Atrial Fibrillation Ablation: Reaching the Mainstream

John D. Fisher; Michael A. Spinelli; Disha Mookherjee; Andrew K. Krumerman; Eugen C. Palma

Disclosures

Pacing Clin Electrophysiol. 2006;29(5):523-537. 

In This Article

Methodology

English language publications through late December 2005 were included in this review if they provided interpretable information on the ablation techniques used, and reported AF outcomes at least 6 months after the procedure. This report excludes small series (<20 patients) unless they were thought to be important because they were among the earlier reports of a technique; or because of unique variations. Papers that describe new technology without the requisite follow-up information were excluded. To include as much current information as possible, abstracts as well as full-length papers were considered. Abstracts were included only if we did not find a full-length publication that appeared to be derived from the abstract. If this basic information was provided, we also looked for additional information: ablation technique, procedure duration, need for repeat procedures, chronicity of the AF (paroxysmal, persistent, permanent), and complications.

In the literature, differing terminology often described comparable procedures. There were also hybrid procedures or variations that defied easy categorization. For analysis purposes in this paper, such reports were grouped at the authors' discretion with the most complex or recent type of procedure that seemed most appropriate for the individual report. The figures have been designed to provide a summary of each ablative method using a common template (Fig. 1).

Diagrammatic representation of the atria. RA and LA = right and left atria; TV and MV = tricuspid and mitral valves; SVC and IVC = superior and inferior venae cavae; S = septum; FO = foramen ovale; CS = coronary sinus; PV = pulmonary vein. The PVs include RS = right superior; RI = right inferior; LS = left superior; and LI = left inferior.

[3,4,5,6,7,8,9,10,11]

For this review, "linear" means ablation lines placed in a predetermined pattern in the right and/or left atrium whether or not these differed from the patterns described in the early AF ablation literature. Linear catheter ablation in the left atrium included patterns that did not specifically involve isolation of the pulmonary veins (PVs). These techniques are passé as stand-alone approaches. "Linear" lesions directed at specific substrate abnormalities are not included in this group (Fig. 2).

Linear lesions. Right atrial lesions are shown. CTL = crista terminalis line; C-TIL = (inferior vena) cavo-tricuspid isthmus line.

[12,13,14,15,16,17,18,19,20,21]

This includes procedures where the ablating catheter was inserted into the PV to ablate foci thought to be responsible for initiation of AF. Concerns for PV stenosis have rendered this passé (Fig. 3).

Focal ablation within the pulmonary vein(s) (PV), targeted at spontaneously depolarizing tissue. Limitations of the technique include absence of depolarizing targets, and PV stenosis.

[22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55]

For this review, the term applies to segmental or circumferential lesions placed at the presumed ostia of the PVs to eliminate electrical continuity (and achieve bidirectional block) between the PVs and the left atrium. Most of these were done without the assistance of computer mapping systems. The proximity of the lesions to the actual PVs meant that many lesions were likely delivered inside the ostia (Fig. 4). This was the first of the "Pandora's Box" approaches (Fig. 5), designed to keep the AF-generating depolarizations trapped within the PVs, but is fading in favor of antral ablation (next below).

Pulmonary vein (PV) isolation. The segmental approach is "guided" by electrograms; targets are the sleeves of atrial tissue entering the PVs, so that only the segments with such sleeves are targeted segmentally (segmental ostial ablation, SOA). The anatomic approach simply encircles the entire ostium with or without electrogram guidance. The endpoint is usually demonstration of electrical isolation of the PV from the atrium. Many reports predated widespread use of CT or MRI or computer-guided mapping, possibly limiting success, and resulting in some lesions being placed inside the ostium (in the vein).

Pandora's box. From a painting by John Waterhouse. This illustrates the origin of most of the atrial fibrillation (AF)-initiating depolarizations within the pulmonary veins, and the desirability of keeping them confined or isolated from the atrium. This is particularly applicable to paroxysmal AF, in patients with relatively normal atrial muscle.

For the purposes of this review, this includes any of several techniques. Most are performed with assistance of a computerized mapping system (Figs. 6 and 7), and are designed to encircle (but not always to isolate) the PVs, usually in association with additional linear lesions as described. The circumferential lines are usually aimed at atrial tissue outside the ostium of the PVs, an area often termed the antrum (pulmonary vein antrum ablation/isolation, PVAI). The ablation lesions may be designed to encircle the left and right PVs individually or in pairs (Fig. 6). Additional ablation lines are commonly placed, e.g., along the back or the roof of the left atrium between the two sets of PVs, and between the left PV encirclement and the mitral valve annulus. (These linear lesions are not grouped with the linear lesion category described above).

Circumferential ablation. Variations include wide area circumferential ablation (WACA), similar to left atrial catheter ablation (LACA), and pulmonary vein antrum isolation (PVAI), which differs in that isolation is an endpoint (see text). Anatomic encirclement of the pulmonary veins (PVs) may be done separately or in pairs as shown, with additional lines along the roof of the left atrium, and from the left inferior PV to the mitral valve annulus (MVL). These extra lines are intended to prevent left atrial tachycardias or flutters that otherwise are common after PV isolation. Their efficacy is controversial. The roof line is an alternative to a posterior line that has been implicated in causing catastrophic atrio-esophageal fistulae.

A three-dimensional non-contact computer map, ESI, together with a three-dimensional computerized tomography (3D CT) reconstruction of the left atrium, shows the excellent anatomic correlation available to the electrophysiologist during ablation. These are displayed together during the procedure, with simultaneous movement to any desired view. As indicated by the torso figures, this is a right posterior-superior view. The dots indicate locations where radiofrequency applications have been delivered. Encirclement of the right and left pulmonary veins and a roof line can be seen. Other ESI and CARTO versions use the CT or MRI images as virtual atria, with the mapping and ablating catheters superimposed.

Wide Area Circumferential Ablation or Left Atrial Catheter Ablation.[31,50,53,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71] These lesions are variations of circumferential ablation as described above. Endpoints are usually the placement of anatomical lesions or achievement of electrogram degradation; demonstration of isolation is often optional.

Pulmonary Vein Antrum Ablation/Isolation.[50,52,54,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147,148,149,150,151] This is similar to wide area circumferential ablation (WACA)/left atrial catheter ablation (LACA), but with isolation of the PVs as the major endpoint. For the data analysis, circumferential antral isolation, PVAI, and WACA/LACA are considered separately and together ( Table I , Table II , and Table III ).

[51,152,153,154,155,156,157,158]

Using techniques such as electroanatomical mapping (CARTO), complex fractionated atrial electrograms (CFAEs) are sought and targeted for ablation. Both spot and linear lesions may be used to ablate the areas with CFAEs. (These linear lesions are not grouped with the linear lesion category described above.) No special emphasis is placed on the PVs. Patients often include those with persistent or permanent AF. It is assumed that continuing AF is more dependent on perpetuation due to atrial disease than due to initiators in the PVs (Fig. 8).

Substrate ablation. Complex fractionated atrial electrograms are sought and targeted for ablation. No special emphasis is placed on the pulmonary veins. This may be particularly useful in patients with atrial muscle disease, as is more common in persistent or permanent atrial fibrillation.

[159,160,161,162,163]

It has been observed that long pauses during ablation, consistent with vagal stimulation, may be associated with a higher likelihood of successful ablation. Some laboratories actively seek signs of bradycardia due to vagal or ganglionic; ablation at such sites may foster a favorable outcome.[122] On a research level, others[160,161,162] are expanding our understanding of the relationship between autonomic and neurohumoral stimulation and the very short refractory periods and rapid firing of PV foci. Ablation of autonomic targets may explain why some phrenic nerve damage may be an unwanted byproduct.[163]

As per the section on "Terminology," above, hybrid procedures are common. Examples include circumferential ablation, with additional isolation of the venae cavae, and placement of a cavo-tricuspid annulus line.

[164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179,180,181,182,183,184,185,186,187,188,189,190,191,192,193,194,195,196,197,198,199,200,201,202,203,204,205,206,207,208,209,210,211]

The traditional Maze operation has been superseded in many institutions by radiofrequency or cryosurgical techniques. Some aim to duplicate the pattern of the traditional Maze; others perform a WACA-like procedure. Many variations exist. PV isolation is an objective in most. Most patients have persistent or permanent AF, and the ablation is usually done in conjunction with other cardiac surgery.

For this review, "cure" means no further AF (by each author's criteria) at ≥6 months after the initial procedure, in the absence of specific antiarrhythmic treatment. "OK" means improvement (fewer episodes, no episodes in the presence of previously ineffective drug therapy, or other author-defined measures) and includes "cure." Some papers did not clearly differentiate between "cure" and "OK," and in such cases they are counted in this paper as an "OK."

Differences among ablation methods and other outcomes were expressed as means and standard deviations. Analysis was by one-way ANOVA for multiple group comparisons, and the unpaired t-test for two groups. Differences were considered significant at P ≤ 0.05.

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