Use of a Pulmonary Valved Conduit in a Growing Long-Term Animal Model—Mid-term Results

Objectives: We established a chronic animal model to evaluate a tissue engineered valved conduit, connecting the right ventricular outflow tract to the bifurcation of the pulmonary arteries, during long-term follow-up and growth up to 24 months.

Methods: Twelve female Swiss white mountain lambs (27–38 kg) were operated and survived the initial perioperative phase. The native pulmonary valve and the complete pulmonary trunk were resected. The conduit was constructed out of a decellularized porcine small intestinal submucosa extracellular matrix biologic scaffold and was implanted in orthotopic position. Follow-up echocardiography and laboratory values (LDH, Hb, HKT, and WBC) were performed directly after surgery and after 1, 3, 6, 12, 18, and 24 months. Animals planned for euthanasia underwent computed tomography (CT) scan prior to termination and the conduit was histologically examined.

Results: Mean follow-up time is 13 months (20 days–24 months). Four animals were killed as planned at 24 months (n: 2), 12 months (n: 1), and 9 months (n: 1). Two animals died due to endocarditis at days 20 and 256 postoperatively. One animal died due to aspiration pnmeumonia at POD 23. Five animals are still ongoing. Mean weight at last follow-up was 53.4 kg (28–67). Investigation of the conduit by echocardiography revealed no severe stenosis or calcifications (dp max 12.8; ±8.5 [mean; SD]) and no greater than mild regurgitation. LDH increased from a preoperative mean 976 ± 78.2 (mean; SD) (889–1,097) to 1,100 ± 181.8 (mean; SD) (771-1,369) (n.s.). CT scan prior to termination (n: 4) revealed no severe calcification or dilatation of the conduit. Subsequent histologic evaluation revealed a variable degree of incorporation to native tissue between individual valve leaflets. Most were moderately populated by stromal cells and showed endothelialization (confirmed by CD31 immunohistology) and little inflammation within the valve. Small foci of chondroid and osseous metaplasia were occasionally observed, predominantly at the suture sites rather than within the leaflets.

Conclusion: The implantation of a valved RV-PA conduit in a growing animal model is feasible up to 2 years. The animals demonstrated, after the initial recovery phase from surgery, good physical development but remain at risk for endocarditis (16%). The function of the valved conduit was satisfactory up to a follow-up of 24 months.

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