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Cryoablation for Septal Accessory Pathways:

Radiofrequency (RF) energy has become the mainstay energy source for catheter ablation of cardiac arrhythmias. It has demonstrated efficacy and an acceptable safety profile, particularly for treatment of supraventricular tachycardia; however, it is not without limitations. These include problems with creation of continuous linear lesions, issues of catheter stability, and difficulty in testing the target while applying energy. All of these limitations have prompted ongoing searches for alternative methods of energy delivery. Perhaps more importantly, the effect of RF application cannot be predicted reliably until after a permanent lesion has been created. This has obvious implications for ablation procedures involving the tissues close to the AV node, where permanent AV block is a most feared complication. Cryothermal energy has been used for many years during surgical ablations. It was recognized that by cooling the myocardium to around 0◦C, transient modification of the electrical properties at that site could be induced, allowing assessment for involvement in a particular arrhythmia, so-called ice mapping. Deeper cooling, or cryoablation, results in a permanent lesion when the desired site is identified. This reduces the number of unnecessary lesions. Dubuc et al.1 first demonstrated the feasibility of this technology for endocardial catheter lesion delivery. The development of an ice ball with catheter cooling causes cryoadherence, allowing for absolute catheter stability during mapping and ablation. Successful use of cryoablation for AV nodal slow pathway ablation in 17 of 18 patients with AV nodal reentrant tachycardia was reported by Skanes et al.2 They confirmed the ability to ice map the slow pathway region of the AV node in 11 of 12 patients, although for 4 of these patients temperatures below −28◦C were required. Transient fast pathway block and AV block were seen in two patients during ice mapping. Normal conduction returned on rewarming in both cases. What are the attributes of the perfect energy delivery system? The ideal system would enable a focused lesion at the site of abnormality, with no or minimal damage to normal surrounding tissue and absolute catheter stability. It would be advantageous to accurately predict the physiologic outcome of the ablation both before and during lesion delivery. Inadvertent injury to specialized conducting tissue, especially the AV node, should be reversible if diagnosed early. Finally, there should be no recurrence following successful ablation.