Heart Block
💓 Do You Know Your Heart Blocks? Let’s Find Out!
🩺 Case Scenario 1
A 76-year-old man presents to the Queen Elizabeth Hospital ED after a witnessed syncopal episode at home. He reports fatigue and light-headedness over the past week. He is alert but bradycardic at 32 bpm and hypotensive at 80/50 mmHg. ECG shows a wide QRS with complete AV dissociation. There is no known ischemic heart disease. See ECG below.
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• Bradycardia (<40 bpm)
• Syncope
• Hypotension
• Cannon A waves, variable S1 (AV dissociation)
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• Mobitz I: progressive PR prolongation, dropped QRS
• Mobitz II: fixed PR, sudden dropped beat
• Mobitz II often has wide QRS
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• Ischaemia: Inferior MI
• Drugs: Beta-blockers, CCBs, digoxin
• Electrolytes: Hyperkalemia
• Metabolic: Hypothyroidism
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• P and QRS dissociation
• Escape rhythm (junctional or ventricular)
• Atrial rate > ventricular rate
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• ABCs, IV access, Bloods, VBG, Troponin, Pad monitoring
• Atropine 500 mcg IV (may be ineffective)
• Transcutaneous pacing
• Isoprenaline or Adrenaline, Some Suggest Dopamine: I dont use it
• Urgent cardiology for TV pacing
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• Mobitz I: AV node (better prognosis)
• Mobitz II: His-Purkinje (more serious → pacing)
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• There is evolving Ventricular standstill (no escape)
• Risk: asystole → requires immediate pacing
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• Symptomatic complete HB
• Mobitz II (even if asymptomatic)
• Symptomatic bradycardia
• Asymptomatic with HR <40 or pauses >3 sec
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• Complete HB: atrial rate > ventricular
• AJR: junctional rate > atrial
• Fusion/capture beats suggest AJR
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• Mobitz I or complete AV node block
• Usually transient
• May respond to atropine, Use Adrenaline in Cardiogenic shock
• Transvenous pacing if required, Rarely needs permanent pacing
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• Lenègre’s disease
• Lev’s disease
• Infiltrative: amyloid, sarcoid
• Drugs: beta-blockers, CCBs, digoxin
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• Perivalvular abscess near AV node
• PR prolongation or new BBB
• Fever + conduction delay = urgent TEE
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• Lyme carditis
• Hyperkalemia
• Hypothyroidism, Others like Sarcoid, cause irreversible Block- Read the question carefully
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• Sudden syncope due to abrupt ↓CO
• Often from transient complete HB
• ECG: Sinus arrest, asystole or escape rhythm
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• HR <30 bpm
• Wide QRS
• Irregular rhythm
• This implies Shock, poor perfusion, a periarrest state, and requires emergency pacing
🧪 Case Scenario 2: Calcium Channel Blocker (CCB) Overdose
A 55-year-old woman presents to the QE-II ED after ingesting verapamil with alcohol. She is drowsy, BP 85/50 mmHg, HR 38 bpm. ECG: complete heart block, wide QRS escape rhythm. Glucose is 12.3 mmol/L. No benzos, opioids or paracetamol toxicity.
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• Bradycardia
• AV block (including complete)
• Wide QRS
• QT prolongation (occasionally)
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• L-type calcium channel blockade
• ↓ AV conduction and contractility
• ↓ Perfusion to conduction system from hypotension
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•There are some similarities, but generally Hyperglycemia (CCB)
• Preserved CNS in CCB
• Pulmonary edema more likely in verapamil toxicity
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• IV calcium (chloride or gluconate)
• High-dose insulin + dextrose (HIET)
• Noradrenaline or adrenaline
• Glucagon
• Temporary pacing if unstable
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• Refractory shock
• Lipophilic drug sink (e.g., verapamil)
• Improves myocardial function and SVR
