The current status of heart transplantation and the development of "artificial heart systems"

Abstract

Background: In view of the major technical advances in ventricular assist devices (VAD) in recent years, the authors discuss the question whether these "artificial hearts" are still no more than a temporary measure for patients awaiting heart transplantation (HTx), or whether they can already be used as an independent form of long-term treatment.

Methods: Statistics from Eurotransplant regarding heart transplantations and transplant waiting lists in Germany are presented. Technical developments in cardiac support systems, the variation in results depending on the indication, and the findings with respect to quality of life are all discussed on the basis of a selective review of the literature and the authors' own clinical experience.

Results: The waiting list for heart transplantation in Germany has grown to a record size of nearly 800 patients, while fewer than 400 hearts are transplanted each year. Technical advances have improved outcomes in VAD therapy, but the outcome depends on the patient's preoperative condition. The physical performance of patients who have received VAD is comparable to that of HTx patients; nonetheless, HTx patients have a better quality of life.

Conclusions: Chronic VAD therapy has become a clinical reality. Because of the greater number of patients awaiting HTx, many will not receive their transplants in time. When the decision to treat with VAD is made early, it can be used as an alternative form of treatment with a comparable one-year survival (>75%).

Keywords: heart transplantation.

Figure 1

The length of the waiting list and the number of heart transplantations performed each year in Germany, 1998–2008 (data from Eurotransplant, www.eurotransplant.nl)

Figure 2

Systems for use in patients with biventricular heart failure a) A Total Artificial Heart (SynCardia) that is implanted orthotopically and powered by a pneumatic console (photograph reproduced with the kind permission of SynCardia Systems, Inc. [www.syncardia.com]) b) An extracorporeal artificial ventricle (the Thoratec Paracorporeal Ventricular Assist Device [PVAD]), which can be used to assist the function of either the right or the left ventricle of the heart and is powered similarly to the Total Artificial Heart (photograph reproduced with the kind permission of the Thoratec Corporation)

Figure 3

Left ventricular assistance system a) Schematic representation of the current method of left ventricular assistance with an implanted axial pump (Thoratec HeartMate II) and extracorporeal components (controller, batteries) (reproduced with the kind permission of the Thoratec Corporation) b) Chest x-ray

Figure 4

Risk scores regarding the preoperative condition and course of patients receiving ventricular assist devices (VAD) (19). These observations were made in 222 patients who had received VAD as permanent treatment. Note that older, first-generation VAD were used here for reasons related to device approval. (From: Lietz K, Long JW, Kfoury AG et al.: Outcomes of left ventricular assist device implantation as destination therapy in the post-REMATCH era: Implications for patient selection. Circulation 2007; 116: 497–505. Reproduced with the kind permission of Lippincott William & Wilkins, Baltimore.)

Figure 5

Results of the first 100 implantations of an axial pump (HeartMate II) in Europe (2). The individual curves represent survival, transplantations, deaths, and explantations of the VAD (ventricular assist device) after recovery of left ventricular function. These data were acquired retrospectively rather than in a prospective clinical study. (From: Strüber M, Sander K, Lahpor J et al.: HeartMate II left ventricular assist device; early European experience. Eur J Cardiothoracic Surg 2008; 34: 289–94. Reprinted with the kind permission of Elsevier, Oxford, U.K.)

Figure 6

The development of left-ventricular assist technology (illustrative examples). From left to right: 1^st generation: a pulsatile, electrically powered ventricular assist device (VAD) (Thoratec HeartMate I) 2^nd generation: a non-pulsatile axial pump (the Thoratec HeartMate II) 3^rd generation: a non-pulsatile centrifugal pump (the HeartWare HVAD) 4^th generation: a miniature left-ventricular assist device (LVAD) for partial circulatory support (CircuLite Synergy) (Photographs reproduced with the kind permission of the Thoratec Corporation, HeartWare International, and CircuLite, Inc.)