Atrial Septal Defect

Also known as ASD

• Very rare in horses

• Rarely seen as a single defect in dogs & cats

Signalment

Genetics & Predisposed Breeds: Old English Sheepdog, Doberman Pincher, Boxer, Samoyed

Description

• Atrial septal defects occur when the interatrial septum is not completely formed or the foramen ovale has failed to close. The resulting patency between the atria allows shunting of blood.

• Normally small atrial septal defects cause blood to travel from the higher pressure conditions in the left side to the lower pressure conditions in the right side. However, larger defects cause pulmonary hypertension with or without pulmonic stenosis causes shunting to occur in either both directions or from right to left.

• Left to Right shunting can cause blood volume overload of the right atrium, right ventricle, and pulmonary circulation

• Right to Left shunting can cause blood volume overload of the left atrium

• Eisenmenger's physiology= Left to right shunts create pulmonary overcirculation. Pulmonary overcirculation leads to gross changes in the pulmonary vasculature causing an increased pulmonary vascular resistance and the development of pulmonary hypertension. Right ventricular pressures are elevated as a result making shunts reverse when the pressure on the right side of the heart exceeds that of the left. Deoxygenated blood is then able to access the peripheral circulation. Cyanosis is a direct effect of this phenomenon.

• Atrial septal defects are normally located higher in the septum with dogs and lower in the septum with cats

• Cats with low atrial septal defects are likely to have an endocardial cushion defect complex

Diagnosis

History & Clinical Signs

-Often no clinical signs are detected

-Exercise intolerance

-Dyspnea

-Syncope

-Cyanosis (right to left shunting)

-Signs of heart failure may be present:

• ascites (right sided heart failure)

• dyspnea

• peripheral edema

• pleural effusion

Physical Exam

Heart Murmurs

-Soft systolic murmur around left heart base (due to pulmonic stenosis)

-Soft systolic murmur around pulmonic and tricuspid valves (usually heard due to increased blood flow)

-Soft diastolic murmur on right side (tricuspid stenosis; RARE)

Radiographic Findings

-None with small defects

-Right atrial and ventricular enlargement

-May or may not have pulmonary artery enlargement

-Pulmonary overcirculation

Echocardiographic Findings

Care: artefacts can imitate atrial septal defects

-Right atrial and ventricular dilation

-Septal defect

Doppler exam will document abnormal flow through defect

Electrocardiographic (ECG)

-Normal or pattern of right ventricular enlargement

Treatment

-Usually treatment is not necessary with small atrial septal defects

-Treat right sided congestive heart failure when present

-Severe atrial septal defects may need pulmonary artery banding (decreases pulmonary blood flow and therefore volume overload), but this procedure is often only palliative

Prognosis

-Depends on the severity of the atrial septal defect and any other additional defects

From Pathology

Persistent Foramen Ovale, allowing blood flow from left to right atria. Produces volume overload of right ventricle and subsequent raise in central venous pressure and venous congestion.

Incidence:

• Rare in cats and dogs, increased incidence in Old English Sheepdogs and Boxers.
• More common in cattle, often due to failure of growth of septum secundum.

Clinical Signs:

• If small defect no clinical signs.
• If large defect see exercise intolerance, syncope and dyspnoea.

Diagnosis:

• Enlarged right ventricle and atrium on radiology.
• Can visualise on echocardiography.

Treatment:
Usually no management needed.