Echocardiographic assessment of right ventricular systolic function in conscious healthy dogs following a single dose of pimobendan versus atenolol.

OBJECTIVE: To quantify drug-induced changes in right ventricular (RV) systolic function after administration of pimobendan and atenolol.

ANIMALS: 80 healthy privately-owned dogs.

METHODS: Using a prospective, blinded, fully-crossed study design with randomized drug administration, RV systolic function was determined twice at two time periods; before and 3 h after administration of pimobendan (0.25 mg/kg PO) or atenolol (1 mg/kg PO). Indices of RV systolic function included tricuspid annular plane systolic excursion (TAPSE), fractional area change (FAC), pulsed-wave tissue Doppler-derived systolic myocardial velocity of the lateral tricuspid annulus (S'), and speckle-tracking-derived global longitudinal RV free wall strain and strain rate. The effect of treatment on percent change from baseline RV function was analyzed with a linear mixed model including the covariates heart rate, body weight, age, gender, drug sequence, and time period.

RESULTS: All indices showed a significant (p < 0.0001) increase and decrease from baseline following pimobendan and atenolol, respectively. Significant differences from baseline were attributed to drug treatment (p < 0.0001); whereas, effects of other covariates were not significant. The greatest percent changes, but also highest variability, were observed for S' and strain rate (p < 0.0001). Post-atenolol, a significantly greater proportion of dogs exceeded the repeatability coefficient of variation for FAC and S' compared to TAPSE (p ≤ 0.007).

CONCLUSIONS: Echocardiographic indices in healthy dogs tracked expected changes in RV systolic function following pimobendan and atenolol and warrant study in dogs with cardiovascular disease.