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Ann Thorac Surg 2002;73:750
© 2002 The Society of Thoracic Surgeons
a Department of Thoracic and Cardiovascular Surgery, 9500 Euclid Ave, F25, Cleveland, OH 44195, USA
The right ventricle is not a "black box," but it can be very dark. This report from the Columbia team helps shed light on the physiology of right ventricular function in patients on left ventricular assist device (LVAD) support. Typically, the patient with a failing left ventricle has high left atrial pressures, and therefore elevated pulmonary artery pressures. On LVAD support the left atrial pressure drops, therefore the pulmonary artery pressure drops. Then the right ventricle (RV) ejection fraction improves, right atrial pressure drops, and finally the hepatic congestion is gradually relieved. However, when RV contractility (RV stroke work index in this report) is severely impaired then pulmonary artery pressures before LVAD implant may be low because the ventricle cannot generate higher pressures. In this worrisome situation the left atrial pressure on LVAD support will drop to very low levels because blood cannot cross the lungs, and LVAD flow is low. Previous reports have looked at the worst case scenario, patients that required RVAD support in order to generate flow across the lungs, and shown a strong correlation with RVSWI. However, this paper focuses on a more common problem, less severe RV dysfunction that can lead to increased intensive care unit length of stay, prolonged inotrope requirements, and association with organ dysfunction, bleeding, and death. Although the authors are right to suppose that theoretically a right ventricular assist device (RVAD) may be beneficial to decrease right side pressures, decongest the liver, and increase LVAD flow, the RVAD itself has complications. Also the current RVAD technologies require external pumps with a cumbersome drive system and hospital discharge is difficult.
The take home messages in this report cover five points. First, patients with high pulmonary artery (PA) pressures and a high wedge pressure are rarely a problem. The more worrisome patients are the ones with low PA pressures, especially those with a low right ventricular stroke work index (RVSWI). We now calculate RVSWI on all patients who we consider for VAD support. We use this number to help our decision making, just as we use pulmonary vascular resistance to help determine suitability for transplantation. RVSWI is an "imperfect" measurement because it is load dependent, but it is easily calculated, and the load independent measurements are impractical in most clinical settings. Second, avoid bleeding which was very common in their group with RV dysfunction. We replace vitamin K preoperatively because of the deficiency seen in these patients with hepatic congestion. Also, intraoperative aprotinin and fresh frozen plasma are given to reduce bleeding. With less bleeding there is less blood and products transfused which increase RV afterload. Third, be careful not to overfill the right ventricle, especially when weaning from cardiopulmonary bypass. Volume loading can push the RV over the Frank Starling curve into an area of poor contractility. Using a hemoconcentrator on bypass will reduce intravascular volume. Fourth, decrease RV afterload by dropping left atrial and pulmonary artery pressures. The inflow cannula position should not be obstructed by the septum or LV free wall, and cardiac tamponade or ventilation at high pressures may increase intrathoracic pressure and left atrial pressure. Nitric oxide and the phosphodiesterase inhibitor Milrinone are also useful to decrease pulmonary vascular resistance, although currently nitric oxide is very expensive and we use it rarely for selected patients. Finally, use inotropes as needed to increase RV contractility. We frequently use the combination of epinephrine and milrinone because they work by separate mechanisms of action. In particular following chest closure the inotropes are useful to help improve function of the distended and compressed right ventricle. If LVAD flow is adequate with all of these maneuvers (cardiac index 
2.2 l/min/m2) then we rarely proceed to RVAD use. We generally find it is easier to manage prolonged inotrope use than to manage an external RVAD.
Related Article
Ann. Thorac. Surg. 2002 73: 745-750.
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  J. L. Navia, P. M. McCarthy, K. J. Hoercher, N. G. Smedira, M. K. Banbury, and E. H. Blackstone Do left ventricular assist device (LVAD) bridge-to-transplantation outcomes predict the results of permanent LVAD implantation? Ann. Thorac. Surg., December 1, 2002; 74(6): 2051 - 2063. [Abstract] [Full Text] [PDF]
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