Subaortic pannus causing complete outlet obstruction after bioprosthetic aortic valve replacement in a patient with left ventricular assist device: a case report.

BACKGROUND

Subaortic pannus formation complicates bioprosthetic aortic valve (AV) replacement. We report an extreme case in a continuous-flow left ventricular assist device (LVAD) patient.

CASE SUMMARY

A 49-year-old Caucasian female with dilated cardiomyopathy was bridged to transplant with a HeartWare Ventricular Assist Device (Medtronic). Duration of support was prolonged, 6 years & 7 months, due to allosensitization requiring desensitization. Pump thrombosis occurred 2 years & 4 months post-LVAD requiring alteplase thrombolysis. The patient underwent bioprosthetic AV replacement 3 years & 10 months post-LVAD for symptomatic aortic incompetence. Transthoracic echocardiography (TTE) performed 1 year and 2 years post-bioprosthetic AV replacement repeatedly demonstrated an AV closed during all cardiac cycles without incompetence and nil flow through the left ventricular outflow tract (LVOT). Following transplant, analysis of explanted heart revealed a fused AV. A pannus adherent to the underside of the AV had formed across the entire AV outlet, with complete obliteration of LVOT. This subaortic pannus was not visualized on previous TTE. Histologically, the pannus consisted of hypocellular fibrous tissue with chronic inflammatory cells, spindle histiocytes, and myofibroblasts scattered throughout the loose fibromyxoid stroma, the latter highlighted on CD68 immunohistochemical stain (IHC). Partial endothelialization on the pannus surface was highlighted on ERG and CD31 IHC. Neither calcification nor signs of acute inflammation were noted. In contrast to previous cases, there was no evidence of associated thrombus macroscopically or microscopically.

DISCUSSION

Prolonged LVAD support may facilitate subaortic pannus following bioprosthetic AV replacement due to AV closure and altered transvalvular flow. Due to the parallel LVAD circulation, subaortic pannus may develop asymptomatically, without haemodynamic compromise, allowing progression to total LVOT obstruction. This requires consideration prior to LVAD explantation in bridge-to-recovery patients.