Active and passive coronary vasodilation after intracoronary and sublingual nitroglycerin

Nitroglycerin is known to dilate epicardial coronary arteries. It is not known, however, to what extend pressure-dependent passive vasoconstrictive effects may counteract active vasodilation. Therefore, repeated coronary angiograms were performed in 100 patients under standardized conditions before (C) and after 0.16 mg nitroglycerin intracoronarily as well as after an additional 1.6 mg nitroglycerin sublingually. Coronary diameters were determined in stenotic and nonstenotic coronary artery branches. Aortic blood pressure and heart rate were monitored continuously. Aortic blood pressure decreased slightly after intracoronary injection from 146/70 mmHg (C) to 142/77 mmHg and decreased markedly after additional sublingual administration to 129/70 mmHg. Heart rate increased from 78 beats/min (C) to 79 beats/min after intracoronary injection and to 81 beats/min after sublingual administration. Diameters in nonobstructed coronary segments increased in proximal (+7%), medial (+10%), and distal (+12%) segments after intracoronary injection; after sublingual administration a more pronounced diameter increase was observed in all segments (proximal +12%, medial +13%, distal +14%). In obstructed coronary arteries, a stenotic dilation of more than 10% was found in 73% (58/80) after intracoronary injection, but only in 50% (40/80) of the patients after sublingual administration of nitroglycerin. The average diameter increase within coronary stenoses in all patients was 24% after intracoronary injection, but only 10% after additional sublingual administration. In conclusions dilation of epicardial coronary arteries occurs in nonstenotic and stenotic segments. In nonstenotic coronary arteries, there are additive vasodilative effects after intracoronary and sublingual nitroglycerin; in coronary stenoses, however, a maximal effect is achieved after intracoronary injection which is diminished after sublingual administration.