Unusual cause of syncope in a patient with ischemic heart disease

Lithium is a commonly used drug for bipolar mood disorder. Though effective, it has a narrow therapeutic range and has potentially life-threatening effects at higher serum levels. Lithium toxicity can be precipitated by several drug interactions. Many commonly used cardiac drugs have serious drug interaction with lithium which is not commonly known in clinical practice. We present a case where a patient on lithium therapy since 15 years, presented with sinus arrest and syncope due to lithium toxicity, within 2 weeks of initiation of low dose angiotensin converting enzyme (ACE) inhibitor. The patient however needed temporary pacemaker support and had an uneventful recovery, without the need for a permanent pacemaker, once the lithium levels fell down to normal.