Atrial Septal Defect
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Introduction
ASDs are perisistent openings in the interatrial septum after birth, allowing direct blood flow between the atria.
ASDs are relatively common, occurring with an incidence of 1: 1,500 births.
Patent foramen ovales are thought to be present in ~20% of the population and are not considered true ASDs.
The Case of...
a simple case introducing clincial presentation and calling for a differential diagnosis to get students thinking.
Causes and Risk Factors
Pathophysiology
The most common site of ASD is at the region of the foramen ovale, forming an ostium secundum ASD. This arises from excessive resorption or inadequate development of the septum primum, inadequate formation of the septum secundum, or a combination.
- ostium primum type: low, adjacent to endocardial cusion
- ostium secundum type: central: most frequent; patent foramen ovale
- sinus venosus ASD: high
In an uncomplicated ASD, blood shunts from the left atrium the the right, with flow determined by the size of the hole and compliance of the ventricles. Blood flow normally occurs during diastole. The right ventricle and atrium tend to enlarge to handle the increased load. Eisenmenger syndrome can develop, in which increased pulmonary resistance leads to increased right heart pressures and a right-to-left shunt. This results in deoxygenated blood entering the circulation and leads to hyposemia and cyanosis.
Signs and Symptoms
- history
- physical exam
History
Most infants with ASDs are asymptomatic, and the condition is normally picked up during childhood or adolescence by the presence of a murmur.
Symptoms, if present, can include exercise intolerance, fatigue, and recurrent lower respiratory infections.
The most common symptoms in adults are decreased stamina and palpitations resulting from atrial tachyarrhythmias due to right atrial enlargement.
Physical Exam
PFOs are usually asymptomatic because higher pressure in the left atrium keeps the valve functionally closed. However, in people with higher right heart pressure (ie pulmonary hypertension or right heart failure), right-to-left shunting can occur. Occasionally, a venous thrombus can thereby bypass the lungs and enter arterial circulation, resulting in paradoxical emobolism.
A prominent systolic impulse may be felt along the lower-left sternal border due to contraction of the dilated RV (an RV heave). The second heart sound (S2) split becomes widened and fixed, as normal respiratory variation is countered by reciprocal changes in blood volume shunting across the ASD.
Increased flow across the pulmonary valve often creates an systolic ejection murmur at the upper-left sternal border.
A middiastolic murmur can also be heard at the lower-left sternal border due to increased flow across the tricuspid valve.
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
Diagnostic Imaging
On chest X ray, the hear is usually enlarged due to right atrium dilation and ventricle hypertrophy. The pulmonary artery is prominent, with increased vascular markings.
ECG shows right ventricular hypertrophy and incomplete or complete right bundle branch block. Right axis deviation may be present, perhaps due to displacement of the left bundle branch.
Echocardiography can show right enlargement and transatrial blood flow. Catheterization is rarely necessary.
Treatments
Most people with an ASD are asymptomatic and do not need treatment. If the volume of blood is large, however, surgical repair can be done to prevent development of heart failure or pulmonary vascular disease.
Surgery typically is done using direct suture closure or patch placement. Percutaneous repair using an intravenous catheter is also possible using a closure device.
Percutaneous devices are quicker, with less time in hospital, but they require long term followup. ASA is given for 3-6 months until the device entothelializes, but no one is really sure what the longer term outcomes are.
Surgery can be done, using patches. These have intraoperative risks, but after a year followup people are all set to go.
Consequences and Course
Can result in arrhythmias, congestive heart failure, pulmonary hypertension and vascular disease
can also get paradoxical emoboli, though they are not so common.
Resources and References
Topic Development
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