Well, I suppose that with this sort of thing, you just have to try it out for a few years, and see what happens.
There has been a worldwide (of course) recall on the HeartMate II Left Ventricular Assist System, which have been in use since November of 2003. The failure rate has been deemed unacceptable. Apparently the leads that connect the pump to the controller wear down significantly enough to affect pump function. "The estimated probability of the need for pump replacement due to percutaneous lead damage is 1.3% at 12 months, 6.5% at 24 months and 11.4% at 36 months." (as per the FDA site) THAT is significant!!
Left ventricular assist devices are essentially used to buy time for "CHFers" (Congestive Heart Failure patients) who are awaiting transplant, or they may even be used indefinitely in patients who are not candidates for transplant.