Reduced vasodilator capacity in syndrome X related to structure and function of resistance arteries

The combination of angina pectoris, angiographically normal epicardial coro nary arteries, and a positive exercise test is referred to as syndrome X. P revious studies have demonstrated an impaired coronary flow reserve and a p eripheral vascular dysfunction, suggesting that vascular abnormalities in s yndrome X may not be confined to the heart. The aim of this study was to in vestigate whether any vascular disorder of syndrome X is due to intrinsic s tructural or functional disturbances in resistance arteries. We compared 16 patients with syndrome X (56.6 +/- 1.2 years, 3 men) with 15 matched contr ol subjects. Myocardial blood flow was measured with N-13-ammonia positron emission tomography. Forearm blood flow was measured in the brachial artery with high-resolution ultrasound. Gluteal subcutaneous resistance arteries were dissected and mounted on a myograph for measurement of active tension development, lumen diameter, and media thickness. Baseline myocardial blood flow was similar in patients and controls, but dipyridamole-induced hypere mia was decreased in patients (1.67 +/- 0.13 vs 2.31 +/- 0.12 ml/min/g, p < 0.01). Patients and controls had similar baseline forearm blood flow, but h yperemic flow after transient occlusion of the brachial artery was impaired in patients (198 +/- 20 vs 273 +/- 32 ml/min, p < 0.05). isolated resistan ce arteries showed no differences in constriction to noradrenaline, or rela xation to acetylcholine, dipyridamole, or nitroglycerin. Furthermore, the r atio between media thickness and lumen diameter were similar in syndrome X patients and controls. Our data show that when compared with a well-matched control group, syndrome X patients have a decreased coronary and periphera l vasodilator capacity. However, this is not reflected by functional abnorm alities or structural changes as evaluated in subcutaneous resistance arter ies. We conclude that syndrome X is not a generalized intrinsic abnormality of the resistance circulation. (C) 1999 by Excerpta Medico, Inc.