Vagal Stimulation Eases Burden of Paroxysmal Atrial Fib in Sham-Controlled Study

May 16, 2019

SAN FRANCISCO — With neuromodulation increasingly explored as a treatment for atrial fibrillation (AF), a small sham-controlled trial suggests that daily sessions of electrical vagal nerve stimulation can alleviate paroxysmal AF chronically.

Its 26 patients with paroxysmal AF who clipped a stim electrode to the tragus of the ear for an hour each day showed an 85% lower burden of AF at 6 months, compared with 27 similar patients who performed the same daily procedure with a stim clip to the earlobe.

Tragus stimulation is known to access the auricular branch of the vagus nerve and to reduce AF burden acutely, but there's no such association for the earlobe. The current study is new for exploring whether such vagal stimulation can have a sustained, chronic effect on AF.

The current findings are in line with "the emerging paradigm of noninvasive neuromodulation" as a management strategy for AF, and point to the need for further studies to find predictors of good response to vagal stimulation so the treatment can be used more efficiently, said Stavros Stavrakis, MD, PhD, University of Oklahoma Health Sciences Center, Oklahoma City.

Some participants in the study responded very well "and some people not so well," Stavrakis told | Medscape Cardiology.

"Aiming toward identifying those patients who are most likely to respond — with a biomarker or it could be an ECG marker, it could be a blood test — is the most important step. And then using that to select a group of patients to conduct a larger randomized trial."

Stavrakis presented the study, called Transcutaneous Electrical Vagus Nerve Stimulation to Suppress Atrial Fibrillation (TREAT-AF), here at the Heart Rhythm Society 2019 Scientific Sessions.

It does seem to show that transcutaneous vagal nerve stimulation, in mere 1-hour daily sessions, can suppress paroxysmal AF, and the effect persists with repeated sessions, probably because of a chronic neural remodeling effect, said Peng-Sheng Chen, MD, Indiana University School of Medicine, Indianapolis, as invited discussant after TREAT-AF was formally presented here.

Interestingly, "the tragus is near the ear accupoint used to treat tinnitus and toothache in traditional Chinese medicine," Chen said.

In the current study, "there was an increased AF burden in the sham-stimulation group, and that's a little bothering." Probably, he said, the control group developed more AF because of natural progression of the arrhythmia; but it also might represent a proarrhythmic effect. If so, that would have to be considered in future trials of vagal nerve stimulation for arrhythmias.

The study's patients had experienced at least two documented episodes of AF lasting 30 seconds or more in the preceding 3 months; they could not have reduced ejection fractions or NYHA class 3 or 4 heart failure.

The patients, about 54% of them female, were not told which electrode sites were active vs control, and the investigators were also blinded in that only the research nurses were aware of patients' treatment assignments, Stavrakis reported.

Baseline AF burden was measured over the study's first 2 weeks with electrocardiographic patches; it was measured again for 2-week intervals at both 3 and 6 months.

Actively treated patients were less likely numerically, but not significantly, to adhere to the at-home treatment, defined as missing a daily stim session on average of no more than four times a month; 75% met that mark, compared with 83% in the sham-control group.

The overall burden of AF was significantly reduced in the active-therapy group compared with the control group at 6 months and when combining the 3- and 6-month assessments.

It was reduced by only 75% when combining the final and interim 2-week monitoring periods, but by 85% at the final assessment, suggesting a dose-related effect of vagal stimulation on AF suppression, Stavrakis speculated.

Differences in AF Burden and Duration at 3- and 6-Month Ambulatory Monitoring Over 2 Weeks, Active vs Sham Therapy
End Point Ratio of Medians (95% CI) of AF Burden P Vaue
AF burden (6 months) 0.15 (0.03–0.65) .011
AF burden (3 and 6 months) 0.25 (0.08–0.77) .016
Total AF duration (6 months) 0.17 (0.03–0.85) .032
Total AF duration (3 and 6 months) 0.27 (0.07–1.08) .064

The vagal-stimulation group saw a 23% reduction (= .0093) in levels of tumor necrosis factor alpha (TNF-alpha) compared with the control group; no other measured inflammatory markers appeared to be influenced by the treatment.

Stavrakis said a 1-hour duration was chosen for the daily sessions based on earlier research looking at acute responses to vagal stimulation. "The shortest duration that will result in a favorable outcome is unknown," he said in an interview. "And we have to factor in patient compliance."

After his formal TREAT-AF presentation, Stavrakis said there is a need for more research to pin down the optimal duration and frequency of therapy. But also, it will be important to consider that "patients are more likely to do something that is of shorter duration, rather than longer duration."

Stavrakis and Chen report they have no relevant conflicts.

Heart Rhythm Society (HRS) 2019 Scientific Sessions: Abstract S-LBCT01. Presented May 9, 2019.

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