I understand your concern.
Skipping beat at regularity of 3rd or 4th beat is not likely a fib.
Afib causes a completely irregular rhythm.
And heart rate often goes above 100 during the run.
This is likely ventricular trigemini --a benign arrhythmia.
So nothing to worry about
Carvedilol dose should help --the dose can be increased if needed.
However, a holter monitoring also should be planned to capture the heart rhythm during these episodes for confirmation.
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