Key Points
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Cryoablation has an excellent safety profile in the septal region due to:
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Reversibility of electrophysiologic effects at −30° (cryomapping).
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Reversibility of electrophysiologic effects at −80° in applications lasting <10 seconds (cryoablation mapping).
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Catheter adherence to the tissue during cryoablation (cryoadherence).
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Cryolesions’ characteristics (well-circumscibed, discrete) with less risk of perforation, thrombus formation, and coronary artery damage.
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Average acute success rate of septal accessory pathways cryoablation is 84%, with higher efficacy for midseptal and parahissian accessory pathway locations (88%–89%).
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Average recurrence rate of 31% (tends to be higher for midseptal accessory pathway location).
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Complete absence of undesired persistent AVB during cryoablation of right septal arrhythmic substrates.
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Cryoablation should be the energy of choice during perinodal ablations, particularly in young individuals.
Radiofrequency catheter ablation is highly effective for curing patients with supraventricular tachycardias mediated by atrioventricular (AV) accessory pathways. However, radiofrequency ablation of certain accessory pathway locations is associated with a greater rate of first procedure failures, complications, and recurrences. Midseptal and parahisian accessory pathways are located in close proximity to the normal AV conduction system, making their elimination a challenging task because of the increased risk for atrioventricular block (AVB). Moreover, the complex anatomy of the posteroseptal space imposes additional difficulties by reducing the efficacy of conventional radiofrequency ablation and potentially causing coronary artery injuries. In addition, the right AV groove may be a difficult location to achieve adequate catheter contact and stability, resulting in disappointing ablation results and potential complications. These issues can be especially relevant during ablation in pediatric patients, in whom the dimensions of the triangle of Koch and overall tissue thickness are reduced. As a consequence, a significant proportion of patients are subject to high-risk ablations or left untreated because of safety concerns. Thus, a need exists to investigate safer and more efficacious ablation energies that eliminate septal accessory pathways. This is especially so in pediatric patients given the long-term clinical and quality-of-life consequences of permanent AVB.
Cryoablation Energy Features in the Atrial Septal Region
Recently, cryoenergy has evolved as a safe and effective alternative for radiofrequency catheter ablation of several arrhythmogenic substrates and locations. A number of specific features of this new technique make this energy source particularly attractive in the atrial septal region. The ability of this technique to create reversible lesions when the catheter-tip temperature is decreased to −30°C, termed cryomapping, enables testing the functional effects of ablation at a prospective site before the formation of a permanent lesion ( Figure 12–1 C ). In addition, catheter adherence to the tissue during cryoablation delivery allows one not only to perform programmed stimulation during lesion formation (see Figure 12 – 1 D ), but most importantly, to avoid catheter dislodgment. Catheter position at the septal portion of the tricuspid annulus may not always be stable enough, and unintentional catheter dislodgment has been advocated as an important reason for inadvertent AVB during perinodal ablations. Moreover, the possibility of maintaining the cryoablation pulse without the interference of nodal rhythms allows for continuous checking of nodal conduction.
The characteristics of the cryolesion may also provide additional distinct advantages as compared with conventional radiofrequency ablation, especially when collateral tissue damage is a concern. As compared with radiofrequency lesions, cryolesions are well-circumscribed, discrete lesions with sharp borders, and are associated with substantially less extracellular matrix and endothelial disruption, and overlying thrombus formation. Moreover, cryoablation applications at minimal temperatures (−80°C) lasting less than 15 seconds create reversible lesions, enabling some viable cells to survive ( Figures 12–2 and 12–3 ). In this closed-chest pig model, we demonstrated the reversibility of the electrophysiologic effect if cryoapplication is halted within 10 seconds of AVB onset. This finding, together with the absence of long-term deterioration after transient AVB, reinforces the safety profile of cryoablation of arrhythmic substrates in the perinodal region, even during applications at minimal temperatures (−80°C). Finally, cryoablation technology also has the potential advantage of causing less endothelial disruption, and thus less likelihood of perforation or thrombus formation. In contrast, radiofrequency ablation in the coronary sinus and/or close to the coronary arteries can be complicated by perforation, heat-induced damage to the coronary arteries, or thrombosis of the coronary vein. Experimental and clinical studies demonstrate that cryoenergy is associated with a significantly lower risk for coronary artery stenosis than is radiofrequency ablation.
Cryoablation versus Radiofrequency Ablation in Septal Accessory Pathways Ablation
Radiofrequency catheter ablation is the treatment of choice for eliminating accessory pathways, but septal pathway location remains a challenge for interventional treatment. Large series (>50 patients), including both adults and pediatric patients, reported lower acute success rates (87%) and greater recurrence rates (8% to 25%) for septal accessory pathways compared with free wall accessory pathways ( Table 12–1 ). Several circumstances previously discussed may explain these results, such as the increased risk for complete AVB, the complex anatomy of the posteroseptal space, and other technical and clinical issues. Despite the use of cautious and conservative energy applications, there continues to be a significant risk for radiofrequency ablation–induced AVB (3% to 8%), and ablation is deferred in a significant proportion of patients because of safety concerns.
| ANTEROSEPTAL | PARAHISIAN | MIDSEPTAL | POSTEROSEPTAL | RIGHT ANTEROLATERAL | TOTAL SEPTAL ACCESSORY PATHWAYS | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| STUDY | N | SUCCESS | RECURRENCE | SUCCESS | RECURRENCE | SUCCESS | RECURRENCE | STUDY | SUCCESS | RECURRENCE | SUCCESS | RECURRENCE | SUCCESS | RECURRENCE |
| RADIOFREQUENCY | RADIOFREQUENCY | |||||||||||||
| Brugada et al. | 98 | 16/17 (94%) | 39/43 (94%) | 33/37 (89%) | Brugada et al.4 | 88/97 (91%) | ||||||||
| Mandapati et al. | 102 | 28/36 (78%) | 4/28 (14%) | 16/20 (80%) | 2/16 (12%) | Mandapati et al.5 | 41/46 (89%) | 1/41(2%) | 85/102 (83%) | 7/85 (8%) | ||||
| Van Hare et al. | 353 | Van Hare et al.6 | (16%) | (25%) | ||||||||||
| Average | 553 | 44/53 (83%) | 49/57 (86%) | Average | 173/199 (87%) | |||||||||
| CRYOABLATION | CRYOABLATION | |||||||||||||
| Atienza (updated results) | 100 | 7/10 (70%) | 37/41 (90%) | 34/38 (89%) | Atienza (updated results) | 5/9 (56%) | 1/2 (50%) | 83/98 (85%) | ||||||
| Atienza et al. | 22 | 9/10 (90%) | 2/9 (22%) | 11/12 (92%) | 1/11 (9%) | Atienza et al.24 | 20/22 (91%) | 3/20 (15%) | ||||||
| Bar-Cohen et al. | 37 | 15/19 (79%) | 4/15 (27%) | 9/12 (75%) | 7/9 (77%) | Bar-Cohen et al.30 | 5/6 (83%) | 2/5 (40%) | 29/37 (78%) | 13/29 (45%) | ||||
| Drago et al. | 12 | 6/7 (86%) | 4/4 (100%) | Drago et al.29 | 1/1 (100%) | 11/12 (92%) | ||||||||
| Friedman et al. | 15 | 5/6 (83%) | 1/1 (100%) | Friedman et al.26 | 5/6 (83%) | 2/2 (100%) | 11/13 (85%) | |||||||
| Gaita et al. | 20 | 11/11 (100%) | 9/9 (100%) | Gaita et al.23 | 20/20 (100%) | 4/20 (20%) | ||||||||
| Kirsh et al. | 31 | 8/11 (73%) | 3/11 (27%) | 4/5 (80%) | 1/5 (20%) | Kirsh et al.28 | 6/14 (43%) | 8/14 (57%) | 23/30 (75%) | 7/30 (25%) | ||||
| Kriebel et al. | 19 | 2/4 (50%) | Kriebel et al.25 | 1/5 (20%) | 4/6 (67%) | 6/9 (67%) | ||||||||
| Average | 256 | 41/53 (77%) | 7/26 (27%) | 50/56 (89%) | 61/69 (88%) | 9/25 (36%) | Average | 21/27 (78%) | 13/24 (54%) | 183/219 (84%) | 31/99 (31%) | |||
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