Final answer:
An accelerated junctional rhythm occurs when the junctional firing rate exceeds 100 beats per minute, indicating the AV node or an ectopic focus is pacing the heart due to SA node impairment, potentially leading to arrhythmias.
Step-by-step explanation:
When the junctional firing rate exceeds 100 beats per minute, this typically indicates a condition in which the AV node (atrioventricular node) or an ectopic focus within the heart's conduction system takes over pacing responsibilities due to a failure or suppression of the SA node (sinoatrial node). Normally, the SA node initiates impulses at a rate of about 80-100 times per minute. When the AV node surpasses this rate, the condition is often referred to as an accelerated junctional rhythm. This can occur due to various factors including ischemia, drug exposure, or autonomic nervous system imbalances. If such a rhythm becomes chronic, it may lead to arrhythmias or fibrillation, affecting the heart's ability to pump blood effectively.