Effect of pimobendan on myocardial injury and systolic dysfunction in a canine model of supraventricular tachyarrhythmia.

Supraventricular tachyarrhythmia (SVTA) in dogs can cause cardiac dysfunction and may progress to heart failure. Pimobendan, an inotropic agent with calcium-sensitizing and phosphodiesterase III inhibition, is widely used in veterinary medicine. However, its influence on myocardial injury under persistent SVTA remains incompletely understood. This study aimed to evaluate whether pimobendan improves systolic function without exacerbating myocardial injury, using a canine model of rapid atrial pacing (RAP). Fourteen healthy Beagle dogs were allocated to either a control or pimobendan group. RAP was performed for three weeks at 390 bpm. Cardiac function was assessed by echocardiography before (baseline) and after RAP (3W). Concurrently, cardiac troponin I (cTnI) concentrations were measured to assess myocardial injury. In the control group, a significant increase in cTnI was observed at 3W compared with baseline (0.023 ± 0.029 ng/mL vs. 0.176 ± 0.173 ng/mL). Additionally, in the control group, echocardiographic parameters worsened, including fractional shortening (FS) (37.8 ± 4.6% vs. 24.5 ± 6.8%) and stroke volume (SV) (15.8 ± 3.1 mL vs. 10.5 ± 2.0 mL) at 3W compared with baseline. In contrast, the pimobendan group showed no significant differences in these echocardiographic parameters. cTnI concentrations also remained within the normal range without significant differences. These results suggest that pimobendan preserved systolic function without aggravating myocardial injury during sustained SVTA. Pimobendan may therefore be safe and effective cardiac inotropic agent for the treatment of dogs with SVTA.