Tachycardia induced electrical remodeling of the atria and the autonomic nervous system in goats

Atrial fibrillation (AF) shortens the atrial effective refractory period (A ERP). To investigate the role of the autonomic nervous system during this s o-called electrical remodeling of the atria (ERA) and during recovery from ERA we analyzed heart rate variability (HRV). In 12 goats atrioventricular (300:150 beats/min) pacing was performed for 24 hours, interrupted at 4, 8, 16, and 24 hours for recording of 500 atrial (AA) intervals during sin us rhythm and measurement of the AERP(430 ms) at 7. 4 +/- 0.6 sites. After 24 hours, pacing was stopped and the electrophysiological study and recording of the AA intervals was repeated at 4, 8, 16, and 24 hours after cessation of pacing. Time- and frequency-domain parameters were computed from each 50 0 AA interval recording. After 24 hours of rapid pacing the AERP had shorte ned significantly (247 +/- 5.6 to 102 +/- 6.4 ms, P < 0.0001). No significa nt changes in HRV and dispersion of refractoriness (Delta AERP) (47 +/- 7.1 to 44 +/- 4.2 ms) were observed. After cessation of pacing, the AERP prolo nged again (102 +/- 6.4 to 135 +/- 8.8 ms, P < 0.0001) and was paralleled b y a significant increase in Delta AERP (44 +/- 4.2 to 63 +/- 7.2 ms, P = 0. 01). Furthermore, HRV increased significantly. At each time point an invers e relation between the logarithmically transformed vagal parameter HF (lnHF ) and AERP was observed. We calculated the mean lnHF for each goat using al l time points and used the median value to divide the 12 goats into high an d low vagal tone groups. We compared the degree of ERA and recovery from ER A for both groups. The AERP shortened 47.4 +/- 6.5 versus 43.0 +/- 5.0 ms ( NS) for goats with high and low vagal tone, respectively. During recovery f rom ERA the AERP lengthened 23.6 +/- 4.0 versus 42.5 +/- 2.7 ms (P = 0.001) for goats with high and low vagal tone, respectively. Multivariate regress ion analysis indicated a short AERP as the single independent determinant o f the inducibility of AF during ERA and recovery from ERA (P < 0.0002). Dur ing recovery from ERA, the AERP prolonged and vagal tone and Delta AERP inc reased. A high vagal tone during recovery from ERA was associated with a sh ort AERP and an attenuated recovery of ERA.