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A year after paying more than $1 billion to acquire the maker of a complex heart-failure treatment, Medtronic PLC has announced a new Food and Drug Administration approval that expands the market for the costly medical device.

Medtronic announced last week that the FDA granted approval for its HeartWare HVAD System to be used on a permanent basis by patients in end-stage heart failure who are not candidates for transplants. Previously, the device was only approved for patients who needed it until they could get a new heart.

The HVAD System is a left-ventricular assist device (LVAD) that uses a small centrifugal-flow pump to increase blood flow in a patient whose heart can't do the job on its own. The device weights about third of a pound.

More than 6.5 million Americans have heart failure, a progressive disease in which the heart is less able over time to pump enough blood. Of those patients, Medtronic says more than 250,000 have advanced heart failure and are ineligible for heart transplants.

"Heart failure continues to be a growing burden to millions of patients, caregivers and the health care system," Medtronic Vice President Dr. David Steinhaus said in a news release. "Medtronic strives every day to advance the field of mechanical circulatory support."

The HVAD System was originally made by Massachusetts-based HeartWare International, which Medtronic acquired in a $1.1 billion cash-for-stock deal in August 2016. ("HVAD" originally stood for HeartWare Ventricular Assist Device.)

At the time, the HVAD System was only approved in the U.S. as a "bridge-to-transplant" therapy, though HeartWare had long-running clinical trials going to gain "destination" therapy approval as well.

The results of those trials were nuanced.

In the initial "Endurance Destination" trial, the device achieved its primary goal of being statistically noninferior to another destination heart-pump on the market, the HeartMate II (now sold by Abbott Laboratories). However, the trial documented a higher rate of stroke in the HVAD destination population. So a second trial, "Endurance Supplemental," was started using the same device but different blood-pressure maintenance.

In the second trial, the HVAD System failed to meet its primary goal of being noninferior to HeartMate II in terms of neurological injury after 12 months, but it did meet a prespecified secondary goal that measured a combined rate of death, stroke, explant and urgent transplant after 12 months. Together, the trials examined outcomes from nearly 1,000 patients randomized to the two devices between 2010 and 2015.

Based on the totality of the data, the FDA approved the HVAD System for destination therapy.

"The secondary results of Endurance Supplemental (patients enrolled 2013-2015) … were most compelling, since they showed the HVAD as superior to the control group," Medtronic spokeswoman Tracy McNulty said in an email. She noted that 76 percent of patients receiving the HVAD System were alive on the originally implanted device and free of disabling stroke, compared to 67 percent of patients in the control arm, and the findings were statistically significant.