Communications between the two circulatory systems (pulmonary and systemic) are located in the septa separating the atria (atrial septal defects) or the ventricles (ventricular septal defects), or involve communication between the great vessels (aortopulmonary communication). The result is blood shunting from the high-pressure system (systemic circulation) to the low-pressure system (pulmonary circulation). The shunt is left-to-right, while in very large defects it may become bidirectional.
Anatomy
The interventricular septum is formed by the union of several septal components:
Muscular septum, divided into:
- Inlet septum (near the atrioventricular valves)
- Trabeculated septum (extending to the apex)
- Outlet septum (separating the right ventricular outflow tract/infundibulum from the left ventricle)
Membranous septum
(located below the aortic valve and in the upper part of the muscular septum)
| Ventricular Septal Defect (VSD) | Location |
|---|---|
| Muscular type – trabeculated septum (muscular VSD) | Most common form of VSD, often small in size with a high likelihood of spontaneous closure |
| Membranous/perimembranous VSD | Common type extending into the membranous septum and adjacent septa. Possible spontaneous closure through aneurysm formation from neighboring tricuspid valve tissue attachments. Often large defects |
| Muscular type – inlet septum (inlet VSD) | Defects located directly beneath the atrioventricular valves, without a tendency for spontaneous closure. Included among endocardial cushion defects |
| Muscular type – outlet septum (malalignment VSD) | Large defects between the outlet septum and the remaining muscular septum due to failed alignment and connection. Severe congenital heart diseases such as Tetralogy of Fallot are characterized by this type of VSD |
Hemodynamics and Clinical Manifestations
Hemodynamics
The presence of an intra- or extracardiac communication allows part of the blood flow to deviate from its normal course and pass through the defect into the opposite circulation. The direction and magnitude of the shunt depend on both the size of the defect and the pressure difference between the two circulations at the level of the communication.
Since systemic circulation has higher pressures than pulmonary circulation, blood flow through the defect is directed from the systemic to the pulmonary circulation (left-to-right shunt). If the defect is small to moderate, maintaining the pressure difference between the circulations, the amount of blood flow through the defect depends mainly on the size of the communication.
The left-to-right shunt reduces systemic cardiac output and increases pulmonary blood flow. Oxygenated blood from the left chambers (or aorta) escapes into the right chambers (or pulmonary artery), recirculating through the lungs without contributing to systemic oxygenation, thereby increasing pulmonary perfusion.
Small defects are termed restrictive because they significantly limit shunting between circulations. Large defects are nonrestrictive and minimally impede blood flow through the communication. In this case, the pressure difference between the two circulations decreases or pressures equalize, leading to pulmonary hypertension.
Clinical Manifestations
The common clinical manifestations depend on the extent of the left-to-right shunt. When the shunt is limited, patients are asymptomatic. However, extensive left-to-right shunting leads to reduced systemic output and pulmonary recirculation, resulting in signs and symptoms of heart failure:
- Tachycardia
- Easy fatigue
- Tachypnea
- Hepatomegaly
- Poor weight gain
- Frequent respiratory infections
Depending on the type of defect, more specific clinical findings may exist, such as the character and location of heart murmurs, splitting of the second heart sound, etc.
Prevalence
Ventricular septal defect (VSD) is the most common congenital heart disease, occurring in approximately 50% of patients with congenital heart disease. It may occur in isolation (20% of congenital heart diseases) or in association with other cardiac anomalies.
Ultrasound
Ultrasound diagnosis of perimembranous ventricular septal defects is more difficult because of their location, and they must be distinguished from atrioventricular septal defects by the presence of the primary atrial septum.
Perimembranous defects( video) may be associated with chromosomal abnormalities and anomalies in other organ systems. Therefore, detailed fetal anatomical evaluation and karyotyping are necessary. In contrast, muscular-type defects have a lower association with chromosomal abnormalities.
Trabecular muscular ventricular septal defects(video) are easily visualized along the middle portion of the septum extending toward the apex.
Management
Membranous and muscular defects may close spontaneously. Therefore, if there is no significant hemodynamic burden, or if it is adequately controlled with medication, careful observation is appropriate.
Treatment is usually surgical, although in selected cases closure may be achieved with a transcatheter device.
Management is individualized; however, the following general principles apply:
- In infants younger than six months (earlier in trisomy 21), closure is recommended if heart failure is not adequately controlled medically or if pulmonary hypertension is present.
- At one year of age, closure is recommended if Qp:Qs >2:1 or pulmonary hypertension exists.
- Later in life, closure is generally recommended in the presence of left ventricular dilation despite normal pulmonary pressure.
Patients may also be closely monitored, with intervention at the first signs of heart failure or increased pulmonary pressure.
Blood flow through the defect (usually membranous) may affect the aortic valve cusps, causing cusp prolapse and aortic regurgitation. This condition alone is an indication for closure before permanent valve dysfunction develops.
Small defects without hemodynamic burden are compatible with normal activity and do not affect survival.
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