Acute Electrophysiologic Effects and Antifibrillatory Actions of the Long Linear Lesions in the Right Atrium in a Sheep Model

Linear lesions (LL) represent an option for curing of atrial fibrillation (AF) with ablation techniques.Methods and Results: In 11 sheep (w. 72±16[emsp4 ]kg), LL were created with radiofrequency ablation in the lateral, posterior and septal walls of the right atrium (RA). AF was induced before and after LL with burst pacing. Mapping of the AF was performed with a 64-electrode basket catheter deployed in the RA. Quantitative analysis was performed with a custom-made software program. LL were confirmed histologically 7 to 10 days after the procedure. LL were transmural in 78% of their length. Stimulation thresholds and right atrial activation times were increased after LL compared to preablation values. Effective refractory periods of the RA were prolonged significantly in 7 out of 12 regions after generation of LL. Conduction velocities in the RA segments between LL were reduced in lateral, posterior and septal walls. During paced rhythms double potentials were recorded in all animals. AF could be induced in all animals of this model despite the presence of LL in the RA. AF episodes were significantly more regular after LL throughout the RA due to a significant reduction of the number of the wave fronts in the RA. During AF episodes, in the presence of LL, the RA was driven by wave fronts of left atrial origin entering the right side of the septum through interatrial connections.Conclusions: 1) LL profoundly affect electrophysiologic parameters of RA. 2) In the presence of LL, AF manifest a higher degree of regularity as compared to preablation episodes. 3) Dissociation between wave fronts of left atrial origin entering the RA through the interatrial connections is an important mechanism of the antifibrillatory action of the septal LL.