Case Study: Cryoablation of Atrial Fibrillation

In this article, Dr. Sanghvi, who directed the establishment of the atrial fibrillation ablation program at Lenox Hill Hospital, presents his experience with cryoballoon technology coupled with simultaneous monitoring of pulmonary vein activity via the Medtronic Achieve^™ Mapping Catheter.

Background

The patient had been suffering from intermittent palpitations and exertional fatigue for the past several years. His medical workup uncovered episodes of symptomatic atrial fibrillation. He was initially trialed on standard medical therapy including beta blockers. After experiencing a recurrence despite beta blockers, he was initiated on anti-arrhythmic drug therapy. Unfortunately, the medications worked for a limited period of time before he started having recurrent symptoms. Moreover, the medications increased his level of generalized fatigue as well as caused mild GI discomfort, both expected side effects of these medicines. Alternate medications resulted in similar disappointing results. Consequently, after consultation with his physicians, he decided to move forward with an atrial fibrillation ablation procedure.

Cryoablation for Atrial Fibrillation

Physicians at the Heart Rhythm Center at Lenox Hill Hospital have been treating patients with atrial fibrillation using the Arctic Front® Cardiac CryoAblation system (Medtronic CryoCath LP). This technology was recently approved by the FDA on December 17, 2010. The Arctic Front^® CryoAblation system is engineered with a balloon-within-a-balloon design. Liquid nitrous oxide is passed within the inner balloon. A constant vacuum is applied between the balloons to prevent any leakage of refrigerant should the inner balloon be defective. The cryoballoon is available in 23mm and 28mm sizes in order to accommodate varying pulmonary vein anatomy. The balloon is advanced over a 0.035 inch wire via the 12 Fr FlexCath^® unidirectional steerable sheath. The balloon itself has 45o of bidirectional movement. Any tissue in contact with the balloon freezes with tissue temperatures reaching below -50^oC as the liquid nitrous oxide expands to gas. The freeze renders the tissue electrically inert. As a result, the pulmonary veins become electrically isolated when balloon cryothermal ablation is applied to the antrum of the pulmonary veins. Achievement of pulmonary vein isolation has been proven to prevent recurrence of atrial fibrillation.¹

Further system improvement occurred on May 2, 2011 with the FDA approval of the Achieve^™ Mapping Catheter. This circular mapping catheter is available in 15mm or 20mm loop diameters consisting of 8 electrodes. It is engineered to be delivered through the Arctic Front^® CryoBalloon, allowing real-time monitoring of pulmonary vein activity during ablation. As a result, instant feedback is available to the clinician as to whether the ablation is resulting in electrical isolation of the pulmonary vein. Furthermore, a second transseptal puncture does not need to be performed since the Achieve^™ catheter operates within the current Arctic Front^® system.

Our experience with the cryoballoon ablation system has been excellent. To date, we have been able to achieve 100% pulmonary vein isolation with the system. A single transseptal puncture as well as real-time monitoring of pulmonary vein activity during ablation is an added benefit. Our novel approach to maximizing the use of the Achieve^™ catheter has been coupling the cryoballoon technology with the EnSite Velocity^™ Cardiac Mapping System (St. Jude Medical, St. Paul, MN). We create a 3-dimensional representation of the left atrium and its pulmonary veins via the Achieve^™ catheter. We then use the cryoballoon catheter to ablate each pulmonary vein antrum. Typically, two 4- to 5-minute cryothermal lesions are applied per vein after verifying complete occlusion of the antrum via pulmonary vein venography. Our total use of contrast rarely exceeds 50 cc. In addition, we perform high output pacing within the SVC in order to capture the right phrenic nerve during ablation of the right pulmonary veins. Ablation is immediately discontinued should there be a reduction in diaphragmatic excursion as a means to prevent permanent phrenic nerve injury. Pulmonary vein isolation is confirmed after analyzing the Achieve^™ catheter signals. The Achieve^™ catheter not only allows real-time assessment of pulmonary vein isolation, but also reveals time to isolation which would then influence whether additional lesions are required. If complete pulmonary vein isolation is not accomplished with the cryoballoon, we are able to mark breaks in the ablation line on the 3D map, thereby facilitating focal ablation. In this situation, we will exchange out the balloon catheter for a standard cryoablation catheter and target the marked location designating the gap in the ablation line on the 3D map. The short times needed for ablating each vein coupled with 3D marking of potential gaps directing focal ablation has resulted in our total procedure times averaging 2 to 2.5 hours. Post-operatively, patients are able to ambulate 4 hours after having their venous access removed and are typically discharged the following day.

Patient Outcomes

Review of the Continued Access Protocol (CAP AF) registry has revealed that over 15,000 patients have been treated with the cryoballoon worldwide. Major complications have been less than what was seen in the STOP-AF (Sustained Treatment of Paroxysmal Atrial Fibrillation) trial. Phrenic nerve injury has decreased from 11.2 to 4.8% and pulmonary vein stenosis has decreased from 3.1 to 1.3%. Seventy percent of patients treated with the cryoballoon remain AF free at 12 months. The CAP AF registry has shown us that the cryoballoon can be used safely and effectively in patients with paroxysmal atrial fibrillation.

Patient satisfaction has been very high in our institution. Patients are thankful for the reduction in risk due to the need of only a single transseptal puncture. The minimally invasive procedure is preferable to more invasive surgical approaches secondary to quick recovery. Of course, patient outcomes are predicated on cardiac function and left atrial dilation. The STOP-AF trial served as the basis for the approval of the Arctic Front^® system. Patients with left atria larger than 5cm in diameter were excluded from the trial. As such, we offer cryoballoon ablation to patients with paroxysmal atrial fibrillation closely resembling the inclusion criteria for STOP-AF. We have begun extending cryoballoon therapy to persistent AF patients with good success, though long-term follow-up data remains to be seen.

Case Summary

The patient described above is doing very well since his ablation. He was discharged the following day after his ablation without complication and has remained symptom free. Post-ablation surveillance has revealed no recurrence of atrial fibrillation.

Reference

1. Pappone C, Rosanio S, Augello G, et al. Mortality, morbidity, and quality of life after circumferential pulmonary vein ablation for atrial fibrillation: outcomes from a controlled nonrandomized long-term study. J Am Coll Cardiol. 2003;42:185-197.