Abstract
Nine NYHA class III-IV patients awaiting heart transplantation (HTx) were studied with a right ventricular ejection fraction (RVEF) catheter. The first aim of the study was to explore the pulmonary and systemic circulatory effects of dobutamine (D) and/or nitroprusside (N) in these patients. The second aim was to search for the parameter(s) among those usually measured that best predicted RVEF. Baseline data were recorded after 30 minutes of stabilization. Then, three drug regimens were administered in a randomized order for 30 minutes each: D, 4 μg/kg/min; N, 0.25 to 1.0 μg/kg/min; and their combination. Significant changes in RV loading and function were observed with all three therapies. The combination of both drugs was superior to either drug alone. The best predictor of RVEF was pulmonary arterial elastance. The second best was pulmonary capillary wedge pressure (PCWP). Pulmonary artery pressures, pulmonary vascular resistances, and transpulmonary gradient (TPG) were of less predictive value, as shown by a multiple regression analysis. None of the drugs showed any selectivity for the pulmonary vasculature, because the ratio PVRI/SVRI was never changed significantly. Selective pulmonary arterial vascular smooth muscle relaxation is probably not the most important mechanism to explain the unloading and improvement in function of the RV with D and/or N. Improved myocardial pump function appears to be the major factor in unloading the RV via reduction of PCWP and mean pulmonary artery pressure with essentially no change in TPG. The RVEF catheter provides valuable additional information in the screening of HTx candidates for pulmonary hypertension.
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