What does a premature atrial beat (PAB) primarily depolarize?

What does a premature atrial beat (PAB) primarily depolarize?

• A. The ventricles
• B. The AV node
• C. The SA node and atria
• D. The interventricular septum

Answer: (C)

A premature atrial beat (PAB) primarily depolarizes the SA node and atria because it originates in the atria rather than from the SA node. When a PAB occurs, it represents an early electrical impulse that initiates depolarization within the atrial tissue. This depolarization can then spread throughout the atria, resulting in their contraction before the next normal sinus beat occurs.

The unique characteristic of a PAB is that it disrupts the normal rhythm temporarily by causing an early atrial contraction, which then falls under the influence of the SA node’s primary pacemaking activity. Understanding this mechanism is vital, as it helps to identify the PAB on an electrocardiogram (EKG) and understand its implications for overall heart rhythm and function.