Effect of adenosine on transmural flow gradients in normal canine myocardium

Previous reports suggest that in comparison to epicardial flow the response of endocardial blood flow to systemic adenosine is limited. However, intravenous adenosine results in reflex tachycardia and hypotension, which we avoided in six anesthetized dogs by infusing adenosine into the left circumflex (LCx) artery to evaluate the endocardial/epicardial ratio during partial and full vasodilation. The mean (+/- SD) LCx endocardial/epicardial ratio was 1.37 +/- 0.18 with partial vasodilation and 0.81 +/- 0.06 with full vasodilation, which represents an initial increase followed by a decrease when compared with the normal left anterior descending values (p less than 0.05). This biphasic response in the endocardial/epicardial ratio with increasing vasodilation was a direct effect of adenosine, as no hemodynamic alterations occurred during the protocol. These data suggest that in an experimental model with a relative tachycardia the endocardial layer is more sensitive to adenosine but there is a greater capacity to increase flow in the epicardial layer.