Mechanisms of tachyarrhythmias

(A) Enhanced automaticity: nodal action potentials with normal automaticity (solid orange line) compared with enhanced automaticity (dotted blue line) as would be seen with increased pacemaker current (I_f) and/or decreased inward rectifier current (I_K1). An example of an enhanced automaticity arrhythmia, atrial tachycardia, is shown in the figure.
(B) Reentry: a schematic of a reentrant circuit with fast and slow conduction adjacent to a fixed core. An example of reentrant arrhythmia of ventricular tachycardia is shown below the figure.
(C) Triggered activity, DADs: DADs with the first DAD (solid orange line) not reaching threshold to trigger an action potential, but with subsequent DADs reaching threshold (dotted blue line). Bidirectional ventricular tachycardia from a catecholaminergic polymorphic ventricular tachycardia patient is depicted and thought to initiate with DADs.
(D) Triggered activity, EADs: reverence action potentials (solid black line) with a prolonged action potential and a short interval followed by a long interval, which sets up conditions for a single EAD (dotted blue line) or oscillatory EADs. Typical short-long-short cycles initiate torsade de pointes in a patient with drug-induced long QT syndrome.