Atrial Septal Defect and Patent foramen ovale

Essentials of Diagnosis

• Usually asymptomatic until middle age.
  
• Right ventricular lift; S₂ widely split and fixed.
  
• Grade I-III/VI systolic ejection murmur at pulmonary area.
  
• ECG shows right ventricular conduction delay; x-ray shows dilated pulmonary arteries and increased vascularity; echo-Doppler usually diagnostic.
  
• Residual patent foramen ovale can lead to paradoxical emboli and cerebrovascular events.

General Considerations

The most common form of atrial septal defect (80% of cases) is persistence of the ostium secundum in the mid septum; less commonly, the ostium primum (which is low in the septum) persists, in which case mitral or tricuspid abnormalities may also be present.

A third form is the sinus venosus defect of the upper part of the septum. This is often associated with partial anomalous drainage of the pulmonary veins into the superior vena cava. In all cases, normally oxygenated blood from the higher-pressure left atrium passes into the right atrium, increasing right ventricular output and pulmonary blood flow.

Although most individuals with an atrial septal defect have relatively small amounts of left-to-right shunting, those with moderate to severe shunts are at risk of developing severe pulmonary hypertension due to irreversible pulmonary vascular disease. This may then lead to Eisenmenger's syndrome, which is characterized by right-to-left shunting and cyanosis. Atrial septal defects also predispose to atrial fibrillation and paradoxical right-to-left emboli.

Not uncommonly, there is incomplete closure of the septum secundum, leaving a small residual opening or patent foramen ovale. Very small ones can be detected in approximately 25% of autopsies, while large defects (0.5-1 cm) are present in 6%.

Clinical Findings

A. Symptoms and Signs
Most patients with small or moderate defects and those with patent foramen ovale are asymptomatic. With large shunts, exertional dyspnea or cardiac failure may develop, most commonly in the fourth decade or later. Prominent right ventricular and pulmonary artery pulsations are readily visible and palpable. A moderately loud systolic ejection murmur can be heard in the second and third interspaces parasternally as a result of increased pulmonary artery flow. S₂ is widely split and does not vary with breathing.

B. Electrocardiography and Chest X-Ray
Right axis deviation or right ventricular hypertrophy may be present in ostium secundum defects. Incomplete or complete right bundle branch block is present in nearly all cases of atrial septal defect, and superior axis deviation is noted in ostium primum defect. With sinus venosus defects, the P axis is leftward of +15 degrees. The chest radiograph shows large pulmonary arteries, increased pulmonary vascularity, an enlarged right atrium and ventricle, and a small aortic knob.