bjectives : It was postulated that exaggerated artral repolarization waves seen during exercise may extend from the PR segment into the ST segment and T wave, and thus can produce ST segment depressions mimicking myocardial ischemia. The
aim
of
this study is to invertigate hether or not there is any association between P-R segment slope and ST segment depression in exercise ECG for predicting accuracy of myocardial ischemia.
Method : The treadmill exercise test was performed using the modified Bruce Protocol (Korea University Hospital Protocol) in 62 patients with chest pain. The P wave amplitude, PR segment slope and duration, the ST segment duration, and the
J
point depression were studied in Lead Ⅱ and V5 in 39 patients whose exercise ECG suggested myocardial ischemia.
The PR segment slope was determined by measuring the velocity of descent in mm/sec.
Coronary arteriography was performed in all patients, and 50% stenosis in a major cornary
artery was considered a significant lesion.
Results : The overall sensitivity and specificity of the exercise test in 62 patients was
74% and 43%, respectively. The exercise test results in 10 patients were deemed false
positive because of normal coronary arteriograms and left ventricular function. The false
positive group was characterized by more maked downsloping PR segments in Lead
Ⅱat peak exercise (15.9±9.3 mm/sec vs 4.8±5.6 mm/sec, p<0.05) and more rapid peak
exercise heart rates than those of the true positive group (151±26 vs 131±25, p<0.05). The
sensitivity and specificity of exercise-induced ST depression for CAD were changed as
following if positive exercise test within creased PR segment slope is considered as false
positive test: 1) with PR segment is slope over 5 mm/s: sensitivity78%, specificity 39%
2) with PR segment slope over 10 mm/s: sensitivity 83%, specificity 45% 3) with PR
segment slope over 15 mm/s: sensitivity 79%, specificity 46%.
Conclusion : These findings suggest that markedly downsloping PR segment seen in
otherwise positive exercise test by ST segment depression criteria is a sign predicting false
positive exercise test.
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