Permanent Changes of Ventricular Contractility and Compliance in Chronic Volume Overload

Left ventricular volume overload (LVVO) has been created in 18 dogs by anastomosing a Dacron conduit between the infrarenal abdominal aorta and inferior vena cava. The dogs previously were instrumented so that in the awake state LV pressure, systemic arterial pressure, LV dP/dt, myocardial segment length and excursion, and coronary and renal artery velocities could be monitored. The animals were stressed with separate infusions of alpha-adrenergic and beta-adrenergic agonists. Both at rest and with stress, over a 12-wk period, preejection, ejection, and contractility indices decreased. Left ventricular compliance decreased as exemplified by the increased ratio of end-diastolic pressure to end-diastolic length. The shunt was ablated in 7 dogs, and monitoring in conjuction with alpha- and beta-adrenergic stress foan additional 12 wk demonstrated an initial improvement in the previous indices. However, the amelioration plateaued and values similar to the control state were not attained. This suggests that potentially permanent alterations in ventricular function and compliance have occurred.