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Continuous-flow left ventricular assist devices (LVADs), used to bridge many heart patients to transplant, may be associated with changes in coagulation factors that increase the risk of bleeding, researchers said.

Unlike earlier pulsatile machines, use of continuous-flow LVAD devices require anticoagulation medications, but that doesn't account for the greater number of bleeding incidents associated with them, according to Donna Mancini, MD, of Columbia University in New York City, and colleagues.

Instead, decreased or absent high molecular weight von Willebrand factor multimers appear to be playing a role, Mancini and colleagues said online in the Journal of the American College of Cardiology.

"The role of these abnormalities in the high incidence of bleeding deserves further investigation," they wrote in their retrospective study of almost 80 LVAD patients. The authors called for a randomized, multicenter, prospective trial to find the best anticoagulation regimen for patients supported with continuous-flow devices.

Clinical trials have shown that the continuous-flow LVAD devices offer good hemodynamic support and a favorable risk-benefit picture, both for patients heading for transplant and those who will use the device as destination therapy, the researchers said.

But, at the same time, thromboembolic events are frequent, making anticoagulation a necessity, they commented, adding there is some evidence the increased incidence of bleeding can't be blamed entirely on the medications.

To help clarify the issue, Mancini and colleagues conducted a retrospective chart review of all patients who got a continuous-flow LVAD device -- the HeartMate II, manufactured by Thoratec of Pleasanton, Calif. -- between April 1, 2004, and Aug. 1, 2009 at a single large medical center.

Major bleeding was defined as the need for one unit of packed red blood cells more than seven days after the device was inserted. Also, transfusion at transplant was compared with transfusions in patients with the earlier generation HeartMate XVE.

All told, 79 patients (average age 56) had the device implanted -- with 64 intended to go on to transplant and 15 receiving the LVAD as destination therapy, the researchers said.

During the support period, 44 patients had no significant bleeding episodes and 35 patients (or 44.3%) had major bleeding episodes.

Bleeding was more common among older patients (60.1 years on average compared with age 53.4) and those whose heart failure was caused by ischemic cardiomyopathy (58.8% versus 33.3%). Both differences were significant at P=0.03.

Additionally, 61.8% of those with major bleeding had hypertension compared with 46.4% of those who did not have major bleeding, a difference that was significant at P=0.026.

Thirty-five patients with a HeartMate II had a transplant, and their blood product requirements were twice those of 62 transplant patients who had been supported with a HeartMate XVE, the researchers said.

When HeartMate II patients were compared with the subgroup of HeartMate XVE patients who had been on warfarin, the HeartMate II group still had a higher blood requirement, Mancini and colleagues found, implying that something more than anticoagulation medication was involved.

Thirty-one of the patients with a HeartMate II had been tested for von Willebrand syndrome, 18 after major bleeding events and 13 before anticipated surgery, the researchers said. Of those, all had either decreased or absent high molecular weight forms of von Willebrand factor that are needed for platelet adhesion.

In other words, all 31 met the criterion for acquired von Willebrand syndrome, Mancini and colleagues said.

Study limitations included its small size and that not all patients were screened, so little can be concluded about the incidence and timing of the development of acquired von Willebrand syndrome.

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