SVT, betablockers, and exercising

I'm a 26 yr old female, 5ft, 135 pounds.  I've had 3 tachycardia episodes in the past 4 years all brought on by exercising.  The last two have happened in the past month.  The first episode, four years ago, lead to a diagnosis of AV node re-entry.  However, since I didn't respond to the adenosine injections in the last 2 episodes, the doctors suggested that it was not AVNRT after all, but SVT instead.  I've been taking betablockers (cardicor) for the past month. As I mentioned above, all of my episodes have been brought on my exercise.  The doctor told me I should be able to carry on as normal, exercising as usual with the betablockers, but I am SO scared to resume my normal exercise routine.  Are there any cases in which someone has had an episode even while taking betablockers?  

Also, should I avoid activities that produce adrenaline such as riding roller costers, etc?  Or is this something I can expect to do while on betablockers?

Thanks for taking your time to read and respond to my question!

[Michael J. McWilliams, M.D.]

I am not clear on something -- do they have recording of the tachcyardia?  That is very important to generate a list of the possibilities.

Are there any cases in which someone has had an episode even while taking betablockers?

Beta blockers usually decrease the frequency of SVT events.  It is possible to have SVT while on beta blockers.

Also, should I avoid activities that produce adrenaline such as riding roller costers, etc?  Or is this something I can expect to do while on betablockers?

I wouldn't change my activities.  If it happens again, then it is worth looking at what the cause is again.  Sometimes a 30 day home monitor can help in the diagnosis (like a lifewatch monitor).

http://www.lifewatchinc.com/

The other question I have is could this been an exercise induced VT.  You would need a monitor to confirm this diagnosis.  exercise induced VT is usually a very low risk but symptomatic arrhythmia.

Unfortunately the answer is in the monitor or rhythm strip and I don't have access to it.

I hope this helps.  Good luck.