Atrial Fibrillation ECG Characteristics

Atrial fibrillation (AFib) is a common cardiac arrhythmia that has distinct features on an electrocardiogram (ECG). Recognizing these characteristics is essential for accurate diagnosis and effective management of the condition.

Key ECG Features of Atrial Fibrillation

1. Absence of P Waves

In a normal ECG, regular P waves represent the electrical activity initiated by the sinoatrial (SA) node, which signals the atria to contract. However, during atrial fibrillation, the SA node loses control over the atrial rhythm. Instead of organized P waves, the ECG displays irregular, chaotic deflections known as F waves. These small, rapid fluctuations indicate disorganized atrial activity due to multiple ectopic pacemaker sites firing within the atria.

2. Atrial Rate of 350–600 Beats Per Minute

One of the hallmark signs of AFib is the extremely rapid and irregular atrial rate. The F waves typically occur at a frequency ranging between 350 and 600 beats per minute. This high-frequency activity reflects the chaotic electrical signals circulating within the atria, which do not result in coordinated contractions.

3. Irregular QRS Complexes and RR Intervals

In a normal rhythm, the QRS complex appears at regular intervals because it follows the organized impulse from the SA node. In AFib, however, the atrioventricular (AV) node receives erratic signals from the atria, leading to irregular conduction to the ventricles. As a result, the QRS complexes occur at unpredictable intervals, producing a completely irregular ventricular response. This is often described as "irregularly irregular" and is a key diagnostic clue.

These ECG findings help distinguish atrial fibrillation from other types of arrhythmias. Clinicians rely on these patterns to confirm the diagnosis and guide treatment strategies, including rate control, rhythm control, and anticoagulation therapy to prevent stroke.