Catheter Ablation of Atrial Fibrilation
Dr Matthew Wright CCT Cardiology MRCP MB BS PhD is a cardiologist at Guy's Hospital and St Thomas' Hospital.
Atrial fibrillation (AF) is the most common form of sustained heart arrhythmia, with an estimated 1.7% of the general population in the UK affected. The prevalence increases with age, meaning that 6.5% of people will have AF by the age of 65, and 12% by the age of 80.
Atrial fibrillation is responsible for a quarter of all strokes, and managing the condition is complex. It requires risk analysis taking into account the appropriate use of anticoagulation, management of associated medical conditions such as hypertension and diabetes, and control of the patient’s symptoms.
The natural progression of AF is one of patients presenting with paroxysmal AF (self terminating, with episodes lasting less than a week), to one of persistent AF (electrical or pharmacological cardioversion needed to return to sinus rhythm, and episodes lasting longer than a week). The rate of progression from paroxysmal AF to persistent AF varies, but up to 30% of patients are in persistent AF within 5 years. All treatments aimed at maintaining sinus rhythm have been demonstrated to be more effective when patients are in paroxysmal rather than persistent AF, so early recognition and definitive treatment is essential.
The latest guidelines
The latest European Society of Cardiology guidelines for the management of AF (published in 2012) advocate the use of the CHADSVASC scoring system to properly classify patients; from low risk of stroke - not requiring anticoagulation - to those who require formal anticoagulation (Figure 1). Aspirin has no role in the management of AF, having been demonstrated to have similar bleeding complications to Warfarin but without significantly lowering the risk of stroke.
Although Warfarin, and the novel oral anticoagulants such as Dabigatran, Rivoroxaban and Apixaban do increase the risk of a major bleed, the HASBLED score is used to properly assess patients at high risk of bleeding. The vast majority of patients with AF should be on oral anticoagulation.
Despite management of symptoms with beta-blockers, German registry data demonstrates that almost half of patients with ‘stable’, treated AF are admitted to hospital once a year due to uncontrolled symptoms, and a fifth are admitted more frequently. Patients with AF suffer both physically and socially. Quality of life studies suggest that patients with AF have a worse morbidity rate than patients who have suffered a heart attack.
Catheter ablation of AF has progressed dramatically over the last 15 years. The team led by Professor Haissaguerre in Bordeaux, with whom I collaborate, has demonstrated that ectopic beats from the pulmonary veins are responsible for triggering AF in over 97% of cases. Since that seminal study, ablation techniques have improved, as has the safety of catheter ablation.
There is now a large body of evidence that catheter ablation is a very effective treatment for patients with both paroxysmal and persistent AF. Numerous studies have demonstrated that catheter ablation is more effective at maintaining sinus rhythm, more effective at improving patients’ symptoms, and is cost effective when compared to standard medical therapy.
What the data shows
These data have led to the strong recommendation in the latest ESC guidelines for the use of catheter ablation as first line therapy in appropriately selected and counselled patients with paroxysmal AF, and in patients with persistent AF who have failed one anti-arrhythmic medication (Figure 2).
A key point is that catheter ablation is indicated for symptomatic benefit. Symptoms can be difficult to assess in patients with AF as they are often multifactorial. A large French primary practice registry showed that patients’ perception of symptoms changes in relation to age. Younger patients tend to complain of palpitations, those in middle age complain more of breathlessness, and older patients of general fatigue.
Often the easiest way to assess whether a patient can benefit from an AF ablation is to perform a cardioversion. If the patient returns to sinus rhythm and has symptomatic relief then catheter ablation should be discussed.
For patients with persistent AF, long term success is related to its duration (patients with AF duration of less than two years do better), the left atrial diameter (the smaller the better), and the degree of organisation as measured by the coarseness of AF on a standard ECG (the ‘coarser’ the better).
Studies have also shown that for patients with both atrial flutter and AF, those undergoing an AF ablation as opposed to just ablation of typical atrial flutter do much better. It is therefore important for patients with atrial flutter to be assessed for AF with Holter monitoring, as these conditions co-exist in 30% of cases.
However, despite the strong evidence for the effectiveness of catheter ablation for patients with AF, the success rates are still not as good as those for other supraventricular tachycardias, such as AVNRT, and Wolff Parkinson White syndrome, where long-term cure rates are over 95%. Patients often require multiple procedures to have a long term freedom from AF.
The major reason for recurrence of AF in patients with paroxysmal AF who have undergone a catheter ablation is due to the pulmonary veins electrically reconnecting across previously ablated tissue. Over the last four years there has been considerable research into improving the ablation procedure using a number of technologies. Catheter contact is critical to forming stable lesions, yet until recently there was no way that the operator could objectively assess what contact force was being applied.
The latest catheter technology incorporates force sensing technology so that the operator can judge the contact at each individual lesion. Studies have already shown that there is a wide variation in operators with respect to force applied during ablation. It is hoped that by providing information on contact force, that success rates will improve further, (early studies suggesting that this is indeed the case). Bupa Cromwell Hospital uses the very latest in mapping and catheter technologies (Figure 3), and has a very experienced team managing every aspect of the patient’s care.
In summary, the outlook for patients with AF is much brighter. Management of patients requires integrated care however, with appropriate risk assessment of stroke and bleeding risk, thorough assessment of symptoms with ambulatory and exercise monitoring, cardioversion, and assessing whether they are suitable for AF ablation.
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