Thoratec Corp.’s HeartMate II, a device that pumps blood for patients with failing hearts, can form deadly blood clots, according to a report that urges investigation into therapeutic strategies to address the issue.
The implanted device caused 72 blood clots in 66 patients at three institutions, where 895 devices were implanted from 2004 through 2013, according to a study in the New England Journal of Medicine. The report pooled data from the Cleveland Clinic in Ohio, Washington University Barnes-Jewish Hospital in St. Louis, and Duke Medical University Center.
Thoratec’s HeartMate II takes over for the failing heart, and research has shown it can extend patients’ lives, gaining them time to find a donor organ for a transplant. While the exact cause of the increased rate of blood clots “remains unknown,” according to the report, its authors said recommendations for use of the pump “should account for this updated risk profile.”
“I don’t think anybody that’s in this field is ready to say ’Gee, we have to stop using these,’” said Randall Starling, a cardiologist at the Cleveland Clinic and the study’s lead author, in a telephone interview. “The alternative isn’t good. But we have to better understand their limitations and how to manage them.”
The device was recalled in 2012, after Pleasanton, California-based Thoratec found that a component of the implanted device is sometimes attached improperly. Subsequently, the company changed information provided to doctors to ensure that the faulty component is fully connected to the device. The study authors said that changes to the device’s design weren’t directly related to the clots they found.
The blood clots were treated with drug therapy, heart transplant or implanting a new device. Among 11 patients who got heart transplant, one died a month after the surgery. Pumps were replaced in another 21 patients, with a rate of death similar to those who didn’t have the blood clot. Among the 40 patients who didn’t undergo either transplant or device replacement, about half died 6 months after the clot was diagnosed.
Those 40 patients may have been offered a replacement device and opted for medical management, Starling said. They may also have been sicker, either because they weren’t taking their blood thinners, or because their blood thinners had to be stopped due to another complication, such as a bleeding stomach ulcer.
“We don’t think it’s just that,” Starling said. Since the information was gathered from just three medical centers, that may limit the data, he said.
One clue to the clot’s formation was a finding of increased levels of lactate dehydrogenase, which doubled in patients before the clots were diagnosed, the authors wrote. Lactate dehydrogenase is a marker of oxygen levels.
Heart failure, a progressive disease, strikes 1 in 5 Americans older than 40. It occurs when a damaged organ can’t supply enough oxygen-rich blood to keep other organs, such as the lungs, working. There are few treatments, and no cure.
“Thoratec’s top priority is to serve patients with heart failure,” said Gary Burbach, the company’s chief executive officer, in an emailed statement. “We take every potential complication seriously and work closely with clinicians to optimize all aspects of the patient experience with HeartMate II.”
The International Society of Heart and Lung Transplant will highlight the diagnosis and treatment of blood clots associated with the devices at its 2014 meeting, according to its website.
Starling’s group will collect more data on over 1,000 patients, and looking more closely at specifics such as height, weight, sex, and diabetes, as well as patient management issues. It may be that some pumps are running too slow, which may make its components likelier to cause blood clots, Starling said.