Researchers Identify Biomarker that May Foretell Clot Formation in Heart Pump

A multicenter study published online in the New England Journal of Medicine has found an increase in blood clot formation in the HeartMate II left ventricular assist device (LVAD) compared to trial data and prior experience. LVAD-based clot formation is associated with an increased risk of death.

Data from Cleveland Clinic, Duke University Medical Center, and Washington University Barnes-Jewish Hospital found that clot formation, or thrombosis, is developing more frequently in patients receiving the HeartMate II. Since March 2011, clot formation has occurred in 8.4 percent of implants compared to 2.2 percent prior to that date. Additionally, the researchers found that when clots develop, they are occurring much more rapidly than previously noted, with the median time from implant to thrombosis decreasing from 18.6 months to 2.7 months since March 2011.

The researchers – led by Randall C. Starling, MD, MPH, Vice Chairman of Cardiovascular Medicine and Section Head of Heart Failure and Cardiac Transplant Medicine at Cleveland Clinic – also discovered that elevated levels of lactate dehydrogenase (LDH) in the blood mirrored the incidence of thrombosis in patients. They found that LDH levels more than doubled in the six weeks leading up to the diagnosis of thrombosis, identifying an important biomarker caused by hemolysis, or the destruction of red blood cells. Using LDH as a biomarker, physicians could identify HeartMate II patients who are developing pump thrombosis. Early identification and treatment in these patients might reverse the clotting process.

Dr. Starling and his coauthors examined the outcomes of 895 HeartMate II implants in 837 patients at their three institutions from 2004 to mid-2013. They observed 72 confirmed pump thromboses in 66 patients during that time, with the increase in thromboses occurring around March 2011. Confirmed pump thrombosis was defined as a blood clot found in or on the pump during pump exchange, heart transplant, or autopsy.

Patients who developed clots in their pumps were treated with urgent heart transplant or pump exchange and had a mortality rate equivalent to patients who did not have a clot. Mortality among patients with clotted pumps who did not receive a transplant or pump replacement was 48 percent at 90 days after the diagnosis of pump thrombosis.

“LVADs are important devices in heart failure treatment that have greatly improved the quality of life and survival of thousands of patients – patients who have very few, if any, other treatment options,” said Dr. Starling. “We must continue to rely on LVADs to provide life-sustaining treatment for patients while they wait for a scarce donor heart, and to sustain life in patients not eligible for heart transplant. Physicians and patients should take this updated risk profile into consideration when determining the best treatment course for advanced heart failure.”

Starling and his coauthors call for further research to be undertaken to identify any predisposing patient and device factors contributing to the increased incidence of thrombosis, as well as to investigate preventative and therapeutic strategies for patient management.

The HeartMate II device, manufactured by Thoratec Corp., is a mechanical heart pump used in the treatment of advanced heart failure. The device assists the heart’s pumping function by circulating blood in a continuous flow through the vascular system. The device is used primarily in patients in the late stages of heart failure to keep them alive until an organ becomes available for transplant. HeartMate II is also approved in the United States for use as destination therapy, or a permanent solution, in patients who are ineligible for a heart transplant.

This study began when physicians at Cleveland Clinic observed an apparent increase in device thrombosis in patients who received the HeartMate II. A subsequent Cleveland Clinic internal quality review revealed an abrupt increase in HeartMate II device thrombosis. At this point, the initial Cleveland Clinic findings were immediately reported to Thoratec and the FDA. To confirm and strengthen the findings for scientific publication, data from two additional experienced LVAD centers were pooled and similar results were found.

Dr. Starling has consulted for Thoratec Corp. but instructed them to donate all compensation to not-for-profit causes or to the Cleveland Clinic to support research and education.