Hemodynamic Effects of Nitroglycerin in Patients with Angina Pectoris Studied by an Atrial Pacing Method

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Abstract
The hemodynamic effects of nitroglycerin on 20 patients with coronary arterial disease were assessed by using atrial pacing to invoke angina pectoris. This new technique also permitted study of the hemodynamics during pain without the interference of the effects of muscular exercise on the heart affected by coronary artery disease. The pain threshold of each patient was determined by successive pacing runs and the effects of nitroglycerin were evaluated both before and during the pacing up to the level of pain. With regard to the circulatory status at pain an abnormally elevated pulmonary capillary venous "wedge" pressure was an infrequent phenomenon. This difference from the data of studies in which muscular exercise is used is briefly discussed. Sublingual nitroglycerin decreased aortic, pulmonary arterial, right atrial, and pulmonary capillary venous pressures. Stroke volume and cardiac output were reduced and this reduction was accompanied by a compensatory rise in heart rate. Tension-time index was reduced and during pacing at identical rates never reached the level at which angina pectoris was experienced before nitroglycerin. End-diastolic heart size as estimated from conventional chest roentgenograms was reduced by nitroglycerin at every pacing step in all six patients studied by this method. The conclusions were that at all heart rates studied nitroglycerin (a) decreased atrial pressures, (b) decreased heart size, (c) caused peripheral vasodilatation, and (d) allowed the heart to be driven at a higher rate without production of anginal pain. These hemodynamic changes reflect a decreased oxygen requirement of the heart and are consistent with the pain-relieving properties of nitroglycerin.