Nitrates for unstable angina.

The term unstable angina encompasses heterogeneous clinical syndromes. Fissuring of an atherosclerotic coronary artery plaque with superimposed platelet deposition, with or without additional thrombus formation, is invariably responsible for a prolonged episode of angina at rest, increasing frequency of angina at rest, or with minimal exertion of less than 4 weeks in duration and early postinfarction angina. Plaque progression, rather than plaque fissuring, is the most likely mechanism for progressive reduction in walking distance due to angina in patients who previously have stable angina. Coronary artery spasm is responsible for Prinzmetal's variant angina, but its exact role in other forms of unstable angina is unknown. The mainstay of treatment of unstable angina (prolonged episode of angina at rest and recent onset angina at rest, or with minimal exertion with a crescendo pattern) is aspirin, heparin, or both. Both aspirin and intravenous (i.v.) heparin or their combination reduce early mortality and the incidence of acute myocardial infarction in patients hospitalized with unstable angina. However, these agents do not promptly relieve chest pain. There are no placebo-controlled studies evaluating the usefulness of nitrates in unstable angina. In open-label studies, continuous therapy with i.v. nitroglycerin (NTG) for 24 hours or longer has been shown to relieve chest pain in patients with rest angina refractory to therapy with other antianginal agents, including long-acting nitrates. Recurrence of chest pain in patients receiving i.v. NTG is a common problem and probably represents development of pharmacologic tolerance, but this can be overridden by dose escalation; protracted tolerance during short-term use of i.v. NTG is usually not a problem.(ABSTRACT TRUNCATED AT 250 WORDS)