Developmental disorders

III./1.3.: Ventricular septal defects (VSD)

The most frequent developmental disorders of the heart in newborn infants (25 %) involve partial of total defects of the interventricular septum. With an incidence of 2-6:1000, VSDs represent, in most cases, openings of less than 5 mm diameter, which get spontaneously closed before puberty.

Although VSDs may be isolated, they mainly occur in association with other malformations (ASD, patent Botallo's duct, transposition of principal vessels, tetralogy of Fallot). As a rule, septal deficiency appears in the membranous part but it may also affect the muscular part. In the most severe cases, with a total lack of interventricular septum, the heart possesses only a single ventricle (cor triloculare biventriculare).

As with ASD, an opening of the interventricular septum may serve as a shunt between the right and left sides of the heart. Blood flows from the left ventricle of higher pressure into the cavity of the right ventricle. Owing to overloading, the muscular wall of left ventricle undergoes thickening (myocardial hypertrophy). The increasing burden leads to elevated pressure in and decreased elasticity of pulmonary vessels, as a result of which the right ventricle needs to work harder to pump blood into the lungs. After a while, increasing pressure of the right ventricle exceeds that of the left ventricle and the left-to-right shunt will be reversed. At this point, deoxygenated blood gets mixed with the oxygenated blood in the left ventricle, lowering the overall concentration of oxygen in the blood of systemic circulation. Oxygen deficiency, marked by the bluish tint of the infant's skin (cyanosis), causes slow development. Rudimentary VSDs tend to occur in the subaortic region.