Agree with eatshitndie. Worth visiting another specialist. Sounds like a faulty valve as I had a friend who had a similar issue when he was in his 20s. Anything more than 1 minute is an issue and you are having it for 5 mins.
These 3 years I have occasional heart palpitation it was so bad ine night that it woke me up and I dare not move after 5mins of persistent palpitation, I slowly made my way to the BP machine and took my readings, machine could not do any ready with a simple message "out of range". Everything slowed down after 15mins. I went to heart doc for checks and scan and even had machine fitted on me for 24hrs while I go home to sleep. No sign of anything. I still get this occasionally and I know heart beat is in range of 150 when it happens but nothing I can do. I wonder if its a warning sign.