Tailoring the Ablative Strategy for Atrial Fibrillation: A State-of-the-Art Review

Abstract

In spite of technological progress and the improving skills of operators, atrial fibrillation (AF) ablation results appear to date to be at a plateau. In any case, the superiority of ablation over pharmacological therapy in terms of effectiveness, reduction of hospitalizations, and improvement has been well demonstrated in recent randomized trials. Triggers, substrate, and modulating factors (elements of Coumel's triangle) play different roles in paroxysmal and persistent AF, so induction and perpetuation mechanisms of arrhythmia may be different in each patient. Although effective ablative strategies are available for the treatment of paroxysmal AF triggers and persistent AF substrates, an adequate clinical evaluation of the patient is crucial in order to increase the chances of success. Recognizing triggers allows not only performing an effective ablation but also to avoid unnecessary lesions and at the same time reducing the risk of complications. AF beginning and triggers could be recorded by 12-lead ECG, continuous Holter monitoring, or implantable devices. In case of an unsuccessful noninvasive evaluation, nonpulmonary vein triggers should be investigated with an electrophysiological study. Persistent AF needs more effort to perform an accurate substrate characterization. Among the many methods proposed, recently the use of high-density mapping and multipolar catheters seems of particular benefit in order to clarify the arrhythmia mechanisms. Surgical and hybrid techniques allow to treat regions such as the posterior wall or Bachmann's bundle, which is fundamental for an ablative strategy that goes beyond just pulmonary vein isolation. Too often, patients are referred to electrophysiology laboratories without adequate preprocedural screening and planning in order to submit them to a standard "ready-made" procedure. The accurate search for triggers in paroxysmal AF and the correct recognition of the link between a possible underlying heart disease and the substrate in persistent AF could allow us to tailor the interventional approach in order to overcome the current plateau, increasing ablative procedure success and minimizing complications.

Figure 1

“P on T” phenomena: the trigger of arrhythmia is an extra systolic nonconducted atrial beat with a negative P in D1 and aVL and a positive in D2, D3, and aVF (arrow). This suggests an origin from the left (negative P in D1 and aVL) superior (positive in D2, D3, and aVF) pulmonary vein that was confirmed by the Lasso catheter. The isolation of the left superior pulmonary vein stopped the arrhythmia.

Figure 2

The trace shows the trigger of atrial fibrillation. It seems due to an extra systolic beat (^∗), but the endocardial electrogram shows the following sequence: sinus beat (∞), extra systolic beat (^∗), and blocked extra systolic beat (°). This latter is the effective trigger of atrial fibrillation (CS: coronary sinus; ABL: ablator; D: distal; P: proximal).

Figure 3

In the upper panels, Carto V2 (Biosense Webster, Johnson and Johnson) activation maps show the maximum earliness (red zone) of the origin of tachycardia in the right atrium (crista terminalis). In the lower panel, traces during radiofrequency delivery (during AF) with the restoration of sinus rhythm and the appearance of irritative beats identical to tachycardia. In the lower right panel, fluoroscopy during radiofrequency delivery.

Figure 4

High-density mapping (12,275 points) performed with the 3D Precision System and HDGrid omnipolar catheter (Abbott) to research during atrial fibrillation of rotational activity (RA). The figure on the left shows a map during AF that allows identifying areas of interest compatible with rotational activity (cycle length mean map, CLmean), with activity between 120 and 300 msec. Areas of interest appear in sets of different colors, while insignificant areas appear as white and purple (below 120 msec and above 300 msec, respectively). On the right side, the figure shows the standard deviation map (SD map) of the same activity during AF (cycles length between 0 and 50 msec), in order to establish whether the rotational activity identified with the CLmean (at the level of the posterior wall near the left inferior pulmonary vein) is stable over time. The set of different colors indicates stable rotational activity in this region (SD between 0 and 50 msec).

Figure 5

(a) High-density mapping performed with the 3D CARTO 3 V7 system and bipolar PentaRay™ NAV Catheter (Biosense Webster), to research, during AF, rotational (Ras), and focal activities (FA). The green squares indicate the FAs, while the blue squares indicate the RAs. A repetitive RA is clearly visible between the posterior and the inferior wall of the left atrium, involving a large area (calculated at 4.2 cm²), which is more compatible with a real rotor (macroreentrant driver rather than a microreentrant one). Positioning the PentaRay in the same spot at different times (white circles with a distance of ≤1 mm), we reproduced the left atrium identically. The ablation was directed to the treatment of the RAs. In (b), after RF application on the entire rotor seat area, the left atrium mapping during fibrillation demonstrates its complete disappearance (FIRM approach). The procedure was completed with PVI and synchronized electrical cardioversion. No AF recurrence at 12-month follow-up.

Figure 6

Stepwise approach to atrial fibrillation patient (AF: atrial fibrillation, AT: atrial tachycardia, AVRNT: atrioventricular reentrant nodal tachycardia, AVRT: atrioventricular reentrant tachycardia, CT: computed tomography, and MRI: magnetic resonance imaging).