DDx
Diagnostic Considerations
The differential diagnosis of second-degree atrioventricular (AV) block is limited, although the potential etiologies may widely vary. Atrial tachycardias with second-degree block or nonconducted premature atrial stimuli are occasionally mistaken for second-degree AV block. This may be avoided by paying close attention to the P-wave rate, morphology, and regularity, recognizing that sinus arrhythmia is a normal finding in children. Marked sinus arrhythmia is also often mistaken for second-degree AV block.
Differentiating ECG AV block into its subtypes of Wenckebach, non-Wenckebach, 2:1, or high-grade AV is very important.
Differential Diagnoses
Media Gallery
-
A common pattern of second-degree atrioventricular (AV) block consists of gradual prolongation of the PR interval leading up to a nonconducted P wave; this pattern is known as Wenckebach AV block, or Mobitz I AV block. This rhythm strip is an example of classic Mobitz I, or Wenckebach, AV block, in which the PR interval prolongs by sequentially smaller increments, with consequent shortening of the RR intervals until the blocked beat occurs. However, classic Wenckebach block is present in only a minority of cases. Wenckebach block is most easily diagnosed by comparing the PR interval following the blocked beat with the PR interval preceding the blocked beat; if the PR interval shortens following the blocked beat, the block is most likely of the Wenckebach type.
-
If there is no progressive prolongation of the PR interval and the PR interval fails to shorten following a blocked beat, non-Wenckebach AV block (or Mobitz II AV block) is said to be present. This block is usually located more distally in the His bundle or the His bundle branches, or both, and the escape rates are usually slower and less stable.
of
2
