Low- and high-blood flow regions in the normal pig heart are equally vulnerable to ischaemia during partial coronary stenosis

Myocardial perfusion is heterogeneous, even in the normal heart. It is unknown whether the resting normal blood flow level predicts the severity of mismatch between local blood flow and metabolism during acute ischaemia. In the present study local blood flow (measured with radioactively labelled microspheres) and metabolic indicators of ischaemia [tissue contents of lactate and inosine (INO), a breakdown product of adenosine triphosphate (ATP)] were determined in 84-102 simultaneously frozen samples (approximately 0.9 g) of normal (n = 7) and partially ischaemic (n = 4) porcine left ventricles. Ischaemia was induced for 20 min by partially occluding the left anterior descending artery to reduce perfusion pressure from 107 +/- 17 mm Hg to 39 +/- 10 mm Hg (mean +/- SD). Flow reduction in the ischaemic region was strongly variable, both within the subepicardium (range 6-66%, average 34%) and the subendocardium (range 33-84%, average 57%), indicating redistribution of blood flow inside transmural layers in addition to the well-known preferential decrease in subendocardial perfusion. The relative flow reduction during stenosis was not dependent on normal local perfusion level (Spearman rank correlation coefficient -0.002, P = 0.99). Samples with low or high myocardial blood flows before stenosis showed similar increases in lactate content and INO/ATP content ratio, as long as the percentage blood flow reduction was the same. It is concluded that regions with low and high resting flows in the normally perfused heart are equally susceptible to metabolism-perfusion mismatch resulting from coronary stenosis.