Effect of pimobendan on right-heart remodeling in dogs with tricuspid valve dysplasia: an exploratory study

Introduction Tricuspid valve dysplasia (TVD) is a rare congenital heart defect in dogs often resulting in severe tricuspid valve regurgitation (TR). No guidelines for medical therapy have been established for dogs with severe TR. Tricuspid valve repair surgery is available for dogs but carries a moderate risk and high cost. This exploratory study evaluated the effect of oral pimobendan on chamber sizes and remodeling of the right side of the heart in dogs with TVD. Methods Retrospective echocardiographic data from ten dogs with TVD and severe TR were retrieved. All dogs received oral pimobendan (range 0.21–0.31 mg/kg Q12h) for an average of 18 months (range 3–41). The right atrial (RA) diameter, RA area, right ventricular (RV) diameter, RV area and fractional area change, tricuspid annular plane systolic excursion (TAPSE), and dimension of the tricuspid valve annulus (TVA) were quantified, and compared before and at a median of 3 months after starting pimobendan therapy. Results All dogs had severe TR. The normalized RV diameter and TVA decreased after pimobendan administration [1.40 → 1.27 (SD 0.23), p = 0.027; 11.77 → 10.58 (SD 1.95), p = 0.01]. No significant changes in RA area, RA diameter, RV area, TAPSE, peak TR velocity, or RV fractional area change were present after pimobendan therapy (all p > 0.08). No dogs in this study population progressed to right-sided congestive heart failure during the follow-up period. Conclusions and clinical importance Pimobendan reduced the size of the right ventricle and diameter of the tricuspid annulus compared to baseline, which may limit progression of disease in dogs with TVD with severe TR.