Vagal stimulation markedly suppresses arrhythmias in conscious rats with chronic heart failure after myocardial infarction

Our previous study showed that chronic vagal stimulation (VS) prevented the cardiac remodeling and improved the prognosis of chronic heart failure (CHF) rats after large myocardial infarction (MI). Antiarrhythmic effects of VS were assumed to produce such a beneficial outcome. Therefore, we examined the effects of VS on cardiac arrhythmias. The ECG transmitter and a radio-controlled stimulator were implanted in the healed MI rat (n=8). The electrical stimulation of the right cervical vagus started at 3-5 months after MI and lasted for 7 days. ECG data were analyzed for counting the premature ventricular or supraventricular contraction (PVC, PSVC) and for the spectral analysis of heart rate variability. All the rats had a variety of ventricular arrhythmias and the number of PVC or PSVC progressively increased to 5-15% of the total beats. VS effectively suppressed the occurrence of PVCs in 1-2 days. The 24-hour counts of average PVC plus PSVS counts were significantly decreased after VS (793plusmn291 vs. 291plusmn289 counts/hr, p<0.05). The power of high-frequency (0.5-2.0 Hz) oscillations of R-R interval was significantly increased by the VS (1.26plusmn0.47 vs. 3.73plusmn0.74, p<0.01, before and 1 day after stop VS). These results showed that VS markedly suppresses arrhythmias in conscious CHF rats. The antiarrhythmogenic properties may partially account for the beneficial effect of VS on survival of CHF rats