Unstable angina.

Unstable angina has only been recognized as a distinct entity for about 50 years. The term is used to describe a symptom complex that is neither stable angina pectoris nor acute myocardial infarction. There are a number of other terms used to describe essentially the same symptom complex; these include pre-infarction angina, crescendo angina, intermediate coronary syndrome and threatening infarction. This entity excites interest since it represents a change in the pattern of symptoms. Some of the reasons for this change in pattern are beginning to be become clearer and have become more relevant since there is a large choice of treatment available. However there is considerable debate as to the circumstances in which a particular therapy might best be used. A better understanding of the complex pathophysiology of unstable angina may help determine the optimal form of treatment, may help prevent the problem and may also indicate the direction of future research. For many years it was believed that unstable angina was due to episodic changes in myocardial oxygen demand superimposed on advanced fixed narrowings of the coronary arteries. It is now apparent that there are alternative or additional mechanisms. These include episodic reductions in the myocardial oxygen supply due to coronary artery spasm,112 platelet activation and transient thrombus formation.