atrioventricular (AV) conduction block

Last edited 06/2020 and last reviewed 05/2021

Atrioventricular heart block is caused by disorders of the atrioventricular node.

• atrioventricular block is a failure in the conduction of electrical impulses from the atria to the ventricles
  • may be caused by conduction defects at the AV node (situated between the atria and ventricles), bundle of His and/or bundle branches
  • the AV node captures waves of depolarisation from the atria, which are then transferred to the ventricles via the bundles of His and the Purkinje system
• atrioventricular block may be intermittent or permanent
  • can progress from minimal asymptomatic conduction delay to the ventricles (first-degree), to partial second-degree) atrioventricular block, or complete (third-degree) atrioventricular block, in which there is no conduction between the atria andventricles
  • partial atrioventricular block is usually asymptomatic, it carries a high risk of progression to complete block
• prevalence of atrioventricular block (based on clinical studies) range from 0.015% to 0.1%, although it is common for people to have coexisting abnormalities of both the sinus node and the AV node
• dual-chamber pacing and single-chamber atrial pacing (in patients with sick sinus syndrome without atrioventricular block), as opposed to single-chamber ventricular pacing, are considered to be ‘physiological’ pacing modes because AV synchrony is maintained and the frequency of contractions of the atria and ventricles varies with metabolic demand, mimicking the heart’s natural rhythm4

Atrioventricular (AV) Block (2)

Click here for ECG findings and further information about AV block

Reference:

1. NICE (February 2005).Dual-chamber pacemakers for symptomatic bradycardia due to sick sinus syndrome and/or atrioventricular block
2. Alpaslan M. Atrioventricular (AV) Block. doctorecg.com (accessed 3/6/2020)