| Percutaneous catheter ablation has become a routine treatment for many symptomatic cardiac arrhythmias. Radiofrequency ablation has become the mainstay of therapy for many atrial arrhythmias because it is an exceedingly safe and effective technology. However, the demand for specific ablation lesion characteristic has highlighted some of its limitations. We investigated the use of cryoablation using a new catheter on the sinus node and atrioventricular node as well as on the myocardium. The goals of this study were threefold (1) To determine if a successful site might be identified prior to the ablation, and what temperature range is appropriate to ice mapping; (2) To access the ability of catheter cyroablation to permanently abolish conduction of the sinus node and AV node with prior ice mapping of the target area; (3) To examine the histology and ultrastructure of the lesions produced by hypothemal energy in the myocardium including the sinus node and the atrioventricular node.[Methods and Results!Electrophysiological studies with recordings of heart rate, sinus node recovery time, point of Wenckebach block, 2:1 point, AH interval, HV interval were performed on 18 mongrel dogs with different temperature. Transient, AV conduction block issuccessfully induced with mild hypothermal cryoablation (?40 ??50 ) . Evident electrophysiological changes of sinus node is also not happened until the cryoablation temperature is lowered to ?50. An exposure time of 4, 6, 8 minutes makes the cryoablated lesion much more larger than that of 2 minutes for a liquid N20 cryoprobe. Sinus node is successfully cryoabalted in 7 of 8 dogs via epicardium cryoablation (87.5%). Atrioventricular node is ablated with transvenous catheter of CryoCath. Complete Atrioventriular conduction block is induced in 3 of 5 dogs (60%) with ?5 2 minutes ablation, in all the five dogs with ?5 4 minutes cryoablation(100%). There is no risk of endocardial disruption and thrombus formation occurred. Multiple cryolesions do not form a chronic substrate for ventricular tachycardia. Histologic analysis of the atrial pre-nodal region, atriaventricular node, ablated myocardium were performed after the procedure. The myocardium had discrete, sharply delimited lesions. Histological modifications of myocardium induced by cryoablation in all temperatures shows heterogeneous necrosis and swelling of the myocardium. What the histopathologic change of lesions shows is consistent with its gross look as well as with the ultra structure changes.LConclusions]We can demonstrate that voluminous, homogenous lesions can be produced in myocardium using transcatheter cryoablation without damaging surrounding cardiovascular structures. One distinct feature that characterizes the positive side of cryoenergy is ice mapping and reversibility. It allows for prediction of success prior to full delivery of the energy and hence to test the effects of the ablation while the lesion is still forming thus reducing the number of ineffective and useless lesions. In addition, it alsoallows for the evaluation of the acute effects on the structures adjacent to the ablation site. Mild hypothermal (?40 ?50) is the appropriate temperature of reversibly ice mapping of canine' s target ablation sites. While the lowest temperature of -75 癈 will block local conduction of sinus node as well as atrioventricular node permanently. Lesion size is related to ablation temperature although in all the lesions the histological changes are heterogeneous.
|
PDF Full Text Request