I had that happen on the very last long run I ever did - December 2016. We all push through tough patches and in fact when I would wuss out, I would "punish" myself with hard hill intervals, etc. But this time it felt differently and at that time I came across a book, "The Haywire Heart". Although the cover also states, "How too much exercise can kill you and what you can do to protect your heart" but most of the book is not dedicated to stories about those who die but Master athletes with a long history of endurance activity who have restructured their heart into the "athlete heart" and because they pushed through a tough patch, suffered atrial fibrillation. The cases cited were stories of Ironmen, etc who survived but where left with a permanent partial impairment and disability. Having pace makers, keeping their heart rate below certain thresholds.
In short, what I came away with was the extreme endurance activity may not kill you. The odds of any negative result are minimal, one might even say miniscule but ... Given odds of even just 5% or lower, given what I felt that day, it scared the living crap out of me. I went to the doctor and never a good sign when the tech who is doing the EKG starts to get this look of grave concern. And then tries to cover it up with "your heart is still there." Ended up with a number of other tests to confirm I do have the athletes heart. I was essentially told to really listen to my body and so a big reason I moved from running to cycling - cycling does not seem to stress my heart anywhere near what endurance running did. Having said that, after my 100 mile ride, some of the old sensations and not good ones are creeping in. So I have made the decision to back off - a self imposed limit of around 100 K on a bike and with rides of that distance, to make sure I am not going too hard and to take one good rest stop for a coffee in the middle but to stop if I feel I am pushing too hard. I seemed to be able to go just about as hard as want or can for rides of 60 minutes or so but my body is suggesting I watch that.
The bottom line is my friendly advise is to go see a doctor just to make sure. There a hundred factors why your heart rate went where it did that are of no reason to be concerned. There are two or three that are a concern. Here is a link you may find useful.
https://www.velopress.com/category/the-haywire-heart/http://www.velonews.com/cycling-to-extr ... nce-sportsFor my two cents, this is not an issue that develops overnight. We read about 80 year nuns completing an Ironman and contrast that with the same few odd stories of people who die during or immediately after a race. What is not "sexy" or interesting are the athletes that have pushed past a very personal line that they should not be passing. Training is controlled damaging of our bodies and includes inflammation which is terrible over the long run so that when it repairs, we are stronger, faster and have more stamina and endurance. I do not think it is a coincidence that most of the freaks of nature, the outliers who are able to do incredible feats usually are not starting their athletic careers until they are in the 50s or older. They do not have the years of accumulated abuse where youthful enthusiasm means we ignore the call for moderation, for restraint and maybe even sanity. To qualify for Boston, I did two 40 K long runs with that last 5 K at marathon pace. Put some ice, some gels, some pills and a day or two later, I was good to go again. Can get away with that at 40 but 54, not so much. I have always said, experiment of one, if it is not broke, no need to fix it. But when your body and your heart in particular sends such warning signs that may or may not mean anything, I think it is foolish and silly to believe dedication and will power can over come anything. Because it cannot and may fact lead to some very serious consequences in a unlucky few.
Hoping for single-digit highs next weekend!
I can't deal with that kind of heat for 50k.
I knew the course cutoff was 8:30/km and I was still able to keep close to that, even with alllll the walking... until the weird ear thing. That's what got me really thinking "this could be a bigger health thing", and I shut it down.