Ventricular tachycardia as the main manifestation of primary cardiac lymphoma in a dog

An 11-year-old cocker spaniel was referred with a one-day history of lethargy. Upon presentation, cardiac auscultation revealed a tachyarrhythmia. Two-dimensional transthoracic echocardiography with concurrent electrocardiographic tracing showed biventricular systolic dysfunction, mild left atrial dilation, functional mitral and tricuspid regurgitations, and sustained wide-complex monomorphic tachycardia (heart rate: 330 beats per minute), primarily consistent with ventricular tachycardia. Laboratory test results were unremarkable, except for an elevated serum concentration of cardiac troponin I (2.84 ng/mL). Initially, despite the intravenous administration of lidocaine and esmolol, cardioversion was not achieved. Oral amiodarone was subsequently added to the antiarrhythmic protocol, resulting in the restoration of sinus rhythm, followed by an improvement in the dog's clinical condition and biventricular systolic function on repeated echocardiographic examination. Accordingly, the dog was discharged from the hospital on amiodarone therapy. However, four days later, the dog returned with a relapse of symptomatic ventricular tachycardia. Despite prompt management, the dog succumbed to the progression of ventricular tachycardia into ventricular fibrillation. Interestingly, although repeated echocardiographic examinations did not reveal abnormalities suggesting a cardiac tumor, macroscopic and histological findings led to the diagnosis of primary cardiac lymphoma of T-cell origin. This case contributes to the currently limited scientific literature on primary cardiac lymphoma in dogs. Moreover, it contributes to raising awareness among veterinary cardiologists about the potential limitations of two-dimensional transthoracic echocardiography in detecting cardiac lymphoma in dogs, as well as the possible arrhythmogenic role of this rare condition in the species.