Vagally-mediated afib? If so, any special concerns or handling?

[gk1970]

Hello.  I have had one known bout of afib; at the end of January I went to the emergency room after near fainting and was told I was in afib.  A later Holter and event monitor showed normal beating.  I'm on aspirin and 50 mg toprol.  From what I've read, I suspect that mine is vagally-mediated afib since a stress test turned up no adverse results, the passing out occurred a few minutes after getting out of bed, and I had a positive tilt-table test reaction.  Can vasovagal syncope and vagal afib be tied together, since both involve the vagal nerve?  Are there other special concerns if it is vagally-mediated afib?  I have read that beta-blockers are not recommended with vagal afib, but my cardio says that it would still help with the ventricular response (and apparently it hasn't triggered another afib bout yet).  My resting heart rate is already fairly low and is in the range of what they apparently see in athletes, but I'm actually very sedentary.  Without toprol my resting heart rate can get down to around 54, with toprol I've seen it get down to 44.  My cardio says that this really wouldn't be a problem unless it's symptomatic, but besides a lazy disposition I've no symptoms.  Should I worry about the toprol?  I used to drink a lot of coffee/tea/sodas but I cut way back on caffeine two days before the bout; could I have caused a vagal crash if my system had adjusted to an artificially-enhanced adrenergic tone?  I'm 31, non-smoker, very light occasional drinker, vegetarian (ok cholesterol, but still too fat), blood pressure ok and no underlying heart disease found.

[CCF-M.D.-CRC]

Dear gk,
I think "vagal afib" is somewhat of a misnomer.  This term arose from the finding that fit people with slow resting heart rates had a slightly higher tendency to develop afib.  The vagus nerve is the nerve responsible for the lower heart rate.  However, the vagus nerve does not actually cause the afib.  What we know now is that there are triggers in the pulmonary veins that fire very rapidly and start the afib.  These triggers are suppressed by the normal heartbeat so someone with a higher heart rate probably has slightly less firing than someone with a slower heart rate.    

So the afib is not directly linked to the vagus.  The syncope and the slow heart rate are however both related to the high vagal tone.  As far as the beta-blockers go I would see how you feel with them. If you are having side-effects I would talk to your doctor about switching to another medication or even considering an ablation to eliminate the afib triggers.  I don't think that caffeine (even in high doses) would have enough effect to reset your bodies vagal level.

[gk1970]

I forgot to mention that I'm male, if that affects anything.  What I was getting at regarding the "vagal crash":  I was wondering if years of consuming a lot of caffeine could have artificially increased the adrenergic (non-vagal) tone in my system such that my vagal side got accustomed to it and balanced it out.  Then when I quit caffeine more or less cold turkey perhaps the adrenergic tone dropped rapidly but the vagal tone remained high, resulting in a vagally-dominated imbalance.  If I already had a predisposition to vagal sensitivity (as demonstrated by the positive tilt-table test), seems like this situation could have been a trigger for vagal afib.  And hopefully since it was an unusual situation, I won't be triggering such bouts very frequently.  I guess I'm hoping that it may have been an isolated incident.  Does anyone ever have just a single bout of afib or is it always recurrent?

Thanks again!