Simple Summary
Focal junctional tachycardia with type I isorhythmic AV dissociation is a rapid, abnormal heart rhythm—where the upper and lower chambers of the heart beat independently of one another. This rhythm is well recognized in humans and dogs, but has never been reported in cats. This report aims to describe the first known case of this dangerous rhythm in a nine-year-old cat experiencing heart failure and fever. Diagnostic tests revealed an arrhythmia, enlarged cardiac chambers, and thickened heart muscle. Furthermore, analysis of the pleural effusion was suspicious for neoplasia. Despite intensive medical care, the cat passed away suddenly. A tissue examination after death revealed severe inflammation of the heart muscle. We conclude that severe heart inflammation can cause this rare heart rhythm and mimic cancer in feline patients. This finding expands our understanding of this condition in cats, and alerts veterinarians to consider heart inflammation as an uncommon, but possible, differential diagnosis. This manuscript also discusses management of a complex, life-threatening arrhythmia.
Abstract
Focal junctional tachycardia (FJT) is a regular, narrow QRS complex tachycardia with subtle cycle length irregularity, frequently associated with isorhythmic atrioventricular dissociation (IAVD). Its presentation may be paroxysmal or non-paroxysmal. This rhythm is well recognized in humans and dogs. However, to the best of the authors’ knowledge, FJT has not been previously published in cats. This case report describes a 9-year-old neutered male domestic shorthair cat presenting with signs of congestive heart failure, hyperthermia, and a non-paroxysmal FJT. Electrocardiography demonstrated a narrow QRS tachycardia with type I synchronization IAVD, consistent with suspected FJT. Transthoracic echocardiography revealed severe biatrial enlargement, concentric ventricular hypertrophy and echocardiographic measures suggestive of high probability of pulmonary hypertension. There was apparently preserved global systolic function and diastolic dysfunction. These findings were consistent with a non-specific cardiomyopathy phenotype stage C. Pleural fluid cytology initially suggested a lymphoproliferative disorder; however, postmortem histopathological examination confirmed diffuse lymphocytic myocarditis without evidence of neoplasia. Despite intensive supportive and antithrombotic therapy, the cat experienced sudden death. To the authors’ knowledge, this is the first description of suspected FJT with type I IAVD in a cat. This case highlights myocarditis as a critical differential diagnosis in cats presenting with a lymphocytic effusion, structural echocardiographic changes, and complex supraventricular arrhythmias. It also discusses the diagnostic challenges and prognostic implications associated with inflammatory myocardial disease in this species.