What is a distinguishing feature of automaticity foci in fibrillation arrhythmias?

What is a distinguishing feature of automaticity foci in fibrillation arrhythmias?

• A. They are highly responsive to overdrive suppression
• B. They are parasystolic and not susceptible to suppression
• C. They originate only from the SA node
• D. They only activate during bradycardia

Answer: (B)

The correct choice highlights that automaticity foci in fibrillation arrhythmias are parasystolic and exhibit characteristics that make them resistant to suppression. In the context of arrhythmias, automaticity foci are sites outside of the sinoatrial (SA) node that can initiate electrical impulses independently.

In fibrillation, these foci can generate impulses at their inherent rate, creating a disorganized and ineffective rhythm. The "parasystolic" nature indicates that they can function autonomously and are not easily influenced by the heart's normal conduction system, which often tries to suppress them in a healthy rhythm. This resistance to suppression helps explain why fibrillation arrhythmias can sustain themselves, typically leading to chaotic heart activity.

The other options do not accurately reflect the nature of automaticity foci. For instance, automaticity foci are not exclusively from the SA node, and they can activate even in the presence of normal rhythm conditions, rather than being limited to bradycardic situations. Understanding the unique characteristics of these foci can help in managing and treating different kinds of arrhythmias effectively.