Echocardiographic Assessment of Cardiac Function

Echocardiography was performed blindly using the Vevo 770 High-Resolution Micro-Imaging System (Visual Sonics) with a 15 MHz linear-array ultrasound transducer. The left ventricle was assessed in both parasternal long-axis and short-axis views at a frame rate of 120 Hz. End-systole or end-diastole were defined as the phases in which the left ventricle appeared the smallest and largest, respectively, and used for ejection-fraction measurements. To calculate the shortening fraction, left-ventricular end-systolic and end-diastolic diameters were measured from the left-ventricular M-mode tracing with a sweep speed of 50 mm/s at the papillary muscle as previously reported^{47 (link)}. Imaging and calculations were done by an individual who was blinded to the treatment applied to each animal and this code was broken only after all data was acquired. At the end of the experiments, Animals were sacrificed by barbiturate overdose (150 mg/kg pentobarbital sodium, intraperitoneal injection) and cervical dislocation, and their hearts harvested for histological studies.