What generally causes a premature beat?

What generally causes a premature beat?

• A. A junctional rhythm occurring unexpectedly.
• B. An irritable automaticity focus firing spontaneously.
• C. A sinus tachycardia episode.
• D. A suppression of the automaticity foci.

Answer: (B)

A premature beat typically occurs when an irritable automaticity focus fires spontaneously, leading to an early heartbeat. This firing can happen in response to various triggers, such as stress, caffeine, or electrolyte imbalances, which increase the automaticity of certain cells within the heart. When these cells depolarize earlier than the expected sinus beat, it results in a premature contraction, which can manifest as a premature atrial contraction (PAC) or a premature ventricular contraction (PVC).

Understanding that this automaticity focus acts independently of the primary pacemaker (the sinus node) helps clarify why an irritability in these areas can lead to premature beats. The key factor is that whereas the sinus node typically sets the rhythm, in cases of premature beats, ectopic pacemakers momentarily take over and produce an early heartbeat, disrupting the regular rhythm of the heart.