# A Rare Case of Complete Atrioventricular Block Induced by Lithium Toxicity: Impact of Drug Interactions With Telmisartan

## TL;DR

A rare case shows lithium toxicity causing heart block, possibly worsened by telmisartan, highlighting the need for careful drug monitoring.

## Contribution

This paper reports a unique case of lithium-induced complete AV block without typical toxicity signs, emphasizing drug interactions with telmisartan.

## Key findings

- Lithium toxicity caused complete AV block in a patient without typical neurological or gastrointestinal symptoms.
- Telmisartan was identified as a potential contributor to lithium toxicity and subsequent arrhythmia.
- Heart rate normalized as lithium levels decreased, confirming the drug interaction as the likely cause.

## Abstract

Lithium is primarily associated with gastrointestinal and neurological side effects, while, to the best of our knowledge, cardiac toxicity is rarely reported. We present a unique case of lithium toxicity manifesting as a complete atrioventricular (AV) block, occurring without typical signs of lithium toxicity such as tremors, gastrointestinal disturbances, or altered mental status. A 55-year-old woman with bipolar disorder and hypertension presented with worsening mood lability and an increasing frequency of panic attacks. Lithium therapy was initiated to stabilize her mood and manage worsening psychiatric symptoms. However, while receiving treatment in the acute ward, she developed bradycardia with complete AV block, despite the absence of neurological symptoms or any reported discomfort. Elevated serum lithium levels strongly suggested lithium toxicity as the underlying cause. As lithium levels decreased, her heart rate normalized, and her sinus rhythm was restored. A review of her medication regimen identified the antihypertensive agent telmisartan as a potential contributor to lithium toxicity, which ultimately resulted in severe arrhythmia. Following her recovery, a detailed evaluation with a 24-hour Holter electrocardiogram (ECG) revealed no significant arrhythmias or pauses, further supporting the conclusion that the bradycardia was primarily due to the interaction between lithium and antihypertensive medications. This case emphasizes the importance of recognizing atypical presentations of lithium toxicity, particularly cardiac manifestations, and highlights the potential for drug interactions with antihypertensive agents. Clinicians should maintain vigilance and ensure close monitoring when co-prescribing these medications to mitigate associated risks.