Automaticity
Also calledautomatism · pacemaker activity · spontaneous depolarization
Definition
The intrinsic ability of specialized cardiac cells to depolarize spontaneously during phase 4 of the action potential, reach threshold and initiate an impulse without an external stimulus. In the sinus node this phase 4 depolarization is driven largely by the funny current (I_f), a mixed sodium-potassium inward current, and the rate depends partly on the slope of phase 4. The sinus node normally has the highest intrinsic rate; the other (subsidiary, or latent) pacemakers take over only when sinus impulses fail to form or to propagate, and their escape rhythms typically run at about 40 to 60 bpm from the AV junction and 20 to 40 bpm from the ventricles. Enhanced normal automaticity, or abnormal automaticity arising in partially depolarized cells, can produce ectopic beats and tachycardias.
Sources
- Al-Khatib SM, Stevenson WG, Ackerman MJ, et al. 2017 AHA/ACC/HRS guideline for management of patients with ventricular arrhythmias and the prevention of sudden cardiac death. Circulation. 2018;138(13):e272-e391. doi.org/10.1161/CIR.0000000000000549
- Ashkanani AA, Ashkanani AH, Alkandari MF, et al. An accessible algorithm for the quick and precise interpretation of atrioventricular blocks in electrocardiograms. Ann Noninvasive Electrocardiol. 2026;31(4):e70207. doi.org/10.1111/anec.70207
- Kusumoto FM, Schoenfeld MH, Barrett C, et al. 2018 ACC/AHA/HRS guideline on the evaluation and management of patients with bradycardia and cardiac conduction delay. Circulation. 2019;140(8):e382-e482. doi.org/10.1161/CIR.0000000000000628
- Antzelevitch C, Burashnikov A. Overview of basic mechanisms of cardiac arrhythmia. Card Electrophysiol Clin. 2011;3(1):23-45. doi.org/10.1016/j.ccep.2010.10.012
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.