Possible Mechanisms of the Beneficial Effects of Nitroglycerin in Patients with Effort Angina: Potential Roles of Collateral Circulation

Summary

Although nitrates are very effective for the treatment of effort angina, the precise mechanisms of the beneficial effects are still unclear. In order to clarify what the mechanisms of the beneficial effects of one of these nitrates, nitroglycerin, we performed exercise stress tests on patients with effort angina and examined the effects of nitroglycerin on coronary and systemic hemodynamics using the following two exercise protocols. In the first, a noninvasive study, 105 patients with stable effort angina were evaluated, and in the second, an invasive study, 50 patients with stable effort angina were employed. In the noninvasive study, the rough correlation between the severity of coronary stenosis and the exercise tolerance time was shown, and those patients with collaterals showed a greater increase in exercise time after sublingual nitroglycerin administration compared to those without collaterals. In the invasive study, the reduction in pulmonary arterial end-diastolic pressure during 3 min of exercise correlated well with the increase in exercise time after pretreatment with sublingual nitroglycerin. Furthermore, the coronary angiogram during exercise-induced angina showed the more enhanced collateral opacification after pretreatment with nitroglycerin. Thus, the effects of nitroglycerin on the exercise tolerance time are considered to be due to: (1) relaxation of the stenotic coronary artery and the improvements of coronary circulation, (2) reduction of preload due to decreae in the systemic peripheral vascular resistance, (3) improvement of myocardial energy efficiency possibly due to reduction of ventricular volume, and (4) increase in coronary blood flow to the ischemic area through collaterals.

It is well known that nitrates, such as nitroglycerin, are very effective for the treatment of effort angina. However, the precise mechanisms of the beneficial effects of nitroglycerin are still unclear. We will discuss how nitrates affect

pathophysiologic aspects of effort angina and how they improve myocardial ischemia during exercise.