Patients treated with the HeartMate II left ventricular assist device (LVAD) may be at higher risk for device thrombosis, based on the findings of a study published online Nov. 27 in the New England Journal of Medicine. Researchers found an increase in the number of thromboses compared with the results of pre-approval clinical trials.

The device became a key component of treatment for advanced heart failure, but a review of data at one center found a sudden increase in thromboses, explained the authors, led by Randall C. Starling, MD, MPH, of the Cleveland Clinic in Ohio. To determine whether these were isolated incidents, the investigators combined data from two other centers to determine the number of device thrombosis cases and of elevated lactate dehydrogenase (LDH), its biomarker.

There were 895 HeartMate II (Thoratec) devices implanted in 837 patients at the Cleveland Clinic, Washington University Barnes-Jewish Hospital and Duke University Medical Center.

There were a total of 72 thromboses in 66 patients and 36 others were suspected. The incidence of device thrombosis increased from 2.2 percent to 8.4 percent three months after implantation. Thromboses happened quicker between March 2011 and January 2013—before March 2011, thrombosis happened an average of 18.6 months after implantation and after March 2011, the average time dropped to 2.7 months.

Elevated LDH levels followed a similar pattern. LDH elevation more than doubled prior to thrombosis, from 540 international units per liter (IU/L]) to 1,490 IU/L in the weeks before diagnosis.

These incidents led to significant morbidity and mortality. There were 11 patients who required heart transplants and 21 who needed pump replacement. Among 40 thromboses in 40 patients who did not undergo either a transplant or a replacement, mortality was 48.2 percent within six months after thrombosis.

Starling and colleagues noted that their data differed from an analysis done by the Interagency Registry for Mechanically Assisted Circulatory Support (INTERMACS), a registry that gathers clinical data from patients with circulatory support devices. INTERMACS found that cases of thrombosis increased from 2 percent before May 2011 to 5 percent after that month. The differences, the authors explained, may be due to underdiagnosed pump thrombosis prior to 2011 and the possibility that elevated LDH did not always lead to clinically obvious device thrombosis.

They stressed the need for a closer look into patient and device variables that could put patients at risk as well as ways to prevent this type of incident.

“We recognize that LVADs provide life-sustaining treatment for many patients with advanced heart failure,” the authors wrote. “However, recommendations for LVAD therapy should account for this updated risk-benefit profile.”