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.

C. Diagnostic Studies
Echocardiography can demonstrate right ventricular volume overload with a large right ventricle and atrium, and sometimes the defect itself. Echocardiography with saline bubble contrast and Doppler flow studies can demonstrate shunting. A transesophageal echo is helpful when transthoracic echo quality is not optimal, and it improves the sensitivity for small shunts and patent foramen ovale. Radionuclide flow studies quantify left-to-right shunting, and MRI can also elucidate the anatomy. Cardiac catheterization remains the definitive diagnostic procedure, since it can demonstrate an increase in oxygen saturation between the venae cavae and right ventricle due to the admixture of oxygenated blood from the left atrium, quantify the shunt, and measure pulmonary vascular resistance. Right and left ventricular contrast angiography may demonstrate associated valvular abnormalities or anomalous pulmonary venous drainage.

Prognosis & Treatment
Patients with small shunts may live a normal life span. Large shunts cause disability by age 40. Raised pulmonary vascular resistance secondary to pulmonary hypertension rarely occurs in childhood or young adult life in secundum defects but is more common in primum defects. After age 40, pulmonary hypertension, cardiac arrhythmias (especially atrial fibrillation), and heart failure may occur in secundum defects. Paradoxic systemic arterial embolization is a concern, especially in patients with pulmonary hypertension or venous thrombosis. Patent foramen ovales are not associated with significant shunting and therefore are asymptomatic. However, they are the lesion responsible for most paradoxical emboli and are one of the most frequent causes of cryptogenic strokes. However, the risk for such events is relatively low except in patients with associated atrial septal aneurysms, who require aggressive anticoagulation or closure of the defect. Infective endocarditis does not occur with increased frequency.

Small atrial septal defects do not require surgery. The risks are now sufficiently low so that patients with left-to-right shunts and pulmonary-to-systemic flow ratios between 1.5 and 2.0 may be operated on if the total clinical picture warrants. Ratios exceeding 2.0 are an indication for surgical closure of the defect.

Transcatheter techniques are now widely used for closing atrial septal defects and patent foramen ovales. These involve the deployment of an umbrella-like occlusion device from a femoral venous approach. The devices work best in patients with centrally located secundum defects.

Surgery should be withheld from patients with pulmonary hypertension with reversed (right-to-left) shunting (Eisenmenger’s syndrome) because of the risk of acute right heart failure. Relocation of pulmonary veins is required in patients with partial anomalous venous drainage. In ostium primum defects, in addition to closure of the defect, suture of the valve clefts - especially those of the mitral valve - is advisable if mitral regurgitation of any significant degree is present. The surgical mortality rate is low (< 1%) in patients under age 45 who are not in cardiac failure and those who have systolic pulmonary artery pressures less than 60 mm Hg. It increases to 5-10% in patients over age 40 with cardiac failure or with systolic pulmonary artery pressures greater than 60 mm Hg.

Brochu MC et al: Improvement in exercise capacity in asymptomatic and mildly symptomatic adults after atrial septal defect percutaneous closure. Circulation 2002;106:1821.
Kerut EK et al: Patent foramen ovale: a review of associated conditions and the impact of physiological size. J Am Coll Cardiol 2001;38:613.
Martin F et al: Percutaneous transcatheter closure of patent foramen ovale in patients with paradoxical embolism. Circulation 2002;106:1121.
Mas JL et al: Recurrent cerebrovascular events associated with patent foramen ovale, atrial septal aneurysm, or both. N Engl J Med 2001;345:1740.