Effect of radiofrequency ablation on atrial myocardium

Successful RF ablation of atrial fibrillation supposedly requires the creation of continuous linear lesions. This study aimed to determine the potential role of functional modifications of atrial myocardium in the vicinity of anatomic RF lesions.

In 10 normal beagles (group A), a multiplexer mapping system and an epicardial multi-electrode were used to reconstruct atrial activation patterns during pacing at two cycle lengths before and after attempts to induce two linear right atrial lesions with a standard ablation catheter, respectively. An intercaval "drawback" was repeated 3 times over 5 min at a set temperature of 70 degrees C, followed by a transversal "point-by-point" ablation from the interatrial septum to the right-lateral tricuspid annulus at 70 degrees C/60 s each. Induction of atrial flutter was attempted before and after each ablation. In another 6 beagles (group B), a high-resolution multi-electrode was used to study epicardial functional effects resulting from single endocardial RF lesions on the free right atrial wall. Using three energy settings (60 degrees C/30 s, 60 degrees C/60 s, 70 degrees C/60 s), activation patterns were analyzed at two cycle lengths and local effective refractory periods were measured across the lesion.

The lesions induced in group A only marginally affected atrial activation patterns and total activation times. However, as shown in dogs with atrial flutter, regional slow conduction was enhanced and functional conduction blocks were facilitated at high atrial rates, resulting in a significant prolongation in the revolution time of respective reentrant circuits. Apart from inducing anatomic lesions, single endocardial RF lesions (group B) were shown to delay epicardial conduction in adjacent myocardium in an energy- and rate-dependent way. Furthermore, an energy-dependent prolongation of effective refractory periods by far exceeding the size of anatomic lesions was observed.

Continuous linear atrial lesions are hard to achieve with conventional ablation techniques. However, RF lesions induce changes in conduction and refractoriness around the anatomic lesion, which are likely to contribute to the overall effect of respective therapeutic interventions.