Atrioventricular block

Last revised by Rohit Sharma on 21 Dec 2021

Atrioventricular block, AV block or heart block is a conduction disturbance and a type of arrhythmia where the impulse transmission between the cardiac atria and ventricles is either transiently or permanently delayed or completely blocked 1.

Atrioventricular block can be found in healthy young individuals and prevalence seems to increase with age and other types of heart disease 2.

Atrioventricular block can be associated with the following conditions 3:

The diagnosis and classification of an atrioventricular block are based on the electrocardiogram (12-lead ECG or Holter monitor) 1-4:

  • 1st degree: prolongation of the PR interval (PR >200 ms) 2
  • 2nd degree: intermittent atrioventricular conduction 4
    • Mobitz type 1 (Wenckebach): progressive prolongation of the PR interval ultimately ending in a non-conducted P wave 
    • Mobitz type 2: intermittent non-conducted P waves with constant PR and stable PP intervals
  • 3rd degree: absence of atrioventricular nodal conduction resulting in a pattern where P waves are unrelated to the QRS complexes

Possible symptoms include fatigue, exercise intolerance, dyspnea, chest pain, dizziness, syncope and cardiac arrest. The presence and frequency of clinical symptoms also depend on degree 1.

Complications of atrioventricular block include 3:

An atrioventricular block is a conduction disorder that can arise from different locations within the cardiac conduction system. Subject to the type this includes the atrioventricular node, the bundle of His and the Purkinje system 4.

There are various possible functional and structural causes that are also related to the degree of atrioventricular block:

Management and prognosis depend on the degree of atrioventricular block and clinical symptoms. In higher-degree atrioventricular block pacemaker implantation is indicated to prevent syncope and sudden cardiac death and it should be considered in all symptomatic patients 1,2.

The Wenckebach sequence was first described by the Dutch physician and internist Karel Frederik Wenckebach in 1899 5. The two types of second degree atrioventricular block were differentiated by the Russian-German physician and internist Woldemar Mobitz in 1924 6.

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