BackgroundPimobendan is widely used for the treatment of dogs with heart failure via the oral route. A new injectable form of pimobendan is now available and its potential usefulness via intravenous route has been recently demonstrated in dogs. However, the cardiovascular effects of intramuscular (IM) administration of injectable pimobendan have not been investigated yet.HypothesisIM administration of pimobendan may have the same hemodynamic effect as the IV route.MethodsSix healthy Beagle dogs underwent a placebo-controlled double-blind crossover study. The early cardiovascular effects after a single dose of IM and IV injections of pimobendan (0.2 ml/kg; Pimo IM and Pimo IV, respectively) were compared to the same volume of IM placebo (Saline IM) in anesthetized dogs. Clinical [heart rate (HR) and blood pressure (BP)] and echocardiographic hemodynamic parameters [left ventricular (LV) inflow waveforms of diastolic early wave (eV), atrial systolic wave (aV), diastolic early mitral ring velocity (e′), peak velocity (pV), stroke volume (SV), cardiac output (CO), and systemic vascular resistance (SVR)] were monitored with 15 min intervals for 120 min.ResultsDiastolic BP decreased significantly at 30 min in Pimo IM compared to Saline IM. Mean eV and CO values significantly increased from 75 min, e′ from 60 min, pV from 75 min, and SV from 15 to 120 min, whereas SVR significantly decreased at 30–60 min in Pimo IM compared to those of Saline IM (P < 0.05). Compared with the Pimo IV, eV and pV were significantly lower at 30–60 min (P < 0.05) while SV was significantly higher at 90–105 min in Pimo IM (P < 0.05). Other hemodynamic parameters (BP, HR, SVR, CO, e′, and E/e′) did not significantly change between Pimo IM and IV.ConclusionsThe hemodynamic effect of pimobendan following IM and IV injection was described. Our results suggested that IM administration of pimobendan is equally comparable and possibly interchangeable with IV administration. This warrant further studies to investigate the clinical effectiveness of IM pimobendan in treating dogs with congestive heart failure or in heart failure cases unable to receive IV or oral administration.

Background: Pulmonary arterial (PA) wave reflection provides additional information for assessing right ventricular afterload, but its applications is hampered by the need for invasive pressure and flow measurements. We tested the hypothesis that PA pressure and flow waveforms estimated by Doppler echocardiography could be used to quantify PA wave reflection.Methods: Doppler echocardiographic images of tricuspid regurgitation and right ventricular outflow tract flow used to estimate PA pressure and flow waveforms were acquired simultaneously with direct measurements with a dual sensor-tipped catheter under various hemodynamic conditions in a canine model of pulmonary hypertension (n = 8). Wave separation analysis was performed on echo-Doppler derived as well as catheter derived waveforms to separate PA pressure into forward (Pf) and backward (Pb) pressures and derive wave reflection coefficient (RC) defined as the ratio of peak Pb to peak Pf.Results: Wave reflection indices by echo-Doppler agreed well with corresponding indices by catheter (Pb: mean difference = 0.4 mmHg, 95% limits of agreement = −4.3 to 5.0 mmHg; RC: bias = 0.13, 95% limits of agreement = −0.25 to 0.26). RC correlated negatively with PA compliance.Conclusion: This echo-Doppler method yields reasonable measurement of reflected wave in the pulmonary circulation, paving the way to a more integrative assessment of pulmonary hemodynamics in the clinical setting.

Background: Pulmonary arterial (PA) wave reflection provides additional information for assessing right ventricular afterload, but its applications is hampered by the need for invasive pressure and flow measurements. We tested the hypothesis that PA pressure and flow waveforms estimated by Doppler echocardiography could be used to quantify PA wave reflection. Methods: Doppler echocardiographic images of tricuspid regurgitation and right ventricular outflow tract flow used to estimate PA pressure and flow waveforms were acquired simultaneously with direct measurements with a dual sensor-tipped catheter under various hemodynamic conditions in a canine model of pulmonary hypertension (n=8). Wave separation analysis was performed on echo-Doppler derived as well as catheter derived waveforms to separate PA pressure into forward (Pf) and backward (Pb) pressures and derive wave reflection coefficient (RC) defined as Pb divided by Pf.Results: RC by echo-Doppler agreed well with RC indices by catheter (RC: bias = 0.13, 95% limits of agreement = -0.25 to 0.26). RC correlated negatively with pulmonary arterial compliance and right ventricular systolic function. Conclusions: This echo-Doppler method yields accurate measurement of reflected wave in the pulmonary circulation, paving the way to a more integrative assessment of pulmonary hemodynamics in the clinical setting.