Downloaded from http://journals.lww.com/asaiojournal by BhDMf5ePHKbH4TTImqenVAHxkFJp/XpPk1L/H3vMGwqMxG9jwOd8eJPG+b4DlKuAX44qu/vwzmc= on 07/30/2018 Effects of Continuous Flow Left Ventricular Assist Device Support on Skin Tissue Microcirculation and Aortic Hemodynamics KENNETH N. LITWAK,* SHIN’ICHIRO KIHARA,* MARINA V. KAMENEVA,* PHILIP LITWAK,* ARKADY URYASH,* ZHONGJUN WU,* AND BARTLEY P. GRIFFITH† Continuous flow ventricular assist devices (CFVADs) are thought to be the next generation of circulatory assist de- vices. With many now in various stages of development or clinical trial, it is important that the physiologic aspects of these pumps be critically analyzed. In this study, 15 calves were divided into two groups. One group received a CFVAD, and the other a sham implant. Two additional animals were used in an acute study to examine aortic blood flow patterns from a CFVAD. Tissue perfusion was measured on all animals before surgery and then weekly thereafter. Before surgery, there was no difference in hemodynamics or tissue perfusion between studied animals. Postoperatively, CFVAD animals had statistically significant increased diastolic pressure. Sig- nificantly decreased pulse pressure, pulse index, and tissue perfusion were also observed in CFVAD animals. Results from the flow pattern studies suggested that at moderate levels of pump support (40 –75%), the amount of blood flow distal to the outflow graft anastomosis decreased approximately 25% because of increased regurgitant blood flow in the aorta. These results suggest that the diminished tissue perfusion is likely due to changes in aortic hemodynamics and provide some insight into the distribution of flow from CFVADs. ASAIO Journal 2003; 49:103–107. C ontinuous flow ventricular assist devices (CFVADs) are seen as the next generation of circulatory assist devices. There are many types of these devices now in stages of development or in the early stages of clinical trials. 1–5 Associated with these devices are many hemodynamic differences compared with the normal circulation and the currently available pulsatile ventricular assist devices (VADs). The primary difference is decreased pulse pressure with increased pump flow. This is due to continuous pump flow during the diastolic portion of the cardiac cycle, raising diastolic blood pressure. 3 Another major difference is the potential for regurgitant pump flow during periods of hypertension or pump stoppage, as these pumps have no valves. 6 Moreover, the distribution of pump flow in the aorta and the potential effects of such changes on overall blood flow are poorly documented. 6–8 Changes in aortic hemodynamics could have profound implications for end-organ function, as well as vascular structure and function. Indeed, there have been recent reports of changes in aortic structure and function with continuous flow pump support. 8 Discussions of microvascular blood flow with CFVAD support are equally limited, mostly reserved for coronary microcircu- lation or nondescript end-organ function. 9 –13 The purpose of this study was to examine the effects of chronic continuous flow pump support on skin tissue microcirculation. Further- more, in an effort to relate these effects to blood flow patterns, we conducted acute studies to examine aortic hemodynamics with varying amounts of continuous flow pump support. Materials and Methods Chronic Studies: Implantation Procedure Fifteen male Jersey breed calves (55–70 kg) were divided into two groups: pump implant (PI, n = 8) and sham implant (SI, n = 7). In the PI group, continuous flow pumps were implanted in the left thoracic cavity in a left ventricular apex to descending thoracic aorta bypass. Briefly, animals were pre- anesthetized with atropine sulfate (30 – 45 mg subcutaneously) and then anesthetized with Methohexital (10 mg/kg intrave- nously). Animals were immediately intubated and anesthesia was maintained with isoflurane (1.5–3.0%) mixed with oxygen and room air. The carotid artery was permanently catheterized with a polypropylene catheter. A 5th rib interspace thoracot- omy was done. The dacron outflow graft was preclotted in the animal’s blood and then anastomosed onto the descending thoracic aorta. The pump was assembled and the apical can- nula was inserted directly into the left ventricular apex, after the apex had been cored with a custom circular coring knife. The pump circuit was de-aired with multiple needle punctures in the outflow graft. Main pulmonary artery (PA) and pump flow were measured using implanted ultrasonic flow meters (Transonic Animal Research Flowmeters T206 series, Tran- sonic System Inc., Ithaca, NY). Pump speed was adjusted so that pump flow was 50 – 80% of PA flow. The thoracotomy was closed in a three layer pattern. Anticoagulant therapy (couma- din, 2.5–12.5 mg orally) was administered the night before the surgery and then daily thereafter. International normalized ratios (INRs) were adjusted twice weekly to maintain an INR of 2.5–3.5. SI animals were also subjected to a thoracotomy. A short (2– 4 cm) length of preclotted dacron graft was anastomosed From the *Department of Surgery, University of Pittsburgh, Pennsyl- vania; and the †Department of Surgery, University of Maryland, Bal- timore, Maryland. Submitted for consideration February 2002; accepted for publica- tion May 2002. Correspondence: Dr. Kenneth Litwak, University of Pittsburgh, 215 McGowan Institute, 3025 E. Carson St., Pittsburgh, PA 15203. DOI: 10.1097/01.MAT.0000047866.05294.05 ASAIO Journal 2003 103