Page 1892 - Cote clinical veterinary advisor dogs and cats 4th

948 Subaortic Stenosis

Technician Tips SUGGESTED READING AUTHORS: Pascale M. Y. Smets, DVM, PhD, DECVIM;
Patient monitoring and handling greatly depends Kooistra HS: Failure to grow. In Ettinger SJ, et al, Sylvie Daminet, DVM, PhD, DACVIM, DECVIM
EDITOR: Leah A. Cohn, DVM, PhD, DACVIM
VetBooks.ir gus: upright position during and after feeding, ed 8, St. Louis, 2017, Elsevier, pp 88-91.
on the underlying condition (e.g., megaesopha-
editors: Textbook of veterinary internal medicine,
monitoring for respiratory signs, which could
be indicative of aspiration pneumonia).

Subaortic Stenosis Client Education
Sheet

BASIC INFORMATION boxer, dogue de Bordeaux, golden retriever, • Moderate cases often show exaggerated or
and possibly other breeds. long-lasting panting after exercise as their
Definition only clinical sign.
• Most common cardiac congenital malforma- ASSOCIATED DISORDERS
tion of large-breed dogs • Mild/moderate aortic regurgitation/ PHYSICAL EXAM FINDINGS
• Hallmark is a narrowing of the left ventricular insufficiency: very commonly observed They are often unremarkable except for a
outflow tract (LVOT) just below the aortic echocardiographically in dogs with SAS; systolic, ejection-type (crescendo-decrescendo)
valve. generally inaudible on auscultation heart murmur, heard loudest at the left heart
• May be fixed (fibrous nodule, band, annulus, • Mitral valve dysplasia, PDA, and a variety of base (between the third and fifth intercostal
fibromuscular tunnel) or dynamic (systolic aortic arch abnormalities have been associated spaces) or at the thoracic inlet (immediately
anterior motion of the mitral valve [SAM]) with some SAS cases. lateral to the trachea). This murmur results
• Jet lesions associated with SAS can damage from the turbulent blood flow in the LVOT
Synonyms the aortic valvular endothelium and predis- and ascending aorta.
Subvalvular aortic stenosis (SAS) pose to bacterial endocarditis. • Intensity of the heart murmur grossly cor-
relates with severity of disease:
Epidemiology Clinical Presentation ○ Grades I-III/VI: mildly to moderately
SPECIES, AGE, SEX DISEASE FORMS/SUBTYPES affected dogs
• First noted in puppies < 12 months old Many distinct malformations are grouped under ○ Grades IV-VI/VI: severely affected dogs
(usually after 4-8 weeks of age) the heading of SAS. • Murmur may radiate cranially up the carotid
• The severity of narrowing is progressive (or Fixed obstruction: arteries to the neck and head or to the right
rarely regressive) during a puppy’s growth, • Grade I: small, raised nodules of thickened hemithorax.
and the true severity of SAS cannot be endocardium • A weak and late-rising femoral pulse (pulsus
determined until the dog is fully grown • Grade II: narrow ridge of thickened endo- parvus et tardus) is typical in severe cases as
(12-18 months, depending on breed). cardium that partially encircles the LVOT a consequence of the obstructive lesion and
• Depending on the study, SAS is the most • Grade III: fibrous band, ridge, or collar delayed rate of left ventricular ejection.
common congenital heart defect of dogs or completely encircles the LVOT • A diastolic heart murmur is rarely heard with
is second to patent ductus arteriosus (PDA). • This grading system is used for gross patho- aortic valve insufficiency.
• Uncommon in cats, but dynamic LVOT logic findings. It is unrelated to murmur • Premature beats and pulse deficits (due to
obstruction occurs commonly with hyper- intensity or clinical signs. ventricular arrhythmias) may be detected in
trophic obstructive cardiomyopathy (p. 505). Dynamic obstruction: severe cases.
• Systolic anterior motion of the mitral valve
GENETICS, BREED PREDISPOSITION ○ Narrowing of the LVOT and papillary Etiology and Pathophysiology
• Large-breed dogs (especially Newfoundlands, muscle distortion caused by left ventricular • Predisposing anatomic characteristics of the
golden retrievers, rottweilers, boxers, German hypertrophy allows slight displacement of LVOT such as increased mitral-aortic sepa-
shepherds, Bouvier des Flandres, Bernese the mitral valve such that a small amount ration, decreased (steep) aortoseptal angle,
mountain dogs, bullmastiffs, and dogues of mitral regurgitation occurs. malaligned interventricular septum, and a
de Bordeaux) • Septal hypertrophy or malalignment small aortic annulus (which increases the
• Bull terriers are predisposed to valvular aortic ○ The left ventricular hypertrophy induced shear stress and stimulates cellular prolifera-
stenosis (thickened leaflets and hypoplastic by SAS may further contribute to left tion in the LVOT) are strongly suspected.
valvular annulus), a different disease but with ventricular outflow obstruction because ○ The persistence of embryonal endocardial
the same result of obstruction between left of hypertrophy of the interventricular tissue that retains potential capacity for
ventricle (LV) and aorta. septum. chondrocyte proliferation was historically
• Hereditary transmission has been demon- ○ The aortic arch may be congenitally suspected, but evidence is lacking.
strated in Newfoundland dogs (autosomal malaligned with the long axis of the ○ Some of these predisposing factors are
dominant abnormality in the PICALM gene), interventricular septum, resulting in SAS suspected to be heritable, especially in
golden retriever, bullmastiffs, and dogue due to protrusion of the interventricular the golden retriever, boxer, and dogue
de Bordeaux (autosomal recessive in these septum into the subvalvular area. de Bordeaux.
breeds). ○ Other dogs with SAS have LVOT obstruc-
• No apparent sex linkage HISTORY, CHIEF COMPLAINT tion without evidence of the anatomic
• Mildly affected dogs can produce more In most cases, the condition causes a heart abnormalities listed above.
severely affected offspring. murmur in an apparently healthy/asymptomatic • An important consequence of SAS, regardless
puppy. However, severe cases may exhibit of subtype or causative mechanism, is left
RISK FACTORS • Exertional fatigue or syncope ventricular pressure overload that results in
A decreased (steeper) aortoseptal angle is often • Congestive heart failure (CHF) (rare) ○ An increase in left ventricular systolic
seen with SAS and represents a predisposing • Sudden death; sometimes the first clinical pressure and a pressure gradient across
anatomic factor for SAS development in the sign in severe cases the stenotic lesion
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