Mechanisms of Coronary Artery Spasm

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Abstract
The term coronary artery spasm (CAS) refers to a sudden, intense vasoconstriction of an epicardial coronary artery that causes vessel occlusion or near occlusion. Although CAS may be involved in other coronary syndromes, it represents the usual cause of variant angina. The variant form of angina was first described in 1959 by Prinzmetal et al,1 who used this term to indicate that angina attacks, unlike the most common form of effort angina, occurred at rest and were associated with ST-segment elevation, rather than ST-segment depression, on the ECG (Figure 1). Because myocardial ischemia occurred in the absence of any change in myocardial oxygen demand, the authors hypothesized that it was caused by an increased tonus of vessels at the level of coronary stenoses.1 Figure 1. (Top) ST-segment elevation in anterior leads, with reciprocal mild ST-segment depression in inferior leads and V6, during an angina attack in a patient with variant angina. (Bottom) Normalization of the ECG after spontaneous resolution of chest pain. Some years later, in fact, coronary angiography, performed during spontaneous angina attacks, demonstrated that CAS is the usual cause of variant angina.2–4 Coronary angiography also showed that CAS could occur at the site of a stenosis (either minor or severe) or in angiographically normal coronary arteries,5 usually at a localized segment of an epicardial artery (focal spasm) (Figure 2).6 However, sometimes CAS involves 2 or more segments of the same (multifocal spasm) or of different (multivessel spasm) epicardial coronary arteries, or may also involve diffusely one or multiple coronary branches.7 Figure 2. Occlusive spasm of the left circumflex coronary artery and near occlusive spasm of the left anterior descending coronary artery (arrows) during coronary angiography (left, top), associated with dramatic ST-segment elevation at monitoring ECG leads (left, bottom). Complete resolution of spasm (right, …