Left ventricular diastolic and systolic performance during chronic experimental aortic regurgitation

Abstract

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.

Fibrosis, Myocyte Degeneration and Heart Failure in Chronic Experimental Aortic Regurgitation

“…To document the development of eccentric LV hypertrophy and to assess LV function and AR severity over time, two-dimensional, M-mode and Doppler echocardiograms were performed prior to surgery and serially following operation for up to 3 years using an approach previously validated in our laboratory [5][6][7][8]. For this procedure, animals were sedated and placed in the left lateral decubitus position.…”

“…Echocardiograms were obtained using the 5-mHz, shortfocus transducer of a Hewlett-Packard 77020 Echo-Doppler system. LV internal dimensions, posterior wall and interventricular septal thicknesses, mass, fractional shortening, and end-systolic stress, as well as transaortic valvular RF were measured as previously described [5][6][7][8].…”

“…The model manifested LV enlargement and hypertrophy, alterations in diastolic per-formance and infrequent development of congestive heart failure (CHF) [5,6]. Modification of this model to permit induction of more severe AR resulted in greater enlargement and hypertrophy and more frequent progression to CHF and systolic dysfunction [7], emulating the full spectrum of the disease observed in man.…”

Protein Turnover in Compensated Chronic Aortic Regurgitation

“…A thoracotomy was performed, an electromagnetic flow probe placed around the ascending aorta, and a sharp, bevel-tipped catheter, introduced into the carotid artery via cutdown. was advanced retrograde into the LV by perforating an aor tic valve cusp, as we have previously described [2][3][4], After creation of AR. electromagnetic flow probe recordings were analyzed to mea sure regurgitant fraction (the ratio of retrograde to anterograde flow).…”

“…the heart adapts to the vol ume overload of aortic regurgitation (AR) with left ven tricular (LV) dilatation and hypertrophy [1,2], Experi-be maintained for several years [2][3][4] and during which congestive heart failure may supervene [2][3][4],…”