Effects of electric stimulations applied during absolute refractory period on cardiac function of rabbits with heart failure.

The effects of electric currents applied during absolute refractory period (ARP) on the cardiac function of rabbits with heart failure due to myocardial infarction (MI), and the safety of this method were investigated. Thirty rabbits were randomly assigned equally to 3 groups: sham-operated group, LV-anterior wall cardiac contractility modulation (LV-CCM) group, and septum-CCM (S-CCM) group. A thoracotomy was performed on all the rabbits. Electric pulses were delivered during the ARP on the anterior wall of left ventricle in CCM group and in the septum in S-CCM group, respectively. The left ventricular systolic pressure (LVSP) and maximum positive left ventricular pressure change (+dp/dt(max)), heart rates, ventricular tachycardia, ventricular fibrillation were observed. It was found that, as compared with the baseline, LVSP, and +dp/dtmax were significantly increased, on average, by 15.2% and 19.5% in LV-CCM group (P<0.05), and by 8.5% and 10.8% in S-CCM group (P<0.05). LVEDP was significantly decreased and -dp/dt(max) increased both in LV-CCM group and S-CCM group (P<0.05). CCM had no effect on heart rate and induced no arrhythmia in short time. It is concluded that electric currents delivered during the ARP could significantly enhance the contractility of myocardium safely, suggesting that CCM stimulation is a novel potent method for contractility modulation.