Aspects of the medical therapy of angina pectoris.

Patients with stable and unstable angina may experience, in addition to a fixed decrease in their coronary flow reserve, transient impairment of coronary flow, which may precipitate spontaneous angina attacks. In stable angina the cause of impairment of flow is vasoconstriction at the site of stenosis or in distal vessels. In unstable angina the cause of impairment of flow is dynamic thrombosis and vasoconstriction. In variant angina, angiographic studies with vasoactive substances indicate that the coronary spasm is caused by a localised alteration in which a segment of a coronary artery becomes temporarily hyperreactive to constrictor stimuli. Patients with chronic stable angina may also experience a variable ischaemic threshold. A recent study in patients with occlusion of a single coronary artery indicates that, in stable angina, the constriction of distal and/or collateral coronary vessels may be an alternative pathogenic mechanism, in addition to constriction at the stenotic site.