Bradycardia-induced transient myocardial dysfunction in 3 dogs

Bradycardia-induced cardiomyopathy is a reversible form of myocardial dysfunction caused by prolonged bradyarrhythmia, most commonly due to high-grade atrioventricular block or sinus node dysfunction. Although bradycardia-induced cardiomyopathy is well recognized in human medicine, it remains underreported in veterinary literature. This case series describes 3 dogs diagnosed with 3rd-degree atrioventricular block that presented with clinical signs including exercise intolerance, syncope, and cardiomegaly. Each dog underwent comprehensive diagnostic evaluation, including physical examination, thoracic radiography, echocardiography, and electrocardiography. Bradycardia-induced transient myocardial dysfunction was suspected, based on the presence of bradyarrhythmia in conjunction with cardiac enlargement and preserved systolic function. All dogs were treated with permanent pacemaker implantation. Postoperative follow-ups documented marked clinical improvement, with resolution of exercise intolerance or syncope. Radiographic and echocardiographic reassessments demonstrated reductions in atrial and ventricular internal dimensions, supporting the reversibility of myocardial remodeling once normal heart rate was restored. No major complications were observed during follow-up periods that ranged from several months to > 4 y. Key clinical message: These findings supported the presence of bradycardia-induced transient myocardial dysfunction in dogs and underscored the importance of recognizing bradyarrhythmia as a potentially reversible cause of cardiomyopathy. Early diagnosis and timely pacemaker implantation can result in substantial clinical and structural cardiac recovery.