AF-ABLATION

AF Ablation in London — Dr Boon Lim, Electrophysiologist

In 1998, a cardiologist called Michel Haïssaguerre published a paper in the New England Journal of Medicine that fundamentally changed how we understand and treat atrial fibrillation. He demonstrated that in most patients, the electrical triggers for AF originate from the pulmonary veins — the blood vessels that drain into the left atrium from the lungs. By electrically disconnecting those veins from the rest of the heart, it was possible to eliminate AF at its source.

That procedure — pulmonary vein isolation, or PVI — is now the cornerstone of all AF ablation. Over the past 25 years, the technology has evolved beyond recognition, but the underlying principle remains: find the source, isolate it, and give the heart a chance to beat normally again.

I have performed over 2,500 AF ablation procedures at Imperial College London and OneWelbeck Heart Health. What I want to give you here is the honest, transparent account that I give every patient sitting in my consulting room — the information you need to make a properly informed decision.

What is Pulmonary Vein Isolation?

The pulmonary veins are four blood vessels that carry oxygenated blood from the lungs into the left atrium. In patients with AF, abnormal electrical activity from within or around these veins fires chaotically, triggering the atria to quiver rather than contract. PVI works by creating a continuous ring of scar tissue around each pair of pulmonary veins, electrically disconnecting them from the atrial muscle. Once isolated, the triggers cannot escape into the atrium, and the pathway for AF is eliminated.

The procedure is performed through catheters — fine, flexible tubes — introduced through small punctures in the groin and guided under X-ray to the heart. We use advanced three-dimensional mapping systems, including CARTO (Johnson & Johnson) and Precision (Abbott), to create a detailed real-time map of the heart’s electrical activity, and also Pulse Field Ablation (PFA) including Affera (Medtronic) and Farapulse (Boston Scientific). This allows us to deliver energy with extraordinary precision.

The Latest Technology: Pulsed Field Ablation

Until recently, ablation energy was delivered as either radiofrequency (heat) or cryoablation (extreme cold). Both approaches are effective, but they are non-selective — they damage whatever tissue they contact, including occasionally structures adjacent to the pulmonary veins such as the oesophagus or phrenic nerve.

Pulsed field ablation, or PFA, represents the most significant technological advance in this field since cryoablation. Rather than using thermal energy, PFA delivers precisely calibrated electrical pulses that cause irreversible electroporation selectively in cardiac muscle cells — while largely sparing the surrounding structures. The clinical results are compelling. The ADVENT trial (NEJM, 2023) demonstrated non-inferior efficacy to thermal ablation, with zero cases of oesophageal fistula in the PFA arm. We now offer PFA at OneWelbeck Heart Health as part of our advanced AF ablation programme.

Am I a Suitable Candidate for AF Ablation?

AF ablation is most effective for patients with symptomatic paroxysmal or early persistent AF — particularly those whose symptoms have not been adequately controlled by antiarrhythmic medication, or who prefer not to take long-term medication. The 2024 ESC AF guidelines and 2023 AHA/ACC/HRS guidelines both give catheter ablation a Class 1A recommendation as a first-line rhythm control strategy in appropriately selected patients with symptomatic paroxysmal AF.

Factors I assess at consultation include: the type and duration of AF, left atrial size, the presence of modifiable risk factors (weight, sleep apnoea, blood pressure, alcohol intake), and your overall fitness and treatment preferences. Optimising these factors before ablation significantly improves success rates — this is something I discuss in detail with every patient.

What Happens on the Day of the Procedure?

At OneWelbeck Heart Health, AF ablation is routinely performed as a day-case procedure — you arrive in the morning and, in most cases, return home the same evening. This is not a compromise on safety. Our team recently published evidence in the journal Heart Rhythm (Kanthasamy, Finlay, Lim et al., 2025) demonstrating excellent safety outcomes across 450 consecutive patients undergoing AF ablation in our ambulatory day surgery centre, with complication rates comparable to major hospital-based series.

The procedure is performed under general anaesthesia. Before we cross into the left atrium, a transoesophageal echocardiogram (TOE) confirms there is no clot in the left atrial appendage. We then create the map, deliver ablation energy around each pulmonary vein, and confirm electrical isolation. Procedure time is typically 60 minutes.

What Are the Success Rates?

For paroxysmal AF in appropriately selected patients, single-procedure success rates — defined as freedom from AF without antiarrhythmic drugs at 12 months — are typically 70–80%. Some patients require a second procedure, and overall success rates with repeat procedures are higher. For persistent AF, results are somewhat lower with a single procedure, though improving with the adoption of PFA and enhanced substrate mapping techniques.

I always discuss realistic expectations with patients before proceeding. Ablation is not a guaranteed cure, but for most patients with paroxysmal AF it offers a substantially better prospect of sustained rhythm control than ongoing medication alone. I will always seek agreement to address this together, addressing risk factors and lifestyle factors are paramount and will enhance your chances of successfully restoring normal sinus rhythm and is what you can do (sometimes this is enough!). Together with a safe and effective ablation strategy, this is a handshake between patient and doctor to deliver the best outcomes.

One Welbeck Day-Case Programme

Our 2025 Heart Rhythm paper establishes a published standard of care for day-case AF ablation in the UK. It demonstrates that with the right patient selection criteria, procedural expertise, post-procedural pathway, and facility infrastructure, same-day discharge following AF catheter ablation is safe, effective, and reproducible. We are proud to have contributed this evidence to the field.

Paroxysmal vs Persistent AF

The 2024 European Society of Cardiology guidelines classify AF by the pattern of episodes:

• Paroxysmal AF: self-terminating episodes lasting less than seven days — most typically a few minutes to a few hours. The heart returns to normal rhythm on its own.
• Persistent AF: episodes lasting more than seven days, which require cardioversion — either electrical or pharmacological — to restore normal rhythm.
• Long-standing persistent AF: continuous AF for more than twelve months.
• Permanent AF: a designation used when both patient and physician have agreed not to pursue rhythm control, and the focus shifts to rate control and stroke prevention.

It is worth noting that permanent AF is a therapeutic decision, not an irreversible biological state. I have had patients reclassified from permanent to long-standing persistent when their circumstances or preferences changed — and who then went on to achieve excellent results from ablation.

Why Does It Matter for Ablation?

From an ablation standpoint, paroxysmal AF is significantly more amenable to catheter ablation than persistent or long-standing persistent AF, and understanding why helps patients set realistic expectations.

In paroxysmal AF, the arrhythmia is driven predominantly by triggers from the pulmonary veins. Pulmonary vein isolation — disconnecting those veins electrically from the atrial muscle — is therefore highly effective. Single-procedure success rates at 12 months in appropriately selected patients with paroxysmal AF are typically 70–80%.

In persistent AF, the arrhythmia has had longer to remodel the atria. A process called atrial fibrosis — scarring of the atrial wall — begins to develop, and the AF substrate extends beyond the pulmonary veins. This additional substrate may require more extensive ablation to address, and success rates are somewhat lower with a single procedure, though they continue to improve with techniques such as pulsed field ablation and high-resolution substrate mapping.

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