Mobitz type 2 second-degree atrioventricular (AV) block

Etiology

• increased vagal tone
• antiarrhythmic agents
• anterior wall myocardial infarction
• conduction system disease, generally His-Purkinje system
  • bundle branch block

Pathology

• conduction block without a preceding conduction delay.
• the conduction block is generally in the His-Purkinje system & often associated with a bundle branch block
• 2nd degree AV block type 2 especially in association with bundle branch block, often portends development of transient 3rd degree AV block (complete heart block)

Clinical manifestations

• feeling of a skipped beat
• lightheadedness
• syncope or near-syncope
• chest pain if heart block is related to myocarditis or ischemia

Laboratory

• chem7, serum calcium, serum magnesium
• digoxin level should be obtained for patients on digoxin
• cardiac-specific troponin-I
• myocarditis-related laboratory studies if clinically relevant
  • Lyme titers
  • HIV serologies
  • enterovirus polymerase chain reaction [[[A13564|PCR]]
  • adenovirus PCR, Chagas titers

Diagnostic procedures

• electrocardiogram (ECG)
  • unexpected nonconducted atrial impulse
  • no change in PR interval preceding a non-conducted p-wave
  • R-R intervals between conducted beats are constant
  • QRS complex is likely to be wide, except in patients where the delay is localized to the bundle of His

* ECG image

Complications

• patients with Mobitz type 2 second-degree AV block have a propensity to progress to complete heart block

Management

• avoid AV nodal agents
• treat myocardial ischemia if present
• transcutaneous pacing pads should be applied to all patients, including asymptomatic patients
  • transcutaneous pacemaker should be tested to ensure capture
  • insertion of a transvenous pacemaker if transcutaneous pacemaker does not capture, even in asymptomatic patients
• symptomatic patients
  • atropine 0.5-2.0 mg IV
    • goal of therapy is to improve conduction through the AV node by reducing vagal tone via atropine-induced receptor blockade
    • only effective if block is at the AV node
    • patients with infranodal second-degree heart block are unlikely to benefit from atropine. In addition
    • patients with deinervated hearts (eg, cardiac transplant are not likely to benefit
  • transcutaneous pacemaker in patients resistant to atropine
  • bradycardia refractory to atropine & transcutaneous pacemaker not available
    • dopamine 5-20 ug/kg/min
    • epinephrine 2-20 ug/min
    • isoproterenol 2-10 ug/min
  • permanent pacemaker
• guidelines for permanent pacemaker
  • persistent, advanced Mobitz type 2
  • transient Mobitz type 2 with bundle branch block

More general terms

• second-degree atrioventricular (AV) block

Additional terms

• HV interval