Doctors began implanting left ventricular assist devices (LVADs) decades ago to keep heart failure patients alive while they waited for weeks or months for an available transplant organ. Today improved designs are being installed as final fixes. Indeed, the distinction between an LVAD used as a bridge to transplant and as a permanent aid “is disappearing,” says Kiyotaka Fukamachi, head of the Cleveland Clinic’s Cardiovascular Dynamics Laboratory. “Some patients who received an LVAD as a bridge have been living with it for two or three years.”

A healthy left ventricle pumps freshly oxygenated blood through the aorta to the body. LVADs help the ventricle or take over its operations if the chamber is weak or has stopped functioning. First-generation designs, which still prevail, are pulsatile: an implanted pump pushes blood in pulses like a natural heart. Second-generation LVADs are smaller, relying on a rotor that continuously streams blood. Engineers are evaluating experimental, third-generation devices that use magnetically levitated rotors, reducing moving parts.

Yet “no one approach is necessarily better than the others,” Fukamachi says. “The choice depends on a patient’s circumstances.” The pulsatile machines, including Thoratec Corporation’s HeartMate I and World Heart Corporation’s Novacor, may still provide the best option if a patient needs a full takeover. Continuous-flow models such as MicroMed Cardiovascular’s DeBakey can be smaller and simpler because they do not require valves or a vent tube. Levitated machines may show less wear over time. (In the U.S., HeartMate I is approved for bridge and permanent therapy; ­Novacor is approved for bridge. Other models are in ­trials.)

Complications are involved, of course. A wire must protrude from the body to a controller and batteries, leading to infection in up to 15 percent of patients. Blood clots can form inside pumps, so patients must live on anticoagulants, which increase the chance for problematic bleeding. Device failure occurs, too. But doctors are likely to implant more LVADs because heart donors remain scarce. Only 2,100 transplants are performed in the U.S. every year, whereas 3,500 to 4,000 people are perennially on the waiting list.