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Atrio-Ventricular Block

AV Blocks:  defined as a delay in conduction from the atria to the ventricles

 

First degree: PR interval >0.20 sec, slowed conduction without a missed beat

· Can be due to underlying AV nodal disease, increased vagal tone or AV nodal blocking agents

· Varies with HR (longer PR with bradycardia)

 

Second degree: missed beats, often in a pattern, ie. 2:1, 3:2, 4:3 etc.

· Mobitz type I (wenckebach): progressive PR prolongation preceeding a non-conducted p-wave

o Most often involves the AV node (75% of the time)

o Generally benign, can occur in young adults with high vagal tone and endurance athletes

o Increasingly common with advanced age

o Can occur with underlying heart disease: myocarditis, acute inferior MI (RCA supplies the AV node in 90% of pts), MV surgery

o Remember that if the pattern is 2:1, you cannot distinguish this from mobitz type II (often need a long rhythm strip (or consider increasing conduction with atropine)

o Treatment involves discontinuation of any AV nodal-blocking agent, or pacemaker in symptomatic patients

 

· Mobitz type II: PR interval remains unchanged prior to a non-conducted p-wave

o located below the AV node; can progress to complete HB

o Unpredictable/episodic

o Associated with underlying conduction system disease

o Treatment involves stopping any AV nodal-blocking agents, and generally PPM

 

Third degree: complete AV block

· Most often intrinsic AV nodal disease

· PPM is the treatment

 

 

Indications for PPM in 2nd degree AV block:

· Permanent or intermittent 2nd deg AV block regardless of the type or the site of block, with correlated symptomatic bradycardia

· Permanent or intermittent asymptomatic type II second-degree AV block

· Asymptomatic type I or advanced 2nd deg AV block at intra-His or infra-His levels (wide QRS)

· Exercise-induced second-degree AV block (absent at rest)

· 2nd deg AV block of any type in asymptomatic patients with neuromuscular diseases, eg, myotonic muscular dystrophy, limb-girdle dystrophy, etc.

 

 

(Victoria Kelly MD, 5/5/11)