Physiologic and Pathologic Changes in Patients with Continuous-Flow Ventricular Assist Devices

Abstract

The clinical use of the newer continuous-flow pumps for mechanical circulatory support have resulted in superior outcomes including significantly reduced complication rates with improved durability over first generation pulsatile design pumps. However, as with all new technology, the newer LVADs have introduced a different set of management issues, as well as a unique risk profile into the mechanical circulatory support arena that were previously absent or unimportant with pulsatile LVADs. These include the effects of continuous flow on the systemic circulation and end-organ function, risk of thromboembolism, and pump thrombosis related to contact bearings in the blood path, the possible increased incidence of gastrointestinal bleeding, and ventricular arrhythmias, as well as alterations in the unloading characteristics of continuous-flow devices. This manuscript overviews the physiologic and pathologic effects that are associated with continuous-flow pumps and their unique management issues and complications.

Mechanisms of Bleeding and Approach to Patients With Axial-Flow Left Ventricular Assist Devices

“…It also binds to platelet receptors to induce activation, adhesion, and aggregation. 22 Homeostasis of the vWF multimer size is necessary to prevent a pathological coagulopathy and is primarily regulated by the cleavage activity of the metalloprotease ADAMTS13. ADAMTS13 is a protease that binds to and cleaves the vWF protein at a specific site (the A2 domain) that is buried in the tertiary structure of the protein until the molecule unfolds.…”

“…One potential explanation for the acquired von Willebrand disease invokes high shear stress across the calcified aortic valve, inducing a conformational change on the vWF multimers and predisposing them to proteolytic cleavage. 10 Another contributing factor is increased intraluminal pressure within the vasculature and the lowered pulse pressure, 22 which is discussed in detail later in this review. Because axial-flow LVAD physiological characteristics involve high shear stress and narrow pulse pressures, it is intriguing that patients treated with contemporary LVADs have bleeding patterns similar to those described with severe aortic stenosis.…”

“…This is especially true because HMW vWF multimers are essential for platelet-mediated hemostasis in high shear stress areas, such as GI tract malformations and AVMs (Figure 2). 10,22 Unfortunately, although modification in antiplatelet and anticoagulation regimens may mitigate some of the bleeding risk associated with angiodysplasia, the rate of development of new AVMs with continuous flow has not been well established. Therefore, it is unclear whether an isolated bleeding episode from AVMs predicts future bleeding events in either the GI tract or even the cerebral circulation.…”

Cost of Ventricular Assist Devices

“…The field has evolved from large devices that created pulsatile flow like the human heart delivering a normal stroke volume with each mechanical contraction of the pump to small, fully implantable continuous flow devices that move blood continuously. [18][19][20] In 2001, the Randomized Evaluation of Mechanical Assistance in the Treatment of Congestive Heart Failure (REMATCH) trial established the superiority of a pulsatile flow VAD to medical treatment of patients with advanced HF who were ineligible for cardiac transplantation. 9 The favorable outcomes of REMATCH resulted in Food and Drug Administration approval the HeartMate XVE (Thoratec Corporation, Pleasanton, CA) as DT.…”

Arteriovenous malformation and gastrointestinal bleeding in patients with the HeartMate II left ventricular assist device

“…Among these issues may be a potential for gastrointestinal (GI) bleeding. 1,2 GI bleeding is not uncommon in critically ill patients who require intensive support and LVAD therapy. There appears to be a small increase in GI bleeding associated with continuous-flow LVAD support.…”