Pathogenesis of angina pectoris and role of nitrates in relief of myocardial ischemia.

The pathophysiologic mechanism of angina of effort has been understood for one and three-quarter centuries. However, the mechanisms underlying angina at rest are still largely unknown. Coronary spasm, whatever its mechanism, clearly causes Prinzmetal's variant angina. However, evidence that spasm is the cause of all angina at rest is wanting. Rather than spasm, it is suggested that most attacks may be the result of normal fluctuations in the tone of conductive coronary arteries in the presence of critical levels of organic obstruction. The nitrates both relieve coronary spasm and diminish normal coronary tone. They also affect the systemic circulation, so as to favorably influence the level of energy demand.