What happens to atrial automaticity foci during atrial fibrillation?

What happens to atrial automaticity foci during atrial fibrillation?

• A. They are suppressed by the SA node
• B. They pace independently despite overdrive suppression
• C. They only pace when SA node fails
• D. They take over pacing from the AV node

Answer: (B)

During atrial fibrillation, atrial automaticity foci, which are ectopic pacemaker sites within the atria, exhibit independent pacing despite the phenomenon of overdrive suppression typically exerted by the sinoatrial (SA) node. In a healthy heart rhythm, the SA node dominates the pacing due to its higher intrinsic rate, which suppresses the activity of other pacemakers through overdrive suppression.

However, in atrial fibrillation, the normal coordinated electrical activity of the heart is disrupted, leading to chaotic and irregular electrical impulses in the atria. This abnormal electrical activity allows ectopic foci to escape suppression, resulting in them pacing the heart independently. Each focus can initiate impulses at varying rates, contributing to the irregularly rapid heart rhythm characteristic of atrial fibrillation. Consequently, this independence from the SA node is critical in understanding the pathophysiology of atrial fibrillation and its effects on heart rhythm, as it accentuates the arrhythmogenic potential of these foci.