Definition
The AV node is a group of specialized conducting cells found in the middle of the heart. The AV node is responsible for transmitting electrical pulses from the sinus node and the top part of the heart through to the bottom part of the heart. Second degree AV block refers to a condition where the transmission of electrical impulses through the AV node is slower than expected, with occasional times where impulses are not transmitted at all.
Causes
There are two different forms of second degree AV block in children. The first form, type l or Wenkebach, refers to a situation where impulse transmission to the AV node progressively slows with each successive beat until a point where a single impulse is no longer transmitted. Type I AV block in many instances can be a normal finding caused by enhanced vagus nerve activity. The vagus nerve is a large nerve that travels from the brain throughout the body. It has branches to many portions of the heart, including the AV node. When the vagus nerve is activated, it can slow transmission through the AV node, resulting in either first-degree AV block or type l second degree AV block. This can often be seen during sleep in completely normal, healthy children. Less commonly type I AV block may be a manifestation of more diffuse electrical conduction system disease.
Type ll AV block refers to a situation where impulse transmission through the AV node occasionally is blocked without any warning. Type ll AV block is more concerning and can be a sign of impending complete heart block. Type ll AV block can be caused by inflammatory conditions, as a complication of open heart surgery, or as a result of diffuse electrical conduction system disease.
Symptoms
Second degree AV block in children is often diagnosed incidentally on an electrocardiogram (ECG) or some other heart rhythm recording such as holter monitoring. Most children with second degree AV block are asymptomatic. Children with advanced forms of second degree AV block may have symptoms of syncope, dizziness, fatigue, or palpitations.
Treatment
Treatment of second degree AV block in children usually depends on the underlying type and cause. Type l second degree AV block typically does not require any treatment whatsoever. Type ll second-degree AV block usually requires more frequent monitoring and/or consideration of a pacemaker, especially in those with advanced forms.