Ablation of atrial fibrillation

[The activation patterns during atrial fibrillation in an experimental model]

INTRODUCTION AND OBJECTIVES

In atrial fibrillation, along with the mechanisms of complete reentry and random activation focal activation patterns have been described which have been attributed both to propagation from the endocardium and to the existence of zones with automatic activity. The objectives of present study are to analyze and quantify the atrial activation patterns in an experimental model of atrial fibrillation.

MATERIAL AND METHODS

In 11 Langendorff-perfused rabbit hearts atrial fibrillation was induced by atrial burst pacing after right atrial dilatation with an intra-atrial balloon. A multiple electrode consisting of 121 electrodes and positioned in the right atrial free wall was used to construct the activation maps corresponding to 10 segments of 100 ms in 11 different episodes of sustained atrial fibrillation (one per experiment).

RESULTS

Of the 110 segments analyzed, 44 (40%) corresponded to random activation patterns. Fifteen segments (14%) corresponded to complete reentry, and in these cases the number of consecutive rotations ranged from 1 to 2.25 (mean 1.4 +/- 0.4). In 49 segments (44%) a single activation front was seen to pass through the recording area without block; alternatively, two simultaneous fronts were recorded that did not re-excite the zone activated by the other. In two segments (2%) there was a focal activation pattern without evidence of propagation from the epicardium surrounding the activated zone.

CONCLUSIONS

a) in the experimental atrial fibrillation model used, random activation patterns are more frequent than complete reentry patterns; b) complete reentry can occur in areas smaller than 1 cm2, and c) focal activation during atrial fibrillation is rare.

Pretreatment with antithrombotic agents during radiofrequency catheter ablation: a randomized comparison of aspirin versus ticlopidine

INTRODUCTION

D-dimer is a product of fibrin degradation and can serve as a biochemical marker of thrombus formation and reactive fibrinolysis. According to our previous observations, and as reflected by elevated plasma D-dimer levels, lesions produced by radiofrequency (RF) ablation have a thrombogenic effect. Pretreatment with combined aspirin and ticlopidine mitigates this thrombogenicity; however, the effect of either agent alone remains unknown.

METHODS AND RESULTS

In this study, 59 patients undergoing RF ablation were randomized to pretreatment with aspirin (group I; n = 30) or ticlopidine (group II; n = 29) for 3 days prior to RF ablation. D-dimer levels were measured by enzyme immunoassay before and after the electrophysiologic study (EPS), and both immediately and at 48 hours after RF ablation. Results also were compared with those of 31 patients (nonrandomized group III) who had received both aspirin and ticlopidine. At all stages, D-dimer levels were higher in groups I and II when compared with group III. Baseline D-dimer (31+/-20 vs 24+/-13 vs 17+/-11 microg/L, respectively; P = 0.002) rose after EPS to higher levels in groups I and II (91+/-100 microg/L and 51+/-35 microg/L) compared with group III (31+/-17 microg/L; P = 0.001). After RF ablation, D-dimer levels increased in all groups, but this increase was much higher in groups I and II (214+/-210 microg/L and 201+/-222 microg/L) than in group III (74+/-60 microg/L; P = 0.005). At 48 hours, D-dimer levels decreased in all groups, but remained higher in groups I and II (91+/-100 microg/L and 95+/-99 microg/L) than in group III (35+/-31 microg/L; P = 0.009). There were no differences among the three groups in the number of RF ablation lesions or the duration of the RF ablation procedure.

CONCLUSION

Pretreatment with aspirin or ticlopidine alone does not decrease the thrombogenic potential of RF ablation. Only combined therapy with aspirin and ticlopidine has a favorable effect, as reflected by the lower degree of D-dimer elevation.

[Radiofrequency catheter ablation of atrial flutter and atrial fibrillation]

Radiofrequency catheter ablation is now considered as a curative approach in patients with typical atrial flutter. Typical atrial flutter is due to a macrore-entrant circuit within the right atrium and it can be eliminated by a linear lesion in the isthmus between the tricuspid annulus and the vena cava inferior. The electrophysiological criterion of a bidirectional isthmus block has been shown to reduce the recurrence rate of atrial flutter after catheter ablation, thus achieving long-term cure of typical atrial flutter. Acute success rates of 85 to 90% and recurrence rates of 10 to 15% have been reported. The risk of paroxysmal atrial fibrillation continues to be clinically relevant in patients who underwent successful ablation of atrial flutter, in particular in patients with previously documented atrial fibrillation. The incidence of a new onset of atrial fibrillation after ablation of atrial flutter seems to be approximately 20%. Isthmus ablation has also been shown to be beneficial for the majority of patients with typical atrial flutter and atrial fibrillation: In addition to an elimination of typical atrial flutter the isthmus ablation apparently reduces the incidence of paroxysmal atrial fibrillation. At present, atrial fibrillation can only be treated by catheter ablation as a curative approach in the rare cases where an accessory pathway, an AV nodal re-entrant tachycardia, typical atrial flutter or an ectopic atrial tachycardia is the induction mechanism of the atrial fibrillation. The majority of patients with atrial fibrillation is apparently not amenable to a curative local ablation. While AV junction ablation and AV node modification can palliate some of the symptoms of atrial fibrillation by a control of ventricular rate, the arrhythmia persists with the loss of AV synchrony and continued risk of thromboembolism. The surgical MAZE procedure implies a compartimentation of the atria by surgical incisions resulting in areas to small to sustain the arrhythmia. Based on this procedure experimental and clinical studies are currently performed in order to develop catheter ablation cure of atrial fibrillation.