Evaluation of the safety and effectiveness of the CryoMedix cryoablation catheter system for the treatment of atrial flutter and fibrillation.

BACKGROUND: Catheter ablation of atrial flutter and fibrillation (AFL and AF) has typically been performed with radiofrequency energy. Cryoablation has recently been used for AF and AFL, but its success has been limited by the nadir temperature achievable using nitrous oxide as a refrigerant. In this study, a novel approach allowing for use of a liquid refrigerant capable of achieving lower nadir temperatures was tested in a canine model with cavo-tricuspid isthmus (CTI) and left atrial (LA) ablation.

METHODS AND RESULTS: In six dogs, under general anesthesia, standard catheters were placed in the coronary sinus and right ventricular apex, and the CryoMedix cryoablation catheter (CAC) in the right (CTI) and left atrium (for ablation, across the LA roof, mitral isthmus, and LA septum). Double-freezes up to 2 min each were performed, with a 30-s thaw cycle between freezes. Ablated areas were subsequently grossly inspected and photographed and tissues fixed in formalin for histologic analysis to determine if the lesions were contiguous and transmural. In all animals, long linear (from 4-8 cm) transmural atrial lesions were observed on gross and histological examination in the left atrial roof, septum and mitral isthmus, and across the cavo-trisucpid isthmus. In all animals, bi-directional cavo-tricuspid isthmus block was observed after ablation, during pacing from the coronary sinus ostium and low lateral right atrium, respectively. Up to 50% thickness lesions were observed in the right ventricle below the tricuspid valve in all animals. There were no acute complications noted in any animals.

CONCLUSIONS: The CAC system produces extremely negative freezing temperatures, significantly lower than those reported for nitrous oxide based systems. The CTI was easily ablated with the CAC system, producing bi-directional conduction block, suggesting a potential role for the system in the treatment of isthmus-dependent atrial flutter. Transmural LA lesions were also produced with the CAC system, suggesting a potential role in treating AF.