Differences in collateral myocardial blood flow following gradual vs abrupt coronary occlusion

The purpose of the present study was to test the hypothesis that collateral myocardial blood flow is higher if coronary occlusion is preceded by a brief period (45 min) of progressive, gradual stenosis, rather than by abrupt, total occlusion. Seven dogs had three coronary occlusions by a hydraulic occluder, 3 min in duration, and separated by 45 min periods of reperfusion (Group I). Microsphere blood flow was measured 1.5 min after each total occlusion was achieved. To assess the potential effects of multiple occlusions, the first and third coronary occlusions were of the same type, ie, either both abrupt or both gradually progressive over 45 min. Group II included nine dogs with abrupt total occlusion followed by microsphere blood flow measurements 1.5, 10, 20 and 45 min after occlusion, to test the effect of a 45 min duration of total occlusion on collateral flow. The results indicate that the transmural mean collateral myocardial blood flow was 33% higher 1.5 min after total occlusion if the total occlusion was preceded by gradual, progressive coronary stenosis over 45 min (0.093 ± 0.085 ml·min−1·g−1) compared with the abrupt occlusion (0.070 ± 0.062 ml·min−1·g−1, P<0.05). The higher flow was not distributed preferentially to one transmural layer and was not explained by haemodynamic changes between occlusions. The change in collateral flow between abrupt and gradual occlusions (randomised sequence) was not the result of performing sequential occlusions because the transmural mean collateral blood flow did not differ between the first and third occlusions which were both of the same type. Further the difference between abrupt and gradual occlusions is not explained by the longer period of reduced coronary flow to stimulate collaterals during gradual stenosis because transmural mean collateral myocardial blood flow did not increase in Group II dogs between 1.5 and 45 min after abrupt, total occlusion (0.167±.039 to 0.161 ±0.041 ml·min−1·g−1). The mechanism of this higher collateral blood flow after gradual vs abrupt occlusion cannot be determined from these experiments, but these results should be considered in interpreting and designing experiments involving more than one coronary occlusion. The 33% higher collateral flow after gradual occlusion is small but might be expected to limit the severity of ischaemic injury and may have potential therapeutic implications for patients in whom dynamic processes of coronary occlusion are operative.