I had a colleague (RAF) some years ago who also had an anomaly indicated on his ECG at his annual medical. Advice sought and he had to wear a portable heart monitor for a number of days. Logging his activity, taking a rest break every so often. When the results were analysed there was nothing untoward indicated. A further ECG displayed the first result. Third ECG on a different machine - nothing. Turned out to be a faulty lead, by which time 3 others were on portable monitors!