By Riccardo Cappato
Catheter ablation has been proven to effectively cure atrial fibrillation (AF) in variable proportions of patients with this arrhythmia and its popularity continues to escalate. A few years ago, a large international survey was conducted with the aim of providing data on catheter ablation of atrial fibrillation over a wide spectrum of patients, techniques and electrophysiology laboratories with variable experience. The study results reflected the evolution in the predominant techniques during the years following the introduction of this therapy, its increasing penetration in clinical practice and the efficacy and safety observed in 8,745 patients from about 100 EP laboratories between 1995 and 2002. Data from this survey suggested that this therapy was less effective and safe than reported in literature. Meanwhile, catheter ablation of atrial fibrillation has evolved leading to newer techniques applied to broadened indications in sicker patient categories. The impact of recent developments and increasing investigators experience in everyday practice was assessed in a most recent survey which investigated the efficacy and safety of catheter ablation of atrial fibrillation during the years 2003 through 2006. Data relevant to the study purpose were drawn from a questionnaire developed by an independent Steering Committee with the aim of investigating the methods and efficacy of catheter ablation of atrial fibrillation as observed in a large number of EP laboratories worldwide during the above mentioned years.
Eighty five centres provided a complete interview response set. According to the reported evidence, 16,309 patients underwent 20,825 procedures over 18 (range 3–24) months follow-up. This yielded a median of 245 procedures per centre (range 2–2,715) and 1.3 procedures per patient. Single, dual and triple trans-septal punctures were used in 37.1%, 59.8% and 4.1% of centres, respectively. Males represented 60.8% of patients and lower and upper age limit for entry were 15 years and 90 years, respectively. Among entry criteria were: drug refractoriness in 96.5% of centres, paroxysmal AF in 100%, persistent AF in 85.9% and permanent AF in 47.1% of centres. Exclusion criteria included an age equal or higher than 65 years in 50.6%, an upper limit of left atrial size (between 55 and 60 mm of maximal transverse diameter) in 31.8%, a lower limit of left ventricular ejection fraction (between 30% and 35%) in 22.4% and prior heart surgery in 23.5% of centres. Carto-guided ablation or ostial electrical disconnection were the most popular ablation strategies, with the former being used in 48.2% and the latter in 27.4% of all patients. In more than three-fourth of patients in the Carto-guided group, catheter ablation was performed with the aim of producing pulmonary vein isolation, whereas in the remaining patients pulmonary vein isolation was not a required procedure endpoint. Three-dimensional non-contact mapping was used in 4.7% of patients, ablation guided by CFAE in 2.4% of patients while a combination of two or more strategies was reported in 7.4% of patients. Of all patients, 68.1% received radiofrequency current delivered through an irrigated (46.4%), cooled (20.4%) or 8-mm tip electrode (1.3%), 30.7% received radiofrequency current delivered through conventional 4mm tip electrode, 1.2% underwent cryo-ablation, and 0.002% ultrasound ablation.
Of the 16,309 patients, 10,488 (median, 70%; interquartile range, 57.7–75.4%) became asymptomatic in the absence of any anti-arrhythmic drug whereas another 2,047 (10%; 0.5–17.1%) became asymptomatic with the continued use of formerly ineffective anti-arrhythmic drugs. Therefore, 12,535 patients (80%; 74–83.8%) obtained resolution of symptoms after completion of any of the ablation protocols used. The success rate free of anti-arrhythmic drug was 69.9% in 11 centres performing catheter ablation of paroxysmal AF only, 61.3% in 33 centres performing catheter ablation of paroxysmal and persistent AF and 62% in 41 centres performing catheter ablation of paroxysmal, persistent and permanent AF. Success rate free of anti-arrhythmic drug values were correlated with the number of procedures performed per centre (r=0.47). Conversely, success rates with drugs were inversely correlated with the success rates free of drugs (r=-0.57). Not unexpectedly, success rates free of drugs and overall success rates were significantly higher in patients with paroxysmal AF than in patients with persistent AF and permanent AF. Outcome data in relationship with the type of ablation catheter and ablation strategy used were made showed that success rates free of anti-arrhythmic drugs did not differ between 2,892 patients undergoing ablation with the use of a 4mm tip catheter versus 6,674 patients undergoing ablation with the use of an irrigated/cooled tip catheter, while significantly larger overall success rates were observed with the use of a 4mm tip catheter. No differences in success rates were found between 3,722 patients undergoing ablation using a Lasso-guided catheter strategy versus 7,059 patients undergoing ablation using a 3D Carto-guided catheter strategy.
Pre-ablation, sub-cutaneous (4.1%), low-molecular weight (27.5%) or intravenous heparin (7.2%) were used, regardless of whether or not patients were taking long-term oral anticoagulants. A trans-esophageal echocardiogram was required prior to the ablation procedure in 73.2% of centers. During the ablation procedure, 94.9% of centers reported using intravenously administered heparin, of which 79.4% were guided by ACT (minimum ACT range, 200–350sec) whereas 15.5% were not. Post-ablation, 84.5% of centres used oral anticoagulants whereas aspirin was administered in 13.4% of centres and clopidogrel in 2.1% of centres.
A major complication occurred in 741 patients (4.5%). There were 25 procedure-related deaths, 37 strokes, 115 transient ischaemic attacks and 213 episodes of tamponade. Altogether, 216 pulmonary veins sustained significant (>50%) stenosis (assessed by means of pre- and post-ablation pulmonary vein angiography in 71.3% and magnetic resonance in 28.7% of centres), which resulted in the need for a corrective intervention in 48 patients. Atypical atrial flutter of new onset (iatrogenic) was reported in 1,404 patients (8.6%), and was significantly (p<0.001) more frequently observed in centres using exclusively 3D Carto-guided ablation (9.5%) than in centres performing exclusively Lasso-guided ablation (3.6%).
In summary, when analysed in a large number of EP laboratories worldwide, catheter ablation of atrial fibrillation showed to be effective in about 80% of patients, after 1.3 procedures/patient, with about 70% of them not requiring further anti-arrhythmic drugs during intermediate follow-up. These results are dependent on centre and operator experience and can be obtained with an expected 4.5% incidence of procedure-related complications.
Riccardo Cappato is the director of the Centre of Clinical Arrhythmia and Electrophysiology, Policlinico San Donato, Milan, Italy.