What occurs if the SA node misses a cardiac cycle due to a sinus block?

What occurs if the SA node misses a cardiac cycle due to a sinus block?

• A. Heart enters a state of fibrillation
• B. Escape beat from an automaticity focus may occur
• C. Pacemaker implant is required
• D. Heart resumes normal pacing instantly

Answer: (B)

When the SA node experiences a sinus block and misses a cardiac cycle, the heart may lose its primary pacemaker activity temporarily. In this situation, other regions of the heart, known as automaticity foci, can take over the pacemaking function. These foci are capable of generating electrical impulses at a slower rate compared to the SA node. If one of these automaticity foci becomes activated, an escape beat occurs, allowing the heart to continue contracting even in the absence of the SA node's impulses.

This mechanism safeguards the heart from prolonged periods of asystole (lack of heartbeat) and ensures that circulation can continue, albeit at a less efficient rate. The presence of escape beats is a vital aspect of the heart’s intrinsic conduction system, highlighting its ability to maintain rhythm even when the primary pacemaker, the SA node, fails to function temporarily.