The Western Thoracic Surgical Association

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Right Ventricular Free Wall Stress After Tricuspid Valve Annuloplasty in Acute Ovine Right Heart Failure
Tomasz Jazwiec, Marcin Malinowski, Jared Bush, Matthew Goehler, Nathan Quay, Tomasz A. Timek
Spectrum Health, Grand Rapids, MI

BACKGROUND: Contemporary repair of functional tricuspid regurgitation (FTR) is centered on annular reduction with prosthetic rings, yet there is no consensus which annular device is optimal for maintenance of valvular competence and ventricular geometry. Annuloplasty prostheses may have a variable impact on right ventricular (RV) shape and free wall stress (RV-FWS) and therefore differentially affect chamber remodeling and recurrent FTR. In an acute model of ovine right heart failure, we set out to investigate RV-FWS after ring annuloplasty with different prostheses.
METHODS: In 36 healthy sheep (607kg) while on cardiopulmonary bypass (CPB) and with the heart beating, 6 sonomicrometry crystals were implanted around the tricuspid annulus, 1 on each papillary muscle, 4 on the mid RV free wall, and 1 at the RV apex. Pressure sensors were placed in the left, right ventricle, and right atrium. Each study group consisted of nine animals and underwent tricuspid valve annuloplasty with flexible (FLX; 281mm), rigid (RIG; 291 mm) or flexible-rigid hybrid (HYB; 281 mm) ring. The remaining nine animals had no ring implanted and served as controls (CTL). Animals were studied open chest after weaning from CPB and hemodynamic stabilization. Acute right heart failure (ARHF) was induced by pneumatic occlusion of the pulmonary artery to increase RV pressure (RVP) 50% above baseline and concurrent snare occlusion of posterior descending coronary artery. Simultaneous hemodynamic, sonomicrometry, and epicardial echocardiographic data were collected before (baseline) and after induction ARHF for CTL group and with ARHF in all ring groups. RV-FWS was calculated using the modified Laplace formula for thick shells and RV cross sectional area (RV-CSA) and volume were determined from 3D marker coordinates. Geometrical data were indexed to individual body weight and then normalized to the mean weight of all animals. Statistical analyses were performed using one-way ANOVA or a Kruskal-Wallis Analysis, depending on assumptions being met. When the overall tests were found to be significant (p<0.05), pairwise comparisons with a Bonferroni correction were applied.
RESULTS: Table summarizes hemodynamic, echocardiographic, and sonomicrometry data for all study groups. ARHF reduced RV fractional volume change while increasing RVP, tricuspid regurgitation grade, RV-CSA, and RV-FWS in CTL animals versus baseline. During acute right heart failure, all rings significantly decreased RV-FWS versus CTL at both end-diastole and end-systole except RIG at end-systole. There was no significant difference in RV-FWS or tricuspid regurgitation between any ring group and baseline CTL. No significant difference in RV-FWS between FLX, RIG, and HYB rings was observed.
CONCLUSIONS: In normal sheep hearts, acute right heart failure significantly increased RV-FWS which was normalized with equal efficacy by all studied annuloplasty prostheses. Chronic studies of right ventricular failure are needed to evaluate long-term effects of annular prostheses on RV free-wall stress and remodeling and valvular insufficiency.
Table

GroupBaselineAcute Right Heart Failure P value
CTL CTL (n=9)FLX (n=9)RIG (n=9)HYB (n=9)
RV-FVC (%)18 311 319 321 724 70.003
RVP MAX (mmHg)26 441 641 840 643 60.019
RVPED (mmHg)7 317 77 27 26 20.008
TR Grade (0-4)0.5 0.53.2 1.00.9 0.60.6 0.71.6 1.1<0.001
RV-CSA (cm2)
ED24 328 420 322 222 4<0.001
ES18 323 415 217 217 20.002
RV-FWS (kPa)
ED3.1 1.89.1 4.92.4 0.92.6 0.92.5 0.80.028
ES4.4 1.47.2 2.34.1 0.95.1 0.84.9 1.30.027
Values are means SD; RV: right ventricle; RV-FVC: RV fractional volume change; RVP: RV pressure; RV-CSA: RV cross-sectional area; RV-FWS: RV free wall stress; TR: Tricuspid regurgitation; ED: end-diastole; ES: end-systole; MAX: Maximum


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