Paradoxical Response of Epicardial Coronary Arteries and Small Resistance Vessels to Intracoronary Acetylcholine in Vasospastic Angina
This study was carried out to examine the response of epicardial arteries (A-epi) and small resistance vessels (A-res) to intracoronary (IC) acetylcholine (Ach) in patients with and without vasospastic angina. Injection of Ach (20, 50 μg) into the left coronary artery (LCA) was performed in ten patients whose LCAs were angiographically normal. Ach-induced spasm of the left anterior descending artery (LAD) occurred in five patients (group A), and did not occur in the other five (group B). We injected nitroglycerin (NTG; 0.2 mg) into the LCA to remove A-epi tone, followed by the same amount of Ach to evaluate the response of A-res. Thereafter, papaverine (10 mg) was injected into the LCA to evaluate the maximum vasodilation capacity. Flow in the great cardiac vein, measured by Webster’s method, and coronary angiography were performed following the IC injection of each drug. We calculated the coronary vascular resistance ratio (R) to maximum dilator response and measured LAD diameter after each procedure. Percent changes in LAD diameter after IC Ach following IC NTG did not differ in the two groups. The R(NTG)-R(Ach) value was larger in group A than in group B (0.35 ± 0.1 vs 0.12 ± 0.1; P < 0.01). These findings suggest that IC injection of Ach produces significant vasodilation in A-res in vasospastic angina, in contrast to the constriction produced in A-epi by this treatment.