Which pattern in the waveform indicates an irregular atrial rhythm?

An irregular atrial rhythm is characterized by variations in the intervals between P waves on the ECG. When the P-P intervals are inconsistent and irregular, it suggests that the atria are firing at an unpredictable rate, which is a key indication of an irregular rhythm. This can occur in conditions such as atrial fibrillation or atrial flutter, where the atrial electrical activity is chaotic.

In contrast, consistent P-P intervals indicate a regular rhythm, where the atria are depolarizing in a coordinated manner. Similarly, consistent R-R intervals show a regular ventricular rhythm. Irregular R-R intervals reflect variability in the ventricular response, but do not specifically indicate a problem with the atrial rhythm itself. Therefore, irregular P-P intervals are the hallmark of an irregular atrial rhythm, clearly pinpointing that the atrial activity is not synchronized.