Distribution of coronary collateral flow in acute myocardial ischaemic injury: effect of propranolol

The local distribution of coronary collateral flow was mapped using 8 mu tracer microspheres following circumflex coronary occlusions in dogs. Overall flow to the ischaemic posterior papillary muscle and subjacent myocardium decreased to 21% of anterior free wall flow. Collateral flow was non-uniform, however, and was lower in the subendocardium (14%) than in the subepicardium (27%). Brief temporary occlusions with and without propranolol therapy showed that collateral flow was less and the inner/outer wall ratio was unaltered in treated animals. Although propranolol reduces infarct size after coronary occlusions, this effect appears not to be related to increases in collateral flow.