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

Abstract

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.