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Differential Diagnosis

  • Sinus tachycardia
  • AV block second degree ─ Mobitz I (Wenkebach)
  • Multifocal atrial tachycardia
  • Atrial fibrillation
  • Third-degree AV block

Diagnosis

This patient has a Mobitz I (Wenkebach) second-degree AV block, revealed in the ECG by progressive lengthening of the PR interval until there is a nonconducted P wave. The first two arrows below show the PR interval lengthening and then the last arrows a nonconducted P wave.

Learnings

  • There is a progressive lengthening of the PR interval, until there is a nonconducted P wave (see arrows above)
  • The P-P interval is typically constant
  • Medical conditions which may cause Wenkebach include myocardial infarction, myocarditis, electrolyte abnormalities, and postcardiac surgery
  • Medications include beta-blockers, calcium channel blockers, and digoxin 

Pearls for initial management and considerations for transfer:

  • Compare to previous ECG, if available
  • Patients without identifiable cause after history do not require further testing
  • Patients who are asymptomatic without an identifiable cause do not require treatment
  • Patients who are symptomatic with tachycardia, hypotension, chest pain, shortness of breath, or altered consciousness should be transferred
  • Distinguish from Mobitz II second-degree AV block and third-degree AV block, which are not benign rhythms
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