If the SA node fails, which automaticity foci will initiate pacemaking?

If the SA node fails, which automaticity foci will initiate pacemaking?

• A. AV foci at 50-70 bpm
• B. Atrial foci at 60-80 bpm
• C. Junctional foci at 40-60 bpm
• D. Ventricular foci at 20-40 bpm

Answer: (B)

The correct answer indicates that if the SA node fails, the atrial foci, which have an intrinsic rate of 60-80 beats per minute, can take over the pacemaking responsibilities of the heart. The SA node is the primary pacemaker and normally initiates the electrical impulses that regulate heart rhythm. However, in the event of its failure, the heart relies on secondary pacemakers.

Atrial foci serve as these secondary pacemakers because they can discharge impulses independently, although they are not the primary pacemaker. The intrinsic rate of these atrial foci places them in the range of 60-80 bpm, allowing them to potentially maintain a heart rate that is still sufficient to support adequate circulation.

In contrast, while the options involving AV foci, junctional foci, and ventricular foci represent other secondary pacemakers, they operate at lower intrinsic rates. The AV foci contract at 50-70 bpm, which is slower than the atrial foci, and junctional foci discharge at 40-60 bpm, while ventricular foci provide an even slower intrinsic rate of 20-40 bpm. Therefore, in the context of maintaining the highest possible heart rate after the SA node has failed, the atr