A composite driving system for LVAS and IABP: practical and effective driving and weaning. We have devised a new method, termed alternate synchronous driving (ASD), to wean patients from a left ventricular assist system (LVAS) to a pressure assist intraaortic balloon pump (IABP). We have built a new drive unit, VCT200, to apply ASD easily and automatically. After IABP insertion in the final weaning stage, this method drives the LVAS and IABP alternately, with electrocardiogram (ECG) synchronization. The pumping ratio of IABP increases while that of LVAS decreases according to recovery of natural heart function. In in vitro studies, ASD was effective when bypass flow (BF) was less than 50% of total flow (TF) (TF:BF + cardiac output [CO]), and its advantages increased under lower BF conditions. Mean aortic pressure (mAP) and CO increased 10 mmHg and 15%, respectively, with this method (IABP:LVAS = 1:1) when BF was 30% of TF. During in vivo studies, mAP increased 75.7 +/- 6.7 mmHg to 80.1 +/- 3.6 mmHg (p less than 0.001), and the CO increased from 3.1 +/- 0.5 L/min to 3.3 +/- 0.5 L/min (p less than 0.001), while the endocardial viability ratio (DPTI/TTI) increased 20-30%. This method was used in a 62-year-old man in which LVAS was applied after ventricular aneurysmectomy, BF was reduced from 2.2 L/min to 1.1 L/min by using ASD without any change in systemic perfusion. This reduction of BF could not be achieved with LVAS alone. From these data, this system could wean patients from LVAS and then switch to IABP smoothly, easily, and automatically, without hemodynamic instability. 