Atrial Fibrillation Explained: Understanding the Irregular Heartbeat

Atrial fibrillation, commonly referred to as AFib, is a type of heart rhythm disorder (arrhythmia) that affects the upper chambers of the heart, known as the atria. In a normally functioning heart, the sinoatrial (SA) node generates electrical impulses that coordinate the rhythmic contraction of the heart muscles. These impulses typically travel through the atria, causing them to contract and pump blood into the ventricles. However, in atrial fibrillation, this process becomes disrupted, leading to chaotic and ineffective contractions.

What Happens During Atrial Fibrillation?

During AFib, instead of a single, organized electrical signal, multiple erratic electrical impulses circulate through the atria. This results in the absence of regular P waves on an electrocardiogram (ECG), which are normally associated with atrial contraction. Instead, small, irregular waves known as "f waves" appear, indicating disorganized atrial activity. As a result, the atria quiver rather than contract effectively, impairing their ability to efficiently pump blood into the ventricles.

The Role of the AV Node in AFib

The atrioventricular (AV) node acts as a gatekeeper between the atria and ventricles. In AFib, the AV node plays a crucial role in filtering the excessive and irregular electrical signals coming from the atria. While many of these chaotic signals are blocked at the AV node, some manage to pass through to the ventricles. This leads to an irregular and often rapid heartbeat, known as an irregularly irregular pulse. The ventricular response becomes unpredictable, and the heart rate can vary significantly from moment to moment.

Heart Rate vs. Pulse Rate in Atrial Fibrillation

One of the distinguishing features of AFib is the discrepancy between the heart rate and the pulse rate. In this condition, the heart rate—especially in the atria—can be extremely high, often exceeding 300 beats per minute. However, due to the filtering action of the AV node, the ventricles do not respond to all these impulses. As a result, the pulse rate measured at the wrist is typically lower than the actual heart rate. This phenomenon, known as pulse deficit, is a key clinical sign of atrial fibrillation and helps differentiate it from other types of arrhythmias.