Introduction 

Atrial fibrillation (AF) is not only one of the most common arrhythmias, but its prevalence increases with age. AF significantly contributes to morbidity and mortality by causing symptoms such as fatigue, palpitations, or shortness of breath in varying severity and by increasing the risk of stroke, neurodegenerative disease, or even mortality. Rate control and rhythm control are the two main therapy strategies in the treatment of AF. Rate control aims to keep the resting heart rate less than 100 bpm. Rhythm control includes rate control, but also attempts to restore and maintain sinus rhythm for as often and long as possible. The first line treatment for rhythm control is antiarrhythmic drugs to suppress AF and prevent its progression. The discovery of focal activity generating from the pulmonary veins (PV) as a key trigger of AF also introduced electrical isolation of the PVs by catheter ablation as an interventional therapy for AF. Several studies have shown that PV isolation is an effective tool to reduce AF burden and symptoms in formerly symptomatic patients¹ and is often more effective in reducing AF recurrence than antiarrhythmic drugs.^2,3 Older trials comparing rate control to rhythm control showed no benefit of the latter, and perhaps a trend toward increased stroke.⁴ Despite its efficacy, ablation has not been shown to reduce stroke or mortality and carries a risk of complications (1-2%).⁵ However, ablation remains a therapy for improvement of quality of life in symptomatic patients. This review will discuss findings that might support the idea of performing ablation in selected asymptomatic patients, as well as current and future research with special regard to the effects of AF ablation on the risk of stroke.

Determining if a Patient is Truly Asymptomatic 

For patients who have had AF for a long period of time, particularly persistent AF, the symptoms may initially be quite subtle such that patients are mistaken for being asymptomatic. Despite the lack of overt symptoms, AF ablation could still be a feasible way to improve well-being in these patients. Mohanty et al recently showed that ablation could improve quality of life and exercise tolerance in patients with asymptomatic, longstanding persistent AF.⁶ Therefore, a more careful assessment of symptoms may be of benefit in otherwise “asymptomatic” AF. When a patient presents with “asymptomatic” AF, a careful history to elicit features such as progressive decline in exercise tolerance or excessive fatigue is required to ensure that subtle symptoms are not being missed. A trial of cardioversion may also be particularly useful in assessing whether symptoms are secondary to AF or not.

Can AF Ablation Reduce the Risk of Stroke?

If a patient with AF is truly asymptomatic, then performing ablation would only be justified if it could reduce their risk of stroke or mortality. To date, several observational studies have investigated the risk of stroke after AF ablation (Table 1). These studies mainly included patients with a low to intermediate risk of stroke. Although anticoagulation was stopped in varying proportions of patients, the risk of stroke was generally low in all of these. The largest study was performed by Reynolds et al.⁷ Over a 3-year follow-up, they reported an annual stroke risk of 1.6% for patients after AF ablation and 2.7% on antiarrhythmic drugs. Oral anticoagulation was administered in 60% of patients over the entire follow-up period. This might suggest that ablation reduces AF burden sufficiently to reduce the risk of stroke. However, data suggests that as little as 5.5 hours of AF per month could substantially increase stroke risk.⁸ We must remember that only large, prospective randomized trials will inform us on the safety of stopping therapeutic anticoagulation after AF ablation and the factors influencing the risk of stroke after ablation (e.g., AF recurrence, AF burden, underlying diseases). It is on this basis that the Optimal Anticoagulation for Enhanced Risk Patients Post-Catheter Ablation for Atrial Fibrillation (OCEAN) trial (NCT02168829) was designed; this study will assess whether ongoing oral anticoagulation would be superior to antiplatelet therapy alone in patients at intermediate risk of stroke after successful AF ablation. Until such results are available, current guidelines suggesting ongoing therapeutic anticoagulation in higher risk patients should be followed.

Today, more advanced technologies such as implantable loop recorders (ILR) are also available for long-term monitoring of AF burden. The ILR’s ability to detect asymptomatic episodes of AF is especially useful in the context of AF ablation, since studies showed a significant increase in asymptomatic AF episodes after ablation.⁹ The routine use of such technology post ablation may help to identify those patients in whom therapeutic anticoagulation may be safely stopped because of adequate AF burden reduction. 

Can AF Ablation Reduce the Risk of Mortality?

AF is known to significantly increase mortality, mainly by the increased risk for stroke and other thromboembolic events.¹⁰  Yet to date, there is no evidence that rhythm control is superior to rate control in terms of mortality. However, these trials utilized antiarrhythmics for rhythm control. This was an important limitation, since the overall rate of sinus rhythm was not that different in the rate vs rhythm control groups because of the limited efficacy of drug therapy.¹¹ Furthermore, antiarrhythmic drugs can increase the risk of both morbidity and mortality. AF ablation provides better rhythm control compared to drug therapy, and does not have long-term impacts on morbidity or mortality. Again, these remain hypothetical reasons why ablation may yet improve mortality in higher risk patients; however, only large-scale, randomized trials will ultimately offer more insight into the impact of AF ablation on long-term morbidity and mortality.

Conclusion

Prospective studies will improve our knowledge of the influence of AF ablation on long-term outcomes, including the risk of stroke. Implantable loop recorders could make it possible to reliably identify patients that have been “cured” by AF ablation and thus have a low risk of recurrence. If AF ablation offers an improvement of morbidity in a subset of patients (i.e., young and otherwise healthy patients), it can be a reasonable alternative for patients with asymptomatic AF, but for the majority of patients, it will still be restricted to symptomatic relief. 

Disclosures: The authors have no conflicts of interest to report regarding the content herein. Outside the submitted work, Dr. Verma reports grants from Biosense Webster, Medtronic, St. Jude Medical, and Bayer.

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