, M.D., Department of Surgery,
Queen's Medical Center, 1301 Punchbowl Street, Honolulu, Hawaii 96813.
Received August 3, 1977; revision accepted December 7, 1977.
The simple vectorcardiogram offers an alternative source
of noninvasive electrical data for examining acute and
chronic infarctions. The vectorcardiographic representation
of myocardial electrical activity as an equivalent dipole has
proven its utility in diagnosis8512 and theoretical
Evaluation of R wave amplitude changes versus ST-segment depression in stress testing.
P E Bonoris, P S Greenberg, G W Christison, M J Castellanet and M H Ellestad
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Circulation. 1978;57:904-910
doi: 10.1161/01.CIR.57.5.904
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