The left ventricular assist device is based on the principle of the Maillard-Wenkel rotative pump. The materials which make up the pump must present particular mechanical, tribological, thermal and chemical properties. Titanium nitride (TiN) because of its surface properties and graphite because of its bulk characteristics have been chosen. The present study evaluated the in vitro hemocompatibility of TiN coating deposited by the chemical vapor deposition process. Protein adsorption, platelet retention and hemolysis tests have been carried out. In spite of some disparities, the TiN behavior towards albumin and fibrinogen is interesting, compared with the one of a reference medical grade elastomer. The platelet retention test gives similar results as those achieved with the same elastomer. The hemolysis percentage is near to zero. TiN shows interesting characteristics, as far as mechanical and tribological problems are concerned, and presents very encouraging blood tolerability properties.

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Recently, we have developed microcomputer-oriented pacemakers with true software flexibility. The first 25 devices implanted (DPG-1 type) exhibited an unexpected phenomenon caused by a microcomputer error. A safety mechanism switched off all special functions and automatically reset all parameters to standard settings. The problem was solved by noninvasive modification of the software. More than 200 units (TX-1 type), which are rate responsive pacemakers based on the QT principal, were implanted up to May 1984. These pacemakers were built using the same microelectronics as used in the DPG 1 pacemaker. Knowledge gained from clinical evaluation was directly applied not only to the patients receiving new implants but also to the preexisting implantees. This was done by software reprogramming in the implanted unit.

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