# Corticosteroid-Induced Sinus Bradycardia in a Dog with Systemic Lupus Erythematosus: A Case Report

## TL;DR

A dog with an autoimmune disease developed a slow heart rate after receiving a steroid medication, highlighting a rare side effect of corticosteroids in pets.

## Contribution

This is the first reported case of sinus bradycardia in a dog caused by intravenous methylprednisolone therapy.

## Key findings

- The dog's heart rate dropped to 42–48 bpm after methylprednisolone treatment.
- Sinus bradycardia resolved after reducing the corticosteroid dose.
- No other medications or conditions explained the bradycardia.

## Abstract

In this report, we share the case of a 3-year-old mixed-breed dog that developed an unusual heart rhythm issue called sinus bradycardia after receiving a common steroid medication called methylprednisolone. The dog was being treated for an autoimmune condition known as systemic lupus erythematosus. Shortly after starting the treatment, the dog’s heart rate slowed significantly, dropping to 42–48 beats per minute, even though all other vital signs remained normal. Importantly, the dog was not on any other medications that might explain this reaction. After reducing the corticosteroid dose, the heart rate returned to normal, and no further issues were observed. This case highlights the potential for high-dose corticosteroid treatments to affect the heart, even in unexpected ways. By sharing this finding, we aim to help veterinarians recognize and manage similar situations, ensuring safer treatment of pets.

A 3-year-old, 10.2 kg, spayed, female mixed-breed dog was diagnosed with systemic lupus erythematosus. The patient was administered intravenous methylprednisolone at a dose of 2 mg/kg twice daily. Over the next 24 h, the dog’s heart rate dropped to 42–48 bpm, while other vital signs remained stable. A 12-lead electrocardiogram revealed sinus bradycardia without any other arrhythmia. Notably, the dog was not receiving any beta-blockers or undergoing other therapies commonly associated with sinus bradycardia. After tapering the corticosteroid dose, no further episodes of bradycardia were observed. Herein, we report the first case of sinus bradycardia in a dog following intravenous methylprednisolone therapy to improve veterinarians’ understanding of corticosteroid-induced cardiac arrhythmias.