Yonago Acta medica 1997;40:107–116

Isointegral Analysis of Body Surface Electrocardiographic Mapping forAssessing 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 Twave. 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,107

G. U. Ahmmed et al.

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
imagingFig. 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 3min. A dose of 111 MBq of thallium-201 wasinjected 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 inBody 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
109

G. U. Ahmmed et al.

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 (“–2SDarea”). 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.
andandthe 3left-mid left-superior left regions
[7]
[2]
[4]

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

110andleft[4]010220122