At what rate will the junctional foci initiate pacemaking if the atrial automaticity foci fail?

At what rate will the junctional foci initiate pacemaking if the atrial automaticity foci fail?

• A. 20-40 bpm
• B. 30-50 bpm
• C. 40-60 bpm
• D. 60-80 bpm

Answer: (C)

The rate at which junctional foci can initiate pacemaking when atrial automaticity foci fail typically falls within the range of 40 to 60 beats per minute. This rate reflects the intrinsic pacing capabilities of the junctional tissue, which serves as a backup pacemaker when the heart's primary pacemaker, the sinoatrial (SA) node, is not functioning effectively.

In the hierarchy of cardiac pacemakers, the SA node has the highest firing rate, usually between 60 to 100 bpm. If it fails, the atrial foci take over at rates of approximately 60 to 80 bpm. However, when both the SA node and atrial foci fail, junctional pacemakers kick in. Their natural pacing rate is slower, as these foci typically generate impulses at a rate between 40 to 60 bpm. This is because junctional tissue isn't as electronegative or depolarizes as quickly as the other automaticity foci. Therefore, when considering the rate of junctional pacing, the range of 40 to 60 bpm accurately reflects its physiological capacity in the absence of higher pacemaker activity.