2nd Degree Atrioventricular (AV) Block is a condition where the AV Node allows only some sinus-initiated beats to travel through the node into the ventricle, while others are blocked.
This can range in severity from mild (occasional blocked beats) to severe (High-Grade 2nd Degree AV Block).
The mild forms are often a result of higher vagal (parasympathetic) tone and rarely if ever cause clinical signs.
Commonly, this is associated with intracranial (neurologic), gastrointestinal, respiratory, bladder, or ocular disease.
An atropine response test will differentiate vagal from primary nodal causes. Mildly affected patients should be monitored for any evidence of progression.
The severe forms (High-Grade 2nd Degree AV Block) can result in collapse, weakness, exercise intolerance, and lethargy.
This condition is almost always due to a fibrosis/scarring of the AV Node that prevents signals from conducting through appropriately.
In severe cases, a permanent pacemaker is required to ensure the heart rate does not drop below the minimum programmed heart rate.