Prediction of lesion size through monitoring the 0 degrees C isothermic period following transcatheter cryoablation

A prototype steerable 8.5F bipolar catheter fitted with a feedback thermoco uple was tested in 7 anaesthetized pigs (30 kg) guided by the electrocardio gram in order to modify the AV nodal and His-Purkinje system conductive pro perties. Thermal energy was delivered by a pressurized N2O tank (>650 psi) via a cardiac cryo unit (Spembly, Hampshire, UK) into the catheter wherein gas expands resulting in a tip temperature as low as -70 +/- 2 degrees C wi thin 10 seconds. Cryoablation under fluoroscopic and electrocardiographic g uidance was applied at distinct sites in both ventricles for 60 or 120 seco nds. After a follow-up period of 6 weeks, the ablation lesions found were w ell demarcated with small margins of hypertrophy of myocardial cells. With respect to lesion volume variability (8-207 mm(3)) and geometry, a relation ship between the 0 degrees C isothermic period and cryolesion volume was fo und. Results of an in vitro model corroborated this relationship. Therefore , an isothermic period probably can predict the lesion size and its geometr y in terms of lesion depth. This potential therapeutic mode of transcathete r cryoablation deserves further investigation.