The sensitivity of intracoronary injection of acetylcholine in inducing coronary spasm differs in patients with stable and unstable angina.

In an attempt to clarify the role of coronary artery spasm in the pathogenesis of unstable angina, acetylcholine (20 and 50 micrograms) was injected directly into the coronary arteries of 19 patients with unstable effort angina (group 1), 30 patients with unstable spontaneous angina (group 2), and 15 patients with stable effort angina due to coronary artery organic stenosis (greater than or equal to 75%) (group 3). Coronary spasm was defined as severe vasoconstriction (greater than or equal to 90% of luminal diameter) with chest pain and/or ischemic ST-segment changes. Intracoronary injection of acetylcholine induced spasm of at least one coronary artery in 19 patients (100%) of group 1 and 28 (93%) of group 2 but only 3 (20%) of group 3 (p less than 0.01). When acetylcholine was injected into the left and right coronary arteries separately, multivessel spasm (spasm of both coronary arteries) was induced in 5 of 12 (42%) patients of group 1 and in 9 of 23 (39%) patients of group 2. In contrast, intracoronary acetylcholine did not cause multivessel coronary spasm in any of 15 patients of group 3 (0%). These results suggest that coronary arteries in patients with unstable effort angina as well as spontaneous angina are susceptible to spasm and that coronary artery spasm may be responsible at least in part for the genesis of attacks in these patients.