The Effects of Atrial Electrical Remodeling on Atrial Defibrillation Thresholds

Abstract

Electrical remodeling of atrial fibrillation may account for the increase in atrial defibrillation thresholds over time. The aim of this study was to examine the time course of electrical remodeling and the benefit of early defibrillation on the defibrillation threshold. Twenty-six mongrel dogs weighing 27.6 +/- 3.3 kg were induced into AF by repeated high output burst atrial pacing. Eight dogs were paced for multiple time periods of 5, 20, 40, and 60 minutes. Five dogs each had burst pacingfor 4 hours and 8 hours, and eight dogs were paced at a high rate (640 beats/min) for 48 hours. Biphasic atrial defibrillation shocks with a pulse width of 3/3 ms synchronized to the left apical electrogram were delivered to coil electrode catheters positioned in the lateral left and right atria. Defibrillation voltage was increased from 50 V in 20- to 30-V steps until defibrillation was successful. As the pacing period increased, a decrease in atrial fibrillation cycle lengths and atrial effective refractory period was not observed before 8 hours. Similarly, the defibrillation threshold did not change significantly until the 8-hour pacing period was reached. The defibrillation thresholds were 69 +/- 28 V for 5 minutes, 64 +/- 20 V for 20 minutes, 99 +/- 85 V for 40 minutes, 78 +/- 51 V for 60 minutes, 78 +/- 38 V for 4 hours, 124 +/- 33 V for 8 hours, and 133 +/- 32 V for 48 hours (mean +/- SD) (P < 0.05). Atrial electrical remodeling in a rapid atrial pacing canine model is not observed until after 4 hours of burst atrial pacing. The atrial defibrillation threshold increases with increasing duration of burst atrial pacing, and follows a similar time course to other parameters of electrical remodeling.

Effects of Subthreshold Shocks on Wavelet Propagation during Atrial Fibrillation in Humans

“…This effect appears to be transient, with restoration of original NO within 10 seconds. This finding suggests the idea that the electrical shock causes a widespread extinction of electrical wavefronts, which regenerate after the shock [4] and that the shock does not affect the organic substrate [11]. This result is consistent with our previous finding: when computed over a 10second long window, no significant differences are present in the average NO after the shock [12].…”

Transvenous electrical cardioversion of atrial fibrillation in horses: Horse and procedural factors correlated with success and recurrence

“…Likewise, a short R‐AFCL has been associated with a higher cardioversion threshold in humans and dogs. 34 , 35 , 36 …”

“…Likewise, a short R-AFCL has been associated with a higher cardioversion threshold in humans and dogs. [34][35][36] T A B L E 5 Variables included in the multivariable analysis for AF recurrence within 1 year, based on 179 horses (looking at their last AF episode) Catheter design and catheter positioning are identified as decisive factors for successful TVEC. 12,14 The shock catheters should be positioned in order to encompass as much atrial tissue as possible.…”

“…As the AFCL is regarded as a measure for the atrial effective refractory period, 10,27 it can be stated that horses with a shorter R‐AFCL will have more stable AF and will therefore be more difficult to convert. Likewise, a short R‐AFCL has been associated with a higher cardioversion threshold in humans and dogs 34‐36 …”

The Effects of Reverse Atrial Electrical Remodeling on Atrial Defibrillation Thresholds

“…13,16,33 The authors have recently reported an association between electrical remodeling and atrial DFTs, but little is known concerning reverse electrical remodeling and atrial DFTs. 34 The purpose of the present study was to determine the relationship between reverse atrial remodeling and atrial DFTs in canines with chronic atrial fibrillation. The authors hypothesized that maintenance of sinus rhythm would promote reverse electrical remodeling and decrease the atrial DFT.…”