Entirely artificial hearts are saving three-quarters of patients who otherwise would have died as they await heart transplants, according to an international study.

The mechanical devices implanted into the chest can replicate the heart's functions and are powered by a 13-pound battery roughly the size of a toaster that the patient carries around.

The study carried out by 18 cardiac surgeons around the world tracked 47 patients implanted with the SynCardia Total Artificial Heart for at least a year between 1989 and 2011. The results showed that 34 of the patients (72 percent) had received successful live transplants, 12 (24 percent) had died, and one man was still awaiting a transplant.

The patients averaged 50 years of age and wore the artificial hearts on average for just more than 18 months or 554 days. The one outlier is French patient Frederic Thiollet, who has been wearing the device for more than three-and-a-half years as he continues to wait for a new heart.

The report found that the long-term use of the SynCardia was safe, despite two patients dying from device failure. The most common causes of death were infections and hemorrhaging and the study said, "device malfunctions are generally referred to as a rare complication with the (Total Artificial Heart)."

Three of the 34 patients who received live transplants eventually rejected their new hearts and also died. Overall, the study found that the artificial hearts had acceptable results but that some improvements to the device as well as in patient selection and long-term care were needed to improve survival rates.

The device is currently only approved as a bridge device for patients awaiting transplants, but in December 2014 the Food and Drug Administration approved the study of the effectiveness of the SynCardia Total Artificial Heart for permanent use. 

The video below recounts some stories of patients who survived thanks to the artificial hearts. More detail on the study entitled "Results with SynCardia Total Artificial Heart beyond 1 year," which was published in the ASAIO Journal for the American Society for Artificial Internal Organs in December 2014, can be found here.

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