sudden onset of exercise induced tachycardia

[dcisin]

I ama 60 year old male with no history of heart problems.  For the last two years I have been running regularly and have completed five marathons during that time period.  I always wear a heart rate monitor during my runs, and my heart rate response to exercise has been normal and regular, and has improved (decreased) over the two years.  I don't usually watch my heart rate during runs because it has been so consistent, but, after the run, I record the heart rate averages for each mile in my running log.  Last Monday I went out for a normal slow, easy run of about 6 1/2 miles.  Normally during such a run, my heart rate averages for each mile would start at about 113 and rise by mile 6 to about 122.   Last Monday, my heart rate averages for each mile were 121, 145, 159, 157, 171 and188, with a maximum of 200.  I checked the monitor several different days, and it was entirely accurate.  I have never seen an average heart rate above 162, even in the toughest parts of marathons.  I've also never seen my heartrate go over 170.  My doctor didn;t seem to have a good idea what's going on, and has scheduled me for a stress test and echocardiogram.    Any idea what's going on?

[runnertom]

   I also am a 60 yo runner and watch my heartrate from time to time. I also ride a bike seriously and often and am aware of my pulse most times. My observation is that heartrate for a given workload starts fairly low and gradually increases with time. In doing a 10 mile run I used to start at about 145 and end at 175 at a similar perceived exertion level. On the bike, I can be somewhat more scientific and compare speed versus heartrate, although road conditions (wind and grade) make a huge diffrerence. In any case, in the early part of a workout, 20mph would require about 130 bpm but that would go to 150 or more after 50 miles. I strongly suspect that dehydration plays a huge role. Last Sunday my pulse after resting for 30 minutes after a 50 mile ride was 95 as opposed to a normal 45. Pulse was very shallow.
   That being said, you may be going into atrial fibrillation. Signs of this would be a weak, rapid, and irregular pulse. I have had it a number of times as have a number of my companions.  You would normally feel somewhat lousy also although this is pretty variable person to person. I doubt that your pulse really hit 200 at your (our) age. Max should be about 160. I have hit 180 recently but that was under extreme conditions pretty maxed out and it doesn't sound like what you were doing.
   You may have trouble duplicating the problem during a stress test as the duration is too short. Its also been my experience that the heartrate monitors kinda "lock up" and refuse to update if there is any arrythmia going on as they need to see 4 or 5 beats of similar rate to assign a heartrate number.

[dcisin]

Thanks for the comment. Yes, I agree with runnertom.  Because it was indoors, on my normal air-conditioned track, I doubt that electical or environmental factors were in play.  

[runnertom]

Commenting on the doctor's comment, I also have had my monitor interfered with by outside sources, particularly invisible fences for dogs. They typically cause the monitor to report a steady 214 bpm or something similar while in the field. Since you were in a gym and your readings were progressively increasing, I am sure that electrical interference was not the problem.

[Cleveland Clinic]

Let me first tell you that last week I went on a bike ride where my heart rate monitor told me I averaged 183 bmp and had a maximum of 213 bpm. Obviously this was not correct, and was almost certainly secondary to close proximity to high voltage power lines over a large portion of the circuit. Other meterological conditions that can increase the chances of this occurring include windy conditions and high humidity. I suspect that this is what happened to you on your run. But if this recurs, you may want to wear a loop recorder to see what the exact rate is: is it Afib or simply sinus tachycardia. This will tell you the answer and the if any course of action is needed.

[runnertom]

   I have relatively limited experience with Afib and monitors although my brother had it and his monitor tended to report his heart rate fairly accurately when it was way above 200. Only thing is he felt terrible and could not continue exercising. When I have been in Afib is wasn't immediately obvious to me although my legs felt somewhat weak and unfortunately I was not wearing my monitor.
   If you are going into fib, its not the worst diagnosis in the world. A low dose of Toprol seems to have mine at bay. My younger brother however had an ablation.
   As I mentioned in my previous post, you may have trouble reproducing your problem in a test situation. If your problem occurs again while running, I would make it a priority to characterize your pulse-shallow, uneven, missed beats, etc. That may give a head start in arriving at a diagnosis.

[dcisin]

Thanks for your comment.  Atrial Fibrillation sounds like a possibler explanation;  obviously not good news, but at least it explains things.
    I don't think hydration issues were involved.  I was running on an air-conditioned indoor track, and had normal amounts of fluid both before and after.  Weight after was right were it should be, and I didn't feel thirsty.  That said, I have noticed slightly elevated heart rates when running outside when it's hot, but only on the order of 5-10 bpm higher.    Nothing like the numbers I saw last week.
    The run felt absolutely normal; no unusual symptoms.  I wasn't really paying attention, but I think my breathing remained at my normal slow run 4-4 pattern.  I certainly didn't feel tired or breathless afterwards.
   You are absolutely right that folks our age shouldn't be seeing pulse rates at anything close to 200.  I could write off the 200 number as a momentary monnitor malfunction, but it is harder to explain the average for mile 5 of 171 and mile 6 of 188.  I had my maximum heart rates determined on a treadmill four years ago at 183.  I suspect that was pretty accurate, and that my maximum now is about 180.  My reasting pulse is low 50's.  The highest heart-rate I've ever gotten running is 170, and that was pushing at 100% to a point were I was so exhausted I could barely stand.  I've also never gotten a mile average much above 160, and that was pushing real hard on the last mile of a half.   Go figure?
   Anyway, thanks for the ideas.