Atrial septal defect: symptoms, diagnosis, treatment

An atrial septal defect is one or more openings in the atrial septum that allow left-to-right blood flow, causing pulmonary hypertension and heart failure. Symptoms and signs include exercise intolerance, shortness of breath, weakness, and atrial arrhythmia. A soft systolic murmur is often heard in the second or third intercostal space to the left of the sternum. Diagnosis is made by echocardiography. Treatment for atrial septal defect involves surgical or catheter-based closure of the defect. Endocarditis prophylaxis is generally not required.

Atrial septal defects (ASD) account for approximately 6-10% of congenital heart defects. Most cases are isolated and sporadic, but some are part of a genetic syndrome (e.g., mutations of chromosome 5, Holt-Oram syndrome).

Atrial septal defect can be classified by location: secondary septal defect [a defect in the region of the oval window - in the central (or middle) part of the interatrial septum], sinus venosus defect (a defect in the posterior part of the septum, near the mouth of the superior or inferior vena cava), or primary defect [a defect in the anterior-inferior parts of the septum, is a form of endocardial cushion (atrioventricular communication) defect].

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What happens in an atrial septal defect?

Atrial septal defect is a defect characterized by the presence of a connection between the atria, through which blood is discharged from left to right and, unlike the interventricular defect, under a significantly lower pressure gradient. The pressure in the left atrium exceeds that in the right atrium by 8-10 mm Hg. An atrial septal defect is 2-3 times more common in women than in men. Depending on the anatomical location, atrial septal defects are divided into primary (in the lower part of the interatrial septum above the AV openings) and secondary (usually central, the so-called defects of the oval fossa). accounting for up to 66%. As a result of blood discharge, the overload of the right sections increases, and heart failure gradually (slower than with a ventricular septal defect) progresses. The prolonged absence of pulmonary hypertension in atrial septal defect is facilitated by several factors: there is no direct effect on the pulmonary vessels of high pressure of the left ventricle (in case of ventricular septal defect and patent ductus arteriosus, the latter is directly transmitted to the vessels of the pulmonary circulation), the extensibility of the right sections of the heart is significant, the reserve capacity of the vessels of the pulmonary circulation and their low resistance are manifested.

To understand the hemodynamic changes in atrial septal defects (and other defects), it is necessary to understand normal intracardiac hemodynamics. In atrial septal defects, left-to-right shunting occurs first. Most small atrial septal defects spontaneously close during the first years of life. However, with large defects, the right atrium and ventricle become volume overloaded, pulmonary artery pressure and pulmonary vascular resistance increase, and right ventricular hypertrophy develops. Later, atrial fibrillation may develop. Ultimately, increased pressure in the right chambers of the heart may lead to bidirectional shunting and cyanosis (see Eisenmenger's syndrome).

Symptoms of Atrial Septal Defect

In most cases, a small atrial septal defect is asymptomatic. Most children with an atrial septal defect lead a normal life, some even play sports. With age, greater fatigue and shortness of breath during physical exertion are gradually revealed. There is no cyanosis. With a large defect, intolerance to physical exertion, shortness of breath during exertion, weakness and atrial rhythm disturbances, sometimes a feeling of palpitations may be noted. The passage of microemboli from the veins of the systemic circulation through the atrial septal defect (paradoxical embolization), often combined with arrhythmias, can lead to thromboembolism of the vessels of the brain or other organs. Rarely, if the atrial septal defect is not diagnosed in time, Eisenmenger syndrome develops.

Patients with atrial septal defect have a history of repeated bronchitis, and occasionally pneumonia. Children in the first months and years of life often have a severe course of the defect with shortness of breath, tachycardia, delayed physical development, and hepatomegaly. After 2-3 years, the patient's health may improve, and signs of heart failure disappear.

During auscultation in children, a systolic murmur (or ejection murmur) is usually heard in the II-III intercostal space on the left, the gradation of which by intensity is 2-3/6, splitting of the II tone over the pulmonary artery (upper left along the edge of the sternum). With a significant shunt of blood from left to right, a low-pitched diastolic murmur (due to an increase in blood flow on the tricuspid valve) can be heard along the edge of the sternum at the bottom left. These auscultatory data may be absent in infants, even in the presence of a large defect. Distinct epigastric pulsation (of the right ventricle) may be noted.

Diagnosis of atrial septal defect

The diagnosis is suggested by data from a physical examination of the heart, chest X-ray and ECG, and confirmed by echocardiography using color Doppler.

Cardiac catheterization is usually not required unless associated heart defects are suspected.

During clinical examination, cardiac hump is detected at an older age in children with cardiomegaly, systolic tremor is rarely detected, its presence indicates the possibility of an accompanying defect (pulmonary artery stenosis, ventricular septal defect). The apical impulse is weakened, not diffuse. The boundaries of relative cardiac dullness can be expanded in both directions, but at the expense of the right sections: the left border - due to the leftward displacement of the enlarged right ventricle of the left, the right border - due to the right atrium.

The main auscultatory sign that allows one to suspect an atrial septal defect is a systolic murmur of medium intensity, not rough, without pronounced conductivity, localized in the second or third intercostal space on the left near the sternum, better heard in orthostasis. There is a single opinion on the origin of systolic murmur: it is associated with functional stenosis of the pulmonary artery, which occurs due to increased blood flow with an unchanged fibrous ring of the pulmonary valve. As the pressure in the pulmonary artery increases, an accent of the second tone appears and increases over the pulmonary artery.

With the development of relative tricuspid valve insufficiency, atrial overload increases, and cardiac arrhythmia may occur. The ECG typically shows a rightward deviation of the electrical axis of the heart up to +90...+120. Signs of right ventricular overload are nonspecific: incomplete right bundle branch block in the form of rSR in lead V1. As the pulmonary artery pressure increases and the right ventricle is overloaded, the amplitude of the R wave increases. Signs of right atrium overload are also detected.

This defect has no specific radiological signs. Increased pulmonary pattern is detected. Changes in the size of the heart on the radiograph are determined by the size of the bypass. Oblique projections show that the heart is enlarged due to the right chambers. Chest radiography reveals cardiomegaly with dilation of the right atrium and right ventricle, widening of the pulmonary artery shadow, and increased pulmonary pattern.

Transthoracic two-dimensional echocardiography allows direct detection of an echo signal break in the interatrial septum area. The diameter of the interatrial septal defect determined echocardiographically almost always differs from that measured during surgery, which is due to the stretching of the heart by moving blood (during surgery, the heart is relaxed and emptied). That is why it is possible to measure fixed tissue structures quite accurately, while changing parameters (opening or cavity diameter) are always measured with a certain error.

Cardiac catheterization and angiocardiography have currently lost their significance in the diagnosis of atrial septal defect. The use of these methods is advisable only when it is necessary to accurately measure the magnitude of the discharge through the defect or the degree of pulmonary hypertension (in older patients), as well as for the diagnosis of concomitant pathology (for example, abnormal drainage of the pulmonary veins).

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Differential diagnosis of atrial septal defect

Differential diagnostics for secondary atrial septal defect is primarily performed with functional systolic murmur heard at the base of the heart. The latter weakens in the standing position, the right chambers of the heart are not enlarged, incomplete right bundle branch block is not typical. Quite often, atrial septal defect has to be differentiated from such diseases as isolated pulmonary artery stenosis, Fallot's triad, abnormal pulmonary venous drainage, ventricular septal defect, and tricuspid valve malformation (Ebstein's anomaly).

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Treatment of atrial septal defect

Most small defects (less than 3 mm) close spontaneously; approximately 80% of defects 3–8 mm in diameter close spontaneously by 18 months. However, primary atrial septal defects and sinus venosus defects do not spontaneously close.

If the defect is small and asymptomatic, the child is followed with annual echocardiography. Because these children are at risk for paradoxical embolism, some centers recommend using catheter-based closure of the defect (eg, Amplatzer Septal Occluder, Cardioseal device) even for small defects. However, these devices are not used for primary atrial septal defects or sinus venosus defects because these defects are located near important structures.

In the presence of heart failure, therapy is aimed at reducing hypervolemia of the pulmonary circulation and increasing the antegrade flow through the left heart. Diuretics and cardiac glycosides are prescribed. Surgery is indicated for increasing heart failure, delayed physical development, and repeated pneumonia. Hemodynamic indication for surgery is the ratio of pulmonary and systemic blood flow of 2:1, which is possible even with minor clinical symptoms. Based on this feature, the atrial septal defect can be called an "insidious" defect. Traditional surgical correction consists of suturing the defect or its plastic surgery through a thoracotomy approach under artificial circulation. In the last decade, endovascular methods of closing defects using special devices - occluders have been intensively developing. The procedure is performed by puncture of peripheral vessels with subsequent delivery of a special "umbrella" or "button device" to the defect. There are a number of anatomical limitations to this procedure: endovascular intervention is only possible in the case of a secondary atrial septal defect up to 25-40 mm in size, located far enough from the coronary sinus, AV valves, and the orifices of the pulmonary and vena cava.

Patients with moderate to large defects (pulmonary to systemic blood flow ratio greater than 1.5:1) are treated with defect closure, usually between 2 and 6 years of age. Catheter-based closure is preferred if the defect has appropriate anatomical characteristics and is less than 13 mm in diameter. Otherwise, surgical closure is indicated. With defect closure in childhood, perioperative mortality approaches zero and survival is the population average. Diuretics, digoxin, and ACE inhibitors are used before defect closure in patients with large defects and heart failure.

If the patient has a primary atrial septal defect, endocarditis prophylaxis should be performed; in secondary defects and defects in the sinus venosus area, endocarditis prophylaxis is not indicated.