Second degree AV block (Mobitz I) with prolonged PR interval
Second degree heart block, Mobitz type I (Wenckebach phenomenon).
Note how the baseline PR interval is prolonged, and then further prolongs with each successive beat, until a QRS complex is dropped.
The PR interval before the dropped beat is the longest (340ms), while the PR interval after the dropped beat is the shortest (280ms).
Short PR interval (<120ms)
A short PR interval is seen with:
Preexcitation syndromes
AV nodal (junctional) rhythm.
Pre-excitation syndromes
Wolff-Parkinson-White (WPW) and Lown-Ganong-Levine (LGL) syndromes.
These involve the presence of an accessory pathway connecting the atria and ventricles.
The accessory pathway conducts impulses faster than normal, producing a short PR interval.
The accessory pathway also acts as an anatomical re-entry circuit, making patients susceptible to re-entry tachyarrhythmias.
Patients present with episodes of paroxsymal supraventricular tachycardia (SVT), specifically atrioventricular re-entry tachycardia (AVRT), and characteristic features on the resting 12-lead ECG.
Wolff-Parkinson-White syndrome
The characteristic features of Wolff-Parkinson-White syndrome are a short PR interval (<120ms), broad QRS and a slurred upstroke to the QRS complex, the delta wave.
Lown-Ganong-Levine syndrome
The features of Lown-Ganong-Levine syndrome LGL syndrome are a very short PR interval with normal P waves and QRS complexes and absent delta waves.
AV nodal (junctional) rhythm
Junctional rhythms are narrow complex, regular rhythms arising from the AV node.
P waves are either absent or abnormal (e.g. inverted) with a short PR interval (=retrograde P waves).
ECG: Accelerated junctional rhythm demonstrating inverted P waves with a short PR interval (retrograde P waves)
ECG Library Basics
P Wave
PR Interval
PR Segment
Q Wave
QRS Segment
QT Interval
J Point
ST Segment
R Wave
T Wave
U Wave
Osborn Wave
Epsilon Wave
Delta Wave
Advanced Reading
Online
Wiesbauer F, Kühn P. ECG Mastery: Yellow Belt online course. Understand ECG basics. Medmastery
Wiesbauer F, Kühn P. ECG Mastery: Blue Belt online course: Become an ECG expert. Medmastery
Kühn P, Houghton A. ECG Mastery: Black Belt Workshop. Advanced ECG interpretation. Medmastery
Rawshani A. Clinical ECG Interpretation ECG Waves
Smith SW. Dr Smith’s ECG blog.
Wiesbauer F. Little Black Book of ECG Secrets. Medmastery PDF
Textbooks
Zimmerman FH. ECG Core Curriculum. 2023
Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
Brady WJ, Lipinski MJ et al. Electrocardiogram in Clinical Medicine. 1e, 2020
Mattu A, Tabas JA, Brady WJ. Electrocardiography in Emergency, Acute, and Critical Care. 2e, 2019
Hampton J, Adlam D. The ECG Made Practical 7e, 2019
Kühn P, Lang C, Wiesbauer F. ECG Mastery: The Simplest Way to Learn the ECG. 2015
Grauer K. ECG Pocket Brain (Expanded) 6e, 2014
Surawicz B, Knilans T. Chou’s Electrocardiography in Clinical Practice: Adult and Pediatric 6e, 2008
Chan TC. ECG in Emergency Medicine and Acute Care 1e, 2004
LITFL Further Reading
ECG Library Basics – Waves, Intervals, Segments and Clinical Interpretation
ECG A to Z by diagnosis – ECG interpretation in clinical context
ECG Exigency and Cardiovascular Curveball – ECG Clinical Cases
100 ECG Quiz – Self-assessment tool for examination practice
ECG Reference SITES and BOOKS – the best of the rest
ECG LIBRARY
more EKG…
Mike Cadogan
BA MA (Oxon) MBChB (Edin) FACEM FFSEM. Emergency physician, Sir Charles Gairdner Hospital. Passion for rugby; medical history; medical education; and asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | On Call: Principles and Protocol 4e| Eponyms | Books |
