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)