Tissue Doppler Imaging and Two-Dimensional Speckle Tracking of Left Ventricular Function in Healthy Horses After Clenbuterol Application

The cardiac effects of high dosages of the ß²-adrenergic agent clenbuterol have been the focus of several histological, biochemical and echocardiographic studies in the past. Possible effects of a therapeutic dosage on myocardial contractility and velocities have not been evaluated using tissue Doppler imaging (TDI) and two-dimensional speckle tracking (2DST) in equine medicine. Twenty-five healthy horses were treated over 14 days with clenbuterol in a normal dosage (0.8 μg/kg every 12 hours). Before and after the treatment, an echocardiographic examination was performed using B-mode, M-mode, color flow Doppler, and tissue Doppler imaging (TDI). In all horses, the radial and circumferential myocardial functions were recorded in the right parasternal short-axis view (SAX). Pulsed-wave (PW) and color TDI were used for evaluation of peak and mean myocardial velocities; myocardial deformation was documented in 2DST. An improvement of diastolic function after clenbuterol treatment was demonstrated by a significant increase of the early diastolic radial wall motion velocity (E_m) in all myocardial sections except the right ventricular free wall (RVFW) in TDI, as well as an increase of the E/A quotient in the left ventricular free wall (LVFW) and the interventricular septum (IVS). Shortened time intervals, in particular in the LVFW and a tendency of increase of all deformation parameters showed improved relaxation characteristics of the cardiac muscle after treatment. The results can be interpreted as beginning physiologic cardiac hypertrophy due to clenbuterol treatment. No signs of increased rigidity or reduced compliance of the heart muscle could be found at the applied dosage. This study demonstrates the sensitivity of TDI and 2DST in equine cardiology to detect myocardial remodeling before the appearance of obvious findings in conventional echocardiographic techniques. This technique can be used to detect pharmacologic effects on myocardial function.