Short, High-Power Ablation on Par With Standard AF Ablation

Daniel M. Keller, PhD

April 13, 2022

In looking for better ways to perform pulmonary vein (PV) isolation to treat atrial fibrillation (AF) while minimizing risks, especially esophageal injury, researchers have designed new methods to deliver ablative radio frequency (RF) energy. One of the ways is to use higher energy for shorter periods of time. Thus, the High RF Power for Faster and Safer PV Ablation Trial (POWER FAST III) was performed, comparing application of high-power, short-duration (HPSD) energy with conventional low-power, long-duration (LPLD) energy.

There were no significant differences between the two groups in terms of all complications, including esophageal thermal injuries, José Luis Merino, MD, PhD, from La Paz University Hospital, Madrid, who is president-elect of the European Heart Rhythm Association, told attendees at its annual congress in Copenhagen. Efficacy outcomes, too, were essentially the same between the two groups.

The rationale for an HPSD method lies in the mechanism of tissue injury during RF ablation. Two phases occur upon application of the energy: a resistive heating of the tissue at the contact point with the RF catheter, and then a conductive phase in which the heat emanating from the tissue radiates out to adjacent tissue. The idea behind the HPSD method is to modify the relation between the resistive and conductive phases to increase immediate heating around the circumference of the PVs to achieve uniform PV lesions while reducing conductive heating to minimize damage to collateral tissues.

A recently published meta-analysis favored HPSD ablation over conventional techniques in terms of freedom from AF, acute PV reconnections, and procedure duration, but Merino cautioned that the included studies were single-center and nonrandomized, and there was still a question about esophageal injury.

POWER FAST III randomized equally 267 patients with paroxysmal or persistent AF for less than 1 year to LPLD (133 analyzed) or HPSD (126 analyzed) at 12 centers in Spain. LPLD patients received 25 to 40 Watts, according to lesion size and ablation indices, and HPSD patients received 70 Watts for 9 to 10 seconds. Irrigated-tip catheters equipped with contact force (CF) sensors provided CF greater than 5 g for both modalities.

Upper digestive tract endoscopy and brain MRIs were performed more than 72 hours after the procedure. Patients were followed with outpatient clinic visits at 1, 6, and 12 months, and daily ECG monitoring transmitted was by telephone throughout this period.

The two groups were similar in regard to paroxysmal or persistent AF, left ventricular ejection fraction, tachycardiomyopathy, and antiarrhythmic drug therapy, except there were more men in the LPLD group than in the HPSD group (78.2% vs 65.1%).

PV isolation was successful at 98.4% to 100.0% for right and left PVs for both modalities, although "first-pass isolation was significantly better in the conventional group," Merino reported. Isolation for both PV pairs was 82% for LPLD and 66.7% for HPSD (P =.007); for left PVs was 92.2% and 81.4%, respectively (P = .02); and for right PVs was 89.1% and 84.6%, respectively (P = .4).

In terms of acute PV reconnections, there were no significant differences between the two groups whether these reconnections occurred spontaneously or after adenosine infusion. Procedure durations, left atrium dwell times, and fluoroscopy times were essentially the same.

Safety outcomes were equivalent for the two procedures. The primary safety endpoint of esophageal thermal lesions occurred in 6.5% of the LPLD group and in 7.5% of the HPSD group (P = .94).

For overall complications — including pericardial effusion, hematoma/bleeding, atrioesophageal fistula, and stroke/transient ischemic attack/systemic embolism — the rate in the LPLD group was 6.0% and in the HPSD group was 7.9% (P = .64).

There was a nonsignificant trend toward more thromboembolic complications in the HPSD group, which Merino said "warrants further investigation before high-power, short-duration is recommended for regular clinical practice."

Commenting on the trial, Boris Schmidt, MD, Cardiovascular Center Bethanien, Frankfurt, Germany, asked, "Why would I do high-power, short-duration ablation?" The answers lie in the knowledge that the lesions using HPSD ablation are broader and shallower, thereby possibly sparing esophageal heating when placed over the posterior atrial wall. A second reason may be that with standardized lesions, "one can standardize the point-by-point ablation for pulmonary vein isolation procedures. This was investigated in this study."

However, along this line, one criticism that he raised is that in the HPSD group, no ablation index or lesion size index was used to standardize the lesion set, especially not at the posterior wall.

"As a consequence, we saw an identical number of esophageal lesions in both arms, which is a little bit disappointing," Schmidt said. "On the other hand, it's encouraging that in both arms, it was really, really low." He suggested that the investigators could have considered using temperature monitoring, which may have added a margin of safety in terms of avoiding esophageal lesions.

Finally, he said he found the difference in rates of pericardial effusion in the HPSD and LPLD groups "a little striking," although not statistically significant (4 vs 1; P = .20), raising the possibilities that the difference resulted from no ablation index being used or that the 9-second, 70-Watt ablation parameters might be too much for some regions in the left atrium.

POWER FAST III was funded by a peer-reviewed grant from the Instituto de Salud Carlos III of Spain. Merino has research contracts with Abbott, Boston Scientific, and Medtronic; an educational contract with Abbott and Microport; and is on an advisory board for Sanofi. Schmidt has research contracts from Medtronic, Abbott, and BSCI; and a consulting, royalty, owner, or stockholder relationship with Abbott and BSCI.

European Heart Rhythm Association (EHRA) 2022. Presented April 4, 2022.

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