Symptomatic(?) Bradycardia

Posted By Karen on March 11, 1999 at 17:03:36:







Hi.  I'm a 28 year old woman in decent shape, I do about30 minutes on the treadmill every day, although I've only been back into running for about 3 months now.  I mentioned a low heart rate, about 45 to my doctor in January, (not knowing that exercise can cause that), an EKG was normal but registered 43BPM so my doctor did refer me to a cardiologist.  I am often dizzy and lightheaded, and always annoyingly tired.
Via a holter monitor, the cardiologist found no connection between dizzy spells and heart rate although he was a little concerned that at one point my heart rate dropped as low as 31.  An echocardiogram showed no valve problems, the cardiologist has also ordered thyroid tests and a sleep study which I'll do next week since I am so young and he wants to rule out all other problems.  He determined that the dizzyness is low-blood pressure and recommended more salt and fluids.  That has worked somewhat, I still get lightheaded, but less frequently.
My question is in regards to the stress test they did.  It showed that my heart climbs to a normal range in the 160's, I was on the treadmill for about 10 minutes up to a 14% incline.  The doctor said everything looked fine, and I was probably just that well-conditioned, but when they stopped the treadmill he began to look a little harder since my heart rate quickly dropped back into the 50's within about 1 minute.  He briefly said that when you're well-conditioned, your heart rate will drop quickly after exercise, but that mine had dropped really quickly which could indicate an electrical problem. (I do have some knowledge of how the sinus and AV node work since I took my Grandmother to her appointments when she had a pacemaker put in a couple of years ago.)  
Questions: 1) What is normal slowing in a heart rate after exercise?  
2) I've been running very recreationally, (I'm not a 'serious' runner,)somewhat consistently, with some multi-month breaks, for about 6 years now.  I didn't run for most of 1998 and then got back to it about Christmastime, so I've been running again for about 3 months.  Can your heart stay that well-conditioned even considering  the breaks I've taken, that my rate would be that low?
3)  Does the low-blood pressure cause the tiredness (that's the thing that really bugs me)?  If the salt and fluids have helped with the dizziness, can I expect them to knock out the lightheaded feeling and tiredness as well?  Thanks, it's good to find a site like this!   Karen