Sustenance

Like other percutaneous interventions in cardiovascular medicine, it was the development of a surgical procedure which ushered in the era of catheter ablation for AF sustenance. Utilizing the concepts of multiple wavelet reentry, Cox et al. hypothesized that if the atrium were sectioned in order to limit the region of contiguous conduction,

Rapid Atrial Firing

Fig. 8. Initiation of af oy a period ot repetitive firing (asterisks) emanating from the right superior pulmonary vein. The firing is irregular at times. In this patient, the duration of firing would range from several beats to several seconds, either resolving with restitution of sinus rhythm or degenerating into atrial flutter or AF.

Fig. 8. Initiation of af oy a period ot repetitive firing (asterisks) emanating from the right superior pulmonary vein. The firing is irregular at times. In this patient, the duration of firing would range from several beats to several seconds, either resolving with restitution of sinus rhythm or degenerating into atrial flutter or AF.

Fig. 9. Time-lapse recordings from a subcutaneous (SC) loop recorder (recordings similar to MCL 1) demonstrating a reliable electrocardiographic sequence culminating in AF. On the left, sinus rhythm is interrupted by an APD (arrowhead). This initiates a rapid, uniform atrial tachyarrhythmia (hollow arrows), demonstrated on the center panel. Within minutes, this rhythm would degenerate to "typical" AF, demonstrated in the right panel (curved arrow).

Fig. 9. Time-lapse recordings from a subcutaneous (SC) loop recorder (recordings similar to MCL 1) demonstrating a reliable electrocardiographic sequence culminating in AF. On the left, sinus rhythm is interrupted by an APD (arrowhead). This initiates a rapid, uniform atrial tachyarrhythmia (hollow arrows), demonstrated on the center panel. Within minutes, this rhythm would degenerate to "typical" AF, demonstrated in the right panel (curved arrow).

AF sustenance could not occur (2). Utilizing a series of "linear" surgical incisions, which permitted atrioventricular conduction but severely limited contiguous conduction, these investigators developed and deployed the Maze procedure (61,62). The high rates of long-term success reported by groups performing this procedure has served as clear proof of concept. In subsequent years, modified and less extensive surgical procedures also demonstrated high rates of efficacy. This led investigators to conceptualize that AF sustenance could be prevented without the severe limitation of contiguous conduction

Fig. 10. Endocardial view of a 1-d-old lesion (L) deployed in the right atrium percutaneously utilizing radiofrequency energy. Unablated myocardium stains red. (See color plate 3 appearing in the insert following p. 208.)

(63,64). Together with the development of catheter and imaging technologies, these observations emboldened interventional electrophysiologists to embark on a program of mimicry of atrial incisions utilizing catheter ablation. Technically, anatomy-based transmural "linear" lesions, which function as complete conduction barriers, can be deployed (65) (Fig. 10). Histologically, these lesions are quite similar to surgical incisions (66). Unfortunately, the accumulated experience with linear catheter ablation to inhibit AF sustenance is comprised of several different catheter technologies. In most studies, there is no conclusive evidence that the conceptualized lesions were successfully deployed. Nonetheless, multiple trials evaluating the efficacy of linear ablation have been reported (Table 2). Results thus far are short-term, with serial results from single centers demonstrating a progressive failure rate (80). However, several important observations have been made. First, superior efficacy has been consistently demonstrated in procedures that incorporate left atrial ablation relative to those which do not (80a). Data from animal models have long suggested that AF sustenance is primarily a "left atrial problem." The encouraging results from surgical ablation procedures with lesions limited to the left atrium have reinforced this concept (81-83). Furthermore, several investigators have reported the phenomenon of post-ablation drug "sensitization"—successful AF suppression by an antiarrhythmic drug/dose which had previously failed to do so (67,69,74). In the case of right atrial ablation, the "partial success" group (AF suppression on a previously inefficacious antiarrhythmic drug) appears to be significantly larger than the "complete success" group (drug-free AF suppression). Third, several investigators have reported early post-ablation failures (no change from pre-ablation syndrome or exacerbation of syndrome) which improve with time (69,74). This phenomenon has also been observed early after surgical AF ablation, and may be the result of transient inflammation-mediated alterations in atrial electrophys-iology, particularly contiguous to lesion zones (84).

In contrast to the evolution of focal ablation procedures described here, linear ablation

Table 2

Results of Linear Atrial Ablation Trials for Suppression of AF

Cure

Table 2

Results of Linear Atrial Ablation Trials for Suppression of AF

Cure

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