Abstract 2517: The Effect of Irregularity on Sympathetic Nerve Activity in Human Subjects
Background: We have recently shown that atrial fibrillation is associated with an increase in sympathetic nerve activity (SNA) compared to sinus rhythm. It remains unclear, however, whether these findings are true at various rates and whether the magnitude of sympathoex-citation is related to the degree of irregularity.
Methods and Results: Using custom-made software, atrio-ventricular sequential pacing with pre-determined rates (100, 120 and 140 bpm) and irregularities (SD = 0, 5, 15 and 25% of mean cycle length) was performed in 23 patients referred for electrophysiologic evaluation. Pacing at each rate/irregularity was performed for 2 minutes, with 2 minutes of recovery in between. Blood pressure (BP), central venous pressure (CVP), and SNA were measured at baseline and during the last minute of the 2-minute pacing segments. Univariate analysis showed that as the irregularity increased, SBP increased (r = 0.44, p <0.001) but MAP and DBP did not change significantly (p = 0.97 and 0.40, respectively). A significant correlation was found between the pacing irregularity and SNA with greater sympathoexcitation noted at greater degrees of irregularity (r=0.2, p = 0.04). A five variable linear model using DBP, MAP, CVP, and degree of pacing irregularity to predict SNA was highly statistically significant (r=0.46, p<0.001). After controlling for hemodynamic changes, for every 1% increase in irregularity, there was a 6.1% increase in SNA.
We have shown for the first time that greater degrees of irregularity cause greater sympathoexcitation and that the effects of irregular pacing on SNA are independent of the hemodynamic changes.