Characterization of global and regional left heart function using advanced echocardiography following intravenous administration of pimobendan in awake dogs

Abstract

Background Pimobendan is commonly used in veterinary cardiology; however, its impact on myocardial deformation in conscious dogs over time remains poorly characterized. Objectives This exploratory and descriptive study aimed to characterize the effects of intravenous pimobendan on left heart function using advanced echocardiography and to identify the myocardial deformation component most closely associated with stroke volume increase. Methods Five healthy, conscious, male Beagle dogs received a single bolus of pimobendan. Conventional echocardiography, tissue Doppler imaging, and 2D speckle-tracking echocardiography were performed at baseline and up to 24 h post-administration. Longitudinal, circumferential, and radial left ventricular strain were assessed, along with left atrial function, stroke volume, and cardiac output. Results Pimobendan induced a significant increase in left ventricular systolic performance. Radial strain increased markedly from 30 min to 6 h, while circumferential strain increased transiently up to 4 h, primarily at the endocardial and mid-myocardial levels. Longitudinal strain increased from 30 min to 8 h, with a pronounced regional effect characterized by a greater enhancement of the apical segment, resulting in an accentuated base-to-apex strain gradient. Stroke volume increased significantly for up to 8 h and showed the strongest statistical association with longitudinal strain, particularly the apical component. Left atrial contractile function also improved transiently following treatment. Conclusion Intravenous pimobendan produces a sustained improvement in left heart function in healthy, conscious, male Beagle dogs. The increase in stroke volume was most strongly associated with longitudinal myocardial deformation, especially at the apical level. Confirmation in females, other breeds, different age groups, and cardiac patients is warranted.