What electrical event usually precedes atrial bigeminy?

What electrical event usually precedes atrial bigeminy?

• A. A compensatory pause
• B. A single PAB during normal pacing
• C. Elevated heart rate
• D. A normal sinus rhythm

Answer: (B)

Atrial bigeminy is characterized by a pattern where every normal atrial beat is followed by a premature atrial beat (PAB). This means that for every regular sinus depolarization, there is a subsequent ectopic atrial impulse that occurs sooner than the next expected sinus beat.

The electrical event that typically precedes atrial bigeminy is the occurrence of a single premature atrial beat during a period of normal pacing. This PAB interrupts the regular rhythm of the sinus node, resulting in the bigeminal pattern of one normal beat followed by one premature beat. The impulse from the ectopic focus is what creates the premature atrial contraction, leading to the characteristic alternating rhythm.

In contrast, a compensatory pause usually follows a premature beat, and while elevated heart rates and normal sinus rhythms can exist in various contexts, they do not specifically precede atrial bigeminy in the same manner that a single PAB does. Thus, the presence of the premature atrial beat, arising during a state of normal pacing, directly triggers the bigeminy pattern.