Dose-response scrutiny of coronary vasodilation after intracoronary verapamil in man. A quantitative cineangiographic study.

The effect of various doses of intracoronary verapamil on the diameter of angiographically normal left coronary artery segments was investigated in 22 patients with and without coronary atherosclerosis by quantitative angiography. Very low doses (50 micrograms) were given in 3 patients; doses of 250 micrograms, 350 micrograms and 500 micrograms were administered in 7, 6 and 13 patients, respectively. A single dose was administered in 15 patients, while two increasing doses of verapamil were tested in 7. The effect of verapamil was compared in each patient with that of nitroglycerin (NG; 0.6 mg), administered sublingually in all as the last step of the study. An additional group of 8 patients served as the control. These patients received 4 intracoronary injections of contrast medium without drugs and a fifth injection following 0.6 mg of sublingual NG. In the control group no significant changes in coronary artery diameter were observed following the four control injections of contrast medium, while a 18 +/- 9% increase in vascular diameter was observed following NG. When verapamil was injected a dose-dependent vasodilation was observed, which began to be significant with doses higher than 250 micrograms. Mean percent variations of coronary artery diameter relative to control were -0.2 +/- 3.6%, 4.6 +/- 5.5%, 11.4 +/- 7.5% and 19.9 +/- 10.7%, in response to verapamil doses of 50, 250, 350 and 500 micrograms, respectively. Subsequent nitroglycerin induced a 21.5 +/- 10.7% mean percent coronary artery dilation (NS vs verapamil 500 micrograms and vs NG in the control group). Thus, verapamil induced a dose-dependent coronary vasodilation which at a dose of 500 micrograms was comparable to that induced by NG. Both with verapamil and NG the smallest vessels exhibited the greatest vasodilation. It is concluded that at the doses used in this study, injection of verapamil into the left coronary artery is safe and markedly decreases tone in the large coronary arteries. This finding supports the use of verapamil in clinical conditions in which the role of coronary vasoconstriction is proven or thought to be relevant.