Search

Introduction: Catheter-based cryoablation has been shown to produce punctate and effective cardiac lesions to treat focal targets. However, sequential applications are required to produce a continuous linear lesion needed to cure macroreentrant arrhythmias with large critical isthmuses. The purpose of this study was to compare and contrast linear cardiac lesions produced with sequential applications using a novel cryoablation system to those produced using radiofrequency (RF) energy. Methods and Results: Seven mongrel dogs were prepared for femoral venous insertion of the ablation catheter (either a 10-French, 6-mm tipped, bipolar cryoablation catheter (N = 5, cryo group) or a 7-French, 4-mm tipped, bipolar RF ablation catheter (N = 2, RF group)). Ablation of the cavotricuspid isthmus was performed by delivering applications at sequential locations across the isthmus. The cryo group received 6 to 10 (mean 8 ± 1.4), 5-minute applications at 3 to 5 separate sites with a mean nadir temperature of −74.5 ± 1.6°C. Each dog in the RF group received 9, 90-second applications with a mean temperature and power of 62 ± 0°C and 32 ± 3.6 W. No acute or chronic complications were associated with either form of ablation. Immediately and six weeks after the index procedure, electroanatomical mapping showed the presence of bidirectional isthmus conduction block in all dogs. Gross and histopathologic examination revealed the presence of linear lesions, which were continuous and transmural. Conclusion: Similar to RF ablation, catheter-based cryoablation can produce linear, transmural lesions in the cavotricuspid isthmus resulting in permanent bidirectional isthmus conduction block.

The Metrix™ Atrioverter Expanded Indication Trial evaluates the safety and efficacy of an implantable atrial defibrillator in patients with symptomatic, recurrent and drug refractory atrial fibrillation who also have structural heart disease. In this ongoing multicenter study, all patients are anticoagulated and concomitant antiarrhythmic drug treatment is left to the preference of the physician. Holter monitoring is performed prior to enrollment in the study. Spontaneous episodes of atrial fibrillation (AF) are treated under physician observation and when patients are ambulatory, the device is programmed in a monitoring mode. The atrial defibrillation threshold is measured at implantation and at 3, 6 and 12 months thereafter. The performance of the AF detection and R-wave synchronization algorithm is assessed at implantation, at regular follow-up intervals, and each time the patient visits the hospital for treatment of a spontaneous episode of AF. An echocardiogram is performed prior to implantation, at 3 and 6 month follow-up and for patients with an implanted heart valve, after 20 and 50 atrial defibrillation shocks have been delivered. The study started on October 1997 and will end after the last patient enrolled completes his/her six-month post-implantation follow-up, unless a safety issue arises. As of September 1998, 6 patients (2 patients with tachycardia induced cardiomyopathy, 1 patient with a mitral valve prosthesis, 2 patients with hypertrophic cardiomyopathy and 1 patient with congenital heart disease) have been enrolled in the study. Over 350 shocks have been delivered for atrial defibrillation testing or termination of spontaneous AF episodes. There have been no reported cases of ventricular proarrhythmia or inaccurately synchronized shocks and no complications of device therapy in this population.