First Degree Heart Block

Definition

• There is delay, without interruption, in conduction from atria to ventricles
• ‘Marked’ first degree heart block is present if PR interval > 300ms

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Causes of First Degree Heart Block

Clinical significance

• As an isolated finding this is a benign entity that does not cause haemodynamic instability
• No specific treatment is required

ECG Examples

Example 1

• Marked first degree heart block
• PR interval > 300 ms, P waves are buried in the preceding T wave

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Example 2

• Sinus bradycardia with 1st degree AV block
• PR interval > 300 ms

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Example 3

• Normal sinus rhythm with 1st degree AV block
• PR interval 260 ms

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Advanced Reading

Online

Textbooks

• Zimmerman FH. ECG Core Curriculum. 2023
• Mattu A, Berberian J, Brady WJ. Emergency ECGs: Case-Based Review and Interpretations, 2022
• Straus DG, Schocken DD. Marriott’s Practical Electrocardiography 13e, 2021
• 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

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LITFL Further Reading

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