Ventricular septal defect

What is Ventricular Septal Defect (VSD)?

Ventricular septal defect (VSD) is a hole or a defect in the interventricular septum.

Embryology

The muscular part of the VSD forms first. It grows from the apex to the atria and consists of intertwining muscle fibers. These muscle fibers form a septum, which grows from the ventricular apex toward the atrium - the interventricular septum.Two large masses of loosely organized mesenchyme are formed in the constricted part of the heart (between the atrium and the ventricle) one on its dorsal, another on its ventral wall. This tissue is called the endocardial cushions. Eventually these thickenings will be remodeled and form the basis of the valves and septa of the heart. The separation of two ventricles is completed by 4-5 weeks of embryogenesis. The interventricular opening in the upper part of the interventricular septum is overgrown with connective tissue that proliferates from endocardial cushions. This part of the interventricular septum is called membranous septum.

Anatomy

The interventricular septum is not a flat structure or a straight wall; normally it is curved. From the side of the left ventricle, the septum has a smooth structure, with small trabeculae, like the left ventricle itself. From the side of the right ventricle, especially in the apex, the septum is trabecular. The outlet part of the right ventricle is trabecular, especially in the area of the conical septum. A septal bundle extends downward from the conical septum, which expands downward and partially continues in the form of a moderator cord, which grows together with the anterior papillary muscle of the TC. A conical septum is located between the posterior lower edge and the anterior upper edge. The interventricular septum is divided into the following parts: membranous, inlet, muscular, outlet, and conic. Defects can form in each of them and each of them is characteristic for certain complex defects. The most common independent CHD is a defect in the membranous part of the interventricular septum.

Hemodynamics

With this defect, blood is shunted from the left ventricle to the right. The amount of discharge depends on the size and location of the defect. As a result, the blood flow in the pulmonary artery increases (Qp: Qs is greater than 1), pressure in the pulmonary artery, right and left ventricles. In contrast to an atrial septal defect, in which there is an overload of the pulmonary artery volume, pressure overload also occurs in VSD. Because of this, there is a rapid development of pulmonary vascular disease. After the development of pulmonary hypertension due to increased pressure in the right parts of the heart, the shunt is changed to the right-left (. Eisenmenger syndrome).

Classification

By location:

1. Perimembranous. They are located in the membranous part of the septum.
2. Muscular (trabecular). They can be located in any part of the muscular septum. There are single or multiple.
3. Infundibular (under the pulmonary). The defect is located under the pulmonary valve.
4. Inlet. Located near the septal leaf of the tricuspid valve.

By size:

1. small defects - less than 25% of the aortic valve diameter;
2. medium - 25-75%;
3. large - more than 75%.

By the degree of pressure in the ventricles:

1. Restrictive (high systolic pressure gradient between the ventricles).
2. Non-restrictive (no or insignificant systolic pressure gradient).

Workup

• Doppler echocardiography, transesophageal echocardiography. The main diagnostic feature is the visualization of the defect. It provides both morphological and hemodynamic data: size, location, number of defects, etc.
• Chest X-ray. Patients with small defects often have no changes. Significant changes in the pulmonary pattern appear when the Qp/Qs (ratio of pulmonary and systemic blood flow) is 2:1 or more: increased heart shadow, increased vascular pattern of the lungs, pulmonary artery is dilated.
• ECG. Changes appear in case of presence of large shunts: signs of an overload of the left ventricle and left atrium. Signs of an overload and hypertrophy of the right heart indicate high pulmonary hypertension.
• CT, MRI. Useful in cases of complicated anatomy of the defect, when it is accompanied by other CHD.
• Catheterization of the cavities of the heart: according to medical reasons for the calculation of hemodynamic parameters, determination of operability.

Clinical presentation

The degree of increase in pressure in the PA and, accordingly, clinical manifestations, depends on the magnitude of the left-right shunt and pulmonary resistance. Pulmonary vascular resistance is high immediately after birth; VSD may remain undetected because a slight gradient will not result in a meaningful reset.

By 4-6 weeks, children with a large defect may develop the first symptoms of heart failure - shortness of breath, especially when feeding, excessive sweating, lack of weight gain. Some children with small VSD have no symptoms.

Due to the accumulation of fibrous tissue near the defect, they are often able to close on their own. However, a decrease in symptoms of heart failure over time does not necessarily indicate that the defect has decreased. This is due to an increase in pressure in the pulmonary artery, the development of pulmonary vascular disease. 

After its development, the shunt changes to the right-left, clinically this manifests itself by cyanosis. Of course, the development of these symptoms depends on the size: it is very unlikely that heart failure and pulmonary hypertension will develop in children with small defects.

Treatment

Surgical treatment of VSD is rarely urgent. In most cases, surgery can be delayed until an older age. There are no clearly identified indications for surgery; there are indirect signs that can be guided by. In any case, the decision is made based on clinical findings, the size of the defect and the patient's condition. The indications for surgical treatment are:

1. The presence of persistent symptoms of heart failure, tolerance to drug therapy.
2. Lag in physical development, frequent hospitalizations associated with the failure of conservative treatment.
3. The pressure in the pulmonary artery is more than 50% of the systemic pressure - correction is recommended by the end of the first year of life, because more often than not, this defect will not close spontaneously and is more likely to lead to PH.
4. Presence of aortic regurgitation.
5. PA pressure less than 50% of system pressure - correction can be postponed.

Correction methods:

1. One-step radical correction - closing an isolated defect with a patch made of synthetic materials.
2. Two-step correction (banding of the pulmonary artery in the neonatal period and radical correction in older age) - at the moment is not used.
3. X-ray endovascular correction - for muscle and, rarely, perimembranous defects. There are a significant number of contraindications and complications for this method.