What commonly occurs in atrial fibrillation?

Atrial fibrillation is characterized by an irregularly irregular rhythm due to chaotic electrical signals in the atria, which leads to a lack of organized atrial contraction. In this condition, the normal sinus rhythm is disrupted, resulting in the absence of distinct P waves on the electrocardiogram (ECG) and giving rise to the "irregularly irregular" appearance of the rhythm.

This disorganized atrial activity can cause varying intervals between the QRS complexes, which is a defining feature of atrial fibrillation. Patients may notice palpitations or a fluttering sensation in the chest, further emphasizing the nature of this arrhythmia.

The presence of regular P waves corresponds with normal sinus rhythm, while a consistent PR interval is observed in organized atrial depolarization. A constant heart rate, on the other hand, is not characteristic of atrial fibrillation, which often presents with a variable heart rate depending on the conduction through the AV node. Hence, the chaotic nature of the atrial firing in atrial fibrillation gives rise to the irregular rhythm, making it the correct and defining feature of this condition.