Absence of coronary vascular reserve in myocardium distal to a fixed coronary stenosis

In a study to test the hypothesis that vascular reserve is exhausted in the setting of a resting blood flow deficit, the left anterior descending or circumflex artery was cannulated and perfused from the left carotid artery. After reactive hyperaemia had been assessed a stenosis was produced with a screw clamp. In the first experiment a moderate stenosis (diastolic perfusion pressure 40 mmHg) was produced in the left anterior descending artery (three dogs) or left circumflex artery (three dogs). Blood pressure was held constant with aortic constriction during intracoronary adenosine infusion (6 μmol·min−1). The stenosis was then adjusted to the preadenosine perfusion pressure. In the second experiment the anterior interventricular coronary vein was also isolated and segment length crystals were placed in the ischaemic and non-ischaemic zones. Severe stenosis (flow reduction of at least 50% and evidence of decreased segmental shortening) was produced in the cannulated left anterior descending artery (eight dogs). Intracoronary adenosine was given with aortic pressure held constant by transfusion and coronary venous drainage. In the first experiment resting coronary flow (ml·min−1) decreased from 41(3) to 29(6) (p<0.05) with stenosis. Coronary flow increased from 29(6) to 34(7) (p<0.05) with adenosine and to 50(10) (p<0.05) with stenosis adjustment. Subendocardial flow (ml·g−1·min−1) decreased from 0.89(0.26) to 0.78(0.23) (p<0.05) with adenosine and then increased from 0.94(0.49) with perfusion pressure adjustment. Subepicardial flow tended to increase with adenosine, and increased further with stenosis adjustment. In the second experiment subendocardial, subepicardial, and coronary flow did not change with adenosine. Thus there was no demonstrable vascular reserve in any layer of myocardium with a resting flow deficit.