Heart Rate Drop When Running

I am 61, and a lifelong runner. Lately I am running 15-20 miles a week. I run with a heart monitor. This year I have had some odd things happen during runs. For example, sometimes when I run I will breath very very hard but my heart rate will be relatively low - 117 - 134. A couple days ago I was struggling with my breathing when suddenly my heart rate jumped to 147 and my breathing smoothed right out - felt like it should have given the effort. Today I was two thirds of the way through my run and my heart rate, which had been around 127, dropped to 60. I stopped running immediately. My heart rate dropped to 50, then 48. After a few minutes of walking it went back to 98 and then went down gradually into the normal range as I walked , then 50. The heart rate drop has happened before during runs but never that far - usually it drops to 95 or so. My resting pulse is usually 48-52.  I had a comprehensive work up by an electromyocardiologist and everything looked ok (according to his nurse). I have a follow up visit scheduled on Oct 23. Should I keep running or knock it off until this gets figured out. Any idea what is going on?  My blood pressure is pretty good - yesterday it was 120/72.  

[Bromley]

134 is not necessarily low bpm at age 61. See http://****.***. According to this page, 3 of five different calculation methods give your AT at 135bpm.  This is a very very hard training session.

I do not have the tenacity to run everyday at AT, nor any single day.  I would definitely wear out over a few days and I know my heart rate would tend to become sensitive to exertion. However, I can not say how things should be for you.  I would call your doctors office and ask about continuation of running until the 23rd.