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Ann Thorac Surg 2001;71:S162-S165
© 2001 The Society of Thoracic Surgeons
a Department of Cardiothoracic Surgery, Stanford University School of Medicine, Stanford, California, USA
Address reprint requests to Dr Robbins, Department of Cardiothoracic Surgery, Falk Cardiovascular Research Center, Stanford University School of Medicine, Stanford, CA 94305-5407
e-mail: robbins{at}leland.stanford.edu
Presented at the Fifth International Conference on Circulatory Support Devices for Severe Cardiac Failure, New York, NY, Sept 15–17, 2000.
Abstract
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.
Originally a totally implantable design, the Novacor Left Ventricular Assist System (LVAS) (Novacor Corp, Oakland, CA) was intended for destination therapy in the treatment of end-stage congestive heart failure and therefore, served as an alternative to cardiac transplantation. A partially implanted version of this system has functioned well in a bridge to transplantation over the past 16 years. An objective of this article is to describe the strategy for clinical utilization of a totally implantable Novacor LVAS. The clinical results with the Novacor LVAS at Stanford University and the preclinical animal experience with the totally implantable system will be reviewed. A description of the next generation Novacor II LVAS will be included to provide the current concept for the implementation of a definitive totally implantable therapeutic system.
Stanford clinical experience
The records of patients supported with the Novacor LVAS at Stanford University Medical Center from September 5, 1984 until September 10, 2000 were reviewed. The inflow conduits and outflow grafts that connect the pump between the left ventricular apex and ascending aorta were made of low porosity, woven polyester (Cooley, Meadox Medical, Oakland, NJ) from 1984 through 1997. Since 1998, a gelatin-sealed, knitted polyester graft with integral wall reinforcement, manufactured by Vascutek (Sulzer Vascutek Ltd, Renfrewshire, Scotland) has been used for the inflow conduit. A major change in the valve design to improve flow resulting in modular, sinused valved conduits was introduced in 1996.
The Novacor LVAS was implanted in 53 patients (48 men, 5 women) as a bridge to transplantation. The first 22 patients utilized an early console-based system. All subsequent patients received a wearable, portable configuration and the last 26 had valve conduits. The last 17 patients of the final group had the Vascutek inflow conduit (Fig 1). The mean age of the patients was 44 ± 13 years (range, 16 to 62) and the mean body surface area was 2.00 ± 0.24 (range, 1.61 to 2.57) square meters. The mean time of LVAS support was 56 ± 76 days (range, 1 to 374) and the cumulative experience was 8.1 years.
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The overall incidence of embolic cerebrovascular accidents was 24.5%. This was divided into a 30.6% incidence (11 out of 36) in patients with the Cooley inflow conduits (woven, unsupported, crimped polyester) and a 11.8% incidence (2 out of 17) for patients that received Vascutek inflow conduits (knitted, gelatin-sealed, supported polyester). There was a 43% incidence of bleeding (23 out of 53) and a 30% incidence of infection (16 out of 53). The causes of death for the 18 patients during the 16-year study who died while awaiting cardiac transplantation are as follows: Multiorgan system failure, 6 patients; sepsis, 4 patients; bleeding, 3 patients, CVA, 2 patients; respiratory failure, 2 patients; right ventricular failure, 1 patient.
Sixty-six percent of the patients supported with the Novacor LVAS (35 out of 53) were successfully transplanted. This number increased to 89.7% (35 out of 39) if the 14 patients who died within 30 days of LVAS implantation are excluded.
Totally implantable LVAS preclinical animal studies
The totally implantable configuration of the Novacor LVAS was placed in 4 sheep. All animals received humane care in compliance with the "Guide for the Care and Use of Laboratory Animals" published by the National Institutes of Health (NIH Publication No. 85–23, revised 1985). The system consisted of a pump/drive unit, volume compensator, belt skin transformer, and controller/battery. The system was placed through a posterior-lateral thoracotomy with the inflow conduit inserted into the left ventricular apex and the outflow conduit anastomosed to the descending aorta. A brief period of venous inflow occlusion was used for the placement of the left ventricular apical cannula, thereby avoiding the need for cardiopulmonary bypass. Five ovine implants of the functioning belt skin transformer and eight ovine experiments with an externally actuated volume compensator were carried out in addition to partially implantable and totally implantable systems.
The results of the preclinical animal studies are summarized in Table 1. Both the belt skin transformer and volume compensator studies provided durable support (longest implants 3 and 2 years, respectively) without technical difficulties. The cumulative duration of support for the 4 sheep with totally implantable systems was 1 year with 1 animal supported for 260 days [1].
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Information on the Novacor II LVAS was obtained from World Heart Inc (Oakland, CA, US base of World Heart Corporation, Ottawa, Canada). The Novacor II LVAS concept represents an attractive approach for a totally implantable, definitive treatment of end-stage congestive heart failure. It has a dual-chambered pump (four total valves) and a shared pusher plate (Fig 2). The pusher plate is suspended and driven directly by a magnetic drive obviating the need for bearings, cams, or linkages. The bias field (permanent magnet) is modulated by a coil driven field with a high energy conversion efficiency. The force is proportional to the current and has precise controllability (Fig 3).
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The objective of the initial design of the Novacor LVAS was to develop a totally implantable system to provide definitive therapy for end-stage congestive heart failure. The electrically powered, pulsatile Novacor LVAS has provided reliable, efficacious support as a bridge to transplantation. Worldwide, more than 1,170 patients have received the Novacor LVAS, 84 of whom have been supported for more than 1 year, with the longest duration of support being 4.1 years. Confirming reliability documented on the bench, [1, 2] only 8 patients (0.7%) have required pump replacement and 2 patients have undergone urgent cardiac transplantation secondary to recipient induced driveline damage (n = 3), management error (urine aspiration by vent tube and electrolyte in external connector) (n = 2), device malfunction (encapsulation leak and premature bearing wear) (n = 2), normal bearing wear (3.6 and 3.7 years, respectively) (n = 2), and valved-conduit endocarditis (n = 1).
The worldwide incidence of embolic cerebral vascular accidents has been reduced from 21% (60 out of 288) for patients with the Cooley inflow conduit to 12% (24 out of 202) for patients with the Vascutek inflow conduit by reducing particulate embolisms from a friable pannus [3]. Animal experiments with an expanded polytetrafluoro-ethylene inflow conduit suggest that further reduction in embolic complications may be expected. The current anticoagulation regimen at Stanford University consists of warfarin (target International Normalized Ratio, 2.0 to 2.5) and 75 mg clopidogrel (Bristol-Meyers Squibb, NY, NY) daily. The two cerebral vascular accidents that have occurred in the Vascutek conduit patients at Stanford have been small and there was no visible thrombus in the pump at the time of explantation.
The current Novacor LVAS utilizes a percutaneous driveline for the delivery of energy and venting of the system. Although the totally implantable configuration of this first generation system provided reliable animal support, refinement of the system for destination therapy as envisioned by the Novacor II design would provide a smaller, lighter, quieter, and lower cost system without the need for volume compensation.
Axial flow and centrifugal pumps represent potentially attractive options for long-term circulatory support. They are small, simple, inexpensive to manufacture, and can be fully implanted without the need for a volume compensator. There are, however, several issues that may limit their efficacy. Although some degree of pulsatile flow is realized with these pumps through augmentation by the native left ventricle, there is a nonphysiologic state of reduced pulsatility that may have late pathologic consequences. In addition, the bearings of these devices are lubricated with blood which may limit durability. One potential solution to this is the use of magnetic levitation for turbine suspension, however, this refinement adds complexity, size, and increased power requirements. High shear rates and auto control represent additional challenges. Finally, these pumps are not fail-safe because there are no valves in the system and mechanical failures result in the equivalent of severe aortic insufficiency.
The concept of the Novacor II design incorporates most of the characteristics deemed important for the next generation of left ventricular assist systems; it would be small, fully implantable, low in cost to manufacture, and it would provide physiologic pulsatile flow. In addition, this system would be fail-safe, easy to control, highly reliable, and free of bearings, so it would provide long-term durable support.
Footnotes
Drs Oyer and Portner are consultants to World Heart Inc, manufacturer of the Novacor assist system.
References
This article has been cited by other articles:
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  M. E. Stone Current Status of Mechanical Circulatory Assistance Seminars in Cardiothoracic and Vascular Anesthesia, September 1, 2007; 11(3): 185 - 204. [Abstract] [PDF]
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 N. C. Dang, V. K. Topkara, B. T. Kim, M. L. Mercando, J. Kay, and Y. Naka Clinical outcomes in patients with chronic congestive heart failure who undergo left ventricular assist device implantation J. Thorac. Cardiovasc. Surg., November 1, 2005; 130(5): 1302 - 1309. [Abstract] [Full Text] [PDF]
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N. C. Dang, V. K. Topkara, M. Leacche, R. John, J. G. Byrne, and Y. Naka Left ventricular assist device implantation after acute anterior wall myocardial infarction and cardiogenic shock: A two-center study J. Thorac. Cardiovasc. Surg., September 1, 2005; 130(3): 693 - 698. [Abstract] [Full Text] [PDF]
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 M. Haddad, R. G. Masters, P. J. Hendry, A. Kawai, J. P. Veinot, G. Lavallee, and T. V. Mussivand Intercontinental LVAS Patient Transport Ann. Thorac. Surg., November 1, 2004; 78(5): 1818 - 1820. [Abstract] [Full Text] [PDF]
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 E. L. Kukuy, M. C. Oz, and Y. Naka Long-Term Mechanical Circulatory Support Card. Surg. Adult, January 1, 2003; 2(2003): 1491 - 1506. [Full Text]
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W. L. Holman, J. E. Davies, B. K. Rayburn, D. C. McGiffin, B. A. Foley, R. L. Benza, R. C. Bourge, P. Blood, and J. K. Kirklin Treatment of end-stage heart disease with outpatient ventricular assist devices Ann. Thorac. Surg., May 1, 2002; 73(5): 1489 - 1494. [Abstract] [Full Text] [PDF]
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