Development of collaterals. Application of external subcritical fixed constrictors in a canine model.

A canine model for a standardized induction of collaterals is presented with a fixed external constrictor that is not designed to induce an occlusion of the coronary artery and at least over the timespan of 6 weeks does not impair perfusion under resting conditions in the myocardium-at-risk. The coronary constriction was standardized by a reduction of the postocclusive reactive hyperemia of 50%. Flow measurements were performed by flowmeter and by radioactive microspheres acutely and after an interval of 6 weeks of constriction. The results showed an increase of the collateral flow from 21.2 +/- 11.8 ml/100 g/min-1 to 42.8 +/- 16.2 ml/100 g/min-1 (p less than 0.05). The regional perfusion exhibited a transmyocardial gradient in favour of the subepicardial layers with 49.3 +/- 25 ml/100 g/min-1 as compared to 33.1 +/- 17.3 ml/100 g/min-1 (p less than 0.05) of the endocardial layers. Reactive hyperemia, as determined by flowmeter, was decreased by 21% after 6 weeks on account of slow progression of the coronary constriction due to intimal reactions, whereas reactive hyperemia, as determined by the microsphere method, increased by 9% due to additional collateral channels.