Effect of thoracic epidural anesthesia on heart rate variability in a porcine model

Heart rate variability (HRV) is increasingly recognized as a means of evaluating autonomic tone. Thoracic epidural anesthesia (TEA) has been previously demonstrated to suppress the electrical storms in patients. However, the effect of TEA on HRV during sympathoexcitation remains unknown. In this study, we aimed to determine the effects of TEA on HRV response to left stellate ganglion stimulation (LSS) in a porcine model. In 12 anesthetized pigs after insertion of an epidural catheter to T1 level, a median sternotomy was performed to expose the heart and the left stellate ganglion. A 56-electrode sock was used for obtaining epicardial activation recovery interval (ARI). Animal received LSS at 4 Hz for 30 sec. After 30 min of bupivacaine epidural injection, LSS was performed in the same way as the baseline condition. LSS significantly increased low-frequency normalized units (LF: 44.9 ± 6.7 vs. 13.6 ± 3.1 msec² baseline, P < 0.05) and decreased high-frequency normalized units (HF: 11.5 ± 4.6 vs. 41.9 ± 5.1 msec² baseline, P < 0.05). As a result, LF/HF significantly increased from 0.3 ± 0.2 to 3.9 ± 1.4 during LSS TEA significantly attenuated the LF/HF from 3.9 ± 1.4 to 1.6 ± 0.8 with increased HF components from 11.5 ± 4.6 to 26.5 ± 3.2 msec² LF component significantly correlates with global ARI (r = -0.81) and dispersion of repolarization (r = 0.85). HRV can precisely reflect the cardiac autonomic tone and TEA modulates the HRV by enhancing the HF components probably through a parasympathetic nerve system.