Atrioventricular block:

Atrioventricular block:

Atrioventricular (AV) block is a cardiac electrical disorder defined as impaired (delayed or absent) conduction from the atria to the ventricles. The severity of the conduction abnormality is described in degrees: first-degree; second-degree, type I (Wenckebach or Mobitz I) or type II (Mobitz II); and third-degree (complete) AV block. This classification scheme should be applied only during sinus rhythm and not during rapid atrial arrhythmias or to premature atrial beats.


Heart block can be first, second, or third-degree, depending on the extent of electrical signal impairment.

First-degree heart block: The electrical impulse still reaches the ventricles, but moves more slowly than normal through the AV node. The impulses are delayed. This is the mildest type of heart block.

Second-degree heart block is classified into two categories: Type I and Type II. In second-degree heart block, the impulses are intermittently blocked.

Type I, also called Mobitz Type I or Wenckebach’s AV block: This is a less serious form of second-degree heart block. The electrical signal gets slower and slower until your heart actually skips a beat.

Type II, also called Mobitz Type II: While most of the electrical signals reach the ventricles every so often, some do not and your heartbeat becomes irregular and slower than normal.

Third-degree heart block: The electrical signal from the atria to the ventricles is completely blocked. To make up for this, the ventricle usually starts to beat on its own acting as a substitute pacemaker but the heartbeat is slower and often irregular and not reliable. Third-degree block seriously affects the heart’s ability to pump blood out to your body.


The most common causes of AV block are:

  • Idiopathic fibrosis and sclerosis of the conduction system (about 50% of patients)
  • Ischemic heart disease (40%)
  • The remaining cases of AV block are caused by
  • Medications (eg, beta-blockers, calcium channel blockers, digoxin, amiodarone)
  • Increased vagal tone
  • Valvulopathy
  • Congenital heart, genetic, or other disorders
  • Atrioventricular block may be partial or complete. First-degree and second-degree blocks are partial. Third-degree blocks are complete.


Symptoms depend on the type of heart block you have:

  • First-degree heart block may have no bothersome symptoms.

Second-degree heart block might cause:

  • Dizziness
  • Fainting
  • The feeling that your heart skips beats
  • Chest pain
  • Trouble breathing or shortness of breath
  • Nausea
  • Fatigue

Third-degree heart block, which can be fatal, might cause:

  • Intense tiredness
  • Irregular heartbeats
  • Dizziness
  • Fainting
  • Cardiac arrest


To diagnose your condition, your health care provider will consider:

  • Your overall health and medical history
  • Any family history of heart block or heart disease
  • Medicines you are taking
  • Lifestyle choices, such as the use of cigarettes or illegal drugs
  • Your description of the symptoms
  • A physical exam
  • An electrocardiogram (ECG) records your heart’s electrical impulses
  • Testing with a Holter or event monitor to track your heart’s rhythm for a period of time.  
  • An electrophysiology study is an outpatient procedure in which a thin, flexible wire is threaded from your groin or arm to your heart to test the heart's wiring system. 

Note: Unusual cases of arrhythmia such as atrioventricular block associated with a supraventricular arrhythmia or pathological bradycardia should be submitted to the Director, Compensation and Pension Service. Simple delayed P-R conduction time, in the absence of other evidence of cardiac disease, is not a disability.

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