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24

Congenital Heart Disease

Brian A. Scansen DVM, MS, DACVIM (Cardiology)
Department of Clinical Sciences, Colorado State University, Fort Collins, CO, USA

Congenital heart disease (CHD) accounts for a small as well as briefly describing the pathophysiology of such
subset of dogs and cats presenting for veterinary care, lesions. Figure 24.1 provides gross postmortem examples
estimated to account for less than 10% of cardiac disease of several of these defects.
in these species. However, the spectrum of CHD is broad
and complex – making the diagnosis, treatment, and Left‐to‐Right Shunting Lesions
prognosis for these animals more challenging. Successful
diagnosis and treatment of CHD provides great poten- A shunt is defined as an abnormal mixing of blood in the
tial impact on patient survival – e.g., correctly diagnos- heart or great vessels. The consequences of mixing
ing and closing a patent ductus arteriosus (PDA) can between the left and right heart (shunting) vary depend-
give an animal an additional decade or more of life. Since ing on their magnitude and direction. In a left‐to‐right
some forms of CHD are curable, it is imperative that shunt (meaning from the systemic circulation to the
animals with CHD not be missed during pediatric pulmonary circulation) the signs are principally of
general examination. volume overload to the lungs and the left heart because
the normal amount of blood flowing to the lungs is
augmented by the amount added from the shunt before
Etiology returning to the left heart. Conversely, right‐to‐left
shunts (where blood is diverted from the venous system
Causes of CHD to the systemic arterial system) result in poor oxygena-
tion and cyanosis.
The precise etiology of CHD in nearly all veterinary
species is not known. In humans, both genetic and envi- Patent Ductus Arteriosus
ronmental factors (drug use, toxin exposure, or infec- The ductus arteriosus is a normal structure in the fetus
tious diseases during pregnancy) have been implicated in derived from the left sixth aortic arch and allows for the
the genesis of CHD. In some breeds of dog there is a clear diversion of blood away from the lungs in utero when the
familial component, though the genetics have not been lungs are not expanded by air. Within the first 12–24
fully elucidated for any defect. Examples of diseases with hours after birth, the ductus begins to constrict in
a well‐recognized inheritable component include patent response to increased oxygen tension and is closed
ductus arteriosus (PDA) in the poodle, atrial septal within the first week of life. If the ductus remains open,
defect (ASD) in the standard poodle and Doberman the fall in pulmonary vascular resistance allows flow
pinscher, subaortic stenosis (SAS) in the Newfoundland, from the aorta to the pulmonary artery. Persistent
pulmonary valve stenosis (PS) in the beagle, tetralogy of patency of the ductus arteriosus is the most common
Fallot and related defects in the keeshond, ventricular CHD of the dog and appears to be the second most
septal defect (VSD) in the beagle and English springer common defect of the cat. Definitive therapy is an option
spaniel, and tricuspid valve dysplasia (TVD) in the for animals with PDA (via either interventional closure
Labrador retriever. or surgical ligation) and long‐term survival is excellent
The following paragraphs define some of the more after closure if heart failure or frequent arrhythmias have
common congenital heart malformations seen in animals not yet developed.

Clinical Small Animal Internal Medicine Volume I, First Edition. Edited by David S. Bruyette.
© 2020 John Wiley & Sons, Inc. Published 2020 by John Wiley & Sons, Inc.
Companion website: www.wiley.com/go/bruyette/clinical