Introduction: Due to the low atrial mass (i.e. low likelihood of reentry), small animals have long been considered unsuitable for atrial tachyarrhythmia (AT) models.
Objective: Based on the concept that „Atrial fibrillation (AF) begets AF”, we hypothesized that spontaneous AT may occur in rats following repeated burst atrial pacing.
Methods: Wistar rats were randomly assigned into two groups: sham stimulation (SHAM; n=7) and active sti-mulation (STIM; n=15). All rats were implanted with radiotelemetry ECG devices and 24-h ECG monitoring was performed before and 1 week after the stimulation protocol. Rats in the STIM group were subjected daily to transesophageal atrial burst pacing for 2 consecutive weeks. Rats in the SHAM group were subjected to the same protocol, but were not stimulated. Arrhythmia inducibility and the occurrence of spontaneous AT were assessed. The dynamic changes in the autonomic tone were also evaluated using 24-h ECG-derived heart rate variability (HRV) analysis.
Results: Atrial pacing triggered AT in all STIM rats (28.9% of stimulation cycles were followed by AT), whereas no AT episode was induced in the SHAM. After the stimulation protocol, one SHAM presented a single episode of AT, whereas all STIM rats presented spontaneous AT (median 1.5; range 1-12 episodes; p=0.01). Among the SHAM rats, there was no signifi-cant change in any of the HRV parameters during the study (all p>0.05). A significant increase in parasympathetic tone (i.e. SDNN, RMSSD) was noted in the STIM rats during the stimulation period compared to baseline (both p<0.05). After the end of stimulation, SDNN continued to increase (p<0.01) and a significant decrease in the LF/HF ratio (p=0.03) was noticed.
Conclusions: T his study demonstrates the occurren-ce of spontaneous AT in rats following repeated atrial burst pacing and illustrates for the first time the „AF begets AF” concept in rats. Our results suggest that vagal hyperactivity, which develops during and pro-gresses after the end of the stimulation may contribute to the increased atrial arrhythmogenicity observed in this model. This work was supported by a grant of the Romanian National Authority for Scientific Research and Innovation, CNCS – UEFISCDI, project number PN-II-RU-TE-2014-4-1544.