Mechanical correlates of contraction-excitation feedback during acute ventricular dilatation

OBJECTIVE: The purpose was to examine the mechanical correlates of the electrophysiological changes that occur during acute left ventricular dilatation. METHODS: Ten isolated, retrogradely perfused, ejecting rabbit hearts were studied. Left ventricular volume was adjusted by varying left atrial perfusion pressure. Left ventricular pressure was measured directly. Changes in left ventricular chamber dimensions at the level of an epicardial electrode were evaluated with two dimensional echocardiography and wall stress was calculated from these measures. Regional left ventricular electrophysiological properties were measured at two left atrial perfusing pressures. RESULTS: Increases in left atrial perfusion pressure resulted in significant increases in left ventricular end diastolic and end systolic pressures, epicardial and endocardial circumference, and wall stress. Only changes in diastolic wall stress correlated with changes in ventricular refractoriness (r = 0.69, p = 0.027). CONCLUSIONS: Left ventricular dilatation results in shortening of ventricular refractoriness in the isolated, ejecting rabbit heart. Regional changes in refractoriness are best correlated with changes in wall stress.