First degree AV block

Background

First-degree atrioventricular (AV) block, or first-degree heart block, is defined as prolongation of the PR interval on an electrocardiogram (ECG) to more than 200 msec(5 small squares on the EKG tracing). First-degree AV block is considered “marked” when the PR interval exceeds 300 msec(more than 7 small squares on the EKG tracing).

Differential Diagnosis

AV blocks

• First degree AV block
• Second degree
  • Second degree AV block type I (Wenkebach)
  • Second degree AV block type II
• Third degree AV block
• AV dissociation without complete heart block

See Also

• AV blocks