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Actions of isoflurane on myocardial perfusion in chronically instrumented dogs with poor, moderate, or well-developed coronary collaterals.

The influence of isoflurane on myocardial perfusion (determined by the radioactive microsphere technique) in normal regions and areas distal to a left anterior descending (LAD) coronary artery occlusion was evaluated in dogs that were chronically instrumented for measurement of systemic and coronary hemodynamics and had varying degrees of coronary collateral development. In 17 dogs, an Ameroid constrictor was implanted on the LAD coronary artery to produce a slowly progressive occlusion that stimulated development of the collateral circulation. Collateralization was allowed to progress in three groups of dogs to a poor (3 +/- 1 days), moderate (19 +/- 4 days), or well-developed (50 days) stage postsurgery. After the indicated period of time had elapsed, the LAD coronary artery was occluded (via Ameroid constrictor and/or balloon cuff occluder). Radioactive microspheres were administered during the conscious state and at 2% and 3% inspired concentrations of isoflurane. A fourth set of microspheres was injected at 3% isoflurane with heart rate and blood pressure adjusted to conscious levels. Isoflurane produced equivalent changes in systemic hemodynamics in all groups, including an increase in heart rate and decreases in arterial pressure and left ventricular peak positive dP/dt. Regional contractile function of normal myocardium was reduced by isoflurane in all groups. Isoflurane (3%) significantly decreased subepicardial, subendocardial, and transmural blood flow in normal and collateral-dependent regions in all groups. Myocardial perfusion returned to levels present in the conscious state when arterial pressure and heart rate were adjusted to those levels present prior to induction of anesthesia. Neither the left ventricular transmural distribution nor the collateral-dependent to normal zone flow ratio was altered from conscious levels by isoflurane in any group with or without changes in blood pressure and heart rate. The results indicate that isoflurane does not redistribute coronary blood flow from collateral-dependent to normal regions in a single-vessel coronary artery disease model. The actions of isoflurane are also independent of the degree of coronary collateral development.