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Mobitz type 2 second-degree atrioventricular (AV) block

Etiology: 1) increased vagal tone 2) antiarrhythmic agents 3) anterior wall myocardial infarction 4) 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: 1) feeling of a skipped beat 2) lightheadedness 3) syncope or near-syncope 4) 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 [PCR - adenovirus PCR, Chagas titers Special laboratory: - 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 [4] Complications: - patients with Mobitz type 2 second-degree AV block have a propensity to progress to complete heart block Management: 1) avoid AV nodal agents 2) treat myocardial ischemia if present 3) transcutaneous pacing pads should be applied to all patients, including asymptomatic patients a) transcutaneous pacemaker should be tested to ensure capture b) insertion of a transvenous pacemaker if transcutaneous pacemaker does not capture, even in asymptomatic patients [2] 4) symptomatic patients a) 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 b) transcutaneous pacemaker in patients resistant to atropine c) bradycardia refractory to atropine & transcutaneous pacemaker not available 1] dopamine 5-20 ug/kg/min 2] epinephrine 2-20 ug/min 3] isoproterenol 2-10 ug/min d) permanent pacemaker 4) guidelines for permanent pacemaker a) persistent, advanced Mobitz type 2 b) transient Mobitz type 2 with bundle branch block [3]

Related

HV interval

General

second-degree atrioventricular (AV) block

Figures/Diagrams

EKG: 2nd degree type 2 AV block

References

  1. Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995, pg 139-40.
  2. eMedicine: Heart Block, Second Degree http://www.emedicine.com/EMERG/topic234.htm
  3. Medical Knowledge Self Assessment Program (MKSAP) 14, American College of Physicians, Philadelphia 2006
  4. Podrid PJ ECG Challenge: Lightheadedness and Slow, Irregular Pulse. Medscape. June 12, 2021 https://www.medscape.com/viewarticle/952667_2