Blood pumps used as heart assist devices are commonly powered by an external battery and control system. If the external power is interrupted, such as by damaging an external cable, patients will have backflow across the pump. If the flow is too high, they may decompensate and die. If the backflow is relatively low, patients can survive until power is restored, but their blood pump must be sufficiently washed to prevent thrombus. Centrifugal blood pumps have been designed for good pumping performance, low blood damage, and avoidance of thrombus when they are running. The present invention recognizes the need to also provide enough washing to prevent thrombus when the pump power is turned off. The invention provides centrifugal pumps with triple or quadruple volute designs, or with axial flow impellers on the same shaft as the centrifugal pump impeller to help drive the rotor in reverse and enhance washing even with relatively low backflow. Also, in the preferred embodiment the centrifugal rotor is supported by low friction mechanical blood immersed bearings, to avoid contact of the rotor with the housing that creates small poorly washed crevices where thrombus can form.
