Aim: To assess the direct effects of nitroglycerin on coronary and collateral circulation, 31 consecutive patients with low exercise capacity resulting from chronic effort angina but who had not suffered previous myocardial infarction were investigated.
Methods: Rapid atrial pacing was used to induce myocardial ischemia, with the same pacing rate before and after an intracoronary injection of 50 micrograms nitroglycerin. Fifteen patients (group A) with an obstructed ischemia-related coronary artery (IRCA) (TIMI flow grade 0 or 1), were injected with nitroglycerin into a major donor artery of the well-developed collateral circulation. Sixteen patients with patent IRCAs (TIMI flow grade 2 or 3) were injected with nitroglycerin into the IRCA. These patients were subdivided according to the morphologic findings of the stenosis in the IRCA: group B, nine patients with eccentric elliptical residual lumens, and group C, seven patients with circular residual lumens.
Results: In group A, 0.21 +/- 0.08 mV of pacing-induced ST-segment depression was consistently ameliorated to 0.08 +/- 0.05 mV after pretreatment with nitroglycerin (P < 0.0001). In group B, the extent of ST-segment depression was markedly improved from a basal value of 0.21 +/- 0.05 mV to 0.05 +/- 0.03 mV with nitroglycerin (P < 0.001). In contrast, in group C ST-segment depression remained unchanged despite pretreatment with nitroglycerin (0.21 +/- 0.04 mV to 0.21 +/- 0.05 mV, P = NS).
Conclusion: These results indicate that the contribution of the dynamic stenosis of the IRCA to effort angina differs greatly among patients and depends on the morphologic findings of the stenosis in the IRCA, and also that collateral circulation responds effectively to intracoronary injection of nitroglycerin in all patients with a well-developed collateral circulation.