Sinus Node Dysfunction After Acute Lithium Treatment at Therapeutic Levels

Lithium carbonate (lithium) has been used extensively for the treatment of a variety of psychiatric conditions. It requires close monitoring of serum concentration due to its narrow therapeutic window. Cardiac toxicity range from asymptomatic electrocardiographic changes to fatal arrhythmias may occur even at the therapeutic levels. We report a case of psychiatric inpatient who developed asymptomatic severe bradycardia most likely related to sinus node dysfunction due to acute lithium treatment at therapeutic level. After withdrawal of lithium, a time sequential improvement of severe bradycardia examined by repeated electrocardiogram, including Holter monitoring, suggested a relationship between the lithium toxicity and sinus node dysfunction. Other factors such as baseline sinus bradycardia and lower limit of normal thyroid function might be associated with severe bradycardia. This case emphasizes the need, when prescribing lithium, for clinicians to regularly monitor their patients' electrocardiogram and serum lithium levels to prevent serious or fatal complications, such as cardiac arrest.