Editors' ChoiceHeart Failure

A Better Bionic Heart

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Science Translational Medicine  09 Dec 2009:
Vol. 1, Issue 10, pp. 10ec35
DOI: 10.1126/scitranslmed.3000680

A science-fiction world peopled by bionic humans comes a bit closer with a recent report by Slaughter et al. of the successful application of a new type of internally implanted heart pump—a continuous-flow left ventricular–assist device. With this pump helping to mechanically move blood from the left ventricle of the heart to the ascending aorta, the number of heart failure patients who survived for 2 years without experiencing a stroke dramatically increased relative to a previously used apparatus, the pulsatile displacement pump.

Both pumps are implanted in line between the left ventricle and the aorta to aid a weak and failing heart. The pulsatile displacement pump works like a car piston—a diaphragm moves up and down inside a housing, pulling blood in from the ventricle side and pushing it out the aorta side in discrete spurts, just as in the natural circulation. Although the pump works successfully in many patients, there have been concerns about the formation of clots as blood passes through the artificial device, causing ischemic stroke. The new pump consists of a rotor placed directly in the line of flow that propels blood forward by means of screw-shaped fins on it sides. It has fewer moving parts and is smaller than the first-generation pump.

In the newly reported clinical trial, one group of patients with severe, untreatable heart failure received the pulsatile displacement pump and the other group was implanted with the new continuous-flow left ventricular–assist device. After being fitted with their heart pumps, both groups of patients felt much better and, for example, could walk considerably further in 6-min intervals—which resulted in an average of 312 m walked a year after device insertion compared to 177 m before. Both devices similarly delivered improved cardiac output. None of the patients had more strokes than did untreated heart failure patients, a sign that neither of the implanted devices caused blood clots.

The big difference in the performance of the two heart pumps was that patients had fewer problems with the continuous-flow device itself. It needed to be replaced one-eighth as often as the older, pulsatile displacement pump, and, because each replacement required a new surgical procedure, patients with the new pump showed improvements in the rate of sepsis, general infection, and rehospitalization. Because they experienced fewer of these surgery-related adverse events, twice as many patients with the continuous-flow pumps survived for 2 years relative to those with the older model. Thus, the continuous-flow left ventricular–assist device was superior to the pulsatile pump, but not because its streamlined rotor caused less clotting and smoother blood flow. Instead, it prevailed because it was simpler and could be implanted with ease and few complications, and because it lasted longer and required fewer replacements. These findings remind us that the success of the bionic human, and our own health, may ultimately depend on one thing—good engineering.

M. S. Slaughter et al., Advanced heart failure treated with continuous-flow left ventricular assist device. N. Engl. J. Med. 361, 2241–2251 (2009). [Abstract]

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