The inter-atrial defect indicates a congenital cardiac abnormality that allows blood to flow between the right and left atria, which should not normally be the case as the atria are separated by the inter-atrial septum which, only if it is defective or missing, causes oxygenated blood to flow from the left atrium to the right side of the heart, mixing with venous blood

A so-called ‘shunt’ situation then occurs, which can lead to oxygen levels in the arterial blood being lower than normal (hypoxemia).

Children are usually asymptomatic, but after the age of 20, complications can occur, including pulmonary hypertension, heart failure and atrial arrhythmias.

In adults, symptoms of inter-atrial defect include dyspnoea, exhaustion and atrial arrhythmias.

The diagnosis of an inter-atrial defect is made by echocardiography while the treatment consists of catheterisation or surgical repair for more severe cases.

The consequences of an interatrial defect depend on the size and duration of the shunt. In fact, if the defect is small, this condition may present no appreciable signs or symptoms.

An inter-atrial defect is classified according to where it is located

Ostium secundum is a fossa ovalis defect, which is located in the central part (or middle) of the interatrial septum (it accounts for more than 80% of cases).

It may be single or present as numerous small cribriformities and is generally considered the true inter-atrial defect.

Venous sinus is a defect in the posterior portion of the septum, close to the superior vena cava or inferior vena cava and many times associated with abnormal return of the right superior or inferior pulmonary veins to the right atrium or vena cava. The sinus venosus type defect is statistically present in 5 – 10 % of septal defects.

Normally when the left superior cardinal vein begins to regress, the sinus venosus dislocates to the right of the forming septum and leaves space for the development of the septum secundum.

This defect results from the failure of the venous sinus to shift to the right and thus the lack of space for the development of the septum secundum.

It is usually located on the atrial floor near the inferior caval mouth and high up under the orifice of the superior vena cava.

Ostium primum, on the other hand, is a defect in the anteroinferior face of the atrioventricular septum (endocardial cushion defect) due to the lack of development of the inferior part of the septum primum.

In practice, the defect results from an abnormality in the development of the septum of the atrioventricular canal, which lacks its lower part that divides the atrioventricular valves.

In one patient, an interatrial defect can therefore have different origins, even though the various types are part of the same family of interatrial defects.

Several combinations of one or more of these defects may also coexist in the same patient.

Symptoms

An inter-atrial defect often presents without symptoms: sneezing, coughing or abdominal compressions during defecation may lead to transient increases in pressure in the right section of the heart, but this anomaly is usually asymptomatic.

Asymptomaticity affects most patients with small or moderate atrial septal defects but even if they are larger they may not cause symptoms in young children.

Major shunts may cause slow growth in early childhood and exercise intolerance, dyspnoea on exertion, fatigue and/or palpitations in older patients.

In general, it has been found that about 14% of adults with an interatrial septal defect experience heart failure and another 20% arrhythmias.

In a small percentage of patients (5%), however, clinical signs of heart failure may occur earlier.

The cause of these rare cases appears to be particular intracardiac haemodynamics that, during intrauterine life, did not allow the atrium and left ventricle to develop properly.

Causes of inter-atrial defect

The interatrial defect is a congenital cardiac malformation (i.e. present from birth) but some defects in the interatrial septum close spontaneously during the first few years of life.

DIA is the second most frequent congenital heart disease after the interventricular defect.

It is found more frequently in the female sex and has an incidence of 4 in 1,000 children.

In addition, it is more prevalent in individuals with Down syndrome and Noonan syndrome.

It is to all intents and purposes a pulmonary hyperafflux disease whose level of severity varies depending on the size of the defect, pulmonary resistance and volumetric capacity of the right ventricle.

Some defects are diagnosed as early as during pregnancy by means of a fetal echocardiogram, which allows the doctor to visualise images of the baby’s developing heart.

In many children, however, the defects are not detected until after birth, in some cases not even until adolescence or adulthood.

Diagnosis

The ascultatory objective test is very important and is the first opportunity to detect two possible pathological murmurs.

In fact, here the doctor may detect a grade 2 to 3/6 mesosystolic (ejective systolic) murmur due to increased flow velocities through the pulmonary valve and a fixed split S2 at the upper left border of the sternum in children.

To be certain of an inter-atrial defect, the doctor may require the patient to undergo three specific tests:

• Electrocardiogram, a test that in the case of small defects shows no abnormalities, while in those of modest size it shows a sign of volume overload right section of the heart that may lead to right branch block.
• Chest X-ray, which in the case of a small interatrial defect shows a normal chest, while in modest ones it shows enlargement of the right atrium and auricle, dilatation of the right second arch and clear lung fields due to hyperafflux (i.e. enlarged heart).
• Echocardiogram, which is the test of first choice, as it makes it possible to localise and quantify the DIA and study its effects on the right atrium and ventricle and the pulmonary artery.

Cardiac catheterisation is rarely necessary unless transcatheter closure of the defect is planned.

Complications of the inter-atrial defect

If the interatrial defect is not corrected, the subject may have very serious cardiac problems in the future, although these occur in adulthood.

The most common complications are:

• right heart failure, the right side of the heart is forced to work harder to pump the excess blood into the lungs;
• arrhythmias;
• pulmonary hypertension, which consists of increased pressure in the pulmonary arteries.

Survival is reduced in patients who develop pulmonary hypertension, but fortunately only 0.1% die within the first year of life and often because complex cardiological pathologies persist.

On the other hand, those who reach the age of 50-60 years and have a smaller defect still begin to complain of palpitations due to atrial cardiac arrhythmias, which frequently lead to heart failure.

A situation of paradoxical embolism, i.e. caused by the passage of microemboli from the venous circulation through the inter-atrial septal defect, can lead to cerebral events or systemic thromboebolic events such as stroke.

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