First-degree AV block has a PR interval > 0.20 seconds. It occurs at the AV node and is classified as a supra-His block.

An isolated prolonged PR interval does not represent first-degree AV block. First-degree AV block may be seen in healthy patients. It is also a side effect of digitalis and similar cardiac drugs. First-degree AV block is usually not clinically significant, and the patient typically does not develop worsening symptoms in subsequent years.

Case 1

7-Year-Old Boy With First-Degree AV Block ECG

Related Video – One Quick Question: What are the First-Degree Heart Block Criteria??