Effect of propranolol and isoprenaline on regional left ventricular blood flow in experimental myocardial ischaemia

AUTHORS' SYNOPSIS: The distribution of left ventricular (LV) blood flow was studied in open chested dogs with acute myocardial ischaemia before and after propranolol and isoprenaline. Regional LV flow was measured with radioactive microspheres and local tissue injury estimated from ST segment elevation in epicardial electrocardiograms. Propranolol reduced blood flow throughout the LV, more so in non-ischaemic than ischaemic regions, but ST segments became less elevated. Isoprenaline increased flow to non-ischaemic regions and the subendocardial portion of ischaemic areas; subepicardial flow in ischaemic regions did not change. Concomitantly, ST segments became more elevated and new ST segment elevations appeared. This disparity between changes in ST segment elevation and blood flow indicates that these beta-adrenergic agents do not alter ischaemia through primary changes in blood flow distribution. Alternative mechanisms are discussed.