Evaluation of a New Systolic Time Interval, the Q-V Peak: Effects of Heart Rate, Contractile State, and Loading Conditions in Dogs

The authors investigated the effects of alterations in heart rate, contractility, and loading conditions on a newly defined systolic time interval, the Q-V peak, in 46 anesthetized dogs. The Q-V peak was measured as the time from the beginning of the electrocardiographic Q wave to the moment at which the blood flow rate reached its peak in the ascending aorta as determined with an electromagnetic flowmeter. The Q-V peak did not change significantly as the heart rate was varied by atrial pacing between 70 and 110 beats/minute. The Q-V peak shortened when the contractility was augmented with dobutamine (p = 0.0001) and was prolonged when it was depressed with propranolol (p = 0.0001). However, the Q-V peak did not change significantly when the left ventricular end-diastolic pressure or the mean aortic blood pressure was increased to 130% or decreased to 70% of the baseline values. These findings suggest that one may also evaluate left ventricular performance by measuring the time to systole, which the authors define as the Q-V peak.