Paroxysmal AV block overview

• Atrioventricular block may be classified anatomically by the site of block, usually divided into atrioventricular nodal, intra-Hisian (within the His bundle itself), and infra-Hisian (below the His bundle).
• Paroxysmal AV block is defined as a delayed escape rhythm which repetitively blocks conduction from the atria to the ventricles, thereby causing syncope, conduction defects such as asystole and sudden cardiac death.
• It may or may not be associated with Phase 3 or Phase 4 conduction defects.
• It may be due to an increased vagal tone, innately low adenosine levels or an intrinsic conduction defect, all of which lead to different ECG presentations.
• Insufficient data is available regarding the exact etiology, diagnostic study of choice and treatment of paroxysmal AV blocks.
• It can be thought of more as a disease of exclusion. However,efforts must be made to have a standardized approach to such patients.
• The site of block may be clinically important and can be determined by invasive EPS when not apparent from the ECG and clinical circumstances.
• In general, atrioventricular block at the atrioventricular nodal level is associated with slower progression, a faster and more reliable atrioventricular junctional escape mechanism, and greater responsiveness to autonomic manipulation such as atropine, isoproterenol, and epinephrine administration.
  • In contrast, atrioventricular block within or below the His bundle may progress rapidly and unexpectedly, is associated with a slower and more unpredictable ventricular escape mechanism, will not respond to atropine but will sometimes improve with catecholamines.