Cardiovascular · Year 1 · from Cardiovascular

Case 2: Beta-Blocker Overdose - Cardiogenic Shock

Clinical Image

Source: Clinical illustration of beta-blocker poisoning management - Educational use

Patient Presentation

A 52-year-old man with a history of depression is found unresponsive by his wife. Empty bottles of metoprolol succinate (extended-release) and propranolol are found nearby. EMS reports initial heart rate of 38 bpm and blood pressure of 72/40 mmHg. He was intubated in the field for airway protection.

Demographics

  • Age: 52 years
  • Sex: Male
  • Past Medical History: Depression, hypertension, type 2 diabetes
  • Medications: Metoprolol succinate 100 mg daily, lisinopril 20 mg daily, metformin
  • Suspected ingestion: ~50 tablets of metoprolol ER, ~30 tablets of propranolol

Chief Complaint

Found unresponsive with empty medication bottles

Physical Examination

  • Blood pressure: 68/38 mmHg (on norepinephrine infusion started by EMS)
  • Heart rate: 34 bpm
  • Temperature: 35.8°C (hypothermic)
  • Pupils: 3 mm, reactive
  • Cardiovascular: Bradycardic, weak peripheral pulses
  • Lungs: Intubated, clear on auscultation
  • Extremities: Cool, mottled

Workup

  • Point-of-care glucose: 52 mg/dL (hypoglycemic)
  • ECG: Sinus bradycardia with first-degree AV block, QRS 110 ms
  • ABG: pH 7.22, PCO2 32, PaO2 280 (on 100% FiO2), lactate 6.8 mmol/L
  • Basic metabolic panel: Na 138, K 5.2, Cr 1.4, glucose 54
  • Echocardiography: Severely reduced LV function (EF 15%), diffuse hypokinesis
  • Toxicology screen: Negative for coingestants

Diagnosis

Severe Beta-Blocker Toxicity with Cardiogenic Shock

Treatment

  1. Supportive care: IV fluids, vasopressors (norepinephrine, epinephrine)
  2. Glucagon: 5 mg IV bolus, then 2-5 mg/hour infusion
  • Bypasses beta-receptor to activate adenylyl cyclase via glucagon receptor
  1. High-dose insulin euglycemia therapy (HIET):
  • Regular insulin 1 unit/kg bolus, then 1-10 units/kg/hour
  • Dextrose infusion to maintain glucose 100-250 mg/dL
  • Potassium supplementation as needed
  1. Calcium chloride (or gluconate) for inotropy
  2. Atropine for bradycardia (often ineffective in severe toxicity)
  3. Consider temporary transvenous pacing if refractory bradycardia
  4. Lipid emulsion therapy if refractory shock
  5. ECMO consideration for refractory cardiogenic shock
  6. Decontamination: Whole bowel irrigation for extended-release formulation
  7. Psychiatry consultation after medical stabilization

Physiological Principles Demonstrated

  • Beta-receptor blockade effects: Beta-1 blockade reduces heart rate (negative chronotropy) and contractility (negative inotropy). Beta-2 blockade can cause bronchospasm and hypoglycemia (blocks glycogenolysis and gluconeogenesis).
  • Glucagon mechanism: Glucagon activates adenylyl cyclase via the glucagon receptor, bypassing the blocked beta-receptors to increase cAMP and improve cardiac contractility.
  • High-dose insulin mechanism: Insulin improves cardiac metabolism by promoting glucose uptake and utilization in the stressed myocardium, improving contractility independent of beta-receptors.
  • Extended-release considerations: Metoprolol ER releases drug over 24 hours; toxicity may be prolonged and delayed, requiring extended monitoring and treatment.

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