LEFT-VENTRICULAR DIASTOLIC AND SYSTOLIC PERFORMANCE DURING CHRONIC EXPERIMENTAL AORTIC REGURGITATION

To study the time course of left ventricular structural and functional responses to chronic aortic regurgitation, aortic regurgitation was surgically induced in rabbits, and Doppler echocardiography was performed preoperatively and serially postoperatively for up to 2.5 yr. Twenty-five New Zealand White rabbits underwent surgical induction of aortic regurgitation and 13 control animals underwent sham operation. Left ventricular endocardial and epicardial surfaces were digitized from M-mode echocardiograms to measure the rates of change of cavity dimensions and wall thicknesses during diastolic relaxation and systolic contraction. Aortic regurgitant animals developed left ventricular dilatation and eccentric hypertrophy that remained relatively stable throughout the follow-up period. Compared with baseline values, left ventricular mass increased 120% and left ventricular internal dimension at end diastole increased 40%, whereas posterior wall thickness at end diastole and fractional shortening remained relatively stable. Left ventricular diastolic performance was enhanced at 6 mo after operation, a finding associated with increased volume load and heart rate following induction of aortic regurgitation. Diastolic performance was then reduced at 12 mo after operation and demonstrated no further decline throughout the remainder of the follow-up period. In contrast, left ventricular systolic performance was not altered following operation and remained preserved until the final assessment at up to 2.5 yr. Thus alterations in diastolic performance occurred without impairment of systolic performance during long-term follow-up of chronic experimental aortic regurgitation.