Page 231 - Cote clinical veterinary advisor dogs and cats 4th

99.e2 Atrial Septal Defect

Atrial Septal Defect Client Education
Sheet
VetBooks.ir

BASIC INFORMATION
○ Pulmonary hypertension (e.g., dyspnea,
collapse/syncope, cyanosis) +/− signs of be present. Confirmation and assessment of
severity requires examination by an experi-
Definition hyperviscosity if right-to-left or bidirec- enced echocardiographer. Acquired ASDs are
A congenital cardiac defect characterized tional shunting lesion (exercise intolerance, unusual and occur in patients with marked
by incomplete formation of the interatrial weakness, neurologic deficits, seizures) atrial enlargement caused by severe valvular
septum and communication between the left disease.
and right atrium. Acquired atrial septal defects PHYSICAL EXAM FINDINGS
can also occur from rupture of the interatrial • Possibly no abnormal physical findings with Differential Diagnosis
septum. mild defects • Physical/radiographic: pulmonic stenosis,
• Heart murmur present due to increased tricuspid dysplasia, tetralogy of Fallot
Synonyms transvalvular right heart blood flow • Echocardiographic
ASD, ostium primum/secundum defect, per- ○ Murmur of relative pulmonic stenosis (soft ○ Artifact: normal echo dropout in the fossa
sistent atrioventricular canal/atrioventricular systolic murmur, loudest at left heart base) ovalis. Unlike echo dropout, an ASD has
septal defect/endocardial cushion defect ○ Murmur of relative tricuspid stenosis (soft sharp, not tapered, edges; is generally
(together with ventricular septal defect), sinus diastolic right-sided murmur; rare) observable in multiple views; and may be
venosus defect. Patent foramen ovale is some- ○ With endocardial cushion defects, located at the very base of the atrial
times incorrectly used as a synonym for ASD. murmurs of mitral or tricuspid regurgita- septum (septum primum defect) or caudal
tion may be present. roof of the atrial septum (sinus venosus
Epidemiology • Split second heart sound (delayed pulmonic defect).
SPECIES, AGE, SEX valve closure; left-to-right shunting through ○ Patent foramen ovale (the components
• All mammalian species the ASD increases the volume of circulation of the atrial septum are normally formed
• Usually early in life. Small defects may go through the right heart chambers) but their fusion has been prevented post-
undetected or be incidental findings. • If CHF is present natally, usually by increased right atrial
• An acquired atrial septal defect (ASD) may ○ Ascites, peripheral edema, dyspnea from pressures due to another congenital heart
occur in patients with severe atrial dilation/ pleural effusion malformation, classically severe pulmonic
mitral regurgitation. • With right-to-left or bidirectional shunting, stenosis)
a murmur may be absent and cyanosis is
GENETICS, BREED PREDISPOSITION possible. Initial Database
Dogs: boxer, Doberman pinscher, standard • An acute change from signs of left-sided • Echocardiogram: defect noted in atrial
poodle, and Samoyed CHF to signs of right-sided CHF in a patient septum with two-dimensional imaging
with severe mitral regurgitation may be ○ Color/spectral Doppler assists in character-
Clinical Presentation consistent with an acquired ASD. izing increased pulmonic/tricuspid
DISEASE FORMS/SUBTYPES velocities, flow across defect. Quantitative
• Congenital (most common) versus acquired Etiology and Pathophysiology Doppler can estimate the pulmonary/
(severe atrial enlargement causes a tear in • Presumed genetic cause for congenital lesions, systemic shunt flow ratio.
the interatrial septum) although specific mutations have not been • Thoracic radiographs: variable, ranging
• Septum primum ASD versus septum identified from normal to right-sided cardiomegaly,
secundum ASD • Direction of blood flow depends on pulmonary artery enlargement, pulmo-
○ Embryologically, the septum primum is the caliber of the defect and the relative nary overcirculation. Pulmonary arterial
continuous with the endocardial cushions, resistance to flow into the left and right tortuosity/enlargement or pulmonary
and its absence creates an ASD on the ventricles. undercirculation is possible with pulmonary
floor of the atria. The septum secundum • Smaller (restrictive/resistive) defects main- hypertension.
forms from the roof of the atria in utero tain a left-to-right atrial pressure gradient, • Electrocardiogram: normal or may have
and grows down toward the septum resulting in left-to-right flow and subsequent evidence of right heart enlargement (S waves
primum; its incomplete formation creates right heart volume overload and pulmonary I, II, aVL, aVF; right axis deviation; tall P
an ASD near the center of the atrial overcirculation. Right-sided CHF may waves).
septum (more amenable to closure by develop. • CBC, serum chemistry panel, urinalysis
surgical or catheter-based interventional • Large defects may result in increased usually unremarkable. Erythrocytosis may
procedures). pulmonary vascular resistance/pulmonary be present with right-to-left or bidirectional
hypertension, right ventricular hypertrophy, shunting defects.
HISTORY, CHIEF COMPLAINT and bidirectional or right-to-left shunting • Arterial blood gas analysis may indicate
• With mild defects, there may be no clinical with signs of pulmonary hypertension (Eisen- hypoxemia in cases of bidirectional or right-
signs. menger physiology), arterial hypoxemia, and to-left shunting.
○ Incidentally detected murmur absolute erythrocytosis.
○ Incidental finding of cardiomegaly on Advanced or Confirmatory Testing
thoracic radiographs DIAGNOSIS • Saline contrast echocardiography may help
○ Incidental echocardiographic identification confirm the presence of small defects and/
• With larger defects, overt signs may be Diagnostic Overview or bidirectional shunting.
evident. The diagnosis of an ASD is suspected from • Transesophageal echocardiography
○ Congestive heart failure (CHF), predomi- the presence of a soft left basilar systolic • Cardiac catheterization and angiography yield
nantly right-sided (e.g., abdominal disten- murmur on cardiac auscultation, most often quantitative information, confirm defect,
tion from ascites, dyspnea due to pleural in a young animal. Dyspnea, exercise intoler- identify concurrent defects, and facilitate
effusion, peripheral edema) ance, collapse, or signs of erythrocytosis may interventional therapy.

www.ExpertConsult.com