Approach Considerations
Perform a fingerstick glucose test, because beta-blockers may be associated with hypoglycemia, especially in patients with diabetes and in children. Also measure serum electrolytes, because hypokalemia may contribute to cardiac arrhythmias. Co-ingestions or concomitant medical conditions may alter other serum electrolytes, so these should be monitored closely, especially in patients with seizures or altered mental status. Measure cardiac enzymes to rule out myocardial infarction in any hemodynamically unstable patient.
Blood gas (arterial or venous) analysis may be helpful for managing metabolic acidosis from seizures or cardiogenic shock or rare cases of severe bronchospasm, respiratory acidosis, or hypoxia. Acidosis from poor cardiac perfusion may be manifested by low serum bicarbonate.
In a severe overdose that impairs myocardial contraction, chest radiographs may show evidence of pulmonary edema.
Electrocardiographic (ECG) results after beta-blocker overdose may include the following:
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Progressively worsening sinus bradycardia
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Increased PR intervals
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Loss of atrial activity
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Atrioventricular junctional rhythm
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Widening of the QRS complex
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Atrioventricular block
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Idioventricular rhythm
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Asystole
A prolonged QT interval has been observed after sotalol overdose. Ventricular fibrillation and ventricular tachycardia are uncommon because of the antidysrhythmic effects of most beta-blockers, with the exception of sotalol.
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Beta-blocker toxicity. Bradycardia is evident on a rhythm strip from a 48-year-old man who presented to the emergency department after a generalized tonic-clonic seizure. The patient was also hypotensive (82/55 mm Hg). The family reported that he was taking a medication, which proved to be propranolol, for a rapid heart rate. Propranolol is the most common beta-blocker involved in severe beta-blocker poisoning. It is nonselective and has membrane-stabilizing effects that are responsible for CNS depression, seizures, and prolongation of the QRS complex.
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Beta-blocker toxicity. Sotalol is associated with the rhythm shown below in both therapeutic doses and toxic ingestions. Sotalol has been used as a class III antiarrhythmic agent to control dangerous ventricular tachydysrhythmias in some individuals. It causes polymorphic ventricular tachycardia (torsade de pointes) in approximately 4% of patients. Rarely, prolongation of the QT interval has been reported with propranolol.
