An analysis of the time relationships within the cardiac cycle in electrocardiograms of normal men: V. The effect of changing heart rate upon the Q-T interval and the T-P interval and their respective relationships to the cycle length (R-R interval)

Abstract

Of interest to many investigators has been the question of determining exactly what happens to the Q-T interval, the T-P interval, and the cycle length (C) as measured in the electrocardiogram while the heart rate is changing. Lombard and Cope, 1 measuring systole and diastole by mechanical means, found that diastole shortened more rapidly than systole with increase in heart rate. Bazett 2 found that the ratio K = Q−T c was temporarily increased immediately after exercise. White and Mudd 3 found that the Q-T to C relationship was not altered after exercise. Blair, Wedd, and Young 4 noted that immediately after exercise the Q-T and C were shorter than before exercise and that, as the C returned to the resting level, the Q-T lengthened, although at a slower rate, until it too had reached the resting level. However, the Q-T continued for a time to lengthen beyond that level while C remained constant. White, Kossmann, and Ershler 5 in their study found that the ratio Q−T c became smaller immediately after exercise. In two previous reports 6,7 it was shown that the Q-T to C and T-P to C relationships [K(Q-T) and K(T-P)] were not disturbed immediately after exercise, but no information was available as to what happened while the heart rate was changing. It was for the purpose of obtaining information about this phase that this study was undertaken.