Discussion
As shown in analyses of the randomized unblinded trial (Multicenter Study of MagLev Technology in Patients Undergoing Mechanical Circulatory Support Therapy with HeartMate 3 [MOMENTUM 3]), the design of HeartMate 3 LVAD results in enhanced hemocompatibility and lower risk of pump thrombosis and reoperations to replace or remove the pump compared with axial-flow LVADs.(1,2) . However, outflow graft occlusion may lead to acute hemodynamic compromise, hence prompt diagnosis and treatment are imperative to avert poor outcomes. The mechanisms involved in ouflow cannula obstruction include twisting of the outflow graft, intraluminal obstruction or extrinsic compression.(5) Duero Posada et al reported two patients who developed a thrombus between the outflow graft and bend relief that caused extrinsic compression provoking near total occlusion and hemodynamic compromise leading to urgent cardiac transplantation. (6) In our case, the obstruction occurred at the level of the bend relief and consisted predominantly of chronic inflammatory with evidence of foreign body reaction. In an analysis of 26 HVAD outflow grafts tissue ingrowth was present in 24 (92%). The most common site was distal anastomosis with microscopic evidence of chronic inflammatory infiltrates, giant cells, neointima formation and fibrosis. The median depth of tissue was 1 mm leading to reduced pump flow that didn’t translate into hemodynamic comprise. (7)
Our case highlights the morbidity and mortality associated with outflow cannula occlusion. Albeit infrequent, outflow cannula occlusion should be suspected in LVAD recipients with low flows, normal LDH, and evidence of poor LV unloading and decreased cardiac output. For patients with LVADs as bridge to transplantation, upgrade to higher listing status and hemodynamic support with inotropes or temporary mechanical support are viable options. Alternatively, replacement of outflow graft, LVAD exchange or in patients with prohibitive surgical risk, bend relief dissection and liberalization of the proximal outflow cannula through subcostal incision, and percutaneous endovascular stenting have been reported(9,10). The severity of pulmonary complications and multi-organ failure precluded those approaches in our patient.
Recognizing the mechanism of obstruction of the outflow graft is key to dictate appropriate therapeutic strategies and prevent complications. The role of foreign body reaction as a potential contributor of outflow graft obstruction at the level of the bend relief should be confirmed by careful histopathologic analysis of explanted left ventricular assist device systems.