First degree AV block

Background

• Also known as first-degree heart block
• Defined as prolongation of the PR interval on an electrocardiogram (ECG) to more than 200 msec (5 small squares on the ECG tracing)
• Considered “marked” when the PR interval exceeds 300 msec (more than 7 small squares on the ECG tracing)

Clinical Features

• Vast majority are asymptomatic and diagnosed by chance
• Exercise may reveal decreased tolerance (especially when there is markedly prolonged PR interval and with left ventricular systolic dysfunction)

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

Evaluation

First degree AV block

• ECG
• Consider rare causes:
  • Lyme's disease
  • Lupus
  • Myocarditis
  • Myocardial infarction

Management

• Asymptomatic patients do not require any specific management
• Consider a cardiology consult for patients who may have symptoms attributable to the block (rare)

Disposition

• Outpatient

See Also

• AV blocks