Effects of Nitroglycerin on Responses of the Systolic Time Intervals to Exercise

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Abstract
The effects of 0.6 mg sublingual nitroglycerin on responses of the left ventricular (LV) systolic time intervals to a 4-min exercise step test were determined in 10 patients with angina and 10 normal controls. In normal subjects, the exercise test shortened total electromechanical systole corrected for heart rate (Q2c22 msec but left the LV ejection time corrected for heart rate (LVETc) unchanged. By contrast, in the angina group, exercise failed to shorten the Q2c but prolonged the LVETc 25 msec. In both groups, nitroglycerin shortened the LVETc and Q2c after exercise. By decreasing LV afterload, preload, and hypoxia, and by improving LV function, nitroglycerin abolished the abnormal marked prolongation of LVETc after exercise in angina patients and converted the failure of their Q2c to shorten after exercise into a normal shortening of Q2c. Nitroglycerin also had marked effects at rest, which contributed importantly to its effects on the systolic temporal responses to exercise. Suppression by nitroglycerin of LVETc prolongation after exercise diminishes myocardial oxygen consumption and is antianginal. Most important, assessment of this action provides an objective, though noninvasive, means to evaluate the efficacy of nitrates in improving LV performance with exercise in angina patients.