What triggers the atrial automaticity foci to take over during a sinus arrest?

What triggers the atrial automaticity foci to take over during a sinus arrest?

• A. P wave depression
• B. Escape from overdrive suppression
• C. Junctional foci activating
• D. Ventricular failure

Answer: (B)

The atrial automaticity foci take over during a sinus arrest primarily due to escape from overdrive suppression. In a healthy heart, the sinus node, which is the primary pacemaker, drives the heart at a higher rate than any other pacemaker sites, which suppresses their inherent automaticity. When the sinus node fails to produce a normal impulse, as occurs in sinus arrest, the atrial foci can emerge as the next pacemakers because they are no longer inhibited by the faster rate of the sinus node. This phenomenon allows them to initiate impulses, effectively taking over the pacing of the heart until the sinus node resumes its normal function or until another pacemaker takes precedence.

In cases of sinus arrest, the other options do not accurately reflect the mechanism by which atrial automaticity foci become activated. P wave depression relates to changes in atrial depolarization but does not specifically trigger foci. Junctional foci can be an alternative source of pacing but do not directly explain the activity of atrial foci in this context. Ventricular failure does not directly initiate the activity of atrial foci; rather, it is more related to the functioning of the conduction system as a whole. Thus, the primary reason atrial automatic