Final answer:
In second-degree AV block type I or Wenckebach, the pacemaker site is typically in the AV node, which serves as the backup pacemaker. This block is characterized by a progressive delay in conduction between the atria and ventricles, resulting in a pattern of progressively lengthening PR intervals on the ECG.
Step-by-step explanation:
In second-degree AV block type I, also known as Wenckebach, the pacemaker site is typically located in the AV node.
During this type of block, there is a progressive delay in conduction between the atria and ventricles until a complete blockage occurs. This delay results in a pattern on the electrocardiogram (ECG), where the PR interval progressively lengthens until a QRS complex is dropped.
The AV node serves as the backup pacemaker in this type of block, generating electrical impulses to maintain a slower heart rate.