Second Degree AV Block, Mobitz Type I (Wenkebach)

Second Degree AV Block, Mobitz Type I (Wenkebach)

David Ray Velez, MD

Intermittent Interruption of Impulse Transmission from the Atria to the Ventricles with Progressive PR Prolongation Prior to Dropped Beats

  • Usually Due to a Reversible Conduction Delay at the AV Node
  • The Majority are Benign and Asymptomatic

EKG Pattern

  • Progressive PR Interval Prolongation Followed by Dropped Beats
  • The Largest Absolute PR Interval Increase is Most Often Between the First and Second Beats of the Cycle
  • The P-P Interval Remains Relatively Constant Throughout the Cycle
  • The R-R Interval Progressively Decreases Throughout the Cycle
  • Often Cycles in a Repeated P:QRS Ratio (3:2, etc.)

Second Degree AV Block, Mobitz Type I (Wenkebach)

Pathologic Causes

  • Myocardial Infarction (MI)
  • Electrolyte Derangements
  • High Resting Vagal Tone – Athletes
  • Cardiomyopathy
  • Myocarditis
  • Post-Cardiac Surgery
  • Medications (Beta-Blockers, Calcium Channel Blockers, Digoxin, etc.)

Treatment

  • Unstable: Atropine
    • Dose: 0.5-1.0 mg IV, Repeated Every 3-5 Minutes as Needed (Up to a Total Dose of 3 mg)
    • Consider Temporary Cardiac Pacing if Atropine Fails
    • *See Antiarrhythmic Pharmacology
  • Stable: The Majority Require No Specific Treatment
    • May Consider Permanent Pacemaker Placement in the Chronic Management of Persistent Symptomatic Bradycardia