Continuous flow left ventricular assist devices and gastrointestinal bleeding.

Sir,

Patients with ventricular assist devices (VAD) encounter multiple complications, of which bleeding should be a major concern. Cardiovascular anesthesiologists, cardiac surgeons, and intensivists need to be cognizant of risks and outcomes secondary to bleeding in recipients of these devices. Bleeding was described as the second most common complication in VAD patients.[1] A retrospective study compared the incidence of bleeding in pulsatile (HeartMate®XVE) and continuous flow (HeartMate®II) devices used as “bridge therapy” in patients undergoing heart transplantation, and found the incidence of perioperative bleeding to be higher in patients bridged with continuous flow devices.[2] Other authors evaluated the influence of the technology of continuous flow devices on the coagulation system in a retrospective analysis, found bleeding to be prominent, and diagnosed acquired von Willebrand syndrome type 2 in all patients.[3] Bleeding abnormalities in VAD recipients could be modeled on the observation described by Dr. Heyde in patients with aortic valve stenosis (Heyde's syndrome). Dr. Heyde first described an association of aortic valve stenosis and gastrointestinal bleeding from colonic angiodysplasia. In addition to the proposed underlying mechanism of mucosal ischemia, which is attributed to the decreased pulse pressure of significant aortic stenosis, that leads to the formation of friable new vessels likely to bleed, acquired von Willebrand syndrome type 2 (loss of the largest von Willebrand factor (vWF) monomers) was observed impaired platelet aggregation has been described as a cause of bleeding in VAD patients, and this too is associated with the absence of large vWF monomers.[4] Additionally, primary hemostasis is a concern in these patients, because of their medication regimen that includes platelet inhibitors and anticoagulation.[3]

Axial flow devices generate a low or non-pulsatile flow, possibly replicating the mechanism in aortic stenosis leading to colonic mucosal ischemia. This, in combination with the high shear stress caused by high impeller speed facilitating the development of acquired von Willebrand disease, might create the ‘perfect setting’ for gastrointestinal bleeding, as observed in HeartMate®II patients. All VAD patients require some degree of anticoagulation to prevent thromboembolic complications; this may differ among the various devices.[5] Although the development of continuous flow devices has allowed a reduction in device size, and an increased durability, infection rates, and thromboembolic complications are still frequent. The anticoagulation protocol for HeartMate®II devices might need to be adjusted to balance the risk of thromboembolic complications and the risk of bleeding, potentiated by the presence of the acquired von Willebrand syndrome. Whether this issue might be resolved in newer generation radial flow devices operating with lower rotational speed, which possibly translates into lower shear stress, needs to be determined in further studies. As continuous flow devices become a mainstay of “bridge to transplant” and “destination therapy,” it is of paramount importance that physicians caring for VAD patients understand the importance of bleeding complications and remain vigilant as to their diagnosis, prevention, and appropriate intervention.