Continuous-Flow Cardiac Assistance: Effects on Aortic Valve Function in a Mock Loop Egemen Tuzun, M.D.,* , † , ‡ ,1 Marcel Rutten, Ph.D.,† Marco Dat, B.Sc.,† Frans van de Vosse, Ph.D.,† Cihan Kadipasaoglu, B.Sc.,* and Bas de Mol, M.D., Ph.D.† , ‡ *Center for Cardiac Support and the Cardiovascular Research Laboratories, Texas Heart Institute at St. Luke’s Episcopal Hospital, Houston, Texas; †Department of Biomedical Engineering, Eindhoven University of Technology, Eindhoven, The Netherlands; and ‡Department of Cardiovascular Surgery, Academic Medical Center, Amsterdam, The Netherlands Submitted for publication December 31, 2009 Background. As the use of left ventricular assist devices (LVADs) to treat end-stage heart failure has become more widespread, leaflet fusion—with resul- tant aortic regurgitation—has been observed more frequently. To quantitatively assess the effects of non- pulsatile flow on aortic valve function, we tested a con- tinuous-flow LVAD in a mock circulatory system (MCS) with an interposed valve. Materials and Methods. To mimic the hemodynamic characteristics of LVAD patients, we utilized an MCS in which a Jarvik 2000 LVAD was positioned at the base of a servomotor-operated piston pump (left ventricular chamber). We operated the LVAD at 8000 to 12,000 rpm, changing the speed in 1000-rpm increments. At each speed, we first varied the outflow resistance at a constant stroke volume, then varied the stroke vol- ume at a constant outflow resistance. We measured the left ventricular pressure, aortic pressure, pump flow, and total flow, and used these values to compute the change, if any, in the aortic duty cycle (aortic valve open time) and transvalvular aortic pressure loads. Results. Validation of the MCS was demonstrated by the simulation of physiologic pressure and flow wave- forms. At increasing LVAD speeds, the mean aortic pressure load steadily increased, while the aortic duty cycle steadily decreased. Changes were consistent for each MCS experimental setting, despite variations in stroke volume and outflow resistance. Conclusions. Increased LVAD flow results in an impaired aortic valve-open time due to a pressure overload above the aortic valve. Such an overload may initiate structural changes, causing aortic leaflet fusion and/or regurgitation. Ó 2010 Elsevier Inc. All rights reserved. Key Words: left ventricular assist device; continuous flow; aortic valve; mock circulation. INTRODUCTION Aortic valve commissural fusion and resultant insuffi- ciency have recently begun to be considered complica- tions of the prolonged use of left ventricular assist devices (LVADs), whether they produce pulsatile or nonpulsatile flow [1, 2]. Previous reporters have sug- gested that these complications result from certain local hemodynamic forces that affect aortic valve function during LVAD support [1–3]. To date, no detailed flow analyses or hemodynamic assessments have been available concerning the effects of reduced or nonpulsatile flow on aortic valve function during the cardiac cycle. We believe that the increased pressure load above the aortic valve due to increased LVAD flow may result in reduced aortic valve-open times and, consequently, may lead to aortic valve complications. The objective of the present study was to quantitatively assess the complex interaction between reduced or nonpulsatile aortic flow and aortic valve function in a mock-loop circulation using a nonpulsatile LVAD. The assessment was undertaken to calculate the aortic valve’s average mechanical load, open time, and trans- valvular flow at different pump-flow settings and to determine the correlation between LVAD flow and aortic valve function. 1 To whom correspondence and reprint requests should be addressed at Cardiovascular Research Laboratories, Texas Heart Institute, 6770 Bertner Avenue, Houston, TX 77030. E-mail: etuzun@heart.thi.tmc.edu. 0022-4804/$36.00 Ó 2010 Elsevier Inc. All rights reserved. 1 Journal of Surgical Research -, 1–5 (2010) doi:10.1016/j.jss.2010.05.040 ARTICLE IN PRESS