Over the past decade, I've attended many sessions on how to ablate persistent atrial fibrillation (AF). These are often panel discussions in which experts describe their approach.
One constant in these sessions is that the number of (often disparate) ways to ablate persistent AF matches almost perfectly to the number of experts on the panel. No one has a clue.
The cornerstone of AF ablation is to electrically isolate the pulmonary veins (PVI). This works reasonably well in patients with paroxysmal AF but PVI for persistent AF is less successful.
Lower success rates plus the observation that patients with persistent AF often have evidence of both structural and electrical atrial disease have led to the idea of ablating additional areas outside of the pulmonary veins. It makes intuitive sense that more (ablation) ought to be better.
But, as it so often is in the practice of medicine,less proved as good as more when tested in a rigorous trial. In 2015, Atul Verma, MD, and colleagues published the results of the STAR AF II trial, which randomized patients with persistent AF to PVI alone or to two other strategies of PVI plus more ablation. They observed no differences in the primary endpoint of freedom from AF.
Despite this strong evidence, the idea of additional ablation for persistent AF remained strong. One year after STAR AF II, a group of influential electrophysiologists published a nonrandomized study of 52 patients and concluded that isolation of the posterior wall of the left atrium "provides additional benefits" over standard PVI.
Two years later, many of these same authors wrote a review article on approaches to ablation of nonpulmonary vein triggers that included this line: "Therefore, empirical isolation of the left atrial posterior wall should be performed in all patients undergoing AF ablation." Their seven citations for this proclamation included observational studies and small randomized controlled trials.
These opinions plus the plausibility of posterior wall isolation led many electrophysiologists to accept the practice of adding it to standard PVI in patients with persistent AF. This became a therapeutic fashion.
The CAPLA study
At the 2022 European Society of Cardiology Congress, Peter Kistler, MD, from the University of Melbourne, presented CAPLA, an international multicenter randomized trial that enrolled 338 patients with symptomatic persistent AF to PVI alone or PVI plus posterior wall isolation. The primary endpoint was freedom from AF (or atrial flutter) at 1 year.
Their results were clear. Freedom from AF in the two groups were nearly identical (53.3% and 54.1%). Procedure times were longer in the PVI plus posterior wall group. Complications were low — 2.9% overall, not different among the groups.
The authors concluded that "these findings do not support the empiric inclusion of posterior wall isolation for persistent atrial fibrillation ablation."
Comments and Lessons
The specific messages from CAPLA are that it confirms STAR-AF II and teaches electrophysiologists that adding posterior wall isolation does not improve AF recurrence rates. That's good to know because less ablation near the esophagus makes the procedure safer. In fact, the main way patients can die from AF ablation is thermal injury to the esophagus, which runs just behind the posterior left atrial wall.
This is why empiric or routine posterior wall ablation never made sense to me. Every extra ablation lesion in that area increases the odds of causing a death. In absolute terms, severe thermal injury to the esophagus is low, but it is the asymmetry of risk that bothers me.
Proponents of posterior wall isolation might argue that there may still be patients that could benefit. For instance, patients with obesity and persistent AF may have fibrosis and triggers on the posterior wall and they may do better with posterior wall isolation. My answer to that is to show me the data.
Another push-back to CAPLA may be that it used radiofrequency energy. There are now new energy sources. Pulsed field ablation, which uses electrical energy, will allow safer and more durable posterior wall ablation. My rebuttal is the same: show me those data, too.
The most important message from CAPLA transcends any specific strategy to ablate one arrhythmia and informs the way we establish knowledge in the practice of medicine.
In the case of adding posterior wall isolation to standard PVI, it was the dangerous combination of observational studies, underpowered trials, biologic plausibility, and expert opinion that created this therapeutic fashion. Always beware of that combination.
CAPLA reminds all clinicians that before accepting new approaches, especially more aggressive ones, testing in adequately powered, well-conducted randomized trials ought to be required. This trial strengthens my belief that the greatest advance in all of medicine has been the discovery of the randomized trial.
John Mandrola, MD, practices cardiac electrophysiology in Louisville, Kentucky and is a writer and podcaster for Medscape. He espouses a conservative approach to medical practice. He participates in clinical research and writes often about the state of medical evidence.
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Cite this: CAPLA Challenges Expert Opinion on Ablation of Persistent AF and Should Change Practice - Medscape - Aug 26, 2022.