The atrioventricular node is a normal electrical pathway between the atria and ventricles and it is located in the right atrium. First-degree AV block pathogenesis can be attributed to an electrical conduction delay in the AV node or His-Purkinje system. First-degree AV block can be associated with normal QRS complex or wide QRS complex on the ECG.

• The atrioventricluar node is the normal electrical pathway between the atria and ventricles. It is located in the right atrium near to the tricuspid valve leaflet.
• The AV node receives blood supply from the right coronary artery in most of the population.
• The bundle of His is the electrical connection between the AV node to the interventricular septum. At the end of the septum, a bundle of His is divided into the right and left bundle branches to the ventricular walls.

• First-degree AV block broadly means the prolongation of the PR interval on the ECG with normal atrioventricular node function.
• First-degree AV block pathogenesis can be attributed to an electrical conduction delay in one of the following:^[1]
  • Atrioventricular node
  • His-Purkinje system which is formed of both bundle of His and Purkinje fibers
• The conduction delay can be also in both the AV node and His-Purkinje system.
• One of the characteristics of first-degree AV block is that there are no beats skipped and it has a regular rhythm.

First-degree AV block with normal QRS duration results from atrial or AV nodal delay.

First-degree AV block with wide QRS complex most often results from delay in conduction in the bundle of His and in some patients, the AV node.

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