Vagally-induced Atrial Fibrillation

November 7, 2007

250px-love_heart.jpgCase by: Alana Choy-Shan, Chief Resident

Commentary by William Slater MD, Associate Professor of Medicine, Division of Cardiology

Following Thanksgiving dinner, a 36 year-old healthy man developed palpitations and heart racing. He was evaluated in the emergency room and was noted to be in atrial fibrillation with rapid ventricular response. All of his other vital signs were within normal limits. He was treated with a beta-blocker for rate control and was started on anticoagulation. Within a few hours, he spontaneously converted to normal sinus rhythm. The following AM, a transthoracic echocardiogram revealed a structurally normal heart. Laboratory tests (including thyroid function tests) and a chest x-ray were normal. Anticoagulation was discontinued and he was discharged to home on a daily aspirin.

1. What triggered this patient’s atrial fibrillation?
2. How should he be treated if another episode occurs?
3. Is there anything he can do to prevent a recurrence?

Patients with “lone AF’, i.e. those without structural heart disease nor a history of hypertension, often get their paroxysms of AF in settings of autonomic fluctuation. Clinicians often easily recognize adrenergic triggers (exercise, emotional stress, alcohol or caffeine) but less commonly are aware that vagal excess is often a common trigger for lone AF.

The development of AF in these patients, as in the majority of patients with AF, requires both a trigger from enhanced automaticity in the pulmonary veins, as well as enhanced excitability of atrial tissue. While vagal tone prolongs refractory periods in ventricular muscle (and is thereby anti-fibrillatory), the opposite occurs in atrial tissue. In the atrium, both adrenergic and vagal tone shorten the refractory period of atrial tissue, thereby promoting the formation of re-entrant wavelets and allowing the development and perpetuation of AF.

Clinically, “vagal” fibrillators can be identified by their paroxysms of AF during sleep, or following digestive precipitants (spicy foods, cold bolus of food or liquid, large meals with resultant gastric distension). These patients can often diminish the frequency of PAF by modifying their dietary patterns appropriately. It is important for the clinician caring for patients with paroxysmal AF to question the patient about triggers for AF; often it is helpful for the patient to keep a diary which, when reviewed with the physician, can often shed clues on modifiable triggers in the patient’s life.

Recognizing the patient with vagal triggers has several implications:
1) the opportunity to modify digestive triggers for the episodes
2) the avoidance of digitalis, which can increase episodes via its vagotonic action
3) the use of disopyramide (Norpace) as an antiarrhythmic, given either as a maintenance BID drug (usually 200 mg CR BID) or as “pill in the pocket” therapy (usually 300 mg po of short-acting drug) to terminate episodes of AF. Besides its class 1A antiarrhythmic properties, disopyramide has anticholinergic properties which make it particularly useful to block the vagal influences triggering AF in “vagal” fibrillators. In patients who find the anticholinergic side effects (urinary hesitance, constipation) bothersome, the drug can be given with pyridostigmine (Mestanon), a cholinesterase inhibitor.

Young patients with paroxysmal AF in the absence of heart disease often prefer “pill in the pocket” therapy to terminate an episode rather than daily maintenance antiarrhythmics. A trial of short-acting beta blocker (propranolol 20 mg) should be tried first; it may be repeated at regular intervals (ex:q2) hours until termination of the arrhythmia. Often, the addition of a short acting benzodiazepine is helpful as well in fostering termination. Only if this program is ineffective at terminating bouts of AF should an antiarrhythmic be used. Disopyramide is then a good choice for the group where vagal tone is important in the development and perpetuation of AF.

Image courtesy of Wikipedia

5 Responses to Vagally-induced Atrial Fibrillation

  1. Bob Moore on December 31, 2010 at 10:57 pm

    This has been my experience since 1985 when I was 33. Have been on Norpace since developing chemically induced lupus from procainimide in 1995. No ER gets this. Most of my episodes self correct. But every now and again I have one that dos not and I tell them the above is the case and they never believe me and I have to go the Nitro, morphine stress test route. Thanks for this posting. I will keep a copy in my wallet and car and maybe I’ll get better treatment and save me and the health care system resources.

  2. John Bedson on February 9, 2012 at 3:56 am

    If you want a “safe” vagolytic, why not just use propantheline bromide?

  3. Elizabeth Perez on May 25, 2012 at 11:24 am

    How would a benzo work? I’m trying benadryl as an anticholinergic to suppress vagal influence on atria

  4. Tim Madden on August 1, 2012 at 10:04 pm

    I have been having AF episodes since 1998, I am now 45. most episodes correct them selves. But there have been a few that I needed the hospital to be safe. 1 time , it came on as I just sat watching tv, after eating a big bowl of mac and cheese, I stood up, and my heart raced lke never before. called an ambulance, they hooked up ekg. my rate was 260 per mn.
    They gave me nitro. I was used to AF by then , but that one scared the crap out of me , i feel i panicked, which triggered such a high rate.
    My last big episode was as I slept, woke me right up. Went to hospital , they did the same old tests, and found no damage , and no reason for it. Got a good Cardi doc, he explained a little about vagal AF. made sense, he put me on toporol, and gave me a pill in pocket just in case. That was on my 45th birthday, 10 months later , still episode free, , cept for 2 second palps that go away , not often though.

  5. Mei Hu on December 31, 2012 at 2:38 pm

    So, did benadryl work successfully as a vagolytic?

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