Beta-blocker and Calcium-channel blocker toxicity

Relevant Agents

  • Beta-blockers: Atenolol, metoprolol, propranolol, sotalol.
  • Cardioselective calcium-channel blockers: Verapamil and diltiazem.

Effects on the ECG

A prolonged PR interval is an early sign of beta-blocker or calcium-channel blocker toxicity — even in the absence of significant bradycardia.

Specific Agents

Two beta-blockers have additional important toxic effects:

  • Propranolol behaves more like a tricyclic antidepressant in overdose than a beta-blocker, due to its blockade of myocardial and CNS fast sodium channels.
  • Propranolol toxicity is associated with QRS widening and a positive R’ wave in aVR (signs of sodium channel blockade), which portend the onset of coma, seizures, hypotension and ventricular arrhythmias.

ECG Examples
Example 1
ECG Sinus bradycardia 1st degree AV block

Sinus bradycardia with 1st-degree AV block:

  • Heart rate 45 bpm.
  • PR interval 240 ms.

This type of ECG pattern is commonly seen in the early stages of beta-blocker / calcium-channel blocker poisoning.

Example 2
ECG Junctional bradycardia

Slow junctional rhythm:

  • Regular rhythm at 30 bpm.
  • Narrow QRS complexes
  • No visible P waves

Example 3
ECG High grade block CHB

Complete heart block:

  • Sinus rhythm – P waves occur at a rate of around 90 bpm.
  • 3rd degree AV block – there is no relationship between the P waves and QRS complexes.
  • Slow escape rhythm (30 bpm) with a RBBB morphology – this could be either a ventricular escape rhythm or a slow junctional rhythm with RBBB.

Example 4
ECG Sinus bradycardia prolonged QT Sotalol OD

This ECG demonstrates the key features of sotalol overdose:

  • Sinus bradycardia.
  • Very long QT interval (~600ms).

NB. This patient is at significant risk of Torsades de Pointes.

Example 5
ECG sodium channel blockade Flecainide

This ECG demonstrates some of the key features of propranolol overdose:

NB. Normally the heart rate would be slower than this in a propranolol overdose (this is actually an ECG of flecainide poisoning — another sodium-channel blocking agent).


Advanced Reading



LITFL Further Reading




Emergency Physician in Prehospital and Retrieval Medicine in Sydney, Australia. He has a passion for ECG interpretation and medical education | ECG Library |

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