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:
Symptoms depend on the type of heart block you have:
Second-degree heart block might cause:
Third-degree heart block, which can be fatal, might cause:
To diagnose your condition, your health care provider will consider:
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.
Chronic congestive heart failure, or; workload of 3 METs or less results in dyspnea, fatigue, angina, dizziness, or syncope, or; left ventricular dysfunction with an ejection fraction of less than 30 percent
More than one episode of acute congestive heart failure in the past year, or; workload of greater than 3 METs but not greater than 5 METs results in dyspnea, fatigue, angina, dizziness, or syncope, or; left ventricular dysfunction with an ejection fraction of 30 to 50 percent
Workload of greater than 5 METs but not greater than 7 METs results in dyspnea, fatigue, angina, dizziness, or syncope, or; evidence of cardiac hypertrophy or dilatation on electrocardiogram, echocardiogram, or X-ray
Workload of greater than 7 METs but not greater than 10 METs results in dyspnea, fatigue, angina, dizziness, or syncope, or; continuous medication or a pacemaker required
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