Evaluation of extravascular resistance in the unloaded fibrillating left ventricle of the dog.

In open-chest anaesthetized dogs the relative magnitude of extravascular resistance in the superficial and deep left ventricular myocardium was estimated from the flow through the isolated vascular segments inserted at different depths of the myocardium. It was confirmed that in the normally working heart extravascular resistance was significantly greater in the deep than in the superficial layer. In the unloaded fibrillating left ventricle no difference in extravascular resistance between these layers could be detected. Since it had been found previously that subendocardial preponderance of ischaemia persists in the unloaded fibrillating left ventricle (Sedek and Michałowski, submitted for publication), the present observation is a further challenge for the current view that the subendocardium is more vulnerable to ischaemia because extravascular resistance is greater in this layer.