irregular heart rate from exercise

[vegwalker]

I'm a 64 year old male with low body fat. I've exercised 6 days a week for many years. My routine has been to, in addition to my moderate sessions, twice a week push myself to the limit for about a minute at the end of my exercise session. I usually can get my heart rate up to 160 to 164.

A couple of weeks ago right at the beginning of an exercise, when I hadn't even worked up a sweat, my heart rate monitor showed my pluse rate in the upper 170's. I stopped and it took about a half hour for it to work its way back to under 90 and another half hour to get back to 70. I did some interenet research and the issue of dehydration caught my eye. I started drinking more and my next several exercise sessions, including those that I pushed mysefl, were normal - except for one a week later where it elevated abnormally to 160 at the start of a session for just a few minutes and then came back down and I continued exercising with no problem. Again, since then I've had many normal exercise sessions.  During none of these episodes did I feel any different. Had I not been wearing a HRM, I wouldn't even have known that my pulse rate was elevated. And BTW, the monitor on my exercise machine read the same as my wrist monitor.

This morning it happened again, and I'm pretty sure, although not positive since I don't know how accurate my scale that reads hydration is, that I'm not dehydrated. At the start of my exercise my pulse rate jumped to the upper 170's and stayed there for about 5 to 10 minutes. When I tried my exercise bike again after it came down, it went back up to the 150's with very little exertion. I stopped and have been wearing my HRM for the past hour to see what happens. For a brief period it went down to 56 even though I wasn't totally resting and then leveled off at 70 to 80 except for normal increases to 120 or so when I run up the stairs. I feel fine, but wondering why this has started.

[Michael J. McWilliams, M.D.]

Hello,

I think this is an interesting question, but I am not sure that you are going to get an answer to your satisfaction.  An EKG and exercise stress test could record the rhythm, but only if it happens during the test.  It is probably worth investigating.  Call you doctor and make an appointment to discuss your concerns. There are so many things that it could be, the most likely is a normal fast rhythm (sinus tachycardia).  

I don't think this is incredibly helpful for you.  It is difficult to speculate without seeing the rhythm on monitor.  As heart rate monitors become more common, this is an increasingly common reason for a clinic visit.

Good luck.  Let us know if you have additional tests.

[vegwalker]

Thanks. Yes, I was hoping for a bit more comfort from your answer, but I appreciate you're saying you don't know when that's the case.  Not sure where to go from here. After I wrote my question I decided that I still wanted to get some exercise today so I got on my bike and rode for an hour with no problems. Started normally and rode most of the hour at around 128 BPM and cooled down to normal pulse in normal time. I think before I go for a stress test that isn't likely to be timed to pick up the problem, I'm inclined to experiment with other possibilities. Like maybe I need to not exercise first thing before breakfast. I'm also not sure about the dehydration thing. I'm a vegan so I eat a lot of whole grains which requires more water to digest than with a mainstream diet. Only problem with this theory is why now. I've been a vegan for many years. Anyway, if anything else happens to occur to you, I'd appreciate you're posting it.

[Michael J. McWilliams, M.D.]

I agree with the why now question --- I doubt it is related to diet if you have been a vegan for a long time.  If  you have no symptoms and it doesn't happen every time you exercise, an event recorder could capture the initiation when you press an activator button when it starts.  It is important know what the rhythm is to answer any questions about it.

I think the only way to know is talk to your doctor about tests.