Autonomic Dysfunction: a potential cause of Atrial Fibrillation?

First, what is atrial fibrillation? Atrial fibrillation (A-fib) is the most common arrhythmia that presents as irregular rates or rhythms of your heart beats. It creates a miscommunication between the top and bottom chambers of your heart that disrupts the normal amount of blood flow from your heart. A-fib symptoms may be transient, coming and going on their own or be chronic and require treatment10.

The nervous system connection: Your autonomic nervous system is a part of your overall nervous system that controls all your involuntary functions such as your heart to beat, your lungs to breathe or your bowels to move. When the system starts acting up, we call this dysautonomia1. You can get a wide range of symptoms, including issues regulating blood pressure, body temperature, bowel and bladder functions1.

Within your autonomic nervous system is the vagus nerve. It is the 10th cranial nerve and controls or shares the parasympathetic (rest and digest) functions of many organs. Included in that list of organs is your heart.





How are researchers using the vagus nerve to treat atrial fibrillation? In clinical studies, researchers stimulate the vagus nerve at high voltages to induce or cause atrial fibrillation so that they can study it. They have found that when you have your first episode of atrial fibrillation, it will stimulate remodeling, a restructuring of both the electrical and physical make-up of the atrial tissue (chamber of the heart) making it more prone to recurrent a-fib events5.

So it would sound counter-intuitive that the same vagal nerve stimulation, just at lower voltages would actually be used to TREAT atrial fibrillation. In a recent study, they found that this low-level vagus nerve stimulation “reversed the electrophysiological changes of atrial remodeling…2,3” This also decreased the inducibility of the subject to another A-fib episode3,4. This method of treatment is quite invasive but it opens up the discussion of other treatment approaches that look for a cause. Currently the standard treatment is to cauterize the problem area in the atria.

The exact mechanism of action as to why low-level vagal nerve stimulation works is still being researched but some proposed mechanisms include:

  •      Inhibits the neural activity in the cardiac autonomic nervous system4.
  •      Eliminates gradient differences in the layer surrounding the ganglionated plexi (the complex nerve network of the cardiac autonomic system)5
  •      Mediated by a nitric oxide (NO) signaling pathways.2

    Screen Shot 2016-08-31 at 10.27.52 AM
    Figure 1.0

Researchers have been looking for a noninvasive approach to low-level vagal nerve stimulation and have found that by stimulating a branch of the vagus nerve near the tragus (Figure 1.0), it may yield the same outcomes8,9. This approach uses patches hooked up to a TENS (transcutaneous electrical nerve stimulation) machine that delivers the low-level electrical stimulation8. Similar to the invasive approach, it decreased the sympathetic (fight or flight) nerve activity and decreased the inducibility of the subject to another a-fib episode8,9.

An integrative approach: There are several therapies available that are used for autonomic regulation, one of them being acupuncture6. There have been a few studies on the effectiveness of acupuncture for preventing recurrences of atrial fibrillation7. Of people using drug therapy (amiodarone), 27% of them had a return of their a-fib while patients using acupuncture had a 35% return rate7.

Please do not try these therapies at home. Contact a licensed medical provider to consult on whether you are right for these therapies.

References:

  1.    http://www.mayo.edu/research/departments-divisions/department-neurology/programs/autonomic-nerve-disorders
  2.     Stavrakis S, et al. Inhibition of atrial fibrillation by low-level vagus nerve stimulation: the role of the nitric oxide signaling pathway. Journal of interv Card Electrophysiol 2013; 36:199-208
  3. Sheng X, Scherlag B, Po S, et al. Prevention and reversal of atrial fibrillation inducibility and autonomic remodeling by low-level vagosympathetic nerve stimulation. Journal Of The American College Of Cardiology 2011;57(5):563-571.
  4. Yu L, Scherlag B, Po S, et al. Low-level vagosympathetic nerve stimulation inhibits atrial fibrillation inducibility: direct evidence by neural recordings from intrinsic cardiac ganglia. Journal Of Cardiovascular Electrophysiology 2011;22(4):455-463.
  5. Lin Y, Bian N, Li Z, et al. Effects of low-level autonomic stimulation on prevention of atrial fibrillation induced by acute electrical remodeling. Thescientificworldjournal 2013; 2013:781084
  6. Li Q-Q, Shi G-X, Xu Q, Wang J, Liu C-Z, Wang L-P. Acupuncture Effect and Central Autonomic Regulation. Evidence-based Complementary and Alternative Medicine : eCAM. 2013;2013:267959.
  7.    A. Lomuscio, S. Belletti, P. M. Battezzati, and F. Lombardi, “Efficacy of acupuncture in preventing atrial fibrillation recurrences after electrical cardioversion,” Journal of Cardiovascular Electrophysiology, vol. 22, no. 3, pp. 241–247, 2011.
  8. Clancy JA, Mary DA, Witte KK, Greenwood JP, Deuchars SA, Deuchars J. Non-invasive vagus nerve stimulation in healthy humans reduces sympathetic nerve activity. Brain Stimul 2014;7:871–877.
  9. Stavrakis S, Humphrey MB, Scherlag BJ, et al. Low level transcutaneous electrical vagus nerve stimulation suppresses atrial fibrillation. J Am Coll Cardiol 2015;65:867–875.
  10. https://www.nhlbi.nih.gov/health/health-topics/topics/af
  11. He B, et al. Autonomic Modulation by Electrical Stimulation of the Parasympathetic Nervous System: An Emerging Intervention for Cardiovascular Diseases. Cardiovascular Therapeutics. 2016;34: 167-171

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