Left Ventricular Assist Devices — Reasons to be Enthusiastic

Despite advances in medical treatment, the prognosis of advanced heart failure remains poor 1. The clinical advent of cardiac transplantation in 1967, while being an extraordinary development in itself, intensified preexisting research into mechanical circulatory support devices that might serve either as a bridge or an alternative to biological heart transplantation 12. The first successful mechanical bridge to cardiac transplantation was reported in 1969 3, but the first electrically driven implantable left ventricular assist device 22 marked the introduction of clinically relevant left ventricular assist support systems. Since then a full range of short-term, median-term and long-term left ventricular, right ventricular and biventricular implantable or paracorporeal systems have become available 11,13. The Novacor and TCI HeartMate systems are currently the most widely used systems. offer a survival and functional benefit in selected cardiac transplant candidates; are feasible as long-term alternatives to cardiac transplantation in selected patients; are suitable as bridges to recovery in situations of potentially reversible myocardial dysfunction; serve as valuable backup in high risk conventional cardiac surgery; allow the exploration of biological implications of ventricular assist device therapy; and help to understand societal, i.e. economic and ethical, implications of modern medicine. Although randomised studies comparing LVAS to conventional medical therapy in the transplant candidate population or non-transplant candidate population have not yet been completed, some are on the way and the results are eagerly awaited 24. So far, there are only a few reports comparing cohorts of a similar clinical profile treated either by medical therapy, by LVAS or cardiac transplantation. Different multicentre registry results have been presented 10,17. With existing devices, up to 74% of patients undergo cardiac transplantation. These data suggest that, in order to convey a survival benefit to the patient, selection of patients, and timing of implantation, is of critical importance 6. This issue has to be viewed within the context of the declining availability of cardiac donor organs. As the fraction of patients placed on wearable LVAS with ambulatory care increases and patients are able to return to work 15, quality of life while waiting for cardiac transplantation is markedly enhanced 26. While being primarily implemented as a bridge to transplantation, the huge and increasing gap between the number of potential heart recipients and heart donors places a growing role on mechanical circulatory support devices as long-term support systems. In countries with allocation rules which do not give priority to patients who are supported mechanically 7, the unrestricted availability of these devices leads to their use as alternatives to transplantation. There has been, during the last 15 years, a substantial proportion of Novacor as well as TCI-HeartMate recipients who either have not been considered transplant candidates for various contraindications or, while being bridged toward cardiac transplantation, have been switched toward being definite recipients of ventricular assist devices 19,21. These results show the feasibility of using these devices for periods of 1–3 years at least. Among Novacor and TCI HeartMate patient cohorts there has been a small number of patients who have been weaned from support 18. This approach is based on the rationale that during unloading on LVAS support a process called reverse remodelling is initiated that leads to recovery of ventricular function 2,14,20,29. Specific protocols to serially assess native left ventricular function have been developed demonstrating excellent recovery and restitution of function over the short term 5. On the other hand, well founded scepticism remains about the proportion of patients who recover functionally in the long-term course and might benefit from device explantation 16. There is evidence for an expanding role of conventional cardiac surgery in high-risk patients who undergo operation despite severely impaired left ventricular function with a left ventricular assist device standby. In those cardiac surgery units which accept these patients for operation there has been an increasing utilisation of various assist devices including intraaortic balloon pump, extracorporeal membrane oxygenation, midterm support devices such as the paracorporeal Thoratec and Medos left ventricular, right ventricular and biventricular assist devices as well as a long-term assist devices such as the Novacor and the TCI HeartMate 28. With current LVASs, there is still a 20–40% probability that patients will not survive to transplantation 13. Causes of death, predominantly in the early post-operative period after device implantation, include systemic infection and sequelae of coagulation disorders 25. It is of vital importance to improve our understanding of the underlying pathophysiology of homeostatic defence systems 8,27. In addition, the development of less traumatic devices including those that are directly wrapped around the heart and do not directly contact the blood are of major importance 11. This new mode of therapy may be applicable to 0.1–1% of the population. If there are no biological restrictions anymore this creates economic difficulties. The impact of LVAS technology on costs in the face of the increasing donor–recipient gap has been discussed 23. The cost of LVAS technology will fall in the coming decade, devices will get smaller and become totally implantable and the problems of infection and coagulation will be overcome. Who knows how the technology will be applied then? Probably, new modes of combination therapy 9 and novel ethical dilemmas are ahead of us 4.