Aneurysm of the atrial septum

An atrial septal aneurysm (septum interatriale) is defined as an abnormal saccular bulge of the muscular fibrous wall that separates the upper chambers of the heart - the left and right atria.

Epidemiology

The incidence of atrial septal aneurysm in the pediatric population is estimated at 1% and in adults at 1-2%. However, clinical statistics show that it is an incidental finding in 1-2.5% of the general population.

In 60% of cases, atrial septal aneurysm is associated with heart defects, and in 30% of adult patients such aneurysm is an isolated structural defect. [1]

Causes of the atrial septal aneurysms

In most cases, an atrial septal aneurysm appears as a congenital malformation of the atrial septum foramen primum, arising from a disruption in the formation of its primary layer (from mesenchyme of endocardial origin), as well as in atrial septal defect in the form of an open oval window in the heart (between the atria). Such atrial septal aneurysm in children is most often observed in combination with other congenital heart defects, congenital atrial septal aneurysm is also noted in genetically determined syndromes (Marfan, Ehlers-Danlos, Down, etc.).

In cases of syndromic pathologies of connective tissue can be atrial septal aneurysm in the newborn. In addition, taking into account the peculiarities of placental circulation during intrauterine development, it is also possible in the fetus.

Adult atrial septal aneurysm may occur as a primary malformation involving the fossa ovale or the entire septum, or it may be an isolated anomaly. It is also often combined with other structural anomalies of the heart.

Also, the causes of this abnormal septal bulge between the atria are associated with aortic regurgitation, arterial hypertension, coronary heart disease, and infarction (in the presence of intra-atrial thrombi).

In addition, septal aneurysm formation may be secondary to biventricular (affecting both ventricles) heart failure, which develops with subpulmonary stenosis - narrowing of the pulmonary artery below the pulmonary valve. [2]

And in such cases, an atrial septal aneurysm is formed without bleeding, which means that the patient has no defect in the form of an oval window through which interatrial bypass could take place. And, according to some data, the absence of blood discharge is noted in 25-40% of patients with diagnosed atrial septal aneurysm. [3]

Risk factors

Risk factors for septum interatriale aneurysm formation are considered to be:

• Left ventricular hypertrophy;
• hypoplasia of the right side of the heart (ventricle, atrium);
• congenital tricuspid valve anomaly;
• anomalies in the form of congenital transposition of the main arteries;
• aortic stenosis with impaired cardiac hemodynamics;
• Rheumatic mitral stenosis;
• Primary venous sinus defect with shunting of blood from the systemic to the small circulation, associated with abnormal pulmonary venous return (congenital anomaly of the pulmonary vein junction).

Premature infants have twice the risk of atrial septal aneurysm than preterm infants. [4]

Pathogenesis

Intrauterine development of the four-chambered human heart is a complex process involving several mesenchymal tissues of different embryonic origins undergoing remodeling, which is regulated by a number of expressed genes (including TGF-β - gene of transforming growth factor receptor, genes of transcription factors TBX5, TBX20, SOX9, GATA4, NKX2.5, etc.). The morphogenesis of septa and valves is similarly complex.

The mechanism of atrial septum bulging is attributed to its weakening due to genetic mutations affecting the connective tissue, i.e. Disorders in the production of fibrous proteins of the intercellular matrix (collagens and elastin), which reduce the strength and elasticity of the septum interatriale. Weakening of the septum explains the formation of its protrusion and in the presence of defects in the form of an oval opening.

As studies have shown, the pathogenesis of aneurysms in this localization is due to a significant difference in blood flow pressure in the right and left atria: Increased pressure in the right atrium leads to prolapse (bulging) of all or part of the interatrial septum into the left atrium, and with increased blood flow pressure in the left atrium - to bulging of the wall into the right upper chamber of the heart. And the higher the intra-atrial pressure gradient, the larger the aneurysm.

Even in newborns with congenital structural weakness of the atrial septal tissue, experts consider the presence of persistent hemodynamic abnormalities to be a determining factor in aneurysm formation.

The size of the bulge in children averages 4.5-5 mm, while in adults it ranges from 8 mm to 15 mm or more. [5]

Symptoms of the atrial septal aneurysms

Quite often, a small atrial septal aneurysm is clinically asymptomatic. But in case of its enlargement, the first signs may be manifested by general malaise with dyspnea and tachycardia during physical exertion.

There may also be symptoms such as increased fatigue; rapid or irregular heartbeat; and swelling of the legs, feet, or abdominal area of the body. [6]

The types of atrial septal aneurysm, according to the international classification, are distinguished according to the direction of its movement during the cardiorespiratory cycle:

• A type 1R atrial septal aneurysm is defined if the bulge is located only in the right atrium;
• Type 2L aneurysm means a bulge in the left atrium;
• Type 3RL - when the bulkier part of the aneurysm bulges into the right atrium and the smaller part into the left atrium;
• type 4LR - if the maximum excursion of the aneurysm is directed to the left atrium with less excursion to the right atrium;
• Type 5 aneurysm is defined as a bilateral bulge equidistant from both atria.

Also read - Acute and chronic cardiac aneurysms: ventricular, septal, postinfarct, congenital

Complications and consequences

An atrial septal aneurysm disrupts heart function, and its complications and consequences are associated with a risk of wall clots, an increased incidence of peripheral arterial embolism, and the likelihood of transient ischemic attacks or stroke - with potentially life-threatening blockage of blood flow to the brain.

In an aneurysm with interatrial shunting of blood from left to right, the pressure in the right atrium and small circle of circulation increases, eventually leading to right ventricular enlargement with paroxysmal atrial fibrillation and atrial fibrillation, as well as right-sided cardiac hypertrophy and pulmonary hypertension.

When the pressure in the right atrium is initially elevated, blood is dumped from right to left, eventually leading to chronic heart failure. [7]

Diagnostics of the atrial septal aneurysms

Diagnosis begins with a complete history, family history, and physical examination of patients.

Lab tests are taken for laboratory testing, including: clinical blood tests and platelet counts, liver enzyme tests, and urinalysis.

Instrumental diagnostics include chest X-ray, ECG, cardiac ultrasound - transthoracic echocardiography, CT angiography and other instrumental cardiac testing.

Differential diagnosis with atrial septal hematoma, myxoma, echinococcal cyst, cardiac malformations and neoplasms, coronary anomalies, etc. Is performed.

See - Aneurysms: causes, symptoms, diagnosis, treatment

Treatment of the atrial septal aneurysms

In asymptomatic aneurysms or in the absence of complications, the main treatment is conservative with close monitoring of patients.

In newborns - with normal hemodynamics - by the age of 1-1.5 years, spontaneous closure of the interatrial orifice occurs, and most wall bulges between the atria involute.

What medications are used in the medical management of patients with symptomatic atrial septal aneurysm?

First, antiarrhythmic drugs of the β-adrenoblocker group are prescribed, which include Nebivolol or Nebicor, Metoprolol, Amiodarone and other arrhythmia drugs.

To avoid blood clots, anticoagulants or antiaggregants, that is medicines that prevent blood clots, including Aspirin, are used.

In case of severe arterial hypertension take high blood pressure pills, and if there are signs of deterioration of the heart doctors prescribe drugs to prevent and correct heart failure.

If necessary, depending on the etiology, size, intensity of symptoms and risk of complications of the aneurysm, surgical treatment is performed using various techniques. These include not only resection of the bulge with suture or closure of the defect with a pericardial patch in open surgery (the preferred method if there is a risk of systemic thrombosis), but also atrial septal repair with grafts or reinforcement with occluders.

Read also - Aneurysm Treatment

Prevention

Since in most cases atrial septal aneurysm is a consequence of its defects and congenital heart defects, there is no prevention of its formation.

Forecast

The dependence of the prognosis of an atrial septal aneurysm for each patient is determined by the cause of its formation and the presence of complications, in particular, the most severe - stroke.