J Interv Card Electrophysiol (2006) 15:79–81 DOI 10.1007/s10840-006-8519-5
Cryoablation of the pulmonary veins using a novel balloon catheter Arthur Garan · Amin Al-Ahmad · Teresa Mihalik · Catherine Cartier · Lea Capuano · David Holtan · Christopher Song · Munther K. Homoud · Mark S. Link · N. A. Mark Estes III · Paul J. Wang
Received: 26 January 2006 / Accepted: 27 March 2006 C Springer Science + Business Media, LLC 2006
Abstract Introduction. Pulmonary vein (PV) isolation has emerged as a promising technique for the treatment of patients with drug-refractory atrial fibrillation, however, the achievement of transmural lesions has remained a challenge. We evaluated the ability of a novel balloon-based cryogenic catheter system in achieving transmural lesions for PV isolation. Methods. Six pulmonary vein ostia from three excised ovine hearts and lungs were used in this study. The balloon catheter was deployed and positioned at the ostia of the PVs and a full 8-minute ablation was then performed, while the heart was bathed in a circulating bath of normal saline at 37◦ . Thermocouples positioned on the endocardial (balloon surface—tissue interface) and epicardial surfaces of the ostia were used to determine whether transmural freezing was achieved. Results. The mean temperatures measured on the endocardial and epicardial tissue in six PV ablations were −38.8◦ ± 6.9◦ C and −10.0◦ ± 7.5◦ C, respectively. The average pulmonary vein thickness was 3.3 ± 1.4 mm.
A. Garan · C. Song · M. K. Homoud · M. S. Link · N. A. M. Estes III New England Medical Center, Tufts University School of Medicine, Boston, MA, USA A. Al-Ahmad ()· P. J. Wang Cardiac Arrhythmia Service, Stanford University Medical Center, 300 Pasteur Drive, H2146, Stanford, CA 94305-5233, USA e-mail:
[email protected] T. Mihalik · C. Cartier · L. Capuano · D. Holtan CryoCath Technologies, Inc., Montreal, Quebec, Canada
Conclusions. A novel cryoablation balloon catheter is capable of achieving transmural freezing of the pulmonary vein. The catheter has promise for future clinical therapy of atrial fibrillation. Keywords Pulmonary vein · Cryoenergy · Ablation
Introduction Atrial fibrillation (AF) is the most common arrhythmia in adults and is associated with significant morbidity and mortality [1]. Recently, there has been a growing interest in the development of catheter based procedures to treat atrial fibrillation. Catheter based radiofrequency ablation of pulmonary vein (PV) potentials has emerged as a promising technique for the treatment of patients with drug-refractory atrial fibrillation [2–5]. While catheter ablation using radiofrequency energy is promising, there is an increased risk of pulmonary vein stenosis [6]. In order to avoid these complications, the creation of transmural and circumferential lesions around the PV ostium is considered to be a viable alternative [7, 8]. However, it is often difficult to achieve effective PV isolation with conventional ablation catheters. Cryoenergy has been used extensively to treat cardiac arrhythmias [9–12]. We hypothesized that a novel balloon-based cryogenic catheter system may be effective in achieving transmural circumferential lesions for PV isolation. The aim of this study was to test the effectiveness of a cryoablation balloon-catheter in creating transmural lesions and in exploring for potential use in treatment of AF.
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J Interv Card Electrophysiol (2006) 15:79–81
Methods A total of three excised ovine hearts were obtained from Hyclone Labs (Greeley, CO). In each case, the lungs were carefully removed while preserving the left atrial-pulmonary vein connection. The heart was placed in a plexiglass tank containing circulating normal saline maintained at 37◦ C by a thermostat-controlled heater. The pulmonary veins were then cannulated and perfused with 37◦ C saline at physiologic flow rates of 1 L/min/vein. In order to access the four pulmonary veins with the cryocatheter and to allow good visualization, an incision was made over the left atrium and ventricle. PV wall thickness was obtained by measuring in several locations with a standard vernier caliper and then averaged. Prior to cryoablation, a balloon-based cryogenic catheter (CryoCath Technologies Inc.) was deployed and positioned at the ostia of the pulmonary veins. The cryogenic liquid used was nitrous oxide (N2 O). Both the diameter and length of the inflated balloon were approximately 25 mm. A full 8-min ablation was performed. Surface thermocouples, positioned on the endocardial (attached to the surface of the balloon) and epicardial surfaces of the pulmonary veins, were used to determine whether transmural freezing was achieved.
Results The mean minimum temperatures measured on the endocardial and epicardial tissue in six pulmonary vein ablations was −38.8◦ ± 6.9◦ C and −10.0◦ ± 7.5◦ C, respectively. The average pulmonary vein thickness was 3.3 ± 1.4 mm. The time to 0◦ C was 30 sec for the endocardial tissue and 160 sec for the epicardial tissue. The average minimum endocardial pulmonary vein temperature was reached at 330 sec. The mean minimum epicardial pulmonary vein temperature was reached at 350 sec.
ing radiofrequency ablation to make circumferential lesions around the PV ostia has also proven to be challenging as it is difficult to ensure both transmurality and continuity of the lesions. Previous studies have shown that catheter cryoablation is effective in achieving myocardial ablation. In fact, cryoablation has been used extensively for surgical ablation procedures. Our study demonstrates that transmural freezing can be created circumferentially around the PV osteum using cryoablation. Balloon occlusion of the pulmonary vein may also be advantageous in creating deeper lesions by limiting blood flow through the pulmonary vein. In our study, temperature-monitoring using thermocouples demonstrated that transmural freezing occurred rapidly. With freezing, tissue contact becomes more stable allowing for circumferential lesions and reducing the potential for gaps in the ablation line. Use of a balloon catheter capable of achieving transmural freezing may be able to achieve pulmonary vein isolation for the treatment of atrial fibrillation. However, there are challenges to positioning the balloon adequately, given the complex anatomy of the pulmonary vein and the potential confluence with an adjacent pulmonary vein. It is possible that different balloon sizes will be required to compensate for variations in left atrial anatomy. Our study is limited by the fact that the hearts were ex-vivo, with normal tissue perfusion. However, immersion of the pulmonary veins within the circulating bath created a worse-case scenario since in situ the pulmonary veins would not be exposed to circulating fluid at body temperature. Another limitation is that we do not have confirmatory tissue histology that demonstrates tissue damage due to freezing. Although transmural tissue freezing was achieved, it may not mean that a transmural lesion was achieved. With the epicardial tissue achieving a freezing temperature (−10.0◦ ) it is possible that a lesion may not form. Further studies may be required to determine the amount of time needed to form a transmural lesion while transmural freezing is occurring.
Discussion Conclusions Recently, the myocardial sleeves within the PVs have been shown to be a key factor in the genesis of paroxysmal or persistent AF. This finding is supported by the fact that AF can be terminated by ablation of the PV suspected of contributing to initiation. However, numerous studies have shown that conventional ablation methods, while effective in curing AF initially, may not be effective in preventing its recurrence in many patients. The inability to achieve transmural isolation of the pulmonary veins may account for some of these recurrences. In addition, the use of radiofrequency energy in the PVs has been associated with pulmonary vein stenosis. UsSpringer
A novel cryoablation balloon catheter is capable of achieving transmural freezing of pulmonary vein. This catheter has promise for future clinical therapy of atrial fibrillation.
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