In vitro and in vivo evaluation of the thermal patterns and lesions of catheter ablation with a microwave monopole antenna.

BACKGROUND

Radiofrequency (RF) catheter ablation is an effective treatment for supraventricular tachycardia. The effectiveness of the technique is at times limited by the small lesion size produced by RF energy delivery. Previous reports have indicated that microwave energy is capable of producing a larger volume of heated tissue than radiofrequency energy, raising the possibility that microwave energy may offer a potential alternative energy source to radiofrequency for the substrate ablation of certain arrhythmias such as ventricular tachycardia or atrial flutter.

METHODS

The present study evaluated the thermal profiles of a monopole microwave antenna delivering energy at 2.45 GHz frequency in a phantom tissue-equivalent material with dielectric and thermal properties similar to myocardium. In addition, microwave catheter ablations were performed in vivo in the ventricles of goats prior to the examination of the lesions.

RESULTS

The measured thermal profiles in the phantom revealed that the antenna is capable of producing heating to a temperature associated with myocardial necrosis to a controllable depth that can be more than 8 mm, while the endocardial temperature is maintained relatively low. The ablation volume is significantly reduced but is still effective when there is only a partial contact between the antenna and the tissue surface. In vivo studies on goat models confirmed that the monopole antenna can produce a deep transmural lesion in the left ventricle without causing coagulation or charring on the endocardial surface.