1. Are there certain rhythm disturbances that are triggered by exercise at moderate intensity? w/o pain
There are some arrhythmias that are triggered by exercise. However, you mentioned "After the prolonged elevation the HR did eventually slow and get back to resting rate." If the rate slowly declined (ie 140->130->120->100->etc), this strongly suggests sinus tachycardia as the source. Most arrhythmias either start and stop abruptly. The slow down is not gradual.
A holter monitor or cellular rhythm monitor would answer this question.
Could there be other cardiac problems that cause inappropriate elevated HR post exercise?
Yes there could be, but the key to diagnosis is catching the arrhythmia on a monitor so a doctor can look at your rhythm initiation and termination. From what you have written, it sounds like a narrow complex, supraventricular rhythm (you mentioned sinus tachycardia in the first few lines). This is not the type of rhythm that would raise too much concern as a cardiologist. Keep working with your doctors to record the event. You have a normal structural heart. This should be very reassuring.
I hope this helps.
I had an experience like this in my 20's. Only mine would start racing into the 200's during exercise.
The cardiologist told me to message the artery in the neck for awhile or to rub both of my eyes. It seemed to work. Heart slowed down.
Eventually the problem went away. I simply decreased my exercise intensity and made sure my heart rate did not get above a certain point. I eventually was able to increase exercise intensity to the point I ran half marathons.
I concluded that it was most likely caused by stress which I was under at that time.
Unfortunately when I got into my 40's I developed PAC's and later paroxymal AFIB. Again probably percipitated by stress. Thankfully to a good EP I was able to have an ablation which took care of that problem.
If I were you I would go to a cardiologist and have a stress test and stress echo. They might be able to catch the arrythmia, but they would be able to see your heart function. They also might catch it on a holter monitor, but if you are in your 40's you should probably have a stress echo anyway.
It might be that if the tachycardia is persistent that a small does of a beta blocker would basically eleviate the problem if it becomes bothersome. I know that did it for me for a number of years in my 40's.
As I have read when you reach 40's the likely hood of having arrythmias increases. There is also a great body of evidence that runners, basketball players, and hockey players are more apt to develop arrythmias due to being highly conditioned. That's what my EP specialist said at Mayo. This is due to the increased heart size and the stretching of the pulmonary veins.
I would make sure you monitor this.
Thank you for taking the time to respond and share your experience. It is quite frightening when these heart rhythms go off- the feeling of helplessness and fear of a worsening event is enough to send one to the ER (I went 3x). Your suggestions are very helpful.
I had the exact same symptoms and found that I was hyper thyroid.
They have started treatment of the thyroid and my heart rate now comes back down to resting rate minutes after my workout.
I had similar symptoms caused by anxiety. I have started treatment of my anxiety and my heart rate now comes back down to resting rate one to two minutes max after my workout.
Actually, I can train better now and even longer.
I have posted questions in the past about my VERY similar experiences to yours. My onset was in mid/late 30's and I was very active aerobically. My pulse after moderate running or hiking would stay in the 130 range for hours and then very gradually drop to normal over 12 or more hours. This was in the late 80's. I was told that I have sinus tachycardia that cannot be surgically treated so the only option is drugs therapy. I take attenolol. About ten years after the post exercise elevation of pulse rate started I began to experience mild tachycardia after meals....100 to 110 for several hours and also the same with very small amounts of alcohol. All this led to severe generalized anxiety and end of exercising. My advice to you is to see a good psychologist/psychiatrist to ward off anxiety problems that may develop. This condition ended my ability to exercise or have a pulse much above 90 without severe anxiety. Within the past 6 months I developed carotidytis and have had severe migraines all my life. As they say, I am no doctor, but it seems that a common denominator to all these symptoms may exist. Whatever it is is apparently beyond medical science now ( or at least beyond what my HMO is willing to spend on it in my case ) . Good luck to you.