EKG Dictionary
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AV & intraventricular conduction

First-degree AV block

Also called1st degree AV block · first degree heart block · prolonged PR · first-degree AVB

Definition

A PR interval longer than 200 ms in which every P wave still conducts to the ventricles (1:1 conduction, no dropped beats). The delay can lie in the AV node or lower in the His-Purkinje system; a delay in the AV node usually leaves the QRS narrow.

Clinical noteStrictly delayed conduction rather than true block, since every impulse still reaches the ventricles.

See it on 12-lead ECGsFirst-degree AV block in Rhythm Foundations: examples to step through, and how to identify it

Sources

  1. 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
  2. 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.

More in AV & intraventricular conduction

2:1 AV block AV block Bifascicular block Bundle branch block High-grade AV block Incomplete bundle branch block Intraventricular conduction delay (IVCD) Left anterior fascicular block (LAFB) Left bundle branch block (LBBB) Left posterior fascicular block (LPFB) Mobitz I (Wenckebach) Mobitz II Pre-excitation Right bundle branch block (RBBB) Second-degree AV block Third-degree (complete) heart block Wolff-Parkinson-White (WPW)

See it on real ECGs

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