CONGENITAL DEFECTS OF THE 
CARDIOVASCULAR SYSTEM IN DOGS 
D. F. Patterson* 
The development of clinical cardiology in veterinary 
medicine has resulted in the recognition and study of a 
wide variety of congenital cardiovascular defects in 
dogs, many of which are close counterparts of human 
disorders. These include the more common anatomic 
forms of congenital heart disease and a number of con- 
genital abnormalities in cardiac excitation recognized 
by their electrocardiographic features. This paper illus- 
trates how studies of some of these animal models have 
led to new insights into etiologic and pathogenetic 
mechanisms. 
Epidemiologic and genetic studies have shown that 
the common anatomic defects of the cardiovascular sys- 
tem in dogs have a genetic cause. The underlying ge- 
netic abnormality is complex but lesion-specific in na- 
ture. Breeding experiments have proven the feasibility 
of producing dogs with specific defects for a variety of 
research purposes by selective breeding. The genetic 
features, sequelae, and pathogenetic mechanisms in he- 
reditary canine patent ductus arteriosus are reviewed. 
A number of forms of naturally occurring congenital 
heart disease have been utilized in studies of cardiac 
pathophysiology not possible in man. Contributions of 
this work include the identification of a genetically de- 
termined variant in right ventricular wall thickness 
without other defects as a cause of the incomplete right 
bundle branch block pattern, and the first anatomic and 
electrophysiologic delineation of an accessory atrio- 
ventricular conduction pathway in the Wolflf-Parkinson- 
White syndrome. Pathologic studies suggest that con- 
genital defects of the atrioventricular conduction system 
may exist in dogs, pointing to another potential model 
of human cardiovascular disease. Other examples of the 
use of dogs with congenital cardiovascular defects for 
physiologic studies include investigations of the spread 
of activation in right ventricular hypertrophy associated 
with various forms of congenital heart disease, and 
chronic studies of coronary blood flow in dogs with 
fibrous subaortic stenosis. 
INTRODUCTION** 
During the past 20 years, the development of 
clinical cardiology in veterinary medicine has 
resulted in the recognition and study of a v^^ide 
* University of Pennsylvania School of Veterinary Medicine. 
** Supported by U.S. Public Health Service Grants HL 10995 and 
4885 from the National Heart and Lung Institute, National Insti- 
tutes of Health. 
variety of congenital cardiovascular defects in 
dogs. These include a large group of anatomic 
malformations of the heart and major vessels 
and a number of congenital disturbances in car- 
diac excitation v^^hich are recognized by their 
electrocardiographic features. Many of these 
defects bear a close resemblance to cardiovascu- 
lar abnormalities found in man, in their fre- 
quency of occurrence, their anatomic details, 
and in the physiologic derangements they 
produce. It is the purpose of this paper to shov^^ 
how^ studies of some of these animal models 
have led to nev^ insights into etiologic and 
pathogenetic mechanisms. For a more detailed 
discussion of the individual defects, the reader 
is referred to previous reports. 
GROSS ANATOMIC DEFECTS OF THE 
CARDIOVASCULAR SYSTEM IN DOGS 
Gross malformations of the heart and great 
vessels have been shown to occur in 0.5 to 1% 
of dogs presented to a veterinary clinic.^-^ 
Tw^enty-five different lesions have been re- 
ported,* including the most common forms of 
congenital heart disease found in man. There 
appear to be some similarities in the distribu- 
tion of the various types of anatomic defects in 
man and in the dog. A comparison of the rela- 
tive frequencies of the common malformations 
in two veterinary clinic population studies and 
the mean of percentages from heart clinics in 
three children's hospitals^^ is show^n in Table I. 
(The more desirable comparison of the inci- 
dence of defects at birth cannot be made because 
of the lack of reliable data in the dog.) 
While there are differences in the relative 
frequency of individual defects, it is noteworthy 
that 6 lesions comprise over 60% of all defects 
in the dog and human series : Patent ductus ar- 
teriosus, pulmonic stenosis, aortic stenosis, ven- 
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