This patient was diagnosed by the rescue crew as having atrial fibrillation, based on the fact that they thought the rhythm was irregular, and they could not see P waves. They also noted a wavy baseline, and considered it to be fibrillatory waves. In reality, the underlying rhythm is regular, with some PACs (regularly irregular). The P waves are small and hard to see in the baseline artifact. We have marked the P waves in Lead I with small dots.
It pays to look at multiple leads, reduce artifact as much as possible, and look at the strip for evidence of an underlying rhythm.
It is not shown here, but the ECG machine is often able to show that the P waves are present by giving a PR interval and P wave axis in the diagnostics.