Mobitz Type 2 Second Degree Atrioventricular Block
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Contents |
Etiology
- increased vagal tone
- antiarrhythmic agents
- anterior wall myocardial infarction
- conduction system disease, generally His- Purkinje system
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 [[[Polymerase_Chain_Reaction | PCR]]
- adenovirus PCR, Chagas titers
Diagnostic-procedures
-
- 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
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 [2]
- symptomatic patients
-
- 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
- patietns with deinervated hearts (eg, cardiac transplant are not 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 [3]
More General Terms
Additional Terms
References
- Manual of Medical Therapeutics, 28th ed, Ewald & McKenzie (eds), Little, Brown & Co, Boston, 1995, pg 139-40.
- eMedicine: Heart Block, Second Degree [1]
- Medical Knowledge Self Assessment Program (MKSAP) 14, American College of Physicians, Philadelphia 2006
