cal complications and effectiveness,1 and impact on quality of life, it is more difficult to ascertain the future potential of MCSSs. Clinical trials of a totally implantable long-term left ventricular assist device are scheduled to begin in 1992; the data from these trials will have broad implications for continuing development of long-term TAHs and VADs.

TEMPORARY CIRCULATORY SUPPORT

The use of MCSSs for temporary support has evolved, in the absence of totally implantable systems, to meet patient needs and to evaluate the feasibility of mechanically substituting for the pumping action of the heart. These systems have all been connected or “tethered” to cumbersome external power sources by skin-penetrating tubes or wires, limiting acceptance as permanent devices and increasing the risk of infection. They have, however, provided rather substantial and impressive information on pumping efficacy, mechanical reliability, and morbidity and mortality risks that is helpful in predicting the long-term outcomes of using totally implanted devices.

Temporary MCSS use is intended to assist or replace the heart for a limited period of time. Temporary devices support patients until transplantation with a donor heart or while they are recovering from acute depression of cardiac function that is thought to be reversible (e.g., after cardiopulmonary bypass). Although temporary clinical use of MCSSs has been successful in some instances for over a year, the purpose is not to provide permanent circulatory support.

Several MCSSs are currently available for temporary use under a Food and Drug Administration (FDA) investigational device exemption (IDE) 2 (see Table 2.1). Most devices in temporary use are VADs, used to support either the left ventricle, right ventricle, or both. Centrifugal external VADs are not considered here, because their maximum period of use is measured in days.

As of early 1991, the only TAH approved by FDA for temporary investigational use was the Pennsylvania State University heart, also known as the Hershey heart. The Symbion/Jarvik TAH was used for temporary support until 1990, when its IDE was withdrawn by FDA because of questions concerning production and quality control practices on the part of the manufacturer; it is still used for temporary support outside the United States.

From an engineering perspective, certain specific MCSS components and

1  

Efficacy is the measure of a medical technology's effect on a disease state under ideal clinical conditions. Effectiveness, in contrast, is the measure of a technology's effect during general clinical use.

2  

FDA grants approval of an IDE for trial use of a device in humans.



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