We hypothesized that chronic afterload may reduce myocardial function, and that two-dimensional speckle-tracking echocardiography (2D-STE) could quantitatively evaluate myocardial function. Five canine models with experimentally induced chronic afterload (aortic binding) were used. Dogs were examined for systolic myocardial deformations using 2D-STE prior to and 3 and 6 months after chronic afterload induction. We evaluated the peak systolic strain and strain rate in the longitudinal, circumferential, and radial directions. Only the longitudinal strain rate was reduced at 3 month. Longitudinal deformation by 2D-STE may provide more detailed assessment of myocardial function in dogs with chronic afterload.
A 15-year-old castrated male Shih Tzu (weight 8.5 kg) with myxomatous mitral valve disease ingested 8.24 mg/kg of pimobendan (approximately 33 times the recommended dose). On presentation, tachycardia and systemic hypertension were observed. Echocardiography revealed systolic anterior motion of the mitral valve (SAM) and increased fractional shortening. Electrocardiography revealed an increased T wave to R wave amplitude ratio (T/R). SAM disappeared 12 hr after hospitalization. T/R normalized after 24 hr, although the mechanism of the increase in this ratio and its clinical significance remain unclear. Systemic hypertension disappeared 36 hr after hospitalization. These findings suggest that it is necessary to monitor T/R, SAM, and systemic hypertension in dogs who have ingested a large amount of pimobendan.