Pacing the heart : Is it a must in studying mycardial contractile function in isolated hearts perfused using the langendorff system

Background: Myocardial contractile function has been studied extensively in isolated hearts using the Langendorff System. The effects of changing the heart rate on myocardial contractility have not been described. The aim of the present study was to examine the effects of changing the heart rate on studying myocardial contractility in isolated heart models using the Langendorff System, and to determine whether pacing the hearts is required. Methods: Male Sprague Dawley rats were used. Hearts were harvested and perfused using the Langendorff System. Hearts were assigned to either paced or unpaced groups. Hearts were paced at 5 Hz that is 300 beats per minute using an electrical stimulator using a 6020 Stimulator from Harvard Apparatus. Myocardial contractility was measured with a balloon-tipped catheter inserted into the left ventricle via the mitral valve and at constant coronary flow. Indices of left ventricular function were measured Results: The hearts paced showed an increase in left ventricular end-diastolic pressure at 45 and 60 minutes of perfusion (p<0.05) compared to the unpaced hearts. Left ventricular peak systolic pressure was significantly higher in the unpaced group compared to the paced group throughout the one-hour of experimental protocol (p<0.05). In the paced hearts there was a decrease in the generated pressure at the 45 and 60 minute perfusion time (p