I had flutter diagnosed only once, but I am a formally diagnosed AF patient, now free of AF for three years after two catheter ablations, RF energy, not the newer pulsed field ablation (PFA).

Flutter is hard to see on a normal ECG. In my case, the attending asked me if I would accept a dose of adenosine, explaining it would slow my heart, but not change my rhythm. It's a dreadful sensation when they inject it, but I was promised it would fade inside of 15 seconds, and they were spot on. So, the adenosine slows that heart and the attending immediately pointed to the monitor behind me and said, 'See? Flutter.

One of the leads should show an obvious sawtooth wave, sharp and regular....because it is normal sinus, just fast. Too fast. For AF, on the other hand, your Kardia would show two clear indicators: no P-wave, the small blip before that major squiggle that is the QRS complex. That P-wave is the depoloarization of the atrium at which it contracts. It's repolarization wave is 'buried' somewhere in the extreme QRS. Second indicator is that the peak-to-peak timing between the R-waves is all over the place...some long, some short, and no rhythm to speak of...what cardiologists term 'irregularly irregular'. Agan, your Kardia would know if it's AF and so would you if you have a decent graphic depiction on which to base your assessments.

If a wearable/smart watch or your Kardia says something like, 'unknown, possible AF, or undetermined', then it probably is not AF and could be PACs, premature atrial complexes, or SVT, or flutter.

The bark is worse than the bite in the case of SVT, PACs, and AF. They're not generally dangerous, not right away, and usually respond to treatment. What you would most certainly not do is to ignore a high pulse rate of 100+ indicated that lasts without a sizeable break for 24 hours. If this happens, tachyarrhythmia of any kind lasting for 24 hours, get to Emerg and get some attention.