2004 Volume 2 Issue 4 Pages 90-98
Background. Although collateral circulation is important for myocardial salvage in acute coronary syndrome, effects of collaterals are significantly reduced by systemic hypotension. The objective of this study is to evaluate the effects of nitroglycerin and nicorandil on micro-collateral circulation during systemic hypotension.
Methods. Real-time myocardial contrast echocardiography (MCE) was performed in 15 open-chest dogs during occlusion of the left circumflex artery using a snare. Ischemic area was identified using high ultrasound power exposure (burst) just after coronary occlusion. Micro-collateral vessels were recognized by re-opacification during 30 seconds of occlusion. Final subjects for this study were 8 of the 15 dogs that displayed micro-collateral vessels. Flow volume of the donor artery, i.e., the left anterior descending coronary artery (LAD), was measured. Video intensity (VI) were measured and percent wall thickening (%WT) was calculated. Replenishment curves of VI for the ischemic area after burst were obtained and used in the exponential function y=A (1-e-βt), for estimation of myocardial blood flow volume (A×β). These indices were compared at control and during hypotension after nitroglycerin (0.01-0.02 mg/kg) or nicorandil (0.1-0.2 mg/kg) administration.
Results. Equivalent hypotension was induced by each drug. VI, %WT and A×β at the ischemic area were significantly decreased after nitroglycerin (p<0.05) administration, but not after nicorandil. Nicorandil increased LAD flow from 6.1 ±2.3 ml/min to 8.8±2.1 ml/min, but nitroglycerin did not.
Conclusion. Compared with nitroglycerin, nicorandil offers better preservation of coronary collateral circulation, even during systemic hypotension.
