Second degree Type I AV block is anatomically located at which node?

In second degree Type I AV block, also known as Mobitz Type I or Wenckebach block, the conduction delay occurs at the level of the AV node. This form of AV block is characterized by progressive prolongation of the PR interval until a beat (QRS complex) is dropped. The essential feature here is the gradual lengthening of the conduction through the AV node, which leads to the dropping of a QRS complex.

The AV node acts as a critical point in the conduction pathway of the heart, receiving impulses from the atria and transmitting them to the ventricles. In this specific type of block, the impairment in conduction is primarily due to the properties of the AV node, making it the site of the block rather than the SA node, Bundle of His, or Purkinje fibers. The other components play different roles in the conduction system:

• The SA node is responsible for initiating the heartbeat and does not directly contribute to this specific type of AV block.

• The Bundle of His and Purkinje fibers are involved in the conduction of impulses through the ventricles, but they do not typically experience the progressive conduction delays seen in Mobitz Type I block.

Understanding the anatomy and physiology of the cardiac conduction system