We are observing EKG strip 1 in a Holter EKG recording; what can be said about it? There is a sinus rhythm with a normal PQ interval. After 3 sinus beats, a 2:1 AV block develops. When 2:1 AV block occurs, we should not refer to this as Wenckebach (Mobitz I) or Mobitz II, but rather as a high-grade AV block (other forms include: 3:1, 4:1, 5:1, etc.). The 2:1 block can be intranodally localized and behave benignly like a Wenckebach block typically does. However, it could also be infranodally localized with a potentially serious prognosis. Only EKG strip 2 allows us to make a precise diagnosis: here, the criteria for a Mobitz II block are met: sudden and unexpected failure of AV conduction with constant PP intervals (exception: ventriculophasic sinusarhrythmia), and PR intervals. Thus, a pacemaker indication is generally present here, unless there are remediable causes for the AV block.

In general, it is important to note that the indication for a pacemaker must always be made in the context of all available facts and findings.