Atrial septal defects are divided into primary foramen ovale and secondary foramen ovale from the point of view of their occurrence. Primary foramen ovale septal defect is usually included in the scope of endocardial cushion defect, therefore, the clinical term of atrial septal defect refers to secondary foramen ovale septal defect. Secondary foramen type atrial septal defects are classified as: central (foramen ovale), inferior, superior, and mixed.
1. Etiology
The following factors may affect the fetal development and produce congenital malformations.
(1) Environmental factors of fetal development.
Infections, viral or bacterial infections in the first trimester of pregnancy, especially rubella virus and, to a lesser extent, coxsackievirus, have a higher incidence of congenital heart disease in infants born with these infections.
Others: such as lesions of the amniotic membrane, fetal compression, early gestational pre-eclampsia, maternal malnutrition, diabetes mellitus, phenylketonuria, hypercalcemia, the application of radiation and cytotoxic drugs in the early stages of pregnancy, and the mother’s excessive age all have the potential to cause congenital heart disease in the fetus.
(2) Genetic factors: Most congenital heart disease is formed by the interaction of multiple genes and environmental factors.
(3) Other: some congenital heart diseases are more frequent in highland areas, and some congenital heart diseases have significant differences in incidence between male and female genders, indicating that altitude and gender of birthplace are also related to the occurrence of this disease.
Among patients with congenital heart disease, those who can find out the cause are very few, but it is of positive significance to prevent congenital heart disease by strengthening health care for pregnant women, especially by actively preventing rubella, influenza and other rubella viral diseases and avoiding all factors related to the onset of the disease in early pregnancy.
2. Pathophysiology
Atrial septal defect can lead to enlargement of the right atrium and right ventricle, thickening of the ventricular wall, different degrees of pulmonary artery dilatation, increased blood volume in the pulmonary circulation and increased pulmonary artery pressure.
3. Classification
Atrial septal defect can be divided into small, medium and large defects. In young children, the defect less than 0.5 cm is small, 0.5-1.0 cm is medium, and 1.0 cm or more is large. In adults, small defects are usually less than 1.0 cm, 1.0-2.0 cm are medium-sized and small defects, and 2.0-3.0 cm are large defects.
The overall rate of natural closure of atrial septal secondary foramen defects is 87%. Atrial septal defects with defects <3 mm diagnosed before 3 months of life can close to 100% spontaneous closure within 1.5 years of age; many atrial septal defects with defects between 3 and 8 mm can close spontaneously within 1.5 years of age; few defects above 8 mm close spontaneously. It has been statistically reported that 20 of 91 ASDs healed spontaneously, with a self-healing rate of 21.98%. 69.23% of ASDs with a diameter of 0.5-0.7 cm healed spontaneously, 27.27% of 0.8-10 cm healed spontaneously, and 2.27% of >1.0 cm healed spontaneously. The self-healing rate of central ASD was 23.26%, and the vena cava sinus type ASD did not heal spontaneously. the age of spontaneous healing of ASD ranged from 7 months to 6 years, with a median of 1.6 years. The self-healing rate of ASD with enlarged right ventricle was 9.46% and that of ASD with normal right ventricle was 63.64%. It is concluded that ASDs with ASD diameter ≤1.0 cm, central ASDs, normal right ventricle and those aged <6 years, especially up to 2 years, have a higher chance of spontaneous healing. ASDs with ASD diameter >1.0 cm, cavernous sinus ASDs, enlarged right ventricle and those aged 6 years or older have a low chance of spontaneous healing.
Infective endocarditis does not occur in simple atrial septal defects, so prophylactic treatment is not necessary if there are no other co-morbidities.
Small atrial defects in infants and children have the potential to close on their own and generally do not require treatment. Traditionally, it was thought that small atrial defects smaller than 10 mm without heart enlargement and symptoms could be treated without surgery, but nowadays, considering that small atrial defects may have two rare complications, namely paradoxical thrombosis and cerebral abscess, which occur in adult patients with secondary foramen ovale, especially after the age of 60, interventional treatment is advocated for small atrial defects in adults. Most clinicians still believe that a small atrial defect “less than 5 mm” can be treated without treatment. However, regular cardiac ultrasound review is needed.
4. Clinical manifestations and complications
When atrial septal defect exists, blood flows from left to right, right heart blood volume increases, right atrium and right ventricle enlarge, ventricular wall thickens, pulmonary artery dilates to different degrees, pulmonary circulation blood volume increases, and pulmonary artery pressure rises. With the development of the disease, intimal hyperplasia, thickening of the middle layer and narrowing of the lumen occur in the wall of small pulmonary arteries, thus the pulmonary vascular resistance increases, pulmonary hypertension changes from dynamic to resistance, the right atrial and right ventricular pressure increases, the right atrial pressure exceeds that of the left atrium in the late stage of the disease, a right-to-left shunt occurs, and clinical purple crucible and heart failure appear. Rare and serious complications of atrial septal defect can also occur, namely brain abscess and paradoxical thrombosis, causing embolism of the organ arteries.
5. Treatment
Effective treatments for atrial septal defects are surgical repair and surgical occlusion. The technique of atrial septal defect occlusion is well established, and any atrial septal defect with indications for occlusion treatment should be firstly selected for occlusion treatment. The ideal age stage for surgery is 2 – 6 years. For huge atrial septal defect, early surgery should be performed regardless of age, such as large defect, large fractional flow, severe pulmonary congestion, often accompanied by heart failure, pneumonia and other complications, early surgery should be performed, and surgery can be performed in infancy (within 1 year). Very young age is not a contraindication to surgery. The surgical methods include conventional intracardiac repair with extracorporeal circulation, non-stop repair with extracorporeal circulation, and closed repair with non-external circulation. Secondary foramen ovale septal defects can be classified as: central, superior, inferior, or mixed.
The central type of secondary foramen ovale is the most suitable for interventional treatment.
Main indications.
(1) Patients with secondary foramen ovale defect with surgical indications who meet the following conditions: adult secondary foramen ovale defect less than 30 mm in diameter, balloon maximum elongation diameter less than 36 mm, pediatric patients should be evaluated for interventional septal defect diameter according to age and heart size. The secondary foramen ovale type of atrial defect is a central type with the margins of the upper and lower atrial septum greater than 5 mm.
(2) Secondary foramen ovale type atrial defect with diameter <10mm, without cardiac enlargement and symptoms, may not be treated surgically, but may have two rare complications, namely paradoxical thrombosis and brain abscess, which occur in adult patients with secondary foramen ovale, especially after 60 years of age, so interventional treatment is advocated for small atrial defects in adults
(3) The foramen ovale is not closed, especially those who have ever combined with cerebral embolism are suitable for interventional treatment.
(4) Post-surgical residual shunt atrial septal defect, mainly referring to those with left-to-right shunt.
(5) Those with significant residual left-to-right shunts at the atrial level after balloon mitral valvuloplasty and radiofrequency ablation.
(6) Those with atrial septal defect aged above 2 years, because the age of natural closure of atrial septal defect is within 1.5 years.
The main postoperative complications are; cardiac rhythm disturbances, coronary and cerebral artery air embolism, acute left heart insufficiency and residual leak.13, Atrial septal defect sealing treatment may have (1) residual shunt. (2) Dislodgment of the blocker (3) Embolization. (4) Improper position of the blocker. (5) Infective endocarditis. (6) Cardiac arrhythmia. (7) Hemolysis. (8) Pericardial tamponade.
The surgical outcome of atrial septal defects secondary to foramen ovale alone is good, and the mortality rate of inpatient surgery has been close to zero. Approximately 2% of patients require reoperation for recurrent atrial septal defects.
At rest, a pulmonary/body circulation flow ratio of less than 1.5, a pulmonary/body circulation systolic pressure ratio of >0.75, a right-to-left shunt on cardiac ultrasound, elevated pulmonary vascular resistance of 8–12 U/m2 at rest that cannot be reduced to less than 7 U/m2 with pulmonary vasodilators, and clinical manifestations such as purple crucible and hemoptysis (Eisenmenger’s syndrome) are considered contraindications to surgery.
Contraindications for atrial septal defect sealing treatment: (1) Primary foramen ovale type atrial septal defect. (2) Venous sinus type atrial septal defect. (3) Partial or complete ectopic pulmonary venous drainage. (4) Left atrial septum or hypoplasia. (5) Intracardiac, inferior vena cava, or intrapelvic thrombosis. (6) With other congenital heart defects or large vessel anomalies requiring surgical treatment. (7) Eisenmenger’s syndrome.
Relative contraindications: (1) Infants and children less than 2 years of age. (2) Recent severe infection or foci of infection in the body.
The current cost of surgical treatment in China ranges from 8,000 yuan – 15,000 yuan, with a relatively large difference. It may be related to the fast or slow economic development. The price of blocking treatment ranges from about 1 – 2 times of the price of surgical procedure.
6. Fetal foramen ovale is not closed
During the development of the fetal atrium, the primary septum and the continuing septum separate the left and right atrium when they are fully developed, and a live valve-like orifice remains between the two septum, namely the foramen ovale, which relies on the opening of the foramen ovale during the growth and development of the fetus in the mother’s uterus to bring the placenta’s oxygenated blood into the right atrium via the inferior vena cava, and into the left atrium and left ventricle via the foramen ovale, and into the ascending aorta for brain and upper limb development. After birth, the fetus is separated from the placenta and the fetal blood circulation is terminated. The blood pressure in the left atrium is higher than that in the right atrium, forcing the first interatrial septum to close structurally to the foramen ovale, and as the fetus grows older, the foramen ovale valve becomes stiff with adhesions and activity decreases, and fibrous tissue proliferates to occlude the foramen to form a non-traffic foramen ovale, which generally closes within the first year after birth. If the foramen ovale is still not closed in children older than 3 years of age, it is called unclosed foramen ovale. About 25% of the normal population has an unclosed foramen ovale. Ovular foramen insufficiency differs from small atrial defects in that there is no continuous interruption of the interatrial septum on transthoracic ultrasound (TTE) or transesophageal ultrasound (TEE), and there is usually no left-to-right blood shunt. Ovular foramen insufficiency is usually not treated, but interventional occlusion needs to be considered if the patient is older than 40 years old and there are no other causes of recurrent cerebral embolism, etc.