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 mm2, P = 0.037) and area between papillary muscle tips (162 ± 51 vs 302 ± 75 mm2, P = 0.001) increased substantially while systolic excursion of anterior leaflet decreased significantly (23.8 ± 6.1° vs 7.4 ± 4.5°, P = 0.001) with banding. Total leaflet surface area increased from 806 ± 94 to 953 ± 148 mm2 (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.

Myocardial protection using single dose del Nido Cardioplegia with and without topical cooling.

INTRODUCTION: Del Nido cardioplegia (DN) is gaining acceptance in adult cardiac surgery but there is paucity of experimental data regarding its efficacy. We set out to assess the safety and efficacy of single-dose DN with and without topical cooling (TC) versus multi-dose blood cardioplegia (BC). METHODS: Thirty-two healthy adult sheep had pressure-volume (PV) catheters placed in the left (LV) and right (RV) ventricle. Animals were assigned to receive cold (4°C) antegrade solution for a 60-min arrest using: (1) multi-dose (every 20 min) BC with TC (n = 11), (2) single-dose DN with TC (DN-C, n = 10), or (3) single-dose DN without TC (DN-H, n = 11). LV and RV PV-derived indexes, epicardial echocardiographic strains, and blood samples were acquired before CPB and at 1, 2, and 3 h of reperfusion. Dobutamine bolus (2.5 µg) was given after 3 h to test for myocardial reserve. RESULTS: Time to rhythm restoration was shortest (54 ± 29 s, 118 ± 167 s, and 172 ± 170 s for DN-H, DN-C, and BC, respectively; p = 0.024) and number of shocks lowest (1.7 ± 1.8, 3.6 ± 2.8, and 5.6 ± 4.6 for DN-H, DN-C, and BC, respectively; p = 0.020) in DN-H group. Hemodynamic, load-independent myocardial function, echocardiographic, and metabolic data revealed only slight differences between groups. Troponin I levels did not differ between groups. With dobutamine, preload-recruitable stroke work of both LV (136 ± 50%, 131 ± 31%, 142 ± 58% for BC, DN-C and DN-H, respectively; p = 0.993) and RV (161 ± 67%, 185 ± 45%, 166 ± 75% for BC, DN-C and DN-H respectively; p = 0.580) increased similarly. CONCLUSIONS: Single-dose DN cardioplegia with or without topical cooling offered comparable biventricular myocardial protection to multi-dose BC for a 60-min arrest in sheep.

Impact of reductive tricuspid ring annuloplasty on right ventricular size, geometry and strain in an ovine model of functional tricuspid regurgitation.

OBJECTIVES: Reductive ring annuloplasty of the tricuspid annulus represents the contemporary surgical approach to functional tricuspid regurgitation (FTR). We set out to investigate the influence of moderate reductive tricuspid ring annuloplasty on tricuspid regurgitation and right ventricular (RV) size, geometry and strain in an ovine model of chronic FTR. METHODS: Eight healthy Dorsett male sheep (62.8 + 2kg) underwent a left thoracotomy for placement and tightening of pulmonary artery band to at least double proximal pulmonary artery blood pressure. After 8 weeks of recovery, animals underwent sternotomy, epicardial echocardiography and sonomicrometry crystal implantation. Six crystals were placed around tricuspid annulus and 13 on RV free wall epicardium along 3 parallels defining 3 wall regions (basal, mid and lower) and 1 on the RV apex. All animals underwent beating heart implantation of 26 mm MC3 annuloplasty ring during a second cardiopulmonary bypass run after baseline data acquisition. Simultaneous haemodynamic, sonomicrometry and echocardiography data were acquired at Baseline and after reductive tricuspid ring annuloplasty. RESULTS: Implantation of reductive ring annuloplasty resulted in 47 ± 7% annular area reduction (996 ± 152 mm vs 516 ± 52 mm2, P = 0.0002) and significantly decreased RV end-diastolic volume (185 ± 27 vs 165 ± 30 ml, P = 0.02). Tricuspid ring annuloplasty effectively reduced FTR grade (3.75 ± 0.6 vs 0.3 ± 0.5, P = 0.00004) and had little influence on RV function, cross-sectional area, radius of curvature or free wall regional strains. CONCLUSIONS: In adult sheep with 8 weeks of pulmonary artery banding and FTR, tricuspid annulus reduction of 47% with prosthetic ring annuloplasty effectively abolished FTR while maintaining regional RV function and strain patterns.