Mechanical circulatory support systems--a review.

Congestive Heart Failure (CHF) is a major health problem with a high mortality rate. Its ultimate therapy, heart transplantation, is limited by the shortage of donor hearts. Since decades researchers have been working to solve this problem by developing Mechanical Circulatory Support Systems (MCSS) that can replace or assist the failing heart. Short-term and intermediate-term ventricular assist devices are used nowadays frequently to bridge patients with severe heart failure to recovery. Long-term ventricular assist devices (VADs) and Total Artificial Hearts (TAHs) are used increasingly as a bridge to heart transplantations or as permanent circulatory support in patients with end-stage heart failure that are contraindicated for heart transplantation. The early TAHs and VADs were mainly driven from an external pneumatic drive unit. The latest generation TAHs and long-term assist devices are electrically powered, ultracompact, totally implantable, and have small wearable drive/control consoles, allowing patients to return to their daily activities. The article categorizes and reviews the development of MCSS, highlights the medical indications and contraindications of pump implantation, advantages and disadvantages of the various systems, and results of animal and clinical studies.     

Current status of extracorporeal ventricular assist devices in Japan

Extracorporeal VADs are less expensive, their prices reimbursable by the health insurance being about one-sixth of those of implantable VADs in Japan. However, a disadvantage is that, in Japan, their use is restricted to hospitals, necessitating prolonged hospitalization, reducing the patients’ quality of life. According to the Japanese registry for Mechanically Assisted Circulatory Support, the survival rate does not differ significantly between patients with extracorporeal and implantable VADs. As in Europe and North America, extracorporeal VADs in Japan are commonly used as Bridge to Decision or Bridge to Recovery. Extracorporeal VADs are switched to implantable VADs as a Bridge-to-Bridge strategy after stabilization or when cardiac function recovery fails. They are also used as right ventricular assist devices (RVADs) in patients with right heart failure. A special characteristic of extracorporeal VADs in Japan is their frequent use as a Bridge to Candidacy. In Japan, indications for implantable VADs are restricted to patients registered for heart transplantation. Therefore, in patients who cannot be registered for transplantation because of transient renal dysfunction, etc., due to heart failure, extracorporeal VADs are used first, and then replaced by implantable VADs after transplant registry is done. Here, we describe the current status of extracorporeal VADs in Japan, focusing on the environmental backgrounds, along with a review of the relevant literature.     

Domestic and foreign trends in the prevalence of heart failure and the necessity of next-generation artificial hearts: a survey by the Working Group on Establishment of Assessment Guidelines for Next-Generation Artificial Heart Systems

A series of guidelines for development and assessment of next-generation medical devices has been drafted under an interagency collaborative project by the Ministry of Health, Labor and Welfare and the Ministry of Economy, Trade and Industry. The working group for assessment guidelines of next-generation artificial hearts reviewed the trend in the prevalence of heart failure and examined the potential usefulness of such devices in Japan and in other countries as a fundamental part of the process of establishing appropriate guidelines. At present, more than 23 million people suffer from heart failure in developed countries, including Japan. Although Japan currently has the lowest mortality from heart failure among those countries, the number of patients is gradually increasing as our lifestyle becomes more Westernized; the associated medical expenses are rapidly growing. The number of heart transplantations, however, is limited due to the overwhelming shortage of donor hearts, not only in Japan but worldwide. Meanwhile, clinical studies and surveys have revealed that the major causes of death in patients undergoing long-term use of ventricular assist devices (VADs) were infection, thrombosis, and mechanical failure, all of which are typical of VADs. It is therefore of urgent and universal necessity to develop next-generation artificial hearts that have excellent durability to provide at least 2 years of event-free operation with a superior quality of life and that can be used for destination therapy to save patients with irreversible heart failure. It is also very important to ensure that an environment that facilitates the development, testing, and approval evaluation processes of next-generation artificial hearts be established as soon as possible. Working Group on Establishment of Assessment Guidelines for Active Implantable Medical Devices: Next-Generation Artificial Heart System, Inter-agency Committee for the Guideline Program, the Ministry of Health, Labour and Welfare of Japan and the Ministry of Economy, Trade and Industry of Japan, Tokyo, Japan     

Classification et indications des dispositifs d’assistance cardiaque mécanique

Mechanical cardiac support represents a large spectrum of devices, differing by the duration of assistance, the support or replacement of the heart, the mono or bi ventricular assistance, the paracorporal or implantable positioning, the pulsed or continuous flow, the pneumatic or electric power source. We can distinguish: 1) the ECMO/ECLS systems (extracorporeal membrane oxygenation–extracorporeal life support) systems of peripheral extracorporeal circulation, accessible at patient bedside, that benefited from technological developments allowing longer assistance and therefore more indications; 2) the ventricular assist devices (VADs) that comprise pneumatic ventricles (mono- or biventricular, extra- or paracorporal), implantable left-VAD (pulsed-flow electromechanical ventricles and continuous-flow axial pumps), total artificial hearts (partially or totally implantable) and percutaneous left-VAD (available in the catheterization laboratory, still in the development stage). Partial or total mechanical cardiac support, although used in routine for 20 years, remains a technology seldom used outside the operating room. This slow diffusion is due to the small number of indications (end-stage heart failure and different heart failures considered as reversible), but also to its extreme complexity and to the alternative offered by heart transplantation. However, this situation is changing with the decreasing availability of organs and with the improvements of devices.     

How to demonstrate the reversibility of end-organ function before implantation of left ventricular assist device in INTERMACS profile 2 patients?

For the time being, in Japan, two recently approved implantable ventricular assist devices (VADs) are indicated only when a patient has been listed for heart transplantation or approved to be eligible for heart transplantation by in-hospital committee. The reversibility of end-organ dysfunction must be expected before VAD implantation, but it is often hard to prove during worsening clinical status. We report two patients whose end-organ dysfunction had been eventually demonstrated to be reversible by invasive procedures such as transluminal liver biopsy or transient insertion of intra-aortic balloon pumping.     

Artificial heart research and present status of clinical application in Japan

Japan has a long history of research and development of the artificial heart since Atsumi began studying artificial hearts at the University of Tokyo in 1959. Since that time, the University of Tokyo group has been developing different types of artificial hearts, as well as materials, blood pumps, driving mechanisms, and control methods. Other than the University of Tokyo, there are 12 institutes involved in artificial heart research and development in Japan. As for artificial heart clinical application in Japan, four devices were approved by the government; two are domestic, two are imported. Between 1980 and 2004, 697 cases of clinical application of a ventricular assist device (VAD) have been performed, including in 38 pediatric patients under 18 years. Recently, clinical use of percutaneous cardiopulmonary support has been increasing with 600 to 800 cases being performed every year, including in 40 to 60 patients under age 20 years. Although the requirement for clinical use of pediatric VADs is increasing, there is no device, domestic or imported, currently used in Japan; therefore, there is an urgent need for development of a pediatric VAD.     

Development of mechanical circulatory support devices at the University of Tokyo

The development of mechanical circulatory support devices at the University of Tokyo has focused on developing a small total artificial heart (TAH) since achieving 532 days of survival of an animal with a paracorporial pneumatically driven TAH. The undulation pump was invented to meet this purpose. The undulation pump total artificial heart (UPTAH) is an implantable TAH that uses an undulation pump. To date, the UPTAH has been implanted in 71 goats weighting from 39 to 72 kg. The control methods are very important in animal experiments, and sucking control was developed to prevent atrial sucking. Rapid left–right balance control was performed by monitoring left atrial pressure to prevent acute lung edema caused by the rapid increase in both arterial pressure and venous return associated with the animal becoming agitated. Additionally, 1/R control was applied to stabilize the right atrial pressure. By applying these control methods, seven goats survived more than 1 month. The maximum survival period was 63 days. We are expecting to carry out longer term animal experiments with a recent model of TAH. In addition to the TAH, an undulation pump ventricular assist device (UPVAD), which is an implantable ventricular assist device (VAD), has been in development since 2002, based on the technology of the UPTAH. The UPVAD was implanted in six goats; three goats survived for more than 1 month. While further research and development is required to complete the the UPVAD system, the UPVAD has good potential to be realized as an implantable pulsatile-flow VAD.     

Conversion from long-term AB-5000 to EVAHEART using a combined left thoracotomy and sternotomy approach

Because of the extreme donor shortage in Japan, waiting times for heart transplantation exceed 2 years. Since 1980s in Japan, device availability has also been an issue, with only a few paracorporeal ventricular assist devices (VADs) available as a bridge to transplantation or recovery. However, two implantable VADs became commercially available in 2011. Given these constraints in our healthcare system, we report a relatively rare case of bridge-to-bridge use of an implanted EVAHEART after having used a paracorporeal AB-5000 support for an extended period of time. We successfully employed a combined left thoracotomy and median sternotomy approach as a conversion technique.     

Pathology in patients with ventricular assist devices: a study of 21 autopsies, 24 ventricular apical core biopsies and 24 explanted hearts.

BACKGROUND: Ventricular assist devices (VADs) are used as a bridge to cardiac transplantation or as a permanent or sometimes temporary treatment for end stage heart failure. METHODS: Our autopsy and surgical pathology experience with VADs prior to August 2002 was reviewed. Noted were patient's age, sex, underlying (UCOD) and proximate causes of death (PCOD), duration of VAD implantation, presence of native or prosthetic valvar disease and organ complications. Myocardium from biopsies and explanted hearts were blindly assessed for coagulative necrosis (CN), contraction bands (CB), myocytolysis (MC), increased eosinophilia (IE), myocyte waviness (MW) and fibrosis (F). Each was graded as either mild (score 1), moderate (score 2) or severe (score 3). RESULTS: Autopsy patients: Twenty-one patients, with mean age 55 years (range 10-73), comprised 10 women and 11 men. UCOD was ischemic disease in 16 patients, dilated cardiomyopathy in 4 and aortic valve disease in 1. The mean duration of VAD implantation was 125.7 days (range 1-1095 days, S.D.=253.6). Five patients had biventricular VADs, and 16 had LVAD only. Acquired aortic valve fusion was noted in three patients. PCOD was VAD related in six, donor heart problem in four, cerebrovascular accident in four, miscellaneous in three, pulmonary hypertension in two and aortic disease in two patients. Morbidity: local liver necrosis in seven, acquired aortic valve disease in four, gut infarction in three, abdominal aortic aneurysm in two and host cell assault against VAD porcine aortic valves in one case. Biopsies and explanted hearts: Twenty-four patients had a mean age of 53 years (range 38-68, S.D.=8.6). VADs were implanted for 177.8 days (range 7-593 days, S.D.=151.1). Comparison of histologic scores of biopsies with explanted hearts showed the following: CN 1.33 (S.D.=1.4)/0.21 (S.D.=0.66; P<.001); CB: 2.1 (S.D.=0.93)/0.83 (S.D.=0.28; NS); MC: 0.88 (S.D.=1.19)/0.13 (S.D.=0.34; P<.01); IE: 1.71 (S.D.=1.27)/0.38 (S.D.=0.65; NS); fibrosis: 1.08 (S.D.=1.35)/1.75 (S.D.=1.26; NS); and MW: 1.50 (S.D.=1.22)/0.59 (S.D.=0.73; P<.01). Acquired aortic stenosis developed in six hearts, and one heart showed thrombotic occlusion of the left ventricular outflow tract below an aortic bioprosthesis. CONCLUSIONS: VAD significantly reduced the amount of CN, MC and MW in the left ventricle but may lead to acquired aortic stenosis of native aortic valves or total occlusive thrombosis of aortic prosthetic valves. Proximate cause of death was, most often, VAD related.     

The pediatric mechanical circulatory support program in Innsbruck, Austria, and the impact of such programs on lack of donor hearts in Europe

Strategy and results of the Innsbruck Mechanical Circulatory Support Program are presented, and the impact of such programs on pediatric heart transplantation (HTX) in Europe is discussed. Venoarterial extracorporeal membrane oxygenation (vaECMO) and ventricular assist devices (VADs) were used in 21 pediatric patients (median age 3.3 years, 2 days to 17 years) for acute heart failure (AHF) following a bridge or bridge-to-bridge strategy. Twelve patients were treated with vaECMO: eight were weaned after 2-10 days, two died, and two were switched to a VAD. Of the last, one was weaned 47 days later and the other underwent HTX 168 days later. In nine patients, VAD was implanted without preceding vaECMO. One such patient died (cerebral hemorrhage) after 236 days; of the remaining eight patients three were weaned and five underwent HTX. Waiting time for HTX (high-urgency status) varied from 4 to 372 days. Fifteen patients were discharged (follow up: 2-74 months); 14 are doing very well (New York Heart Association (NYHA) Functional Classification Class I, neurologically normal), whereas one suffers from severe neurologic damage, presumably from resuscitation before vaECMO. Data from Eurotransplant on pediatric HTX in 2004, 2005, and 2006 (33, 49, and 34 transplanted hearts, respectively; recipients <16 years of age) are discussed. Mechanical circulatory support (MCS) substantially improves survival with AHF in pediatric patients. Medium-term support (up to 400 days in our patients) is possible and outcome of survivors is excellent. Wide spread use of MCS might slightly aggravate the lack of donor organs, which could result in longer support times.     

Paracorporeal ventricular assist device as a bridge to transplant candidacy in the era of implantable continuous-flow ventricular assist device

Ventricular assist devices (VADs) have long been used as bridge to transplant therapy (BTT). Nipro-Toyobo paracorporeal pulsatile-flow VAD (nt-VAD) was the only device available until April 2011, when implantable continuous-flow VADs (cf-VADs) became available. Although cf-VADs are central to BTT, nt-VAD remains a necessary option. We aimed to clarify the role of nt-VAD in an era of increasing cf-VAD use. We retrospectively reviewed patients who underwent VAD implantation at the National Cerebral and Cardiovascular Center from May 2011 to March 2013. Characteristics were compared between the nt-VAD and cf-VAD groups. Twenty-nine patients (mean age 37.7 ± 11.1 years, 23 males) underwent VAD implantation. Fifteen patients initially received nt-VADs, although 4 were converted to cf-VADs. Of these 15 patients, 3 were too small for cf-VADs and 2 needed bilateral ventricular support. The remaining 10 patients received nt-VADs (7 patients at INTERMACS level 1 and 3 at level 2). The nt-VAD group patients had significantly more preoperative mechanical circulatory support and were in a more critical condition before VAD implantation than the cf-VAD group. The 2-year survival rate was not significantly different. Despite the critical conditions of nt-VAD patients, their overall survival is not statistically inferior to that of cf-VAD patients. nt-VAD is a good option as a BTC for the patient with urgent and critical condition.     

New technologies for mechanical circulatory support: current status and future prospects of CorAide and MagScrew technologies

Congestive heart failure remains a leading cause of morbidity and mortality in the United States, and alternatives to heart transplantation are urgently required. Mechanical circulatory support by ventricular assist devices and total artificial hearts have the potential to provide an alternative to heart transplantation if a small, durable, biocompatible, and totally implantable system is available. In this article, current technologies for mechanical circulatory support by implantable devices are reviewed and the current status and future prospects of the CorAide and MagScrew technologies, which have been developed and tested at the Cleveland Clinic Foundation, are presented.Presented in part at the 40th Congress of the Japanese Society for Artificial Organs, October 30–November 1, 2003, Sendai, Japan     

Mechanical bridge to transplantation with the Vienna heart in TAH and LVAD configuration.

The Vienna heart uses a vacuum formed, pellethane pulsatile ventricle and is available in left ventricular assist (LVAD) and total artificial heart (TAH) configurations. This device was used as mechanical support of the failing heart in nine patients intended for heart transplantation. In two patients with cardiomyopathy an orthotopic TAH was implanted; one survived despite severe preoperative ischemic liver damage, and the other died of sepsis. In seven patients an atrio-aortic LVAD was implanted; six had suffered an acute myocardial infarction with cardiogenic shock, and one could not be weaned off bypass. Three patients survived. These included one 65-year-old with incipient ARDS at operation, and a 40-year-old with preoperative liver and kidney insufficiency who was transplanted in septicemia. In this patient the septic focus, natural and artificial heart, were removed at transplantation. Four patients died. In one we were unable to establish satisfactory circulation, one died after failure of the transplanted heart, one suffered a lethal cerebral embolism and one developed multi-organ failure after repeated attacks of ventricular fibrillation. With the Vienna heart sufficient circulatory support could be established with cardiac outputs between 6 and 8 l/min for the TAH and 3.5 to 4.5 l/min for the LVAD. With this type of support an overall survival rate of 44% could be achieved. Mechanical hemolysis was not a clinical problem and no device failure occurred.     

Axial flow blood pumps

Each year, thousands of cardiac patients await healthy donor hearts for transplantation. Due to the current shortage of donor hearts (approximately 2300 per year), these patients often require supplemental circulatory support until a transplant becomes available. This supplemental support is often provided by a mechanical heart pump or left ventricular assist device (LVAD). This article explores one type of LVAD, specifically the design and development of axial flow ventricular assist devices (VAD). We discuss the design details, and experimental or clinical experience with the following axial flow support systems: Hemopump, MicroMed DeBakey VAD, Jarvik 2000, HeartMate II, Streamliner, Impella, Berlin INCOR I, Valvo pump, and IVAP. All of these devices demonstrate promise in providing bridge-to-transplant and ultimately destination therapy for adult cardiac failure patients.     

Left ventricular and myocardial perfusion responses to volume unloading and afterload reduction in a computer simulation

Ventricular assist devices (VADs) have been used successfully as a bridge to transplant in heart failure patients by unloading ventricular volume and restoring the circulation. In a few cases, patients have been successfully weaned from these devices after myocardial recovery. To promote myocardial recovery and alleviate the demand for donor organs, we are developing an artificial vasculature device (AVD) that is designed to allow the heart to fill to its normal volume but eject against a lower afterload. Using this approach, the heart ejects its stroke volume (SV) into an AVD anastomosed to the aortic arch, which has been programmed to produce any desired afterload condition defined by an input impedance profile. During diastole, the AVD returns this SV to the aorta, providing counterpulsation. Dynamic computer models of each of the assist devices (AVD, continuous, and pulsatile flow pumps) were developed and coupled to a model of the cardiovascular system. Computer simulations of these assist techniques were conducted to predict physiologic responses. Hemodynamic parameters, ventricular pressure-volume loops, and vascular impedance characteristics were calculated with AVD, continuous VAD, and asynchronous pulsatile VAD support for a range of clinical cardiac conditions (normal, failing, and recovering left ventricle). These simulation results indicate that the AVD may provide better coronary perfusion, as well as lower vascular resistance and elastance seen by the native heart during ejection compared with continuous and pulsatile VAD. Our working hypothesis is that by controlling afterload using the AVD approach, ventricular cannulation can be eliminated, myocardial perfusion improved, myocardial compliance and resistance restored, and effective weaning protocols developed that promote myocardial recovery.     

Current state-of-the-art of device therapy for advanced heart failure

Heart failure remains one of the most common causes of morbidity and mortality worldwide. The advent of mechanical circulatory support devices has allowed significant improvements in patient survival and quality of life for those with advanced or end-stage heart failure. We provide a general overview of past and current mechanical circulatory support devices encompassing options for both short- and long-term ventricular support.Heart failure is one of the most common causes of morbidity and mortality in the United States and worldwide. Although transplantation is the gold standard for end-stage heart failure, it is limited by donor supply. In the United States, about 50 000 patients die each year from heart failure but the number of heart transplants remains steady at about 2000 per year (1). Moreover, transplantation is often not optimal or feasible for instances where short-term support may be adequate. While the mainstay of treatment of heart failure has traditionally been medical optimization, non-transplant surgical interventions have grown to play a key role in the care of these patients. Mechanical circulatory support (MCS) options have grown exponentially since the first reports in the mid-twentieth century and are now considered a well-defined and accepted part of heart failure treatment strategies. These surgical procedures comprise an increasingly important part of the armamentarium of the modern cardiac surgeon.Our intent in this review is to provide a targeted overview of the currently available options for device therapy for heart failure. While the entire spectrum of MCS is quite broad and includes techniques such as intra-aortic balloon pump counterpulsation (IABP), and extracorporeal membrane oxygenation (ECMO), we will focus our discussion on ventricular assist devices (VAD) and total artificial heart (TAH) for the adult population.     

Outcome for pediatric cardiac transplantation with and without bridge methods

Heart transplantation is indicated for children with end-stage heart failure or complex inoperable congenital defects. Due to the shortage of pediatric donor hearts, various bridge techniques have been used for pediatric recipients to prolong patient survival until a heart is available. This study evaluates long-term outcome of bridge and nonbridge support for pediatric heart transplantation. Between March 1995 and June 2004, 18 pediatric patients underwent heart transplantation. Six patients (33.3%) underwent biological or mechanical bridge techniques before transplantation. Eight patients (44.4%) required perioperatively extracorporeal membrane oxygenation (ECMO) support. Patient data and records were retrospectively reviewed. Causes of death and long-term outcome were analyzed. Five of eight patients in the ECMO group (62.5%) were successfully decannulated and discharged home with excellent functional classes. No differences in rejection rate, survival rate, and functional class existed between the bridged and nonbridged groups. Overall 1-year and 5-year survival rates were both 83.3% and all have a good functional class. Pediatric heart transplantation can be accomplished with excellent early survival despite multiple prior cardiac operations and relatively severe illness. For the variety in small, low-body-weight pediatric patients, mechanical circulatory support using ECMO is suitable for managing sudden collapse while waiting for heart transplantation, and graft dysfunction after cardiac transplantation. The mortality rate is acceptable in this very high-risk group of patients and long-term outcome is good.     

Human factors issues in ventricular assist device recipients and their family caregivers

Ultimately, for ventricular assist devices (VADs) to be acceptable as permanent alternatives to heart transplantation, patients' and their families' satisfaction with specific features and risks of VADs must be addressed. Of 42 eligible patients who received VADs between February of 1996 and December of 1998, we interviewed 37 patients (17 Novacor, 18 Thoratec, 2 with both devices) and 20 of their primary family caregivers about device related concerns and reactions. Demographic and health related correlates of respondents' concerns were examined. Eleven patients discharged from the hospital with the VAD in place were then reinterviewed 1 month after discharge. At baseline, patients' general perceptions of the VAD were positive, although 22-52% reported specific concerns, including most often worry about infection (52%), difficulty sleeping due to the position of the driveline (52%), pain at the driveline exit site (46%), worry about device malfunction (40%), and being bothered during the day by device noise (32%). The prevalence of most concerns rose with duration of VAD support. Caregivers' perceptions did not differ significantly from patients' perceptions. Outpatients were somewhat more concerned than inpatients about device noise and risk of stroke, but were markedly less concerned about infection. Across all patients, higher levels of device related concerns were correlated with more physical functional limitations and more psychological distress, and reduced quality of life. Demographic characteristics and device type were not uniformly related to device concerns.     

Development of smaller artificial ventricles and valves made by vacuum forming

Implantable prosthetic ventricles and trileaflet valves made by vacuum forming have been developed and implant tested. All components are made from Pellethane. Recognizing the need for smaller as well as larger ventricles, designs with effective stroke volumes of 50, 85, 100 and 130 cc have been tested with several valve types. The pneumatically driven Utah ventricular assist device (UVAD) can be used as a total artificial heart (TAH) or ventricular assist device (VAD) by using the appropriate inflow and outflow adapters. In vitro durability testing has demonstrated ventricular lifetime beyond two years and valve lifetime to nearly one and one half years. The polymer valves have lower regurgitation than mechanical valves. Animal implantation experience includes 21 TAH implants and 16 left ventricular assist device (LVAD) implantations. TAH survival ranges from 2 to 210 days. LVAD animals have lived up to 116 days before elective termination. The animal were healthy and grew normally. The devices exhibit a "Starling's Law" response. One TAH animal survived 72 days before successful explantation followed by transplantation. At autopsy, this animal had no renal infarcts. Hematology data has demonstrated the existance of little or no intravascular hemolysis (PF Hb less than 5 mg%). The "Philadelphia" version of the UVAD vacuum formed ventricles are small enough to be implanted without thrombus provoking connectors. Eight animals have received this TAH and survived up to 120 days. Vacuum forming offers a rapid and inexpensive way to produce reliable and effective total artificial hearts and valves for widespread, temporary clinical application in any size adult human.     

Development of implantable right ventricular assist device

Implantable ventricular assist devices (VADs) are indicated for long waiting periods before transplantation and also as a destination therapy. Meanwhile, right ventricular failure (RVF) is one of the four major complications observed in patients after left VAD (LVAD) implantation, with an incidence of approximately 20%. Preoperative prediction of the complication remains difficult, and the mortality is very high. To date, no implantable right VAD (RVAD) is available for the clinical situation. The possibility of realizing an implantable RVAD with Gyro centrifugal pump (PI-710 pump) was investigated. Eleven chronic animal experiments with LVAD and RVAD implantation were performed. Right heart bypass was established between right outflow and pulmonary trunk, and the pump was implanted in the preperitoneal space. The anatomic fit was good. The mean term of the experiments was 59 days, with excellent pump performance. Stable pulmonary hemodynamics and respiratory function were maintained during all of the experimental terms. No specific abnormal histologic findings of the lung were confirmed; however, tunica media hypertrophy was recognized in some cases. The PI-710 pump is feasible as a clinically implantable RVAD, but further study of histologic and pulmonary vascular changes after RVAD implantation is needed.