Automatic Atrial and Junctional Ectopic Tachycardia

Automaticity is the underlying basis for the initiation of cardiac contraction in sinoatrial nodal or pacemaker cells, with voltage-gated Ca²⁺ cycling an essential component. ¹ Abnormal automaticity, most likely caused by positive ionic influx during phase 4 depolarization, can occur in non-pacemaker cells and result in inappropriate tachycardias. Although the vast majority of paroxysmal tachyarrhythmias are due to reentry, enhanced automaticity is thought to be the most common underlying mechanism for focal atrial tachycardia (AT) and junctional ectopic tachycardia (JET). Triggered and microreentrant mechanisms have been described in atrial but not junctional tachycardias. Clinically, automatic tachycardias are characterized with a “warm-up” onset and facilitation by adrenergic surge or exogenous catecholamines. Both AT and JET tend to be either chronic and persistent or transient and related to specific events.