The quiescent heart: excitability, compliance, and vascular resistance

A rat heart, perfused via the aorta and fitted with a balloon in the left ventricle, was rendered quiescent by a local injection of lidocaine into the region of the atrioventricular node. Once quiescence was established it was extended by injection of formaldehyde into the same site via a coaxial needle. The quiescent heart (QH) was responsive to electrical stimulation and exhibited the same isovolumic pressure development as seen during spontaneous beating. Over a range of ventricular volume, slightly greater left ventricular pressures were found in the QH as compared with the diastolic pressure at the same ventricular volumes in the beating heart (BH). Left ventricular diastolic pressures in the QH were less than those found in the KCl-arrested heart. The QH perfused at constant flow rate with a syringe pump exhibited a constant perfusion pressure. Infusion of vasopressin induced a dose-related increase in perfusion pressure, whereas adenosine or sodium nitroprusside reduced the perfusion pressure. The QH appears to be a useful preparation for the study of vascular resistance free of cyclical intramyocardial pressure and relatively uninfluenced by vasoactive metabolites arising from contracting muscle.