Here is the first thing to do, stop and take a manual HR so that you can compare. You say the watch said 180's but you were in Z2 and not feeling anything abnormal? That tells me it is probably the measuring device..So next time you get those big readings, take a pulse. Then at least you know one way or the other..

But just know that A-fib usually doesnt show up on the monitors as regular beats. In fact there really is no good way to know except for one of those new cheap EKG machines that go through your phone. But I offer this as you said you are not feeling any ill affects, because that is how most figure out A-fib, they feel like shit and running through molasses...

I agree with Monty. I've spent way more money and time and sense figuring out which hr straps are shit. Garmin sucks for me. Wahoo sucks for me. I'm using a polar h10 now. It's been fine for 6 months.

Afib sucks and you will no shit know when it happens. You don't need an ecg to tell you something is wrong.

Stop and take your carotid pulse. 18 beats in 6 seconds is pretty hard to miss.

I am 68. When I turned 60 I asked my Dr to test my hr for signs of issues because I wanted to make sure it was safe for me to continue to train at a high level and I knew my grandfather had died of a heart attack at 64 in 1959.

They ran me thru all sorts of tests at the Mayo sports cardiology clinic and told me I had a strong athletes heart with a very high VO2 and was safe to keep training.

Fast forward to my shoulder surgery pre op at age 67 where they found a fluttering atrial chamber and all has changed.

If you suspect an issue, as Monty suggests, start trying to figure it out and seek good medical advice. I just want to keep training, racing and keeping up with my athletic grandkids for years to come.