Coronary microcirculatory vasoconstriction during ischemia in patients with unstable angina

OBJECTIVE To verify the behavior of coronary microvascular tone during spon taneous ischemia in patients with unstable angina (UA). BACKGROUND In UA, the pathogenetic role of vasoconstriction is classically confined at the stenotic coronary segment. However, microcirculatory vasoco nstriction has been also suggested by previous experimental and clinical st udies. METHODS The study included 10 patients with UA (recent worsening of anginal threshold and appearance of angina at rest) and single-vessel CAD. Blood f low velocity was monitored by a Doppler catheter in the diseased artery. Tr ansstenotic pressure gradient was monitored by aortic and distal coronary p ressure monitoring. Stenosis resistance was calculated as the ratio between pressure gradient and blood flow, microvascular resistance as the ratio be tween distal pressure and blood flow. Measurements were obtained at baselin e, following intracoronary adenosine (2 mg) and during transient ischemia. Aortic and distal coronary pressures were also measured during balloon coro nary occlusion. RESULTS Adenosine did not affect stenosis resistance, while it decreased (p < 0.05) microvascular resistance to 52 +/- 22% of baseline. Angina and isc hemic ST segment shift were associated with transient angiographic coronary occlusion in 7 of 10 patients; however, in no case was ischemia associated with interruption of flow. Despite markedly different flow values, distal coronary pressure was similar during adenosine and during spontaneous ische mia (48 +/- 15 vs. 46 +/- 20 mm Hg, respectively, NS). During ischemia, a m arked increase in the resistance of both coronary stenosis and coronary mic rocirculation was observed (to 1,233% +/- 1,298% and 671% +/- 652% of basel ine, respectively, p < 0.05). Distal coronary pressure was markedly reduced during balloon coronary occlusion (14 +/- 7 mm Hg, p < 0.05 vs, both adeno sine and ischemia), suggesting the absence of significant collateral circul ation. CONCLUSIONS In patients with UA, transient myocardial ischemia is associate d with vasoconstriction of both stenotic arterial segment and downstream mi crocirculation. (J Am Coll Cardiol 2000;35:327-34) (C) 2000 by the American College of Cardiology.