Subendocardial underperfusion during acute aorticopulmonary shunting in anesthetized dogs

Changes in regional coronary hemodynamics during A-P shunting were studied in open-chest anesthetized dogs. During direct A-P shunting coronary driving pressure fell which resulted in decreased coronary flow to the subendocardial region of the left ventricle and abnormal coronary reactive hyperemic responses. When aortic diastolic pressure was augmented during indirect A-P shungting, underperfusion of the subendocardial region was corrected and the coronary hyperemic responses returned to normal. Since shunt flows were equal in both groups, the magnitude of the shunt was not a factor in reducing coronary flow. The present study indicates that acute A-P shunts may cause underperfusion of the left ventricular subendocardium. Thus, under these conditions, the left ventricle is stressed by a combination of an increased workload in the face of reduced subendocardial coronary flow.