PREDICTIVE ACCURACY OF Q-X-Q-T RATIO, Q-TC INTERVAL, S-T DEPRESSION AND R-WAVE AMPLITUDE DURING STRESS-TESTING

The sensitivity, specificity and predictive value for Q-X Q-T ratio, Q-Tc interval, S-T segment depression, R wave change and various combinations of these criteria were compared in 50 healthy, normal persons and 50 persons with angiographic coronary artery disease defined as 70 percent or greater stenosis of one or more major coronary vessels. Use of a positive S-T segment response and an increase or no change in R wave amplitude as criteria for coronary artery disease resulted in 84 percent sensitivity and 96 percent specificity levels and a 95 percent predictive value. The Q-X Q-T and Q-Tc criteria offered no improvement in sensitivity, specificity or predictive value over S-T segment depression. When the study group was limited to 74 persons, 36 without and 38 with angiographically significant coronary artery disease, a Q-Tc interval of 1.08 or more in combination with either slowly or rapidly upsloping S-T depression after exercise predicted coronary disease at a sensitivity level of 76 percent compared with 50 percent with use of the S-T segment alone (P < 0.05). Specificity was not significantly reduced (89 percent for the S-T segment alone, 79 percent with the addition of the Q-Tc interval) (P > 0.05). Use of the R wave response with the presence of upsloping S-T segment depression of 1.5 mm or more 80 msec from the J point improved the sensitivity level from 50 percent for S-T depression alone to 76 percent (P < 0.05); specificity and predictive value were not significantly reduced (81 percent for each [P > 0.05]). The Q-X Q-T ratio could be measured in only 55 patients (74 percent) and offered no improvement over S-T segment depression. Upsloping S-T segment depression of 1.5 mm or more 80 msec from the J point in the immediate postexercise period is most likely a positive test for ischemia. An increase or no change in R wave amplitude in response to exercise in these patients regardless of the degree of S-T segment depression is probably indicative of coronary artery disease. In patients with upsloping S-T segment depression, a Q-Tc interval of 1.08 or more in the immediate postexercise period is a useful measurement in predicting coronary artery disease. © 1979.