Bradycardia and Heart Block
Recognize dangerous conduction disease — the AV blocks, reversible causes, and when pacing is needed.
Learning Objectives
- 1.Identify the types of bradycardia and AV block.
- 2.Recognize the high-grade blocks that are dangerous.
- 3.Find reversible causes and know acute management/escalation.
Overview
Bradycardia ranges from benign to life-threatening. The job is recognizing high-grade conduction disease, looking for reversible causes, and escalating the symptomatic or dangerous patient.
Types
- •Sinus bradycardia — often benign (athletes, sleep, meds).
- •First-degree AV block — prolonged PR; usually benign.
- •Second-degree Mobitz I (Wenckebach) — progressive PR lengthening then a dropped beat; often benign.
- •Second-degree Mobitz II — dropped beats without PR lengthening; dangerous (can progress to complete block).
- •Third-degree (complete) heart block — AV dissociation; dangerous.
Dangerous vs benign
- •Dangerous: Mobitz II, complete heart block, and any symptomatic bradycardia (syncope, hypotension, ischemia, HF).
- •Benign: asymptomatic sinus brady, first-degree block, Mobitz I in the right context.
Reversible causes to find
- •Medications (beta-blockers, non-DHP CCBs, digoxin), ischemia/MI, hyperkalemia, hypothyroidism, increased vagal tone, hypothermia.
Acute management & escalation
- •Symptomatic/unstable bradycardia → ACLS bradycardia algorithm (atropine; transcutaneous/transvenous pacing) — physician-led.
- •Treat reversible causes (hold offending drugs, correct potassium).
- •High-grade block (Mobitz II, complete) often needs a pacemaker — cardiology/EP.
Escalate
Mobitz II, complete heart block, or symptomatic bradycardia is a physician-now situation — escalate and prepare for pacing per ACLS.
Where experienced clinicians slip
- •Confusing benign Mobitz I with dangerous Mobitz II.
- •Missing hyperkalemia or medication effect as a cause.
- •Not escalating symptomatic bradycardia promptly.
Mini cases
Patient with syncope; monitor shows dropped QRS complexes without preceding PR prolongation, then a run of complete dissociation.
Significance?
Show answer
Mobitz II progressing toward complete heart block — dangerous conduction disease. Escalate immediately; this often requires pacing and pacemaker evaluation.
Bradycardia at 38 with a potassium of 7.0 and peaked T waves.
Cause and action?
Show answer
Hyperkalemia-induced bradycardia — a reversible, emergent cause. Treat the hyperkalemia urgently and escalate; correcting potassium may resolve the bradycardia.