What occurs when the SA node fails to initiate electrical activity?

When the sinoatrial (SA) node fails to initiate electrical activity, a junctional escape rhythm can occur as a compensatory mechanism. The SA node serves as the natural pacemaker of the heart, generating electrical impulses that initiate each heartbeat and set the pace for the heart. If the SA node becomes non-functional, the heart has the ability to utilize other pacemaker sites for electrical activity.

In this case, the junctional escape rhythm arises from the atrioventricular (AV) junction, which can take over as a secondary pacemaker. This rhythm typically produces a heart rate that is slower than normal since the AV junction generally paces the heart at a rate of 40 to 60 beats per minute. The electrical impulses in this rhythm may not include atrial contraction because they originate from the junctional area, leading to a rhythm that lacks a P wave or has an inverted P wave occurring after the QRS complex.

This explains why a junctional escape rhythm is a common response to the failure of the SA node; it allows the heart to continue beating through the use of backup pacemaker mechanisms.