Effect of Sympathomimetic Drugs on the Q-T Interval and on the Duration of Ejection

Publisher Website
Google Scholar
Abstract
In comparing animals with different basic heart rates, Q-T showed a relation to cycle length. Absolute differences in Q-T were not large, usually within the error of measurement. With acute changes in heart rate, Q-T might or might not change. There was no evidence that epinephrine, arterenol or isopropylarterenol directly affected the values. The duration of ejection (Ts) proved much more variable than Q-T and could not be correlated with it. It showed a rough relation to the duration of previous diastole. The Ts value was set by hemodynamic factors that regulate the stroke volume, and the relation with previous diastole is probably through the influence of the latter on cardiac filling. Ts is shortened by sympathomimetic drugs, and, over a limited dosage range, the amount of curtailment can be graduated. The amount of this shortening is not affected in large measure by changes in arterial pressure level or in initial tension of the ventricle. The effect of the drugs on the contraction pattern is seen at lower dosage levels than that on cycle length, and the 2 aspects of stimulation are probably independent.