Optimal management of a ventricular assist system. Contribution of flow visualization studies

The Novacor (Baxter Novacor, Oakland, CA) Left Ventricular Assist System (LVAS) incorporates a versatile microprocessor based controller that permits a variety of operating modes. These include internally triggered automatic synchronous counterpulsation, electrocardiogram triggered synchronous operation, and full to empty or fixed rate asynchronous operation. The aim of this pilot study was to determine the extent to which washing of the blood contacting surfaces of the pump may be optimized by suitable choice of operating mode. Visualization of flow fields adjacent to surfaces in confined areas requires small, neutrally buoyant tracer particles for feature extraction. A novel technique using fluorescent tracer particles (100 microns), an argon laser, and a low pass optical filter has been developed for this purpose. Particle motion was tracked from video images and calculations were made of velocity. Flow visualization was performed under conditions that simulated clinically observed hemodynamic conditions, typical of the immediate post-implant period. At a given LVAS output, fluid speed in the vicinity of the inflow valve tended to increase at higher LVAS beat rates (and consequently lower LVAS stroke volumes). This and future work may well be useful in selecting the optimum modes of LVAS operation as a function of the hemodynamic status of the patient.