Bradycardia and heart block due to lithium toxicity.

Lithium remains a cornerstone in the management of mood disorders, including bipolar disorder, mania and schizoaffective disorder, owing to its proven efficacy in relapse prevention and mood stabilisation. However, its narrow therapeutic index necessitates close serum level monitoring to prevent toxicity. Neurological and renal adverse effects of lithium are well recognised, but cardiac complications such as symptomatic bradycardia and varying degrees of heart block are under-recognised, yet they are potentially life-threatening manifestations of lithium toxicity, even at therapeutic or mildly elevated levels. These conduction abnormalities may present insidiously and can be easily overlooked, particularly in elderly patients or those with underlying cardiac disease. Early recognition is critical, as prompt discontinuation of lithium typically leads to rapid clinical and electrocardiographic improvement, often obviating the need for pacing. This highlights the importance of maintaining a high index of suspicion, routine cardiovascular assessment and individualised risk-benefit evaluation in patients receiving lithium therapy to prevent serious morbidity and mortality.