Cardiovascular

Bradyarrhythmias and Heart Block

Disease of the conducting tissue delays or blocks atrial impulses reaching the ventricles, leaving a slow escape rhythm whose site of origin decides how dangerous the block is.

Definition

Heart block is impaired conduction of atrial impulses to the ventricles through the atrioventricular node and His-Purkinje system. It is graded as first degree, second degree (Mobitz I, Mobitz II, 2:1 and advanced) and third degree, or complete. Bradyarrhythmia is the wider term and also covers sinoatrial node disease, sinus pauses and slow escape rhythms. Bradycardia is conventionally a heart rate below 60 beats per minute.

First principles

Where the block sits decides the escape rhythm

First-degree block conducts every atrial impulse but with a long PR interval, the atrium-to-ventricle conduction time. Mobitz I (Wenckebach) lengthens the PR interval beat by beat until one impulse fails. Mobitz II drops beats without that warning. In complete block the atria and ventricles beat independently. The European Society of Cardiology (ESC) groups Mobitz II, 2:1 and advanced block (a P wave to QRS ratio of 3:1 or higher) with complete block. All of them can fail without warning.

You’ve reached the end of the preview

The rest of this extended textbook page is part of full access. Create a free account to read the sample topics in full and try sample questions, then upgrade to unlock every high-yield and extended page, plus the complete question bank.

This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.