Patrice Wendling

June 16, 2016

NICE, FRANCE — An individualized approach to energy dosing during cryoballoon pulmonary-vein isolation (PVI) provides the same success rates as PVI plus an empiric bonus ablation for paroxysmal atrial fibrillation (PAF), but with lower procedure and fluoroscopy time and a better safety profile, a pilot study suggests[1].

"Instead of just anatomically looking for occlusion, we should rather guide our ablation using this [electrophysiology] EP end point of time to PVI to titrate the energy for our patients," lead investigator Dr Julian Chun (Markus Hospital, Frankfurt, Germany) said during a late-breaking EP session at the European Heart Rhythm Association (EHRA) EUROPACE-CARDIOSTIM 2016 meeting.

Second-generation cryoballoon ablation dramatically altered PVI, but because it allows only binary ablation—either on or off—options for energy dosing are somewhat limited. Some have toyed with the empiric bonus freeze or modified the ablation time, but the researchers opted instead to use time to PVI based on real-time PV recordings to guide and individualize ablation. Real-time information allows for rapid visualization of the PV potential and an early time to effect, which could be an indicator for better ablation than a long time to isolation (TTI), he said.

ICE-T Trial

Dr Julian Chun

The single-center prospective ICE-T study evenly randomized 100 PAF patients (mean age 65 years; 59% male) to PVI with a TTI limited to <75 seconds and no bonus freeze (group A) or PVI plus one empiric bonus freeze regardless of TTI (group B), similar to what was used in the FIRE and ICE trial. The procedure was performed in all patients with a 28-mm second-generation cryoballoon, 20-mm spiral catheter, and transseptal access. Ablation time was set at 240 seconds per vein. PV occlusion angiograms were used to assess contact and phrenic-nerve stimulation performed for safety.

The primary end point of single-procedure sinus rhythm after 12 months (including a 90-day blanking period) occurred in 88% of patients in group A and 82% of patients in group B (log rank P=0.804), Chun said.

The individualized strategy shaved nearly 20 minutes off the procedure time (70 min vs 89 min; P<0.001) and 2 minutes off fluoroscopy exposure (10.6 min vs 12.7 min; P=0.03).

Postprocedure troponin T levels were similar between the two groups (1035 ng/L vs 1219 ng/L), whereas lactic dehydrogenase release was significantly higher in group B employing the bonus freeze (259 U/I vs 282 U/I; P=0.038).

No deaths, stroke, cardiac tamponade, atria-esophageal fistula, or major vascular events occurred, but there was a trend for more complications in group B with the bonus freeze (nine vs three; P=0.06); specifically, persistent phrenic-nerve injury (one vs zero), transient phrenic-nerve injury (five vs two), and esophageal lesions (three vs one).

In multivariate analysis, TTI >43 s was the only independent predictor of atrial tachycardia/AF recurrence during follow-up (sensitivity 77%, specificity 74%, area under the curve 0.72).

Peeling Back the 4 Minute Ablation

During a discussion of the results, attendees questioned whether peeling back the 4-minute ablation time might also be an option and spare the phrenic nerve and esophagus. Chun said at the time ICE-T was designed, studies suggesting a 3-minute ablation time were not yet available and that they felt they needed to compare the individualized strategy with 4-minute ablation, the gold standard.

"One could speculate of course that 3 minutes may be enough in certain situations; however, on the other side, completing 4 minutes also appears to be linked to a pretty benign safety profile, and therefore I would give this extra 4 minutes," said Chun, who observed that they have adopted the individualized strategy in practice.

Session cochair Dr Mark O'Neill (King's College London, UK) told heartwire from Medscape the 4-minute cutoff is an empirical number that comes out of experience with the first-generation cryoballoon, but that once the vein is isolated and the lesion around the vein transmural, no additional energy is needed and only translates into more potential complications.

"The anatomy around each vein is different, so to ascribe a fixed delivery time to each vein is probably a little bit behind where we should be with delivery of cryoenergy. So I buy into the idea that short-duration delivery can achieve pulmonary-vein isolation and think we should be a little bit cleverer in how we prescribe energy in the left atrium for isolation veins," he added.

Dr Lucas Boersma (St Antonius Hospital, Nieuwegein, Netherlands), who also was not involved in the study, told heartwire that the concept makes sense but the data preliminary and sample size small.

"I think that the idea is good to reduce the freezing time, but again the optimal strategy here, I'm not sure, but the data allude to the fact the shorter you do the ablations, the fewer complications you have. However, I'm not sure whether you are not also limiting efficacy, because I was a little bit worried about the Kaplan Meier curve, which in the beginning showed a clear difference, but then right at the end you saw one of them drop and they all came together again."

Study coauthor Dr Alexander Fürnkranz (CCB Hospital, Frankfurt, Germany) told heartwire , "In the total trial cohort, a long average TTI independently predicted tachyarrhythmia recurrence despite the fact that a bonus freeze was applied either constitutively or in case of a long TTI. So the question remains, to what extent, or whether at all, a bonus freeze actually improves lesions generated with a long TTI, if we assume that PV reconduction is the problem here. This weakens even more the case for repeated freezing."

Chun reported research grants from CardioFocus, Medtronic, and Biotronik and travel and speaker's honoraria from Biosense Webster, Boston Scientific, CardioFocus, Medtronic, St Jude Medical, and Bayer. Fürnkranz reported honoraria for educational lectures and proctoring for Medtronic.

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