Yonago Acta medica 1997;40:107–116

Isointegral Analysis of Body Surface Electrocardiographic Mapping for
Assessing Exercise-Induced Changes in Repolarization Properties inPatients with Coronary Artery Disease
Gias Uddin Ahmmed, Hiroyuki Miyakoda and Chiaki Shigemasa
First Department of Internal Medicine, Faculty of Medicine, Tottori University, Yonago 683,
Japan
To assess the exercise-induced changes in repolarization properties in patients withcoronary artery disease, we analyzed body surface ECG mapping. The patients studied
had a normal resting 12-lead ECG and were divided into 2 groups: group A (n = 15;
coronary artery narrowing [–], exercise thallium defect [–], ST depression ≥ 0.1 mV [–])and group B (n = 17; [+], [+], [+]). All patients in group B showed significant area (< –10µV•s) in the postexercise ST-T isointegral map. Of the patients in group B, 10 (59%)
showed significant area in the postexercise QRST isointegral map and 15 (88%) showed “–2SD area (less than mean –2SD values in group A)” in the difference map between
resting and postexercise QRST isointegrals. The correlation coefficient between resting and postexercise QRST isointegrals in 87 lead points was significantly lower ingroup B (0.28 ± 0.56) than in group A (0.91 ± 0.06, P < 0.001). Our results indicate thatpatients with ischemic ST depression have a greater decrease in the QRST isointegral
values in the precordial region than patients without ischemia and ST depression.
There are also low similarities between resting and postexercise QRST isointegral
maps. We conclude that ischemic ST depression is related to the dispersion of theexercise-induced changes in repolarization properties.
Key words: body surface ECG mapping; coronary artery disease; exercise test; QRST isointegral mapping

ST depression is used as a marker of myocadialischemia in the exercise-stress ECG test for thedetection of coronary artery disease. ST depression is commonly accompanied by adecrease in the height or inversion of the T
wave. These ST-T changes are attributed to
local repolarization abnormalities due to ischemia. Body surface QRST isointegral mapping
has been used to assess repolarization properties in a variety of diseases (Montague et al.,
1981; Kubota et al., 1984; Gardner et al., 1986;
De Ambroggi et al., 1986; Hayashi et al., 1988,
1989; Tsunakawa et al., 1989; Hirai et al., 1991,
1993; Dambrink et al., 1995). However, there
are few reports on the exercise-induced changes
in the QRST isointegral in body surface ECG
mapping in patients with coronary artery disease. In order to determine whether ischemic
Abbreviations: bpm, beats per minute; ECG, electrocardiography or electrocardiogramST depression reflects the dispersion of theexercise-induced changes in repolarization
properties or not, we quantitatively analyzed
body surface QRST isointegral maps recordedat the same time when exercise-stress thallium201 myocardial imaging test was performed forthe detection of coronary artery disease.

Subjects and Methods

Subjects
We retrospectively studied 32 patients who underwent exercise-stress thallium-201 myocardial
imaging and body surface ECG mapping for thedetection of coronary artery disease. The patients we studied had a normal resting 12-lead
ECG and were divided into 2 groups. Group A
consisted of 15 patients (9 men and 6 women,

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mean age 60 years, range 44 to 75)
Table 1. Patient characteristics
who had atypical chest pain andCoronary Thallium
12-Lead ECG
had neither significant coronary
narrowing imaging
artery narrowing nor exercise
thallium defect nor significant
Group A [15] < 50% No defect No ST depression
exercise-induced ST change.
Group B [17] ≥ 75% Reversible Down-sloping,Group B consisted of 17 patients
defectST depression ≥ 0.1 mV(13 men and 4 women, mean age[ ], number of patients.
68 years, range 57 to 80) who hadsignificant exercise-induced ST
Informed consent was given by all patientsdepression, significant narrowing in at least oneof major coronary arteries and reversible for undergoing this exercise test.
thallium defect. Excluded were patients with
exercise-induced ST elevation, bundle branchCoronary arteriography and left ventricublock or atrial fibrillation, or any physicallographydisability for undergoing an exercise tolerance
test. No patients had congenital or valvular All patients underwent coronary arteriographyheart disease, hypertrophic or dilated cardio- and left ventriculography within 1 month of thismyopathy, hypertensive heart disease or chron- exercise test. Patients in group A had no coroic obstructive lung disease. Vasodilators were nary artery narrowing ≥ 50% and had normal
not discontinued. No patients received anti- left ventricular wall motion. Patients in grouparrhythmic drugs. Excluded were also those B had narrowing ≥ 75% in at least one of major
who showed no separation of T and P waves coronary arteries. Those with akinesis, dyskinesis
during body surface ECG mapping. Patient or aneurysm in any segment of the left vencharacteristics are shown in Table 1.
tricular wall were not included in group B.

Exercise-stress thallium-201 myocardial
imaging

Fig. 1. Electrode placement for 87 lead points. The
vertical distance between two lead points is 40 mm.
E4 is located on the level of the fifth intercostal
space. Leads G4, H4 and I4 correspond to V4, V5
and V6 of 12-lead ECG.

Supine bicycle exercise was begun at 25 W, andthe work rate was increased by 25 W every 3
min. A dose of 111 MBq of thallium-201 was
injected intravenously at peak exercise, andpatients continued to exercise for an additional
minute. A modified 12-lead ECG according to
the Mason and Likar method (1966) wasrecorded at rest, every minute during exercise,and after 1, 2 and 3 min of recovery. Bloodpressure was measured with an automatic
sphygmomanometer (Nippon Colin, STBP680, Tokyo, Japan) on the left arm. The end
point of exercise was determined by thedevelopment of moderate anginal chest pain,
severe shortness of breath or severe leg fatigue,
new ST depression ≥ 0.2 mV at 80 ms from theJ point in at least one lead except leads aVR,
aVL and V1, or the achievement of 85% of ageadjusted predicted maximum heart rate.
Significant ST depression was defined as new108

Exercise-stress body surface ECG mapping

down-sloping depression ≥ 0.1 mV at 1 minof recovery. Tomographic thallium-201 imaging was performed using a gamma camera(Hitachi, GAMMAVIEW, Tokyo) equipped with a high-resolution, low-energy parallel-hole collimator andinterfaced to a dedicated computer system(Hitachi, HARP). Initial imaging was begun
10 min after the termiFig. 2. Resting (R) (upper panel) and postexercise (P) (lower panel) ST-T isonation of exercise andintegral maps of a patient in group A. Isointegral contours are separated by 10
delayed imaging wasµV•s. Shading indicates negative areas. Maximum and minimum are indicatedrepeated 4 h later.
by plus and minus signs.
Thirty-two projections
over a 180-degree arc
were obtained with a 64 × 64 matrix. Short- and QRST isointegrals were calculated for eachaxis, vertical long-axis and horizontal long-axis lead as the algebraic sum of potentials from thetomograms were reconstructed. The left ven- J point or QRS onset to the T-wave offset andtricle was divided into the anterior wall (anteri- expressed in µV•s. Resting and postexercise
or and apical segments) and the posterior wall ST-T isointegral maps, resting and postexercise(inferoposterior and posterolateral segments). QRST isointegral maps and the difference map
Images were interpreted by three observers. A between resting and postexercise QRST isoindefect was classified as reversible (partial or tegrals were constructed. The ST-T and QRST
complete redistribution) or irreversible (no re- isointegral contours were separated by 10 µV•s.
distribution or equivocal). A consensus of the A previous study of normal adults showed that
opinions of the three observers was taken. A re- the normal QRST isointegral map pattern has aversible defect was used as a positive criterion dipolar character with two extremes: one posifor myocardial ischemia.
tive (maximum) and one negative (minimum)(Montague et al., 1981). A QRST isointegral
extreme was defined as a circumscribed peak in
Body surface ECG mapping
the smooth and graduated potential distribution.
Body surface ECG maps were recorded using a The map pattern was defined as nondipolar if
VCM-3000 system (Chunichi Denshi, Nagoya, three or more extremes were present. An addiJapan) at the resting expiratory level before and tional extreme was considered present if an area
1.5 min after exercise. Unipolar ECGs were of equal polarity included at least 2 lead points
recorded simultaneously from 87 lead points on (Dambrink et al., 1995). Body surface was dithe chest and back (59 and 28 leads, respective- vided vertically into right (columns A to D, Lly) with reference to Wilson’s central terminal and M) and left (columns E to K) regions, and(Fig. 1). The Frank X, Y, Z ECGs were also divided horizontally into inferior (lines 1 andrecorded simultaneously. The PR-segment was 2), mid (lines 3 and 4) and superior (lines 5 to 7)
used as a baseline. The onset of QRS, the J regions. Significant area in the postexercise
point and the offset of the T-wave were deter- ST-T or QRST isointegral map was defined as amined from the spatial magnitude. The ST-T new negative area including at least 3 lead
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Fig. 3. Four types of abnormal negative areas in the postexercise ST-T isointegral maps in patients in group
B. Isointegral contours are separated by 10 µV•s. Shading indicates negative areas. Significant area (< –10µV•s) is located in the left-inferior and left-mid regions (a: 57-year-old man), in the left-mid and left-superior
regions (b: 77-year-old woman), in all of the three left regions (c: 78-year-old man) or in both right and left
regions (d: 73-year-old man).

points in which each isointegral value was lessStatistical analysis
than –10 µV•s. The mean and mean –2SD difference maps between resting and postexercise Data are shown as the mean ± SD or as a perQRST isointegrals in group A were construct- centage. For the comparison of statistical siged. When the QRST isointegral difference nificance between 2 groups, the unpaired t-testvalue was less than the mean –2SD in group A was used. A value of P < 0.05 was consideredin at least 3 lead points, the decrease was con- significant.
sidered significant (“–2SD
area”). The correlation coeffiTable 2. Relationship between significant area in the postcient between resting and postexercise ST-T isointegral map and ischemic area in theexercise QRST isointegrals inthallium-201 myocardial imaging
87 leads was used as a marker
Ischemic
Significant area in the ST-T isointegral mapof similarities in the potential
area
Left-inferior
Left-mid
All ofRight
distributions.
and
and
the 3
left-mid left-superior left regions
[7]
[2]
[4]

Anterior
2
Posterior
4
Anterior andposterior
1[ ], number of patients.

110

and
left
[4]

0
1

0
2

2
0

1

2

2

Exercise-stress body surface ECG mapping

Thallium-201 myocardial imaging andpostexercise 12-lead ECG
Results

Group ANo patients had thallium defect and significant ST change.

Exercise variables

Group AThe end point of exercise was leg fatigue in
11 and shortness of breath in 4 patients. Workload was 77 ± 29 W. Heart rate at peak exercise
was 120 ± 12 bpm. Systolic blood pressure atpeak execise was 186 ± 24 mmHg.
Group BThe end point of exercise was anginal chest
pain in 9, ST depression in 5 and leg fatigue in 3
patients. Work load was 51 ± 19 W (P < 0.01
versus group A). Heart rate at peak exercise
was 108 ± 17 bpm (P < 0.01 versus group A).
Systolic blood pressure at peak exercise was
171 ± 19 mmHg.

Group BAll patients showed reversible thallium defect. Four patients showed reversible thallium
defect in the anterior wall, 7 patients in theposterior wall and 6 patients in both anterior
and posterior walls. All patients had significant
down-sloping ST depression. Maximal ST depression was –0.21 ± 0.08 mV.
ST-T isointegral maps

Group A
Figure 2 shows resting and postexercise STT isointegral maps of a representative patient(60-year-old man). All patients had smooth
dipolar pattern maps
both at rest and after
exercise with the positive area located overthe precordium andthe negative area over
the right chest andback. This was considered a normal response.

Fig. 4. Resting (R) and postexercise (P)QRST isointegral maps (upper and middle
panels) and the difference (D) map between resting and postexercise QRST isointegrals (lower panel) in a patient in groupA (the same patient as shown in Fig. 2).
Isointegral contours are separated by 10µV•s. Shading indicates negative areas.

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Fig. 5. Resting (R) and postexercise (P)QRST isointegral maps (upper and middle
panels) and the difference (D) map between resting and postexercise QRST
isointegrals (lower panel) in a patient ingroup B (the same patient as shown in Fig.
3d). Isointegral contours are separated by
10 µV•s. Shading indicates negative areas.
Significant area (< –10 µV•s) is present in
the postexercise map.

Group BAll patients had significant area in thepostexercise map. Seven patients (41%) had
significant area in the left-inferior and left-mid
regions in the postexercise map, 2 patients(11%) in the left-mid and left-superior regions, 4patients (24%) in all three of the left regions and 4
patients (24%) in the right-inferior, (right-mid,)left-inferior and left-mid regions. Four types ofsignificant area in the postexercise map areshown in Fig. 3. Significant area in the postexercise map was not correlated with the ischemic area determined by thallium imaging(Table 2).
QRST isointegral maps
Figure 4 shows resting and postexercise QRST
isointegral maps and the difference map between resting and postexercise QRST isointegrals in a patient in group A (the same patient as
Fig. 2). All three maps show smooth dipolar
patterns. Figure 5 shows resting and postexercise QRST isointegral maps and the QRST iso-integral difference map of a representative patient in group B (the same patient as Fig. 3d). Significant area is observed in the postexercise map.
Figures 6a and b show mean and mean –2SD difference maps between resting and postexercise
QRST isointegrals in group A. Figure 6c shows
the QRST isointegral difference map of a patient in group B (the same patient as Figs. 3dand 5), in which an extensive “–2SD area” isobserved. Figure 7 shows the relationshipbetween resting and postexercise QRST isointegral maps in a patient (group A) with a highcorrelation coefficient and in a patient (groupB) with a low correlation coefficient.

Group AAll patients showed smooth dipolar patternmaps both at rest and after exercise. The positive area covered the precordium with the maximum located in the middle of the left chest andthe minimum at the upper region of the rightchest or right back. All patients showed asmooth dipolar difference map between restingand postexercise QRST isointegrals. The nega-112

Exercise-stress body surface ECG mapping

Fig. 6. Difference maps between
resting and postexercise QRST isointegrals: Mean map in group A(a), mean –2SD map in group A (b)and a difference map of a patient ingroup B (the same patient as shownin Figs. 3d and 5) (c). Isointegral
contours are separated by 20 µV•s.
Shading indicates “–2SD area (lessthan mean –2SD values in group
A)”.

Fig. 7. Relationship between resting and postexercise QRST isointegrals: a patient (group A, the same
patient as in Figs. 2 and 4) with a high correlation coefficient (a) and a patient (group B, the same patient asshown in Figs. 3d and 5) with a low correlation coefficient (b).

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tive area covered most of the chest with theminimum located in the middle of the left chestand the maximum at the upper region of the rightchest or right back. The minimum in mean
and mean –2SD difference maps between resting and postexercise QRST isointegrals was
located in lead F4 (mean = –44.5 µV•s; mean –2SD = –80.4 µV•s). The correlation coefficient
between resting and postexercise QRST isointegrals in 87 lead points was 0.91 ± 0.06.

Group BTen patients (59%) had significant area inthe postexercise map. No patients had a nondipolar pattern map. Fifteen patients (88%) had“–2SD area” in the difference map between
resting and postexercise QRST isointegrals.
The correlation coefficient between resting andpostexercise QRST isointegrals in 87 lead
points in group B (0.28 ± 0.56) was significantly lower than that in group A (P < 0.001)(Fig. 8).

Discussion
The present study demonstrates that patientswith ischemic ST depression had a greater
decrease in the QRST isointegral values in theprecordial region than patients without ischemia and ST depression and had low similarities
between the resting and postexercise QRST isointegral maps. These findings indicate thatischemic ST depression is related to the dispersion of the exercise-induced changes in repolarization properties.
Body surface ECG mapping offers information about potential distributions around theentire thorax. In patients with coronary artery
narrowing, exercise-induced ST depression
most often occurs in the left anterior chest
leads. According to the data from exercisestress ST isopotential mapping, predicting thelocation of ischemic areas is thought to be difficult from the body surface distributions of ST
depression (Kubota et al., 1989). Montague andcolleagues (1990) studied exercise-stress ST
isointegral maps in coronary artery disease andobserved that, with exercise-induced angina,

Fig. 8. The correlation coefficient between restingand postexercise QRST isointegral maps for eachgroup, A and B. [ ], number of patients.

patients with two or three vessel disease had asignificantly greater decrease in the ST isointegral values than patients with single vessel disease. There was, however, considerable overlap among individuals. The reason for a lack ofcorrelation between body surface distributionof ST depression and anatomic site of coronary
artery disease is unclear. Exercise-induced ST
depression is commonly accompanied by adecrease in the height or inversion of the T
wave. Nakajima and coworkers (1988) studied
exercise-stress ST-T isointegral maps in patients with angina pectoris in the absence ofprevious myocardial infarction. They observedthat postexercise ST-T isointegral maps weredivided into 4 types (anterior chest, inferoposterior chest, lateral chest and global) according to the distributions of negative area, whichwere well correlated with the extent of ischemic
area determined by thallium imaging. However, our results demonstrated that significant
area in the postexercise ST-T isointegral map
was not correlated with the ischemic area. The
reason for the discrepancy is not clear. Studies
in a large number of patients are needed.
Exercise-induced ST depression is attributed to a current of injury with ischemia in subendocardial layers. T wave inversion is thought
to be related to the presence of delayed recovery. Exercise-induced ischemia causes not only114

Exercise-stress body surface ECG mapping

ST-T but also QRS changes. R wave amplitude
on the surface ECG is decreased in normal subjects while the increase is seen in patients withcoronary artery disease (Bonoris et al., 1978a,1978b). Ikeda and colleagues (1988) reported
that intraventricular conduction delay secondary to ischemia plays an important role in theincrease in R wave amplitude. ST-T isointegral
map reflects ventricular recovery sequence.
The recovery sequence is affected by activation
sequence and regional recovery properties. The
QRST isointegral map has been reported to be
useful in investigating recovery properties.
Wilson and researchers (1934) reported that the
QRST isointegral is independent of the activation sequence and dependent on repolarization
properties. They proposed the concept of aventricular gradient. Based on this concept ofthe ventricular gradient, Abildskov and workers(1980) introduced the QRST isointegral map.
They demonstrated that the QRST isointegral
map was independent of the activation sequence and useful in detecting abnormalities in
repolarization properties, even in the presenceof QRS deflection abnormalities. Althoughbody surface QRST isointegral mapping has
been used to assess repolarization abnormalities
in a variety of diseases, few reports on exercisestress QRST isointegral mapping are available.
Ohyama and others (1984) studied exerciseinduced changes in QRST isointegral map
patterns in patients with effort angina in theabsence of akinesis or dyskinesis in the left
ventricular wall motion. These investigators
observed that after exercise the maximum of themap moves far from the resting position andsplits into multiple extremes in patients withmultivessel coronary artery disease.
In this study, to assess exercise-inducedchanges in repolarization properties, we performed quantitative analysis of QRST isointegral mapping. Normal responses of QRST isointegral values to exercise have not been determined. We constructed a mean –2SD difference map between resting and postexercise
QRST isointegrals in control subjects (group
A). When the QRST isointegral value in at least
3 lead points was less than the mean –2SD, thedecrease was considered significant (“–2SD

area”). The correlation coefficient between
QRST isointegral maps is independent of thedifference in potential magnitudes and indicatesthe similarities in potential distributions(Hayashi et al., 1989). However, the relationship between resting and postexercise maps has
not been analyzed.
Control subjects (group A) showed a decrease in the maximum QRST isointegral value,
which may result from shortening of QT interval and a decrease in the R wave and T wave
amplitudes in the left precordial leads. Thesepatients showed smooth dipolar ST-T isointegral maps both at rest and after exercise. They
also showed smooth dipolar QRST isointegral
maps both at rest and after exercise and a highcorrelation coefficient between the two maps.
These findings indicate that control subjects
have higher similarities between resting andpostexercise repolarization properties.
Patients with ischemic ST depression in theabsence of previous myocardial infarction(group B) showed a high incidence of the occurrence of a significant area in the postexercise
QRST isointegral map and “–2SD area” in the
QRST isointegral difference map. In addition,these patients showed a low correlation coefficient between resting and postexercise QRST
isointegral maps. These findings indicate thatischemic ST depression is associated withremarkable changes in ST-T and QRST isointegrals and may be related to the regional abnormalities in repolarization properties.
We conclude that isointegral analysis ofbody surface ECG mapping has advantages inassessing repolarization properties in the exercise test for the detection of coronary artery disease. Further studies in patients with previous
myocardial infarction, intraventricular conduction disturbance or left ventricular hypertrophy
are needed.

Acknowledgments: We thank Drs. Takahiro Nawata
and Tetsuya Doi and all the members in the First
Dept. of Internal Medicine, Faculty of Medicine,
Tottori University for their cooperation. We also
thank Messrs. Kenichi Endo and Tsuyoshi Nishio,
Dept. of Clinical Radiology, Tottori University
Hospital for their assistance.

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(Received April 21, Accepted May 26, 1997)

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