A team of scientists from the Medical University of Vienna in Austria have developed a promising method to reduce the likelihood of a common complication following heart surgery: atrial fibrillation.
In a small study published in October 2019 in the journal Circulation: Arrhythmia and Electrophysiology, researchers found that the risk of afib following surgery could be halved by delivering noninvasive low level transcutaneous electrical stimulation (LLTS) to the vagus nerve, which contributes to the autonomic nervous system, a part of the nervous system that regulates involuntary bodily functions, including heart rate, digestion, respiratory rate, and sexual arousal.
"Electrical stimulation of the ear and the vagus nerve that sits on the surface there has a calming effect, in that we are stimulating the largest nerve of the parasympathetic nervous system [part of the autonomic nervous system] and hence the corresponding antagonists," Martin Andreas, MD, lead author and an associate professor in the department of cardiac surgery for the Medical University of Vienna, said in a press release.
For the study, researchers divided 40 postoperative patients into two groups: one-half received LLTS while the rest were given a placebo. The patients who received LLTS for five days post-surgery had a significantly lower incidence of developing atrial fibrillation — 4 patients out of 20, compared with 11 out of 20 in the control group.
“The autonomous nervous system controls the heart rate and influences the threshold for cardiac arrhythmias,” Dr. Andreas said. After surgery, the body is under stress, dealing with inflammatory reactions and oxidative stress, and the sympathetic nervous system — the body’s fight or flight response — gets activated.
This increases the likelihood of developing atrial fibrillation, which affects 1 out of 3 patients who undergo open heart surgery and can lead to further complications.
“Patients who had an episode of atrial fibrillation are more likely to develop another episode and are frequently kept on anticoagulant medication, which increases the bleeding risk and may increase long-term complications,” Andreas said.
A previous study, published in September 2017 in JACC: Clinical Electrophysiology, found that vagus nerve stimulation had a positive effect on incidences of atrial fibrillation post-surgery, but researchers used an invasive device that was implanted inside patients’ bodies. This study shows that a noninvasive option could make a similar positive effect with fewer potential complications.
The LLTS device is already being used to treat vascular occlusions, or blood clots. Noninvasive vagus nerve stimulation has been approved in Europe to treat epilepsy, depression and pain, and in the United States, a noninvasive vagus nerve stimulation device has been approved to treat migraines and cluster headaches.
The current study did not find a significant change in inflammatory markers between the control group and those receiving LLTS, though, which leads the study’s authors to suggest that the treatment lowers incidences of post-operative atrial fibrillation “predominantly through its effect on the cardiac autonomic system rather than through modulation of post-surgical inflammation,” the study notes.
The study’s authors are planning a larger, multicenter trial to confirm their results. "Should this treatment prove to be successful in this indication,” Andreas said in a statement, “we can expect this innovation to be ready for clinical use in four or five years."