A randomized comparison of two ablation catheter designs in patients with paroxysmal atrial fibrillation (AF) may say less about the choice of equipment than the potential, including potential limits, of the ablation approach used by both: pulmonary vein isolation (PVI)
Both cryoablation and more traditional radiofrequency (RF) ablation, performed in 49 patients each, achieved full isolation of all pulmonary veins, as determined by electrophysiologic mapping studies at about 5 months, in almost half of the population.
In those with such “durable” PVI, paroxysmal AF was all but abolished — the median AF burden slashed to almost nothing —whether they had been treated with cryoablation or RF ablation.
Yet of those with full and durable PVI, still a vexing 20% showed recurrence of AF within 4 to 6 months after their procedure’s 3-month blanking period.
Durability of PVI was significantly tied to lower AF burden and fewer recurrences (P < .01), but that was “not sufficient to prevent even short-term AF recurrence in one fifth of paroxysmal AF patients. One clinical implication of this is that simply re-isolating pulmonary veins in re-ablations in many cases will be insufficient to prevent any recurrence of AF,” state researchers in their report published online April 9 in Circulation: Arrhythmia and Electrophysiology.
Even with the recurrences despite durable PVI, AF burden — measured throughout the study by implantable cardiac monitors — on average fell over 95% after ablation by either catheter technique, they report.
“And the median burden after PVI was about half a percent in these patients. So even though they did have recurrence, they really did see improvement,” lead author Samuel K. Sørensen, MD, Copenhagen University Hospital, Gentofte, Denmark, told theheart.org | Medscape Cardiology.
The trial demonstrates that “RF and cryo are equally good at achieving durable isolation of the pulmonary veins in a population with paroxysmal AF, and larger trials have also showed comparable clinical outcome,” he said. It also suggests that such durability, by either form of ablation, is significantly and inversely associated with post-ablation AF burden and recurrence rate.
With current RF ablation and cryoablation catheters, reduction in AF burden should probably be the goal of a first procedure in paroxysmal AF, rather than “the abolishment of every episode in every single patient,” Sørensen said.
“Another implication of the study is that the population of patients with paroxysmal atrial fibrillation is not homogeneous. There are differences, and there are some patients that require something more than PVI, at least if we are to cure them and prevent recurrences,” he added.
“A More Nuanced Assessment”
“In the past several years, there’s been more and more observational and even prospective data to support the idea that AF burden probably does matter in terms of both quality of life and also risk of stroke and hard clinical endpoints — and potentially mortality,” Peter A. Noseworthy, MD, Mayo Clinic, Rochester, Minnesota, said for theheart.org | Medscape Cardiology.
In the current study, in which he did not participate, there were “dramatic reductions in AF burden, even in some of the people who had some recurrence — which I think fits with our clinical Gestalt.” There’s a sense that even patients with recurrent AF after ablation “report a dramatic improvement in their quality of life as it relates to their AFib, as a measure of their AFib burden. And this study pretty nicely demonstrates that.”
The field, Noseworthy said, “should probably move away from AF recurrence as a binary outcome for ablation trials and use a more nuanced assessment that accounts for burden and overall health and well-being of the patient.”
The study is consistent with other research in suggesting that the two ablation technologies “are equally good, at least in paroxysmal atrial fibrillation,” Sørensen observed.
“I think that the right choice of catheter depends much on what setting you are in. If you’re at a smaller center that doesn’t perform many ablations, and you use radiofrequency for other procedures and you’re comfortable with that, I think that’s a great choice.”
Durable PVI in 47%
The RACE-AF trial, performed at a single, high-volume ablation center, had randomly and evenly assigned 98 patients with paroxysmal AF to ablation using one of the two ablation techniques. All had at least three documented episodes within the prior 3 months and no other arrhythmias. They received implantable cardiac monitors a month before their first procedure. All were scheduled for a second procedure at 4 to 6 months for assessment of PVI durability and possible re-ablation.
Bidirectional block was achieved for all pulmonary veins for all 49 RF-treated patients and 47 cryoablation patients, the group reported. Two cryoablations were halted early because of complications.
Electromechanical mapping at the second procedure showed that 76% of 199 individual pulmonary veins had been durably isolated in the RF ablation group and 81% after cryoablation, for a 47% rate of full, durable PVI among the trial’s patients, the group reported.
The median AF burden prior to the index procedure was 5.41% prior in the RF ablation group and 3.98% among patients assigned to cryoablation, and was almost nil in both groups after the procedure and a 3-month blanking period, the declines exceeding 99% in for both ablation technologies.
After the blanking period, 17 patients in both groups developed recurrent AF; among those 34, the post-PVI burden of AF was 0.51% and 0.69% in the RF and cryoablation groups, respectively (P = .15). Nine of the 45 patients overall (20%) who showed durable PVI at the second procedure developed AF recurrences after the first procedure.
The Latest Ablation Catheters
Noseworthy lauded the trial for its “late-model” ablation equipment. As the report notes, the hardware included the contact-force sensing, open irrigated ThermoCool SmartTouch RF catheter (Medtronic) and CARTO 3 System v6.0 electro-anatomical mapping system (Biosense Webster); and the 28 mm Arctic Front Advance cryoablation system (Medtronic).
“It’s always good to have head-to-head comparisons with contemporary data and contemporary technology,” he said.
With advances in hardware and technique, “we’re seeing better pulmonary vein isolation than we used to. But despite that, we’re probably approaching the ceiling for ablation efficacy with PVI alone,” Noseworthy said.
“It probably highlights the need to address non-PV triggers in some subsets of patients. But how to identify those patients up front I think is currently not well established,” he said.
“We need to learn more about how to identify the patients who will require more than PVI, and what they require,” observed Sørensen. “Because optimally, we should be able to identify them prior to the ablation and provide them what they need in the first ablation.”
RACE-AF was supported by Medtronic and Biosense Webster; Sørensen discloses receiving research grants from both companies. Disclosures for the other authors are in the report. Noseworthy discloses serving as an investigator for an ablation trial sponsored by Medtronic and on an expert advisory panel for Optum; he and the Mayo Clinic are involved in a potential equity/royalty relationship with AliveCor, and have filed patents related to the application of artificial intelligence to the ECG for diagnosis and risk stratification.
Circ Arrhythm Electrophysiol. Published online April 9, 2021. Full text