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European Journal of Heart Failure 2000 2(1):13-18; doi:10.1016/S1388-9842(00)00055-6
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© 2000 European Society of Cardiology

Implantable left ventricular assist systems (LVAS): Recent results. A report from a series of meetings sponsored by the Study Group on Advanced Heart Failure of the Working Group on Heart Failure

Paul Mohacsia,*, Mario C. Dengb, Richard Murphyc, Claes-Håkan Berghd, Edoardo Grondae, Michel Komajdaf, Richard Pacherg, Jindrich Spinarh, Karl Swedbergi and John F. Clelandj

a Cardiology, Swiss Cardiovascular Center Bern, University Hospital CH-3010 Bern, Switzerland
b Department of Cardiothoracic Surgery, Muenster University Hospital D-48120, Münster, Germany
c Study Group on Advanced Heart Failure, Secretariat Oxfordshire, OX14 3YT, UK
d Tjadergatan 21, S-42669, Vastra Frolunda, Sweden
e Clinical Cardiology and Heart Failure Unit, Istitute Clinico Humanitas Via Manzoni, 56, 1-20089 Rozzano Milano, Italy
f Group Hospitalier Pitié-Salpêtrière, Service de Cardiologie 47 Boulevard de L'Hôpital, F-75019 ParisCedex 13, France
g Cardiology, University of Vienna Wahringer Gürtel 18-29, A-1090, Vienna, Austria
h Masaryk University, School of Medicine, St Ann's University Hospital Pakarska 53, Brno, 65691, Czech Republic
i Sahlgrenska University Hospital/Östra, Department of Medicine S-41685 Göteborg, Sweden
j Castle Hill Hospital Castle Road, Cottingham, Hull, East Yorkshire, HU16 5JQ, UK

* Tel.: +41-31-632-4464; fax: +41-31-632-4299. E-mail address: paul.mohacsi{at}insel.ch


   Abstract
Top
 Abstract
1. Introduction
 2. Types of implantable...
 3. Indications and...
 4. Clinical results with...
 5. Conclusions
 References
 
Implantable left ventricular assist systems (LVAS) consist of implantable pumps with small control consoles and power sources that can be worn externally. These systems provide far greater patient mobility and independence than external pumps with bulky control consoles. Patients with implantable LVAS can be discharged from hospital and are able to return to work and resume active sports. Most patients have received these systems as a bridge to heart transplantation. Clinical status and quality of life improve dramatically after device implantation and survival on support (60–70% after approx. 100 days of support) is acceptable compared with transplant candidates on medical therapy. Patient selection and adverse events, primarily bleeding, thromboembolism and infection, are important issues with LVAS. In the future, long-term support and bridging to myocardial recovery may become important indications for LVAS.

Key Words: Advanced heat failure (AHF) • Left ventricular assist systems (LVAS) • Mechanical circulatory support (MCS)

Received December 6, 1999; Revised December 22, 1999; Accepted December 23, 1999


   1. Introduction
Top
 Abstract
 1. Introduction
2. Types of implantable...
 3. Indications and...
 4. Clinical results with...
 5. Conclusions
 References
 
Left ventricular assist systems (LVAS) provide mechanical circulatory support to patients with advanced heart failure (AHF). Early LVAS used a pump placed outside the patient’s body (extracorporeal systems), controlled and monitored by bulky external consoles. Patients on these systems were bedridden, which is not acceptable for a patient on the heart transplant list who might have to wait for months for an organ. With paracorporeal systems (e.g. Thoratec and MEDOS), the pump is placed on the patient’s body [1,2]. Current paracorporeal systems use a compact control console, small enough for the patient to carry or push on a trolley. Patients can become ambulant, but the size of the console and the paracorporeal position of the pump restrict their mobility. Recently this problem has been overcome by implantable LVAS in which the pump is implanted within the body. This article reviews clinical experience with these systems.


   2. Types of implantable LVAS
Top
 Abstract
 1. Introduction
 2. Types of implantable...
3. Indications and...
 4. Clinical results with...
 5. Conclusions
 References
 
Extensive clinical experience is available for two implantable LVAS: the Novacor and the HeartMate. The design of these systems is described more fully elsewhere [3]. The Novacor is an electrically powered device implanted in a pre-peritoneal pocket. The inflow conduit is connected to the left ventricular apex; the outflow conduit is connected to the ascending aorta. A percutaneous lead connects the pump to rechargeable batteries and a compact controller. The external components are light and compact enough to be worn on a belt or in a specially designed waistcoat or backpack.

The HeartMate is generally similar to the Novacor. The pump is implanted either in a pre-peritoneal pocket or in the peritoneal cavity. The inflow and outflow conduits are positioned similarly to those of the Novacor. The HeartMate is available as an implantable pneumatic version (IP-LVAS) and a vented electric version (VE-LVAS). With the IP-LVAS an external console sends pulses of air to the pump via a percutaneous vent. Patients can push this console on a small trolley and thereby become ambulant [4]. The VE-LVAS is operated by an electric motor connected to rechargeable batteries and a compact controller via a percutaneous lead. The external components are small and lightweight; therefore, patients can become fully mobile and independent.


   3. Indications and contraindications for LVAS
Top
 Abstract
 1. Introduction
 2. Types of implantable...
 3. Indications and...
4. Clinical results with...
 5. Conclusions
 References
 
Successful LVAS support depends on correct patient selection and timing of implantation. The indications for LVAS support can be classified as elective or acute, and contraindications as absolute contraindications and risk factors that predict a poor outcome (Table 1). The risks of LVAS implantation and subsequent complications are only justified in patients refractory to optimal medical therapy but if implantation is delayed until multi-organ failure develops, the outcome is very poor. For example, the outcome of implantation with the HeartMate has been compared with that of continued medical therapy among patients classified according to their Acute Physiology and Chronic Health Evaluation II (APACHE II) score, a marker of severity in critically ill patients. Patients with scores <11 had a good outcome on medical therapy or LVAS support. Patients with scores >20, indicating severe end-organ dysfunction, had a very poor outcome with either treatment. Patients with scores between 11 and 20 derived the greatest benefit from LVAS [5].


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  		Table 1 Indications for LVAS

 
The condition of the patient also influences the choice of device. The implantation procedure for paracorporeal systems is quick and simple; therefore, they are appropriate if support is needed urgently or if the anticipated duration of support is short. Paracorporeal systems can provide biventricular support. Thus, they are also appropriate for patients with biventricular failure. For the long waiting times faced by most transplant candidates, implantable LVAS are preferable because the greater patient mobility assists recovery and rehabilitation.


   4. Clinical results with implantable LVASs
Top
 Abstract
 1. Introduction
 2. Types of implantable...
 3. Indications and...
 4. Clinical results with...
5. Conclusions
 References
 
4.1. Objectives of LVAS implantation
Most patients have received a LVAS as a bridge to heart transplantation. Some of these patients have remained on support for a long period because no organ was available. The encouraging results with these patients (see below) has led to the concept of LVAS as an alternative to transplantation, also called ‘destination therapy’. In this article the expression ‘long-term support’ is used because most patients described to date have remained on the transplant list.

A few patients have been weaned from LVAS support. In most cases the device was implanted as a bridge to transplantation, but recovery of native ventricular function was observed and the patient was then managed with the objective of weaning.

4.2. Effects of LVAS implantation on clinical status
Implantation of a LVAS (Novacor or HeartMate) produces clear improvements in haemodynamics, exercise capacity, and clinical status [6–10]. Most LVAS recipients are in New York Heart Association (NYHA) class IV before implantation; many achieve class I during prolonged support. Both devices reverse neurohormonal activation [9,11] and improve renal and hepatic function as shown by serum creatinine and bilirubin levels [6,8]. Some patients can be discharged from hospital and can live at home while awaiting transplantation and are able to return to full-time employment and to resume active sports (e.g. golf, cycling, rock climbing). Quality of life after discharge on a LVAS is comparable to that of transplant recipients [12,13] and out of hospital management of LVAS recipients is feasible [14,15].

4.3. Long-term outcome
Since 1997 the European centres implanting the Novacor have contributed data to the Novacor European Registry, which uses standardised definitions of outcome and complications. The latest data from the Registry describe 289 patients for whom a set of data were available at end of 1998 [7]. Table 2 shows the aetiology of heart failure, the indication for the device and the pre-implant characteristics of these patients, which indicated that most patients had severe heart failure.


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  		Table 2 Novacor European Registry: characteristics of patients (n=289)

 
Fig. 1 shows the mean ages and duration of support in patients classified by the aetiology of heart failure. Fig. 2 shows proportions of patients alive (either on support, weaned or transplanted) in these groups. Patients with cardiomyopathy were the largest group (63% of patients) and had the best outcome, with nearly 70% survival after an average support duration of over 100 days. Patients with ischaemic heart disease (26% of patients) had a poorer outcome. In the elective bridging group, overall survival including perioperative mortality rate was better than in the urgent/emergency group. This led to the recommendation to consider LVAS implantation earlier [20]. In all of Fig. 2 groups over half of the surviving patients had received a transplant, some were still on the device and a minority had been weaned. Most deaths occurred in the first 3 months after implantation. Patients receiving a transplant after a period of Novacor support have overall survival of approximately 80% at 6 months [6].


Figure 1
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  		Fig. 1 Patient age and duration of LVAS support according to aetiology of heart failure in the Novacor European Registry [7].

 


Figure 2
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  		Fig. 2 Outcome of LVAS support according to aetiology of heart failure in the Novacor European Registry [7].

 
Two reports have each described 100 patients who received the pneumatic or electric HeartMate, principally as a bridge to heart transplantation [16,17]. In both reports survival to transplantation was approximately 75%. Another publication described 993 patients supported with the HeartMate up to 1997 [10]. The baseline characteristics of patients and the outcome of implantation were similar for the two versions (Table 3), with an overall success rate (survival to transplantation or weaning) of over 60%.


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  		Table 3 HeartMate LVAS: pre-implant characteristics of patients and clinical outcomes [10]

 
The outcome of LVAS implantation varies widely between centres and it would be significantly improved if all centres could perform as well as the best ones. No single factor has been shown to correlate with this variation, but it may reflect differences in patient selection, surgical expertise or post-implant management. LVAS should be implanted only in specialist centres.

4.4. Weaning from LVAS
To date, 25 patients, mainly young patients with dilated cardiomyopathy, have been successfully weaned from the Novacor [7]. The patients were supported for a median of 176 days (range 30–795 days). At 24 months, 59% of patients were alive without transplantation and a further 13% showed recurrent ventricular failure and required transplantation. Myocardial recovery requires at least 2–3 months of LVAS support. It may result from mechanical unloading of the ventricle, reversal of neurohormonal activation or enabling patients to tolerate aggressive anti-HF therapy, particularly β-blockers. So far, very few patients have been weaned from the HeartMate.

4.5. Long-term LVAS support
Fifty patients have been supported by the Novacor for more than 1 year [6]. Overall survival was 82% after a median support duration of 1.54 years (range 1.01 to >4.01). These patients spent 86% of their time out of hospital and complications were not common.

Table 4 compares the outcome of patients supported on the Novacor for >320 days with those supported on the HeartMate for the same period [7,18]. Overall the results are very similar but patients supported on the Novacor tend to have fewer device failures and lower infection rates than those on the HeartMate.


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  		Table 4 Outcome of patients supported on the Novacor [7] or the HeartMate [18] for >320 days

 
4.6. Adverse events
The principal complications reported after Novacor implantation are surgical bleeding, non-surgical bleeding, infection and cerebrovascular accident (CVA). Fig. 3 shows the freedom from event curves for complications in 289 selected Registry patients. Patients are predominantly at risk during the first month after implantation. The principal complications with the HeartMate are infection, haemorrhage, CVA, and device malfunction (Table 5) [16,17]. Early mortality was related mainly to multi-organ failure or perioperative strokes and later mortality due to device failure. It has to be noted that the definition of CVAs are different in different registries. Thus, CVA rates cannot be compared between different LVAS.


Figure 3
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  		Fig. 3 Freedom from event (FFE) curves for complications in 289 selected patients from the Novacor European Registry [7].

 


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  		Table 5 Prevalence of adverse events (%) in two cohorts of 100 patients supported on the HeartMate [16,17]

 
The evidence available suggests differences between the Novacor and the HeartMate in device reliability and CVAs. No device failures have occurred in any patient on the Novacor European Registry, whereas failure has occurred with the HeartMate and has led to death in some cases. The differences in CVAs may reflect the different blood-contacting surfaces of the devices. The blood-contacting surface of the Novacor is smooth polyurethane, which has a thrombogenic effect. Patients require chronic anti-coagulation with heparin, warfarin and aspirin to reduce the risk of thromboembolism. The introduction of an improved anti-thrombotic regimen (the Chicago protocol) and technical improvements to the device have been claimed to reduce the incidence of CVAs to 12% [6]. The blood-contacting surface of the HeartMate consists of textured titanium and flocked polyurethane, which discourages coagulation. Patients, therefore, require only a simple anticoagulant regimen, usually aspirin, 80 mg day–1 and dipyridamole, 75 mg t.i.d. Not all of the CVAs that occur during LVAS support lead to significant disability. Some are detected only at autopsy or on imaging studies.


   5. Conclusions
Top
 Abstract
 1. Introduction
 2. Types of implantable...
 3. Indications and...
 4. Clinical results with...
 5. Conclusions
References
 
Considerable experience has been accumulated with implantable LVAS, principally as a bridge to heart transplantation. Although no controlled comparative trials are available, the overall success rates with these devices (patients alive either on support, transplanted or weaned) compares favourably with the prognosis of transplant candidates maintained on medical therapy for a long period. Quality of life on implantable LVAS can be good and hospital discharge might recoup the cost of the device compared with prolonged inpatient management.

In view of the small numbers of patients listed for heart transplantation, LVAS will have a very modest impact on AHF in population terms if they are used only as a bridge to transplantation. The number of patients eligible for long-term LVAS support may be far greater than the number of transplant candidates. This could become the most common indication for LVAS support. Preliminary results suggest that it is feasible and some patients have remained alive on support for much longer than their expected prognosis at baseline. REMATCH, a comparative trial of the HeartMate vs. continued medical therapy in non-transplant candidates, is in progress [19]. This study may clarify the role of implantable LVAS in this population if enough patients can be recruited.

Weaning from LVAS support also appears promising for patients with acute, reversible ventricular damage.

Important issues with LVAS support include patient selection, adverse events and variation in outcomes between centres. It seems clear that patients should be referred for LVAS implantation before the onset of major organ dysfunction or sepsis, but the optimal selection criteria remain to be defined. They will probably differ for bridging to transplant, long-term support and bridging to recovery.

The incidence of adverse events, mainly infection, thromboembolism and bleeding, needs to be reduced. Improvements in device design, increased clinical experience and refinements in anticoagulant therapy might achieve this reduction.

In conclusion, more patients with AHF should be considered for LVAS implantation, presently mainly as a bridge to transplantation, but possibly also in the future to induce myocardial recovery or as a long-term therapy.


   References
Top
 Abstract
 1. Introduction
 2. Types of implantable...
 3. Indications and...
 4. Clinical results with...
 5. Conclusions
 References
 

  1. El-Banayosy A., Körfer R., Arusoglu L., et al. Bridging to cardiac transplantation with the Thoratec left ventricular assist device. Thorac Cardiovasc Surg (1999) 47(Suppl):307–310.[CrossRef][Web of Science][Medline]
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  4. Tamez D., Myers T.J., Inman R.W., Miller K.A., Frazier O.H. Clinical evaluation of the HeartPak. ASAIO J (1997) 43:M779–M801.
  5. Gracin N., Johnson M.R., Spokas D., et al. The use of APACHE II scores to select candidates for left ventricular assist device placement. Acute Physiology and Chronic Health Evaluation. J Heart Lung Transplant (1998) 17:1017–1023.[Web of Science][Medline]
  6. El-Banayosy A., Deng M., Loisance D.Y., Vetter H., Gronda E., Loebe M., Vigano M. The European experience of Novacor left ventricular assist (LVAS) therapy as a bridge to transplant: a retrospective multi-centre study. Eur J Cardiothorac Surg (1999) 15:835.[Abstract/Free Full Text]
  7. The Novacor European Registry: Personal communication with P. Jansen (Director Clinical Research/Registry, Novacor Division of Baxter CardioVascular Group). The investigators/centers contributed to the Registry are listed below.
  8. McCarthy P.M., Savage R.M., Fraser C.D., et al. Hemodynamic and physiologic changes during support with an implantable left ventricular assist device. J Thorac Cardiovasc Surg (1995) 109:409–418.[Abstract/Free Full Text]
  9. Murall S. Mechanical circulatory support with the Novacor LVAS: world-wide clinical results. Thorac Cardiovasc Surg (1999) 47(Suppl_2):321–325.[CrossRef][Web of Science][Medline]
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  18. Data presented at the International Society for Heart and Lung Transplantation Meeting, 1998.
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 Eur J Heart FailHome page
A. A. Louis, I. R. Manousos, A. P. Coletta, A. L. Clark, and J. G.F. Cleland
Clinical trials update: The Heart Protection Study, IONA, CARISA, ENRICHD, ACUTE, ALIVE, MADIT II and REMATCH
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