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Published: Nov 29, 2013
- The rate of pump thrombosis associated with the HeartMate II left ventricular assist device (LVAD) increased in the last few years, going higher than rates seen in pre-approval clinical trial, and the reasons are unknown.
- Note that the events are happening sooner, with the median time from implantation to thrombosis decreasing from 18.6 months before March 2011 to 2.7 months after that date.
The rate of pump thrombosis associated with the HeartMate II left ventricular assist device (LVAD) increased in the last few years, going higher than rates seen in pre-approval clinical trials, a three-center study showed.
Before March 2011, the rate of confirmed pump thrombosis 3 months after implantation was 2.2%, but by January 2013, the rate had risen to 8.4%, according to Randall Starling, MD, MPH, of the Cleveland Clinic, and colleagues.
In addition, the events are happening sooner, with the median time from implantation to thrombosis dropping from 18.6 months before March 2011 to 2.7 months after that date, the researchers reported online in the New England Journal of Medicine.
“We recognize that LVADs provide life-sustaining treatment for many patients with advanced heart failure,” they wrote. “However, recommendations for LVAD therapy should account for this updated risk-benefit profile.”
The reasons behind the increase in pump thrombosis — which was confirmed in an analysis by researchers at the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS) after the FDA was made aware of the issue — remain unclear, Starling told MedPage Today. He noted that he and his colleagues have had discussions with representatives from Thoratec, which makes HeartMate II.
“To our knowledge, they have looked carefully but haven’t pinpointed anything specific,” Starling said. “So we just don’t know [the reason] at this point.”
In an emailed statement, Thoratec said “there are a number of factors that could contribute to thrombosis, including underlying patient condition, ongoing patient and device management practices, pump implantation technique, and device-related factors. We have performed extensive analysis on HeartMate II and have not identified any change that would cause the increase observed in the INTERMACS registry.”
The company pointed out that the INTERMACS analysis showed a consistently high 6-month survival rate (86%) since the device has been on the market, and that the rate is higher than seen in the clinical trials (75%).
After approval, the HeartMate II device became an important treatment option for patients with advanced heart failure — both as a bridge to transplant and as destination therapy. In clinical trials and postmarketing studies, the rate of pump thrombosis associated with its use was 2% to 4%.
However, a clinical quality review at the Cleveland Clinic demonstrated a sudden increase in pump thrombosis starting around March 2011.
In the current study, Starling and colleagues pooled data from the Cleveland Clinic and two other centers — Washington University Barnes-Jewish Hospital, and Duke University Medical Center — to see whether the phenomenon was real. The analysis included 837 patients (mean age 55) who had a total of 895 devices implanted from January 2004 through May 2013.
Overall, 66 patients had 72 confirmed cases of pump thrombosis, defined as “a thrombus found on the blood-contacting surfaces of the HeartMate II, its inflow cannula, or its outflow conduit at pump replacement, urgent transplantation, or autopsy.”
The rise in the rate of confirmed pump thrombosis initially seen at the Cleveland Clinic was consistent across all three centers and multiple surgeons.
The increase was accompanied by a similar rise in elevated levels of lactate dehydrogenase (LDH), which serves as an indicator of hemolysis caused by thrombus formation in the pump. LDH levels went up from an average of 540 IU per liter to 1,490 IU per liter in the 6 weeks leading up to a confirmed case of pump thrombosis.
Various strategies were used to manage pump thrombosis: urgent heart transplantation in 11 cases, pump replacement in 21 cases, pump removal in two cases, and medical management in 38 cases.
Patients who had a transplant or a pump replacement for thrombosis had a 6-month mortality rate similar to that seen in patients who didn’t have pump thrombosis. However, nearly half of patients who did not undergo transplantation or have their pump replaced (48.2%) died within 6 months.
“We know that this is a potentially very serious, life-threatening complication and when applicable we tend to move quickly to pump replacement or transplantation if that’s applicable to the patient,” Starling said.
He said the issue of increasing pump thrombosis has changed how patients with the devices are currently managed.
LDH levels are measured consistently to watch for increases that suggest pump thrombosis, and anticoagulation is performed more carefully, he said.
“I think that we and other centers in general relaxed … to some degree our anticoagulation based on some reports that appeared in the literature,” Starling said. “And we’ve gone back to following the manufacturer’s recommendations completely: running the INRs between 2 and 3, using baby aspirin, [and] starting heparin 24 hours postop and not letting the patient come off heparin until the INR is therapeutic.”
In addition, a new echocardiographic evaluation called a ramp test is commonly used to check for pump thrombosis in suspected cases.
Starling reported relationships with Thoratec — which makes the HeartMate II device — and HeartWare. His co-authors reported relationships with Thoratec, HeartWare, Abiomed, and Syncardia.
Primary source: New England Journal of Medicine
Source reference: Starling R, et al “Unexpected abrupt increase in left ventricular assist device thrombosis” N Engl J Med 2013; DOI: 10.1056/NEJMoa1313385.
Todd Neale, MedPage Today Staff Writer, got his start in journalism at Audubon Magazine and made a stop in directory publishing before landing at MedPage Today. He received a B.S. in biology from the University of Massachusetts Amherst and an M.A. in journalism from the Science, Health, and Environmental Reporting program at New York University.
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