Autonomic responses during acute myocardial infarction in the rat model: implications for arrhythmogenesis.

Background Autonomic responses participate in the pathophysiology of acute myocardial infarction, but their precise time course remains unclear. Here, we investigated the autonomic activity and ventricular tachyarrhythmias in conscious, unrestrained rats post-infarction. Methods The left coronary artery was ligated in 12 Wistar rats, and six rats were sham operated, followed by 24-h electrocardiographic recording via implanted telemetry transmitters. Sympathetic activity was assessed by detrended fluctuation analysis and vagal activity by time- and frequency-domain analysis of heart rate variability. The duration of the ventricular tachyarrhythmias was measured, and voluntary motion served as a marker of heart failure. Results In sham-operated rats, heart rate and sympathetic activity remained low, whereas vagal activity rose progressively after the fourth hour. Post-ligation, medium-sized antero-septal necrosis was observed, reaching ~20% of the left ventricular volume; tachyarrhythmias were frequent, displaying a bimodal curve, and motion counts were low. Vagal activity decreased early post-ligation, coinciding with a high incidence of tachyarrhythmias, but tended to rise subsequently in rats with higher motion counts. Sympathetic activity increased after the third hour, along with a second tachyarrhythmia peak, and remained elevated throughout the 24-h period. Conclusions Vagal withdrawal, followed by gradual sympathetic activation, may participate in arrhythmogenesis during acute myocardial infarction.