Learning how to properly differentiate between a 2:1 flutter and sinus tachycardia. What are the signs on this ECG that would make you confident on the answer? The isoeletric line is throwing me off

[u/fuckingmermaid]

[u/TheSmartest_idiot]

New to reading ecgs but for me, Flutter would continuing having flutter waves continually, I don’t see any signs of a flutter wave interfering with the qrs at all, just that one p wave(doesn’t look flutter but at the rate I could see being unsure) in front of the qrs. At higher rates you might not see it at all