Malformations Associated With Left-to-Right Shunts And Clinical Features

Malformations Associated With Left-to-Right Shunts And Their Clinical Features In Full Detail

Left to right shunt disorder is the most common type of congenital heart disease. These include atrial septal defect (ASD), ventricular septal defect (VSD), and patent duct arteriosus (PDA).

ASD usually only increases right ventricular volume and pulmonary outflow, while VSD and PDA cause an increase in both pulmonary blood flow and pulmonary pressure. Manifestations of this shunt range from completely asymptomatic to heart failure.

Cyanosis is not an early sign of this disability. However, as discussed above, prolonged left-to-right shunting can eventually lead to pulmonary hypertension and deoxygenated blood shunting from right to left in the systemic circulation, leading to changes in cyanosis (Eisenhower syndrome).

Once significant pulmonary hypertension develops, the structural defects of congenital heart disease are considered irreversible. This is the basis of early intervention, in most cases through surgical intervention.

Atrial Septal Defects and Patent Foramen Ovale

In the normal development of the heart, the patency between the right and left atria is maintained by a series of phenotypes (Osteem Primeum ​​and Osteem Secundum), which eventually become the Farman Oval. This arrangement allows the oxygenated blood from the mother’s womb to flow from the right atrium to the left, which favors fetal development.

In the later stages of fetal development, tissue lumps (septum primum and septum secundum) spread to close the foramen oval, and in 80% of cases, the increasing pressure on the left side of the heart at birth is permanent. As it is connected septa against moisture Oval.

In the remaining 20% ​​of cases, an open foramen oval is formed; Although the flap is large enough to close the opening, the exposed septa can temporarily provide right-to-left flow, such as sneezing during bowel movements or Valsalva’s gait during stress.

Although not usually significant, it sometimes presents as a paradoxical embolism, defined as a venous embolism (e.g., from a deep leg vein) to systemic arteries. Entering the circulation through the moisture disorder.

Unlike the patented foramen oval, ASD has an unusual fixed opening in the atrial septum that allows unrestricted blood flow between the atrial spaces. The majority (90%) of ASDs are defects of the so-called “secondary perforation”, in which the development of the secondary septum is insufficient to cover the other perforation.


Ostium secundum ASD (90% ASD) is a smooth-walled defect near the Foreman Oval, usually without heart failure. Hemodynamically significant injuries are associated with right atrial and ventricular enlargement, right ventricular hypertrophy, and pulmonary artery dilation, reflecting the effects of chronic increasing volume loading.

Ostium primum ASDs (5% of these defects) are found in the lower part of the intratheral septum and may be associated with mitral and tricuspid valve anomalies, which are closely related to the development of primary septum and atrial septum. Reflect endocardial cushion. In more severe cases, additional defects may include VSD and normal AV arteries.

In ASD, sinus venous (accounting for more than 5% of cases) is elevated in the intratheral septum and often occurs with abnormal confluence in the right atrium of the pulmonary veins or in the superior vena cava.

Clinical Features

ASD is usually asymptomatic until adulthood. Although VSD is more common, the most uncommon. Thus, ASD, which is less likely to stop spontaneously, is the most common disability that is diagnosed early in adults. Initially, ASD is caused by a left-to-right shunt.

Decreased pulmonary circulation and pressure in the right half of the heart. In general, this defect is well accepted, especially if its diameter is less than 1 cm; Although most lesions do not usually cause symptoms in childhood. However, over time, chronic volume and stress loads can lead to pulmonary hypertension. Therefore, surgical or intravascular closure of ASD is performed to prevent the development of heart failure, inconsistent embolization, and irreversible pulmonary vascular disease. Mortality is lower, and survival after surgery is better than in healthy people.

Ventricular Septal Defects

Ventricular septal defects allow blood to flow from left to right, and the most common congenital heart defect at birth. The intraventricular septum is usually formed by a muscle strap.

Ascending from the top of the heart, it joins a thin-membered septum that extends below the endocardial cushion. The basal area is the last part of the septum that develops and is approximately 90% VSD site. Most VSDs close automatically in childhood, but only 20% to 30% of VSDs are isolated. The rest are related to other heart defects.


The size and location of ventricular septal defects vary from the smallest membrane septal defect to a large defect that affects almost the entire intraventricular wall. The right ventricle undergoes hypertrophy and is often dilated, with defects associated with significant left to right hemorrhage.

Increased production of the right ventricle and increased pressure on the right side increased the diameter of the pulmonary artery. Pulmonary hypertension is characterized by vascular changes.

Clinical Features

Small IVC may be asymptomatic. In the muscular part of the septum, half of it closes abruptly in infancy or childhood. However, major defects result in chronic left-to-right shunting, which is often complicated by pulmonary hypertension and heart failure.

Progressive pulmonary hypertension which causes shunt failure and cyanosis occurs earlier and more frequently in VSD than in ASD. Therefore, early surgical correction is indicated for such wounds. Small to moderate defects cause right ventricular jet lesions that damage the endothelium and increase the risk of infectious endocarditis.

Patent Ductus Arteriosus

Ductus arteriosus arises from the left pulmonary artery and joins the left subclavian artery in the aorta. During fetal life, it allows blood to flow in the aorta from the pulmonary arteries, ignoring the oxygen-deprived lungs. Within 1 or 2 days after birth, in a relatively healthy 1 month old baby, the ducts constrict and close. These changes occur in response to an increase in arterial oxygenation, a decrease in pulmonary vascular resistance, and a decrease in local levels of prostaglandin E2.

Complete destruction occurs in the first few months of ectopic life, leaving only a fragment of residual fibrous tissue called ligamentum arteriosus. Infants with hypoxia (associated with respiratory or heart disease) may have delayed (or even absent) drainage. About 7% of congenital heart defects occur in PDAs. Most (90%) of these are isolated defects.

Clinical Features

PDAs are left to right high pressure shunts that emit loud “machine” sounds. Small PDAs usually have no symptoms, although large defects can eventually lead to Eisenhower syndrome with sinusitis and congestive heart failure. High blood pressure can also cause patients to develop infectious endocarditis.

Although isolated PDAs should be discontinued as soon as possible, maintaining ductal patency (via administration of prostaglandin E) can be life-saving when PDAs are the only way to maintain systemic or pulmonary blood flow (e.g. As in infants).

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