Another thing to consider, even though the rate changes rapidly and seems that the monitor is not picking up, it is possible that it's accurate. I am not talking about the touch ones. I don't trust those for anyone. The ones that you strap on around your chest though I trust much more. If the A-fib is uncontrolled, it's an elevated rate. Many people with a-fib flip in and out between sinus rhythm and fib many times during the course of a day. So, that can actually account for the fluctuation in readings.

The monitor should be picking up on the ventricular contractions (I believe another poster mentioned this). The a-fib normally shouldn't be too much of an interference in and of itself. Now, yet again as another poster said, if you have low voltage QRS complexes it may make it difficult to pick up and then you'd be back to square one with the unreliability.

The up and down, up and down, may in fact be accurate if you're flipping in and out is basically what I'm driving at in a round about way!

Hope that was somewhat clear(ish)?