Key Points
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Cryoballoon ablation is an accepted alternative strategy for pulmonary vein (PV) isolation.
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Cryoballoon technique is an anatomic-guided ablation approach.
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Cryoballoon ablation for PV isolation is an effective treatment for patients with paroxysmal atrial fibrillation (AF).
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Complete cryoballoon occlusion of the PVs is essential for the PV isolation.
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In patients with persistent AF, cryoballoon ablation appears to be less effective.
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The most frequent complication of cryoballoon ablation is transient phrenic nerve palsy.
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Cryoenergy is safe with respect to PV stenosis in comparison with other energy forms.
More than 8000 Arctic Front procedures have been performed in patients with atrial fibrillation (AF) worldwide, which clearly demonstrates the acceptance of this alternative energy source for pulmonary vein isolation (PVI) as a treatment strategy in the electrophysiologic community. This chapter aims to give a short overview of the evolution of the cryoballoon concept and detailed information about the cryoballoon-based procedure; inclusive are performed studies regarding efficacy. The intent also is to give an overview about recently published sophisticated strategies to improve the cryoballoon-based catheter ablation of AF. Finally, different future directions and safety aspects of the procedure and some potential changes in regard to safety are discussed.
Evolution of the Cryoballoon Concept
Davies et al. described PVI procedures in 31 patients using 4- and 6-mm tip cryoablation catheters. These ablations proved to be difficult in terms of procedural duration. Patients needed 20 ± 13 applications to isolate each vein, which resulted in a total cryoablation time per vein of 65 ± 39 minutes. The fluoroscopy and procedure times were long as well, averaging 69 ± 33 and 290 ± 101 minutes, respectively. The low success rates and long procedure times explain the necessity of progress in the technical evolution of cryoablation in PVI. Therefore, new catheter designs were developed to achieve greater success rates and decrease procedural times.
In 2002, the first curvilinear catheter with a long, linear freezing part was developed to create circumferential lesions at the pulmonary vein (PV) ostium. The spiral catheter consisted of a 64-mm freezing segment, which had the ability for self-expanding to a diameter from 18 up to 30 mm. Theoretically, a single 4-minute application should create a long curvilinear lesion around the vein ostium. Our own working group presented acute isolation rates in 19 patients with this catheter in 59 of 72 (81.9 %) PVs. The median procedure time lasted 4.3 ± 0.8 hours. In 9 patients, an isolation of all veins was possible with the device only; but in 10 patients, an additional tip catheter for PVI of all veins was needed. Strikingly, already 3 months after PVI, the recurrence rate was 50%. Skanes et al. reported their experience in 18 patients with the Arctic Circler. No right inferior veins were treated because of technical difficulties in positioning the catheter at this vein. Acutely, 41 of 45 PVs could be isolated. After a follow-up of 14.8 ± 6.2 months, 22% of the patients had definitively no recurrences. The low success rate was discussed, and the authors claimed that PV blood flow impeded the effectiveness of PVI.
Currently, it is clear, that this catheter configuration was not well designed for PVI. Especially, achieving PVI by creating an antral circumferential lesion was impossible. The self-expanding mechanism during the cooling-down process was advantageous for a stable positioning inside the PV, but at the ostial region, the catheter often dislodged. In spite of the promising initial acute results for PVI, the long-term effectiveness of the system was disastrous. Therefore, in 2002, several centers designed the “block the vein” strategy as an inventive step ( Figure 15–1 ). Based on this strategy, a cryoballoon catheter was designed. The first arranged “PV-ICE-Pilot Study” was designed with the first generation of cryoballoons (21.5-mm, nonsteerable sheath; 20 patients in two centers, PAF, normal LA dimensions). In 74 of 78 of treated PVs (95%), an acute isolation could be achieved. Additional Freezor MAX lesions were also performed in 23 of 78 PVs. The long-term success rate was 84% (16/19); but in 6 patients, additional antiarrhythmic drug therapy was necessary. No severe complications occurred. Right phrenic nerve palsy (PNP) was persistent in two patients but recovered after 12 months. At this time it was clear that several developments concerning the catheter design were necessary: larger diameter, at least two sizes; shorter distal tip to allow better positioning; bidirectional deflection and softer shaft; enhanced robustness by using different materials for each balloon; and an optimized cooling performance.
Cryoballoon-Based Procedures
The cryoballoon catheter was developed to overcome the pedestrian challenge of applying circumferential lesions in a point-by-point manner, and it has been shown to have comparable success rates with conventional radiofrequency (RF) tip ablation techniques. A typical cryoballoon-based procedure is explained later.
The left atrium was accessed via the trans-septal route from the right femoral vein with a steerable 12-French (Fr) sheath to guide a double-walled cryoballoon over the wire. A second trans-septally introduced 8-Fr sheath was used for placement of a multipolar Lasso catheter into the left atrium to map signals before and after ablation at the ostial sides of PVs. After angiography in left anterior oblique 60-degree and right anterior oblique 30-degree or anteroposterior projections, each PV was mapped. With different sizes of Lasso catheters, we mapped inside the PVs and outside at the level of PV antrum. Complete isolation was verified as a reduction of all signals 0.2 mV or greater ( Figure 15–2 ). Exit block from the vein was confirmed by pacing at the location of bipolar signals within PV ostium in all patients.
During sinus rhythm, cryoballoon ablation was performed after mapping the areas of interest distal to the antrum. During AF, the transition zone was defined primarily by anatomic orientation, because the cryoballoon itself does not have any electrodes for recording of local electrical signals.
There are currently two sizes of balloon catheters available (23 or 28 mm). The diameter of the PV was determined by PV angiographies. The balloon size was selected accordingly. With the deflated balloon catheter inside the sheath, a guidewire was placed in one of the PV branches. The balloon was then advanced over the wire toward the PV ostium and inflated.
The degree of balloon occlusion obtained by injection of 50% diluted contrast medium into the PV was judged using a semiquantitative grading: grade 4 = excellent (full retention of contrast medium without visible outflow); grade 1 = very poor (immediate rapid outflow from the PV; Figure 15–3 ). We aimed for at least one cryoballoon ablation with occlusion of grade 4 on every targeted PV. Additional delivery of cryoenergy was applied after the guidewire was placed in different branches of the PV with early branching, which usually allowed for better contact of the balloon at different sites of the PV antrum.
Based on the animal data, we chose an application time of 240 to 360 seconds per freeze. Balloon temperature was measured at the proximal end of the balloon where the vaporized N 2 O was returning back to the console.
During cryoablation of the antrum of the right-sided PVs, diaphragm movement was monitored by either continuous phrenic nerve stimulation with a right atrial stimulation catheter positioned superiorly compared with the balloon position or by continuous monitoring of the phrenic movement during spontaneous breathing ( Figure 15–4 ).
In all patients, PVI of all targeted PVs was the therapeutic aim with the primary use of a cryoballoon only. An observation period after isolation to check for recurrence of conduction was 20 minutes.
In the three-center cryoballoon study, we found that circumferential PVI with the cryoballoon technique resulted in maintenance of sinus rhythm without the use of antiarrhythmic drug therapy in 74% of patients with PAF. In patients with persistent AF, cryoballoon ablation was less effective ( Table 15–1 and Figure 15–5 ).
