heart (TAH), is similar in concept to two VADs but replaces the diseased heart.

The long-term TAHs and VADs now being developed are powered by electricity that is transmitted across the skin surface in a transformer-like arrangement; the patient will carry rechargeable batteries on a belt or in an over-the-shoulder pouch. An implanted rechargeable battery provides temporary power for about 20 minutes, so the patient can change the external batteries or bathe.

MCSS use began in 1969 with the first temporary implant to support a patient awaiting a donor heart for transplantation. Temporary MCSSs are now also in routine—but still investigational—use to allow the heart muscle to recover functioning after open-heart surgery or after it has been damaged by an acute myocardial infarction (heart attack). In all, more than 1,300 TAHs and VADs have been used in these temporary applications, including some with the VAD itself placed outside the body. This report, however, focuses on devices intended for indefinite, long-term use to assist or replace the heart.

TECHNOLOGICAL PROGRESS AND BARRIERS

Several developers have made considerable progress toward both VADs and TAHs that are fully implantable. Technological advances have resolved some of the shortcomings observed in the mid-1980s, when Barney Clark, William Schroeder, Murray Haydon, and Jack Burcham received Jarvik-7 TAHs.

The first implantation of a long-term VAD is expected in 1992, in a clinical trial of a device manufactured by the Novacor Division of Baxter Healthcare Corporation. In this NHLBI-sponsored trial, 20 devices will be implanted over a two-year period by researchers at St. Louis University and the University of Pittsburgh. For the evaluation, each patient will be followed closely for two years. Full trial results will thus not be available until 1996 or 1997. Based on years of research including simulated bench testing and animal trials, the developers of this and other long-term MCSSs have confidence in the mechanical capabilities of their devices, but definitive findings about clinical efficacy and effectiveness will not be known for several years.

Estimating the cost of each device, once approved for routine use, is problematic at present. Based on information from developers, the committee expects that a VAD will cost about $50,000 and a TAH about $100,000, expressed in 1991 dollars. In addition, the hospital and physician care required to implant one will probably cost about $100,000, again based on 1991 costs. Costs for postimplantation care depend heavily on the frequency of such events as device problems and complications that require hospitalization.



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