AV blocks — 1°, Mobitz I/II, complete

Recognize each block by PR pattern and dropped beats; know who needs a pacemaker.

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◆The four blocks

•1° AV block: PR > 200 ms, every P conducts — usually benign, no treatment
•Mobitz I (Wenckebach): progressively lengthening PR until a QRS is dropped, then resets — AV node, USUALLY benign (often inferior MI, drugs)
•Mobitz II: constant PR, sudden non-conducted P (dropped QRS) — INFRA-nodal (His/Purkinje); high risk of progression to complete block → pacemaker
•3° (complete) AV block: P and QRS dissociated, regular at independent rates; narrow QRS = junctional escape, wide QRS = ventricular escape → pacemaker

•Symptomatic bradycardia → atropine 0.5–1 mg IV; if no response → transcutaneous pacing → epi/dopamine drip → transvenous pacer
•Mobitz II or complete heart block → PERMANENT pacemaker (regardless of symptoms)
•Inferior MI causing Mobitz I or transient complete block → usually resolves with reperfusion (vagal-mediated)
•Anterior MI with new block → bad sign (extensive infarction); consider permanent pacing

EKG finding	Block
PR > 200 ms, every P conducted	1° AV block
PR lengthens until QRS drops	Mobitz I (Wenckebach)
PR constant, random dropped QRS	Mobitz II
P and QRS independent (AV dissociation)	Complete (3°) AV block

◆Mobitz I = Wenckebach = AV node — usually benign, monitor
◆Mobitz II = below the AV node = unpredictable → permanent pacemaker
◆Cannon A waves on JVP = atrium contracting against closed tricuspid (complete block, VT)
◆Lyme carditis is a classic reversible cause of high-grade AV block — treat with ceftriaxone before placing a permanent pacer

Quick check

Test yourself before moving on. ~1 min.

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