Valvular complex and tissue remodelling in ovine functional tricuspid regurgitation

OBJECTIVES: Pathophysiology of function tricuspid regurgitation (FTR) is incompletely understood. We set out to comprehensively evaluate geometric and tissue remodelling of the tricuspid valve complex in ovine FTR. METHODS: Twenty adult sheep underwent left thoracotomy and pulmonary artery banding (PAB) to induce right heart pressure overload and FTR. After 8 weeks, 17 surviving animals and 10 healthy controls (CTL) underwent sternotomy, echocardiography and implantation of sonomicrometry crystals on right ventricle and tricuspid valvular apparatus. Haemodynamic and sonomicrometry data were acquired in all animals after weaning from cardiopulmonary bypass. Leaflet tissue was harvested for pentachrome histologic analysis and biomechanical testing. RESULTS: Animal weight was 62 +/- 5 and 63 +/- 3 kg for CTL and PAB, respectively (P = 0.6). At terminal procedure, systolic pulmonary artery pressure was 22 +/- 3 and 40 +/- 7 mmHg for CTL and PAB, respectively (P = 0.0001). The mean TR grade (+0-4) was 0.8 +/- 0.4 and 3.2 +/- 1.2 (P = 0.0001) for control and banded animals, respectively. Right ventricle volume (126 +/- 13 vs 172 +/- 34 ml, P = 0.0019), tricuspid annular area (651 +/- 109 vs 865 +/- 247 mm(2), P = 0.037) and area between papillary muscle tips (162 +/- 51 vs 302 +/- 75 mm(2), P = 0.001) increased substantially while systolic excursion of anterior leaflet decreased significantly (23.8 +/- 6.1 degrees vs 7.4 +/- 4.5 degrees, P = 0.001) with banding. Total leaflet surface area increased from 806 +/- 94 to 953 +/- 148 mm(2) (P = 0.009), and leaflets became thicker and stiffer. CONCLUSIONS: Detailed analysis of the tricuspid valve complex revealed significant ventricular, annular, subvalvular and leaflet remodelling to be associated with ovine functional tricuspid regurgitation. Durable surgical repair of severe FTR may require a multi-level approach to the valvular apparatus.