Third-degree (complete) heart block
Also calledcomplete heart block · 3rd degree AV block · CHB · complete AV block · third-degree AV block
Definition
A total failure of AV conduction in which no atrial impulses reach the ventricles, so the atria and ventricles beat independently (AV dissociation): the P waves bear no fixed relation to the QRS complexes, and because the atrial rate is faster than the ventricular escape rate there are more P waves than QRS complexes. The ventricles are driven by an escape rhythm. A narrow-QRS junctional escape (about 40 to 60 bpm) suggests block at the level of the AV node, whereas a wide-QRS ventricular escape (about 20 to 40 bpm) suggests block below it; a junctional escape keeps the patient's usual QRS shape, so it can be wide if a bundle branch block is already present.
Clinical noteComplete block is one cause of AV dissociation, not a synonym for it: P waves and QRS complexes can also run independently without any block, for example when the atrial rate is similar to or slower than the ventricular rate.
Sources
- 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
- 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
- Samesima N, God EG, Kruse JCL, et al. Brazilian Society of Cardiology guidelines on the analysis and issuance of electrocardiographic reports - 2022. Arq Bras Cardiol. 2022;119(4):638-680. doi.org/10.36660/abc.20220623
Last reviewed 2 October 2026. Every definition in the EKG Dictionary cites the guideline, consensus statement or original paper it comes from.