Effect of Age on Outcomes After Left Ventricular Assist Device Placement

The influence of age on outcomes after left ventricular assist device (LVAD) implantation is not well studied. To address this question, we assessed 222 patients who underwent LVAD placement and were divided into quartiles based on age (years): group 1, <or=44; group 2, 45 to 53; group 3, 54 to 59; and group 4, >or=60. Eighty-four patients died on LVAD support. Six- and 12-month survivals for the four groups of LVAD patients were 67.7, 73.7, 49.8, and 38.2, and 49.4, 57.3, 42.7, and 26.2, respectively (all P<.01). Older patients showed a higher risk of infections, embolic strokes, and respiratory complications. They were the least likely to undergo reoperations postimplantation (56%, 53%, 50%, 46%, P=.06). After adjusting for baseline differences between the groups, there was a trend toward increasing mortality with age, which did not reach significance (odds ratio 1.93; 95% confidence interval 0.95 to 3.92 for the oldest quartile as compared with the youngest). In conclusion, these results suggest in the absence of other high risk factors, age alone should not be used as an independent contraindication for LVAD implantation.

The Novacor left ventricular assist system: clinical experience from the Novacor registry

The electrically powered Novacor left ventricular assist (LVAS) system was first used clinically as a bridge to transplant in 1984. The configuration has evolved to the current wearable model used clinically for the first time in 1993. In 1998, the inflow conduit was modified, reducing embolic events by 50%. Over 1100 implants have been performed worldwide with cumulative support greater than 300 patient years, and only 0.7% requiring replacement. The Novacor is a safe and effective device for bridge to transplant, bridge to recovery, or potentially permanent implant with reliable long-term support for periods as long as 4 years.

Flight Experience with the Novacor LVAS

As Novacor LVAS recipients continue to be discharged from the hospital to await cardiac transplantation, an increasing number of patients either need or desire to use air transportation. To date, two test experiences have been reported with the Novacor LVAS operating in a mock circulatory loop during air travel. One involved the transport of a mock loop on a medical helicopter, and another preceded an international flight of an LVAS recipient from Japan to the United States. In each situation, the LVAS, connected to a water-filled mock circulatory loop, was placed on the aircraft and instrumentation was checked to verify that there was no adverse effect on the Novacor equipment, or on aircraft systems, during flight. Novacor LVAS recipients have also been reported to have flown more than 37 commercial air transports throughout Europe, in both rotary and fixed wing aircraft, without incident. Laboratory testing of electromagnetic emissions were also conducted to include specific frequencies utilized by aircraft instrumentation. These tests show that the Novacor LVAS is well below the International Special Committee on Radio Interference (CISPR 11) emissions limits; these data can be provided to an air carrier anticipating transport of a Novacor recipient. Details of the results from the mock loop field testing, as well as the laboratory testing of electromagnetic emissions pertinent to air travel, are presented. This experience suggests that that there has been no impact on aircraft electronics from the LVAS, nor has the aircraft instrumentation generated any interference with the components of the Novacor LVAS.

Economics of devices

BACKGROUND

The economics of devices used for mechanical circulatory support not only involve the patient, the provider, and society as a whole, but also, importantly, the developers and manufacturers of these new technologies. The combined effects of years of development and testing with significant regulatory, reimbursement, and acceptance barriers make this a capital-intensive and high-risk endeavor. In addition, long-term circulatory support is, today, essentially limited to bridge to transplantation, a "market" of only $100 million. Competition is increasing, with new devices under development and entering clinical trials.

CONCLUSIONS

Economic health for this new industry is dependent on expanding clinical indications to definitive or destination therapy, and perhaps other applications such as bridge to recovery and assisted medical therapies.

The totally implantable novacor left ventricular assist system

The Novacor Left Ventricular Assist System (LVAS) (Novacor Corp, Oakland, CA) was initially console-based and has been available since 1993 in a wearable configuration. It has been successfully used for the past 16 years as a bridge to cardiac transplantation in patients with end-stage congestive heart failure. The Stanford experience represents 53 patients (48 male, 5 female) with a mean age of 44 +/- 13 years (16 to 62) and a mean support time of 56 +/- 76 days (1 to 374). Complications with LVAS use consisted predominantly of bleeding (43%), infection, (30%), and embolic cerebrovascular events (24.5%). Sixty-six percent of the supported patients were successfully bridged to cardiac transplantation. In animal studies, 4 sheep had the totally implantable configuration in place for a cumulative duration of 1 year with 1 animal supported for 260 days. The next generation Novacor LVAS will be small, quiet, and fully implantable without the need for volume compensation. It will also provide physiologic pulsatile flow and will be fail-safe.

Mechanical circulatory support for advanced heart failure: effect of patient selection on outcome

BACKGROUND

Use of wearable left ventricular assist systems (LVAS) in the treatment of advanced heart failure has steadily increased since 1993, when these devices became generally available in Europe. The aim of this study was to identify in an unselected cohort of LVAS recipients those aspects of patient selection that have an impact on postimplant survival.

METHODS AND RESULTS

Data were obtained from the Novacor European Registry. Between 1993 and 1999, 464 patients were implanted with the Novacor LVAS. The majority had idiopathic (60%) or ischemic (27%) cardiomyopathy; the median age at implant was 49 (16 to 75) years. The median support time was 100 days (4.1 years maximum). Forty-nine percent of the recipients were discharged from the hospital on LVAS; they spent 75% of their time out of the hospital. For a subset of 366 recipients, for whom a complete set of data was available, multivariate analysis revealed that the following preimplant conditions were independent risk factors for survival after LVAS implantation: respiratory failure associated with septicemia (odds ratio 11.2), right heart failure (odds ratio 3.2), age >65 years (odds ratio 3.01), acute postcardiotomy (odds ratio 1.8), and acute infarction (odds ratio 1.7). For patients without any of these factors, the 1-year survival after LVAS implantation including the posttransplantation period was 60%; for the combined group with at least 1 risk factor, it was 24%.

CONCLUSIONS

Careful selection, specifically implantation before patients become moribund, and improvement of management may result in improved outcomes of LVAS treatment for advanced heart failure.

Improved outcomes with an implantable left ventricular assist system: a multicenter study

BACKGROUND

Cumulative experience with the Novacor wearable electric left ventricular assist system (LVAS) now exceeds 850 recipients. The pump inflow conduit (IFC) has been implicated in embolic complications.

METHODS

Clinical outcomes were compared for two IFC designs in a retrospective, nonrandomized, multicenter study. The original IFC (woven, unsupported, crimped polyester: control group) and an alternative IFC (knitted, gelatin-sealed, integrally supported, uncrimped polyester: test group) were utilized upon availability in North American and European centers. Differences in cerebral embolism to 180 days postimplant were analyzed.

RESULTS

Four hundred ninety patients implanted between August 1996 and August 1999, were studied. Two hundred eighty-eight received the control IFC and 202 received the test IFC. The groups (control, test) were well matched for age (48, 49 years), etiology (idiopathic 53%[152 of 288], 55% [112 of 202]; ischemic 34% [97 of 288], 33% [66 of 202]) and mean observation time (97, 91 days). The incidence of embolic cerebrovascular accidents (CVA) was 21% (60 of 288) in the control and 12% (24 of 202) in the test group (p = 0.010). Independent risk factors for embolic CVA were found to be preimplant acute myocardial infarction (odds ratio 4.3), age above 50 years (odds ratio 2.1), and ischemic etiology (odds ratio 1.7). There was no difference in survival between the groups (71% [205 of 288], 68% [137 of 202]).

CONCLUSIONS

The alternative (test) IFC has significantly reduced the incidence of embolic CVA. This improvement is likely due to increased resistance to deformation at implant, improved neointimal adhesion, and more favorable blood flow characteristics within the conduit.

Long-term mechanical circulatory support with the wearable Novacor left ventricular assist system

OBJECTIVE

As of July 1st 1999, 36 European patients have lived for more than 1 year supported by the Novacor wearable electric left ventricular assist system (LVAS). All were unresponsive to maximum medical therapy, prior to implantation. These patients offer an unique opportunity to evaluate the feasibility of long-term ambulatory mechanical circulatory support as a therapeutic option for patients in profound cardiac failure.

METHODS

Data was obtained from the Novacor European Registry.

RESULTS

At the time of implantation, median age was 55 (18-67) years. Aetiology was ischemic (9, 25%) or idiopathic (26, 72%) cardiomyopathy, and myocarditis (1, 3%). Median duration of LVAS support was 1.49 (1. 03-4.10) years. Eight recipients had LVAS support times >2 years, of which two were >3 years and one >4 years. The median time spent outside the hospital was 1.27 (0.58-3.83) years, representing 82% of the duration of LVAS support. No mechanical failure was observed during the entire observation period. One pump was replaced electively after 3.67 years due to pump driver wear-out. Twelve patients (33%) are currently on support while 17 were transplanted (14, 39%) or weaned (3, 8%). Seven (19%) patients died after a median of 1.24 years circulatory support.

CONCLUSIONS

Experience with long-term Novacor LVAS recipients has demonstrated effective rehabilitation in this group of patients with refractory advanced heart failure. This suggests that LVAS therapy may offer a safe and realistic option for patients for whom no other effective therapy is available. The patient sub-population that would benefit most from this therapy remains to be defined.

Reliability model from the in vitro durability tests of a left ventricular assist system

A reliability test of the Novacor N100PC left ventricular assist system (LVAS) with valved conduits, including a pump/drive unit with compact controller and LVAS monitor was performed. The initial test objective was to demonstrate sufficient reliability for clinical use as a long-term circulatory support system. The subsequent objective, a test to failure, was intended to provide an assessment of the durability of the design and to determine the LVAS wearout modes. Testing began in April 1993 and was performed with 12 systems on gravity-feed mock circulatory loops. The pump/ drive units were submersed in body temperature saline for the duration of the test. Each of the LVAS units was operated at nominal afterloads of 75, 90, and 105 mm Hg, with test conditions varied to yield nominal pump outputs of 5.6, 7.1, and 8.3 L/min. Failure was defined as the inability of the LVAS to maintain an average pump output of 4 L/min or an average output pressure of 60 mm Hg. After 3 years, all systems remained on test, with durations of 2.3 to 3.0 years. Analysis of the testing to that date, using a constant hazard rate model, indicated a minimum demonstrated reliability of 94% at a 60% confidence level, or 86% at a 90% confidence level, for a 2 year mission time. This greatly surpasses the reliability level included in the STS-ASAIO Long-Term Mechanical Circulatory Support System Reliability Recommendation (80% reliability, 60% confidence level for a 1 year mission time). In the subsequent test-to-failure protocol, all systems ran failure-free for at least 3 years. System failures occurring at longer durations were caused by a single common cause: wear of the energy converter's armature support bearings and shafts. The wearout mode was gradual and could be diagnosed noninvasively before failure. An analysis using a Weibull model was performed, using the test durations of those devices that failed, those that were electively removed from test for analysis of the wear mode, and those that continued on test. As of April 1998, the test results showed a reliability, at a 60% confidence level, of >99.9% for a 1 year mission time, 99.5% for a 2 year mission, and 92.0% for a 3 year mission (>99.9%, 98.3%, and 85.9% for equivalent mission times, at a 90% confidence level). Systems continue on test after as long as 4.9 years.

Long-term mechanical circulatory support system reliability recommendation: American Society for Artificial Internal Organs and The Society of Thoracic Surgeons: long-term mechanical circulatory support system reliability recommendation

Jointly developed by members of the American Society for Artificial Internal Organs and the Society of Thoracic Surgeons along with staff from the Food and Drug Administration, the National Heart, Lung and Blood Institute and other experts, this recommendation describes the reliability considerations and goals for Investigational Device Exemption and Premarket Approval submissions for long-term, mechanical circulatory support systems. The recommendation includes a definition of system failure, a discussion of an appropriate reliability model, a suggested in vitro reliability test plan, reliability considerations for animal implantation tests, in vitro and animal in vivo performance goals, the qualification of design changes during the Investigational Device Exemption clinical trial, the development of a Failure Modes Effects and Criticality Analysis, and the reliability information for surgeons and patient candidates. The document will be periodically reviewed to assess its timeliness and appropriateness within five years.

Long-term mechanical circulatory support system reliability recommendation: American Society for Artificial Internal Organs and Society of Thoracic Surgeons: long-term mechanical circulatory support system reliability recommendation

Jointly developed by members of the American Society for Artificial Internal Organs and the Society of Thoracic Surgeons along with staff from the Food and Drug Administration, the National Heart, Lung and Blood Institute and other experts, this recommendation describes the reliability considerations and goals for Investigational Device Exemption and Premarket Approval submissions for long-term, mechanical circulatory support systems. The recommendation includes a definition of system failure, a discussion of an appropriate reliability model, a suggested in vitro reliability test plan, reliability considerations for animal implantation tests, in vitro and animal in vivo performance goals, the qualification of design changes during the Investigational Device Exemption clinical trial, the development of a Failure Modes Effects and Criticality Analysis, and the reliability information for surgeons and patient candidates. The document will be periodically reviewed to assess its timeliness and appropriateness within five years.

Protocol for releasing Novacor left ventricular assist system patients out-of-hospital

Between September 1984 and April 1995, the Novacor left ventricular assist system (LVAS) has provided more than 13,000 days of mechanical circulatory support to cardiac transplant candidates in the United States and Europe. The duration of support of these 312 patients has ranged between 1 and 370 days, with an average support of 40 days, including use of the console based system and the wearable system. Of this group, 21% have been supported for more than 60 days, with an average support of 118 days. We have seen that patients who have been supported for more than 30 days have recovered from the effects of LVAS implant surgery and have shown a potential for rehabilitation from morbid congestive heart failure. Few changes to the pump settings or the medical orders have been needed after the third postoperative week. The reliability of the LVAS and the degree to which patients can be rehabilitated suggest that restricting patients to a hospital environment is unnecessary. In addition, the increasing wait for a donor heart, the quality of life that can be achieved, and the high cost of inpatient care make it desirable to discharge patients from the hospital and allow them to await a donor heart in a more home-like setting.

Evaluation of an implantable ventricular assist system for humans with chronic refractory heart failure. Device explant protocol

An explant protocol was developed to investigate the effects of implantation of a left ventricular assist system (LVAS) manufactured by Novacor Division, Baxter Healthcare Corporation on the function of end organs (such as the brain, the kidney, the liver), with particular interest in examining possible complications due to LVAS support. Emphasis was placed on an analysis at the time of device removal and/or autopsy of 1) the local LVAS-host interface; 2) remote cardiovascular and end-organ effects; and 3) the impact of chronic circulatory support on the native heart. To accomplish these objectives, tissue and device samples must be obtained in an appropriate fashion to ensure photographic documentation, microscopic examination, microbiologic and biochemical assays, and compliance with regulatory and manufacturer requirements. This article describes the techniques and protocol that were proposed to ensure the quality of device explant and tissue analysis.

Evaluation of an implantable ventricular assist system for humans with chronic refractory heart failure. Study overview. LVAS Study Group. Left Ventricular Assist System

In this summary, the authors provide the background of and proposed protocol for a clinical evaluation of the safety and efficacy of the Novacor N120 Left Ventricular Assist System, sponsored by the National Heart, Lung, and Blood Institute. Although the clinical trial was never carried out, the protocol developed for this trial may be useful to other investigators considering a clinical trial of a circulatory support device. The protocol is summarized here and in five more detailed articles in this issue.

Initial clinical experience with a wearable controller for the Novacor left ventricular assist system

The Novacor left ventricular assist system (LVAS), an implanted electromechanically driven blood pump, has been used in an ongoing clinical trial as a bridge to cardiac transplantation since 1984. The initial configuration included a console based extracorporeal controller. Because patients supported by the device usually become rehabilitated and highly mobile, a wearable control system was developed for the ambulatory patient. Ergonomically designed for portability, comfort, and appearance, it offers the recipient greater mobility, improved self-image, and an enhanced quality of life. This wearable control system consists of a microprocessor based compact controller that drives the implanted pump/drive unit in synchronous counterpulsation to the native heart. Main and reserve rechargeable power packs, each incorporating a "smart" monitoring circuit with charge-level display and alarm, are capable of supporting the pump for as long as 7 hr. An LVAS monitor can be connected to the controller for device monitoring and adjustment or as a power supply in lieu of the main power pack. Clinical evaluation in patients with end-stage heart disease followed the same protocol as the console study. By April 4, 1994, 41 patients had been supported by the wearable system, including 9 patients currently being supported. Mean duration of use was 51 days (range, 1.5-143+ days), compared with 42 days for 170 console patients (range, 0-370 days). Survival to transplant was 66%, which was similar to the survival (60%) for the patients using the console. Post-transplant survival was 100%, compared with 90% for console patients (not significantly different). After recovering from implant surgery and pre-implant morbidity, device recipients had considerable freedom and mobility and were able to move freely within and outside the hospital. Recipients could readily switch between monitored and untethered operation and could manage power pack replacement and recharging.

Clinical experience with the Novacor ventricular assist system. Bridge to transplantation and the transition to permanent application

At Stanford University, a Novacor left ventricular assist system (Baxter Healthcare Corporation, Novacor Division, Oakland, Calif.) was placed as a bridge to heart transplantation in 13 patients. During the hospitalization preceding device implantation, all patients were receiving inotropic support for biventricular failure, 11 had pulmonary edema, 6 had life-threatening ventricular arrhythmias, 5 had liver dysfunction with coagulopathy, and 2 had renal failure necessitating artificial support. The mean cardiac index before implantation of the Novacor system was 1.5. All survivors with the Novacor device had a dramatic increase in cardiac output (mean cardiac index = 3.1). One patient with cardiac allograft rejection died during implantation of the left ventricular assist system. Two patients died of pulmonary sepsis and multiorgan failure after the device was implanted. All patients who had the Novacor device implanted for more than 7 days were able to walk and ride stationary bicycles while awaiting transplantation. Ten patients (77%) underwent successful heart transplantation after a mean of 18 days' support with the Novacor device. One patient died of presumed sepsis 2 days after transplantation. Nine patients (90%) are alive 4 months to 6 years after transplantation. In the overall United States experience, 68 patients (as of May 1990) have had a Novacor left ventricular assist device implanted. Five were still being supported, 39 had received a transplant (62%), and 35 patients (90%) survived the transplant hospitalization (1 died later). No instances of device failure have occurred. Overall, the Novacor assist system provided effective bridging to transplantation, with posttransplant survival similar to results after routine transplantation. Modifications and improvements based on this clinical experience have been made in the areas of patient selection, techniques of operative placement, postoperative management, and design of the assist system. Isolated left heart support with a fully implantable left ventricular assist system will be offered as an alternative to heart transplantation for selected patients by 1992.

Clinical evaluation of the Novacor totally implantable ventricular assist system. Current status

The totally implantable Novacor left ventricular assist system (LVAS) is currently approaching clinical evaluation. In vivo testing and production are underway with National Institutes of Health (NIH) support. Activity over the past year has focused on manufacturing engineering, preproduction quality assurance, and in vivo experiment completion. Subsequent to successful completion of the NIH-sponsored, 2-year preclinical device readiness test (DRT), a number of refinements were identified and approved by the NIH technical/data review board. Most of these were necessitated by obsolescence or unavailability of electronic components and the decision to use only high reliability military (MIL) qualified electronic components and processes. A few additional refinements were identified to increase design margins, all of which were qualified by accelerated testing. The development of production processes, automated test programs, and MIL compliant environmental stress screening procedures was completed. Production of LVAS subsystems, including core electronic components (hybrids, application-specific integrated circuits, and surface mount boards), was initiated. Animal studies are underway. The clinical trial, at Presbyterian-University Hospital of Pittsburgh and St. Louis University Medical Center, awaits completion of in vivo experiments, protocol development, and Food and Drug Administration approval.

Bovine pericardial valves. Nine-year clinical experience with the Novacor left ventricular assist system

The Novacor electrically powered left ventricular assist system (LVAS), currently used in a bridge-to-transplant (BTT) clinical trial, incorporates bovine pericardial (BP) valves (Edwards CVS Division, Baxter Healthcare Corporation). In preclinical evaluation in the adult sheep, BP valves exhibited severe calcific stenosis as early as 8 weeks postimplant (longest implant 158 days, elective termination for calcific deposit). The clinical experience, however, has been in sharp contrast. Eighty-one patients have been supported for a cumulative duration of 9.1 years (two currently on LVAS). Thirty-five (43%) patients were supported for longer than 30 days, and of these, 29 (85%) were transplanted. The longest implant duration was 370 days (alive, 8 months posttransplant). There was no evidence of calcific degeneration of these valves for durations to 370 days. These results are encouraging for ultimate chronic clinical application.

A sophisticated electromechanical ventricular simulator for ventricular assist system testing

With the advent of chronically implanted left ventricular assist systems, new adaptive control algorithms are being developed to allow automatic device control under a variety of hemodynamic conditions. An electromechanical pump is described that accurately mimics ventricular function. A pusher-plate sac pump with tri-leaflet valves is coupled to a high-speed linear motor. Pump chamber volume and pressure are constrained to follow the time-varying elastance model of ventricular function by use of a microprocessor feedback loop.

Chronic ovine evaluation of a totally implantable electrical left ventricular assist system

The totally implantable Novacor left ventricular assist system (LVAS) comprises a pump/drive unit (VAD), electronic control and power subsystem (ECP), variable volume compensator (VVC), and belt skin transformer (BST). The system is now undergoing chronic in vivo evaluation. Cumulative animal testing of VAD, VVC, and BST subsystems are 12.1, 4.9, and 43 years, respectively. The longest implants were 279 days for the VAD, 767 days for the VVC, and 1,148 days for the BST. A chronic implant of the total system was electively terminated at 260 days. The LVAS was powered via the BST. Continuously monitored hemodynamic and pump parameters have demonstrated normal hemodynamics and LVAS operation. Periodic VVC determinations suggest a 0.8 ml/day diffusive gas loss. Tether-free operation has been demonstrated with an Ag-Zn battery backpack. The animal was healthy and free of infection as indicated by routine hematologic, biochemical and serum enzyme determinations. Hemolysis is minimal (plasma free hemoglobin less than 5 mg%). Pump output ranged from 7 to 8 L/min. Severe valve calcification was the reason for elective termination at 260 days. This preclinical in vivo experience, and in vitro reliability studies, demonstrate efficacy of the total system.

Implantable electrical left ventricular assist system: bridge to transplantation and the future

An implantable left ventricular assist system (LVAS) utilizing an electromechanically driven dual pusher-plate blood pump has been employed in a multiinstitutional trial as a bridge to cardiac transplantation. Under development for permanent circulatory support in patients with end-stage heart disease, the LVAS, in this application, derives power and control from an external console via a percutaneous lead. The LVAS was implanted in 20 patients (16 men, 4 women) who were hemodynamically unstable or in refractory cardiogenic shock. The mean age was 44.9 years (range, 25 to 63 years). Preoperative diagnosis was evenly divided between end-stage ischemic disease, cardiomyopathy, and acute myocardial infarction. Implanted in the left upper quadrant within the anterior abdominal wall, the blood pump was connected between the left ventricular apex and ascending aorta. Total support of the systemic circulation and substantial left ventricular unloading were achieved with synchronous counterpulsation for periods up to 90 days (mean, 22.7 days). All patients were stabilized hemodynamically. The mean preoperative cardiac index of 1.5 L/min/m2 increased by a factor of 2. Pulmonary arterial pressures decreased substantially. Serious complications occurred in 16 patients, precluding cardiac transplantation in 10. Most complications (greater than 70%) were in patients who did not receive transplants; the most common complication was bleeding. Twelve of 13 patients with LVAS implants for more than seven days were mobilized, and 4 were fully ambulatory and completely rehabilitated. Orthotopic cardiac transplantation was performed in 10 patients after implants ranging from two to 90 days (mean, 30.3 days).(ABSTRACT TRUNCATED AT 250 WORDS)

Isolated left ventricular assist as bridge to cardiac transplantation

The electrically driven Novacor implantable left ventricular assist device has been implanted in six patients (four men and two women) since Sept. 7, 1984. In four of the six patients (67%) the device was a successful bridge to cardiac transplantation. One patient died of multiple organ failure and Candida sepsis after 16 days of support with the device. One patient died in the operating room of uncontrollable hemorrhage and biventricular failure caused by severe cardiac rejection. Three patients are alive with cardiac transplants 38, 17, and 10 months after transplantation. One patient died after cardiac transplantation of presumed sepsis. The Novacor left ventricular assist device performed in all cases without mechanical or electrical failure. Excluding the intraoperative death, assist duration ranged from 2 to 16 days. The cardiac index (synonymous with device output) ranged from 2.4 to 3.4 L/min/m2. No embolic events (cerebrovascular or systemic) occurred during assistance with the device. Minimal red cell hemolysis was documented during the period of support. The Novacor left ventricular assist device is a safe and effective bridge to cardiac transplantation in patients with refractory cardiogenic shock.

Bioprosthetic valve calcification and pseudoneointimal proliferation in bovine and ovine models

Both porcine (PX) and bovine pericardial (BP) valves have been used in the implantable Novacor left ventricular assist system (LVAS). Results from 58 chronic LVAS implants of greater than 7 days in calves and adult sheep are presented: the PX valve was used in 41 and the BP in 17. With PX valves, the maximum and mean assist durations were 161 and 54 days, respectively, in the calf and 279 and 129 days, respectively, in the sheep. The maximum and mean durations for BP valves were 93 and 38 days (calf) and 153 and 69 days (sheep). In bovine studies with PX valves, severe obstructive pseudoneointimal (PNI) proliferation in the Dacron inflow conduit was the primary cause for termination; valves exhibited moderate calcification. With BP valves, both PNI proliferation and severe valve calcification contributed to a declining pump output, leading to termination. In contrast to the bovine experience, PNI proliferation was not observed in ovine implants. BP valves still became calcified, as evidenced by a progressive decline in pump output (from about twelve weeks) and confirmed at termination. Valve calcification was minimal with the PX valves, even at 236 days. These results favor the adult ovine animal model for extended implants.

In vitro and in vivo testing of a totally implantable left ventricular assist system

The totally implantable Novacor LVAS is being tested under NIH auspices to demonstrate safety and efficacy before clinical trials. Twelve complete systems (submerged in saline at 37 degrees C) are being tested, with an NIH goal of demonstrating 80% reliability for 2 year operation with a 60% confidence level. The systems, which are continuously monitored, are diurnally cycled between two output levels by automatically varying preload and afterload. Currently, 14.3 years of failure-free operation have been accumulated, with a mean duration of 14 months. Using an exponential failure distribution model, the mean time to failure (MTTF) is greater than 8.8 years, corresponding to a demonstrated reliability (for a 2 year mission time) of 80% (80% confidence level). Recent ovine experiments with VAS subsystems include a 767 day volume compensator implant, a 279 day pump/drive unit implant and a 1,448 day BST implant. The last 12 chronic pump/drive unit experiments had a mean duration of 153 days (excluding early postoperative complications). This compares favorably with the NIH goals for complete systems (5 month mean duration). Complete system experiments are currently underway.

The blood interface at artificial surfaces within a left ventricular assist system

A left ventricular assist system presents a very complex set of interfaces to the blood. The interactions of the various components, their junctions, and fluid dynamic effects have been discussed at a macroscopic, cellular and molecular level. Failure of any part of the system can seriously compromise LVAS function or host response whether due to gross thrombosis with occlusion, proliferative PNI formation, or thromboembolic events. It has been stated that: "When artificial hearts are designed properly, nearly any surface goes." Unfortunately, the blood interface within any circulatory support system, and indeed in much simpler systems, is a much more complex function than design, which includes the surface, materials and many other factors (Table 6).

Evolution of the solenoid-actuated left ventricular assist system: integration with a pusher-plate pump for intra-abdominal implantation in the calf

The performance of an implantable left ventricular assist system (LVAS) utilizing a pulsed solenoid energy converter and a pusher-plate blood pump has been characterized in vitro and in vivo. A microprocessor-based electronic control system makes the LVAS completely self-regulating over the range of operating conditions and provides considerable flexibility in various assist modalities. Over forty thousand hours of in vitro and in vivo operating experience has been accumulated with current systems, and significant progress has been acheived in system durability and reliability. A new toggle latch has provided nearly a year of failure-free operation on the bench, without measurable wear. Energy converter efficiencies of 50% have been demonstrated. In vivo evaluation has been highlighted by an animal experiment still in progress after nearly four months of fault-free, continuous synchronous pumping.