With respect to safety, the principal adverse effects associated with the LVADs include bleeding, hemolysis, and organ dysfunction, thromboembolism, infection, right heart failure, and mechanical failure. Thromboembolic complications are low in the TCI device despite the lack of systemic anticoagulation. The overall mechanical failure rate is small, less than 1 percent in 26 patient years of use. The vented electric and pneumatic device experience to date indicates that the devices are similar with respect to adverse event rates. Thus, in 1997 there was a strong rationale for a randomized controlled trial that compared the benefits and cost of vented electric LVADs to medical treatment. The need to perform a randomized controlled study was further emphasized by the lack of rigorous data on survival, quality of life, and cost effectiveness comparing LVAD support with medical therapy.