Catheter cryoablation in the treatment of atrioventricular nodal re-entrant tachycardia and atrial fibrillation

Abstract

Radiofrequency (RF) catheter ablation is a standard treatment for cardiac arrhythmias. However, inadvertent atrioventricular block (AVB) and pulmonary vein stenosis may complicate RF ablation of peri-nodal substrate and pulmonary vein isolation (PVI) for atrial fibrillation (AF) respectively. Moreover, the learning curve and procedural duration are long for RF PVI. By virtue of its favourable lesion characteristics, cryoadhesion, functionality of cryomapping and ability of being delivered through a focal or balloon-based catheter, cryothermy as an alternative energy source for ablation may overcome the limitations of RF. This thesis is divided into three sections. Section I provides an overview on the limitations of RF ablation and cryothermy as an alternative energy source. The study populations and methodology involved in 10 original studies are described. In a prospective study on using catheter cryoablation (CRYO) to treat different arrhythmias, namely AVNRT, atrioventricular re-entrant tachycardia, atrial flutter, AF and right ventricular outflow tract tachycardia in 82 patients, the safety and effectiveness of CRYO in a Chinese population was confirmed except in right-sided and left-sided accessory pathway ablation, for which the acute procedural success rates were lower than those observed in RF ablation. In Section II, 2 randomized-controlled and 2 retrospective case-control studies, comparing CRYO with RF in AVNRT ablation are presented. We had shown that the recurrence rate in 6mm-tip CRYO was still higher than RF ablation. In our pilot study on the use of 8mm-tip CRYO in treating AVNRT, this new approach was found to be safe and importantly, both the recurrence rate and procedural failure (a composite of acute procedural failure, inadvertent AVB and recurrence) were comparable with RF ablation. In the concluding randomized-controlled CRYOABLATE study of this Section, 158 patients were randomized to CRYO (80) and RF ablation (78). The safety of 8mm-tip CRYO for treating AVNRT and comparable recurrence rate and procedural failure rate with RF ablation were confirmed. Additionally, we had shown that both patient pain perception and operator stress were significantly lower in CRYO than RF ablation in another randomized-controlled study. In Section III, 5 prospective studies on cryoballoon (CB) PVI for AF are presented. The initial and maiden experience in Hong Kong is presented. In 122 Chinese patients, the 1-year recurrence-free survival after CB PVI was 77% for paroxysmal and 59% for non-paroxysmal AF and interestingly it reached a plateau of 52% and 30% respectively at 5 years. CB types and left atrial size were the only independent predictors for recurrence. In a prospective case-control study, we had shown that procedural duration, fluoroscopic time and the number of cryoapplications were significantly reduced by using an inner lumen mapping catheter during CB PVI. Last but least, we studied the under-recognized complication of persistent iatrogenic atrial septal defect (iASD) after CB PVI in 119 patients and found that spontaneous closure occurred up to 3 years and in 20% of patients, iASD would become permanent. A higher number of cryo-applications was the only independent predictor. No neurological event was observed over 129.7 patient-years of follow-up. Based on our data, a management algorithm was proposed.