Atrial fibrillation ablation: safety and efficacy

Br J Cardiol 2010;17:255–6 Leave a comment
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Following recent publication of the 2010 European Society of Cardiology (ESC) guidelines for atrial fibrillation (AF) it is timely the BJC publish an article by Gunawardena et al. (see pages 271-6) describing a single centre cohort analysis of their AF ablation procedures.1

The outcomes of patients with AF are well documented (table 1) but frequently remain underestimated by both patients and health professionals alike. AF is associated with increased rates of death, stroke, other thromboembolic events and heart failure, significant hospitalisation, and reduced quality of life and exercise capacity. Despite these sobering facts, many trials have failed to demonstrate benefit in maintaining sinus rhythm (SR) over anticoagulation and rate control. Yet, quality of life is significantly impaired in patients with AF compared with healthy controls, and post hoc analyses suggest maintaining SR may improve quality of life, and could possibly be associated with improved survival. Furthermore, post hoc analysis of the Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) database, assessing a rate versus rhythm control strategy suggested that the deleterious effects of anti-arrhythmic drugs (increased mortality of 49%) may have offset the benefits of SR (53% reduction in mortality).2 Therefore, with an ageing population, and the prevalence of AF set to double in the next 50 years, much expectation surrounds recent developments including new anticoagulation drugs (dabigatran), stroke prevention interventions (left atrial appendage occlusion) and anti-arrhythmic therapies (dronedarone). However, the article by Gunawardena et al., describes the outcomes of a not so recent development, catheter-based atrial ablation.

Patient selection

In the study by Gunawardena et al., 100 patients underwent an AF ablation, in keeping with National Institute for Health and Clinical Excellence (NICE) guidance, they were symptomatic despite drug therapy. Historically, catheter ablation has usually been performed in this group of patients; symptomatic paroxysmal AF (PAF), resistant to at least one anti-arrhythmic drug. This is supported by data from multiple single centre randomised studies, multi-centre prospective studies and meta-analyses comparing drug treatment with catheter ablation, showing superiority of rhythm outcome following ablation. Although data on a direct comparison of drug treatment and catheter ablation as first-line therapy in symptomatic patients with PAF is scarce, given the relative safety of the technique when performed by experienced operators, ablation may be considered as initial therapy in selected patients. Given the risks of long-term anti-arrhythmic therapy, in particular amiodarone, perhaps there is a case for catheter ablation at an earlier stage, particularly in younger patients with a long lifetime exposure risk of drug side effects. This would also be influenced by an increased likelihood of ablation success before atrial cellular and structural changes occur.

Initial AF ablation strategies targeted focal ‘firing’ from the muscle sleeves within the pulmonary veins (PV) that initiate some episodes of AF. Ablation lesions were placed close to the vein ostia in the left atrium (LA) risking stenosis or occlusion of the vein. As the majority of patients with AF recurrence after ablation demonstrate PV reconnection, PV isolation and its maintenance has become the cornerstone of ablation therapy. However, recurrence of AF following these procedures has also been noted, not just from reconnection of the veins, but also from focal ‘firing’ in the antrum of the veins at their insertion into the LA. Therefore, to reduce the risk of PV stenosis and to isolate the antrum, ablation is now more frequently performed by long circumferential lesions encompassing both PV in pairs. In the study by Gunawardena et al., ablation lesions were sited around each vein separately with the goal of isolating all identified veins. However, only 77% of veins were isolated at the time of the first procedure. This may to some degree be explained by the fact that in more recent years technological and imaging advancements have made isolation of all four PV more readily achievable than in historical case series, but is likely to have had an impact on clinical outcome.

A proportion (30%) of the patients in the study by Gunawardena et al. had persistent AF (>7 days AF duration or requiring cardioversion; chemical or electrical). For patients with either persistent or long-standing persistent AF (>1 year duration) the risk–benefit ratio for ablation is less clear. In patients with persistent and long-standing persistent AF, additional ‘substrate modification’ by the ablation of lines and high-frequency signals (complex fractionated electrograms) has helped improve outcome. However, care must be taken to ensure complete conduction block, as gaps in these lines of ablation may provide a substrate for the development of atrial tachycardia utilising conduction routes through these gaps. In this series, additional linear lesions were made in those with persistent AF or those who remained in AF despite vein isolation. Seven patients developed left atrial tachycardia, which would be in keeping with published series.

Patient outcomes

Gunawardena et al. report patient outcome with a ‘real-world’ methodology of failure, partial and ‘clinical’ success. Success was defined by no symptoms, electrocardiogram (ECG) or Holter evidence of AF lasting >30 seconds, and no class 1C or III anti-arrhythmic therapy; ‘partial success’ defined as AF symptoms and objective AF burden substantially reduced on or off previously ineffective anti-arrhythmic therapy; ‘clinical success’ defined as the sum of ‘success’ and ‘partial success'; and ‘failure’ defined as no clinically relevant change in symptoms or AF burden. Cumulative ‘success’, ‘partial success’, ‘failure’ and ‘clinical success’ rates after 22 ± 14 months were 60%, 26%, 14% and 86%, respectively. ‘Clinical success’ rates for paroxysmal and persistent subgroups were 73% and 47% (first procedure) rising to 87% and 83% (all procedures). The definition of clinical success is an interesting one as it essentially reflects the outcome of a procedure as a true reflection of its initial intent, that of symptomatic improvement. In fact it has been proposed that symptom-based follow-up, rather than ambulatory monitoring, may be sufficient, particularly in those where the indication was symptom relief. Although this has not been the usual practice in previous studies it perhaps better defines patient outcome with more clarity. However, the inclusion of a ‘success’ percentage as well as ‘clinical success’ is a necessity as it provides a value that can be benchmarked against other studies. The 2008 Heart Rhythm Society (HRS)/ESC AF consensus document states that being arrhythmia free is the true end point of ablation therapy and remains the ‘gold standard’ for outcome, although it may under represent the true benefit of the procedure.3

Complications from catheter ablation for AF are well documented, in this study mortality was 1% at six months, tamponade 5%, pericarditis 5%, pain 2%, atrial tachycardia 8%, and allergy 1%. These frequencies of complication would not be too dissimilar to published case series. Complications, however, were assessed not as success was, on a per patient basis, but as a percentage of total procedures performed. One could argue that complications per patient are more important in a patient’s treatment journey than complication rates per procedure, particularly as the frequency of further procedures is relatively high (167 procedures in 100 patients).

Summary

This study is a single centre historical cohort of 100 consecutive patients treated in a UK centre with catheter ablation for symptomatic drug refractory AF. The results document outcomes in keeping with published case series with acceptable complication rates. Although medical therapy is the cornerstone of treatment for AF, ablation is assuming an ever greater role. As these procedures become more common and both centres and operators alike become more experienced and comfortable in addressing more advanced disease, the indications for this procedure are likely to expand and encompass more patients.

Conflict of interest

JL has had travel grants from Medtronic, St Jude Medical and Boston Scientific.

Editors’ note

See also the article by Gunawardena et al. on outcomes following catheter ablation of AF in the UK, on pages 269-74 of this issue.

References

  1. Camm AJ, Kirchhof P, Lip GY et al.; the Task Force for the Management of Atrial Fibrillation of the European Society of Cardiology. Guidelines for the management of atrial fibrillation. Eur Heart J 2010; advanced access, doi: 10.1093/eurheartj/ehq278
  2. Wyse DG, Waldo AL, DiMarco JP et al.; Atrial Fibrillation Follow-up Investigation of Rhythm Management (AFFIRM) Investigators. A comparison of rate control and rhythm control in patients with atrial fibrillation. N Engl J Med 2002;347:1825–33.
  3. Calkins H, Brugada J, Packer DL et al. HRS/EHRA/ECAS expert consensus statement on catheter and surgical ablation of atrial fibrillation: recommendations for personnel, policy, procedures and follow-up. A report of the Heart Rhythm Society (HRS) Task Force on catheter and surgical ablation of atrial fibrillation. Heart Rhythm 2007;4:816–61.
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