was averaging approximately two weeks; animal survivals today are approaching one year, and patients have survived for almost 600 days with artificial hearts. The use of temporary ventricular assist devices is becoming more routine, and the development of permanent left ventricular assist devices and total artificial hearts is well under way. Yet with all the progress that has been made, there are currently several complications associated with the permanent application of left ventricular assist devices and total artificial hearts. These can be broken down into durability and biocompatibility (including bleeding, thrombosis, sepsis, calcification, and hemolysis). These factors appear in various degrees in all of the devices and will be discussed, but they do not appear to be insurmountable problems; in fact, several appear to be close to solution.

CURRENT STATE OF THE TECHNOLOGY IN MECHANICAL CIRCULATORY SUPPORT SYSTEMS

Artificial hearts and circulatory assist devices are currently under development in the United States, Korea, Russia, Canada, Switzerland, Japan, Germany, Czechoslovakia, Italy, France, Australia, China, and other countries. A detailed description of all of these devices is beyond the scope of this document, and only those with significant design features or devices sufficiently developed to be nearing clinical trials will be discussed.

The most frequent clinically used mechanical circulatory support systems (MCSSs) are those currently manufactured in the United States (Pae and Miller, 1990). The animal survival times with pneumatically powered devices are essentially the same in the United States and abroad, indicating approximately the same technology level (Total Artificial Heart, 1985; Total Artificial Heart, 1987). Electric motor-driven circulatory assist and artificial heart devices are, at the present time, more advanced in the United States than in any other country, although devices in Japan (Total Artificial Heart, 1985) and Switzerland (Odermatt, 1989) are advancing rapidly.

All of these MCSSs have met with similar difficulties in development and application. These difficulties include device durability and biocompatibility. Various solutions have been implemented for these problems and have allowed devices to function for over a year in vivo and greater than two years in vitro.

Short-Term-Use Devices (fewer than 180 days)

Both total artificial hearts and univentricular or biventricular assist devices can be utilized temporarily for mechanical circulatory support. All of the total artificial hearts that have been utilized clinically have been pneumatically powered devices. The ventricular assist devices that have been



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