MECHANICAL CORRELATES OF CONTRACTION-EXCITATION FEEDBACK DURING ACUTEVENTRICULAR 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 ra bbit hearts were studied. Left ventricular volume was adjusted by vary ing left atrial perfusion pressure. Left ventricular pressure was meas ured directly. Changes in left ventricular chamber dimensions at the l evel of an epicardial electrode were evaluated with two dimensional ec hocardiography and wall stress was calculated from these measures. Reg ional left ventricular electrophysiological properties were measured a t two left atrial perfusing pressures. Results: Increases in left atri al perfusion pressure resulted in significant increases in left ventri cular end diastolic and end systolic pressures, epicardial and endocar dial circumference, and wall stress. Only changes in diastolic wall st ress 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 i n wall stress.