Final answer:
A compensatory pause follows a PJC, representing the time it takes for the SA node to reset and establish normal rhythm after a premature beat, as seen on an ECG.
Step-by-step explanation:
A compensatory pause often follows a Premature Junctional Contraction (PJC) and represents the delay during which the SA node resets its rhythm for the next beat. This pause occurs because after a premature beat, the SA node continues its cycle as if nothing has happened, which means there's a longer gap until the next normal beat occurs leading to a perceptible pause on an Electrocardiogram (ECG).
During the cardiac cycle, the normal sequence of the heart's conduction system involves the SA node initiating the action potential, which travels through the atria and reaches the AV node. There is a natural delay here that allows the atria to contract and pump blood into the ventricles. After this delay, the impulse then continues to the ventricles, leading to their contraction. In the case of a PJC, the compensatory pause is the interval where the heart's natural pacemaker, the SA node, is 'resetting' after being interrupted by a junctional premature beat, which originates near or within the AV node.