Effects of Nitroglycerin on "Maximal" Oxygen Intake and Exercise Electrocardiogram in Coronary Heart Disease

Abstract

Oxygen intake (V O O2 ) was measured during the last few minutes of a multistage treadmill test of maximal exercise in 12 healthy middle-aged persons, 32 patients with angina, and 23 survivors of myocardial infarction free of angina. Repetition of the same test, after each individual rested 30 min and took 0.4 mg nitroglycerin sublingually, increased V O O2 max in patients with angina (by 14.5%, P < 0.001) and in patients with prior infarction (by 6%, P < 0.005) but not in healthy persons. Angina at V O O2 max was prevented in 12 patients. Maximal heart rate was increased by 11% in the angina group and by 4% in the myocardial infarction group; the maximal blood pressure-heart rate product was increased ( P < 0.005) only in patients with angina. [See Equation in PDF file] voltages from 50 to 69 msec after the nadir of S wave (S-T b ) were quantified by computer averaging of 100 beat samples at several intervals during and after exercise. The amount of [See Equation in PDF file] depression during and after exercise was significantly reduced after administration of nitroglycerin in all three groups. We conclude that nitroglycerin: (1) increases maximal circulatory conductance of O 2 in patients with coronary heart disease, whether or not limited by angina, mainly by increased maximal heart rate, and (2) lessens evidence of electrocardiographic myocardial ischemia and lowers frequency if angina pectoris despite the same or a higher pressure-rate index. These effects suggest a reduction in peripheral vascular tone and left ventricular end-diastolic pressure and volume with nitroglycerin.