Focal tachycardia can be due to which mechanisms?

Focal tachycardia can be due to which mechanisms?

• A. Enhanced automaticity or triggered activity
• B. Macroreentry only
• C. Conduction block
• D. Atrial fibrillation

Answer: (A)

Focal tachycardia arises from a discrete ectopic site, and its mechanism is typically enhanced automaticity or triggered activity. Enhanced automaticity means the resting depolarization of the ectopic tissue is steeper (phase 4 slope increases), so it fires spontaneously at a faster rate than surrounding tissue. Triggered activity involves afterdepolarizations that reach threshold and trigger impulses from the focus: early afterdepolarizations during prolonged repolarization or delayed afterdepolarizations with calcium overload can generate these ectopic beats that sustain a tachycardia. These mechanisms explain how a single site can drive a rapid rhythm without requiring a circulating reentrant circuit. In contrast, macroreentry relies on a circuit around an obstacle to sustain tachycardia, conduction block describes a barrier to conduction rather than an initiating source, and atrial fibrillation is a disorganized, multi-wavelet activity rather than a single focal source.

Focal tachycardia arises from a discrete ectopic site, and its mechanism is typically enhanced automaticity or triggered activity. Enhanced automaticity means the resting depolarization of the ectopic tissue is steeper (phase 4 slope increases), so it fires spontaneously at a faster rate than surrounding tissue. Triggered activity involves afterdepolarizations that reach threshold and trigger impulses from the focus: early afterdepolarizations during prolonged repolarization or delayed afterdepolarizations with calcium overload can generate these ectopic beats that sustain a tachycardia.

These mechanisms explain how a single site can drive a rapid rhythm without requiring a circulating reentrant circuit. In contrast, macroreentry relies on a circuit around an obstacle to sustain tachycardia, conduction block describes a barrier to conduction rather than an initiating source, and atrial fibrillation is a disorganized, multi-wavelet activity rather than a single focal source.