RIGHT HEART INTERACTION WITH LEFT VENTRICULAR ASSISTANCE

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Approximately 20 to 30% of patients implanted with mechanical left ventricular assist devices (LVADs) for refractory cardiac failure after open heart surgery at our center and at others have had complications of right heart failure. The cause of the problem is not known but two possibilities are: 1) there is reduced septal contribution to right ventricular (RV) contraction during left ventricular (LV) unloading, and 2) the increased venous return resulting from the LVAD overloads the marginal RV resulting in failure. In order to evaluate this problem in a controlled study, we will determine RV function with LV assistance in an acute anesthetized dog preparation using a pulsatile sac-type VAD. Detailed evaluations of global and regional RV function using pressure, flow, and dimensional measurements of preload, afterload, contractility, and heart rate will be made. Data will be collected under control and LV assist conditions during experimental interventions designed to model a range of pathophysiologic and physiologic conditions. Measurements of atrial, ventricular, and arterial pressure, pulmonary artery blood flow, and cardiac dimensions using ultrasonic crystals in the septum and RV and LV free walls, will be sampled and analyzed by computer. RV function curves and RV pressure-dimension relations with and without LV assistance will be determined during controlled changes in venous return and pulmonary artery banding to provide a wide range of RV preload and afterload. In selected groups of dogs the study will be repeated during septal and/or RV free wall ischemia, produced by ligation of the right coronary artery and/or the septal branch of the left coronary artery, with or without global cardiac depression produced by intracoronary lidocaine. Using this model of lV assistance we will evaluate RV function and test the major hypothesis that in hearts with septal ischemia, RV free wall ischemia, and/or global cardiac depression, LV assist results in an impairment of RV function, and that complete LV unloading is further detrimental to the RV. These studies in an acute animal preparation will complement our clinical LVAD program. Ultimately we wish to use this knowledge to improve patient selection and treatment and to promote successful utilization of chronically implanted LVADs for end stage heart failure.