Experimental investigation to ensure a safety of the exchange of extracorporeal-type ventricular assist devices in long-term-use patients

Ventricular assist devices (VADs) are widely applied for end-stage congestive heart failure patients. Considering the shortage of organs donations in Japan, VADs tend to be used for longer period. The extracorporeal-type Toyobo VAD has been used. Because the guarantee period of the Toyobo VAD is one month due to a potential risk of thrombus formation inside the VAD, it is necessary to exchange the VAD periodically in a long time. In the VAD exchange, the cable-ties are removed and the VAD used including stainless-steel connectors are replaced with a new VAD. In the case of the patient for long-term-usage who can move, there is a danger that the connection parts will be detached just after VAD exchange in case some kinds of loads are added to the VAD. Therefore, it is necessary for both patients and nurses to understand the quantitative load for the detachment of the VAD. In this study, we investigated the load required for the detachment of connectors from cannulae of the VAD before and after the VAD exchange. The VAD was incorporated in a mock circuit and pneumatically-driven in a 37°C controlled water bath. In that condition, the load for the detachment of connectors from cannulae of the VAD was examined using a uni-axial tensile tester. As alternatives to cannulae used for a long time, plastically- deformed cannulae were prepared by heating at 120°C for 7 hours. Influence of the tensile speed, direction of the load applied, and presence of liquid between the connectors and the cannulae on the loads necessary for the detachment were investigated. The load necessary for the detachment in one hour after the VAD exchange was decreased to 50-60% of the load before one. However, in 24 hours after the exchange, the load was recovered to 80% of the load before the VAD exchange. When the perpendicular load of 8.5kgf was applied at the tensile speed of 500mm/min, the time required for the detachment was only 6 seconds. It is important for nurses and patients to pay much attention in order to prevent load acting on the VAD newly changed, especially for one day after the VAD exchange.