An Unusual Presentation of Tetralogy of Fallot in a Dog: A Case Report

Tetralogy of Fallot (ToF) is a complex congenital cardiacanomaly characterized by four main defects: a ventricular septal defect (VSD), obstruction of the right ventricular outflow tract (RVOT) usually associated with pulmonary stenosis (PS), dextroposition (overriding) of the aortic root, and secondary right ventricular hypertrophy (Boon, 2011; Beijerink et al., 2017). It represents the most common cyanotic congenital heart defect in dogs and cats, with a reported prevalence ranging from 0.6% to 6.9% of all congenital cardiac anomalies in these species (Oliveira et al., 2011; Beijerink et al., 2017). Breeds reported to have a predisposition for this condition include the Keeshond, English Bulldog, Miniature Poodle, and several Terrier-type breeds (Strickland and Oyama, 2016). The condition shows considerable variation in presentation and anatomical features. Chronic pressure overload further leads to right ventricular concentric hypertrophy. The systemic delivery of deoxygenated blood is responsible for the hallmark clinical manifestation of cyanosis (Chetboul et al., 2016). In some animals, ToF can remain clinically silent for several years before signs become apparent. However, the majority of affected dogs exhibit marked exercise intolerance and cyanosis, with sudden death being a frequent outcome in this group of patients (Beijerink et al., 2017). This case report underscores the atypical presentation of this congenital disorder that became evident in an adult dog despite years of an apparently normal clinical status.