Effects of diltiazem during tachycardia-induced angina pectoris.

To investigate the mechanism of relief of angina pectoris by diltiazem administration, 14 patients with effort angina were studied using a protocol to control heart rate. Coronary, systemic and left ventricular (LV) hemodynamic function was assessed at rest and during tachycardia stress (atrial pacing)-induced angina before and during diltiazem infusion. Angina occurred in all patients during tachycardia stress before diltiazem administration. During tachycardia stress at the heart rate that produced angina after diltiazem infusion, pressure-rate product, coronary sinus flow and resistance and ST-segment depression were all similar to findings before diltiazem. Although at the onset of angina, systolic pressure was usually slightly lower after diltiazem infusion (138 +/- 11 vs 128 +/- 11 mm Hg, p less than 0.05), the pacing rate at onset of angina was higher in only 3 patients and the pressure-rate product was higher in only 1 patient. After diltiazem, left ventricular end-diastolic pressure increased less frequently after interruption of pacing. The results suggest that diltiazem favorably alters the relation between myocardial oxygen demand and supply at rest, but during tachycardia, anginal threshold and coronary reserve do not change. Diltiazem's potent antianginal action, shown in previous investigations using exercise-induced angina, is not prominent when heart rate is controlled. The major benefit of diltiazem in patients with stress-induced angina is related to reduction of myocardial oxygen demand rather than improved myocardial oxygen delivery.