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.