Key Points
Ventricular septal defects are the most common congential cardiac malformations, and often occur as part of more complex abnormalities, such as tetralogy of Fallot or transposition.
Prenatal diagnosis should be straightforward using a long axis view of the ventricles, followed by a short axis sweep from apex to base.
Many isolated small VSDs, especially of the muscular type, will close spontanteously in utero, or in infancy.
Significant VSDs that contribute to failure to thrive, or those associated with increased pulmonary vascular flow, should be surgically repaired by 6 months of age.
Recent advances in minimally invasive transcatheter septal occlusion devices hold great promise as an alternative to open surgical repair with cardiopulmonary bypass.
Ventricular septal defect (VSD) refers to a congenital malformation in the development of the interventricular septum. VSDs can occur in the muscular or membranous portions of the septum. Muscular VSDs may be further subdivided into inlet, trabecular, or infundibular defects (Soto et al., 1980; Minette and Sahn, 2006). VSDs may also be classified as being either subvalvular or muscular (Capelli et al., 1983). Subvalvular VSDs are directly related to the atrioventricular or semilunar valves, without interposed muscle between the defect and the valve cusps. Such subvalvular defects may be further subclassified as inlet, subtricuspid, subaortic, subpulmonary, or double-committed subarterial, in which the defect is below the pulmonary and aortic valves. Muscular VSDs are bordered on all sides by muscle and are not directly related to the valves. Such defects may be further subclassified as being apical, central, or outlet in location. Most of these VSD types can be defined by echocardiography, although it is important to realize that small muscular defects can be missed by sonography during both the prenatal and the postnatal periods (Capelli et al., 1983).
VSDs usually cause no hemodynamic effects in utero because of the similarity in pressures between the right and left sides of the heart during prenatal life. Most VSDs are also asymptomatic immediately following birth. If the VSD persists after birth, it may allow for the development of a left to-right shunt, which can result in congestive heart failure or pulmonary hypertension.
VSDs are the most common single congenital cardiac malformation, accounting for 26% of all structural cardiac abnormalities (Ferencz et al., 1987). In an earlier population series, the incidence of VSD was 2 in 10,000 total births (Mitchell et al., 1971). However, with the increasing use of prenatal and neonatal echocardiography, the birth incidence of VSDs seems to be much higher than previously suggested (Minette and Sahn, 2006). In one series, 5% of all newborns were found to have an isolated muscular VSD (Roguin et al., 1995). The most accurate estimate of birth prevalence of VSD is 3.5 per 1000 livebirths (Hoffman and Kaplan, 2002). In addition, VSDs are frequently found in association with other cardiac malformations, such as tetralogy of Fallot (see Chapter 52) and transposition of the great arteries (see Chapter 55).
As with an ASD, prenatal sonographic diagnosis of a VSD can be difficult because it relies on visualization of dropout of echoes at the level of the interventricular septum, which is best achieved using a subcostal approach to the four-chamber view. In order to confirm an intact interventricular septum, the septum should also be visualized by means of a long-axis view of the left and right ventricles, together with an apex-to-base sweep along the short axis of the heart (Figures 44-1 to 44-3) (Romero et al., 1988). Small membranous VSDs are still commonly missed on prenatal sonography, despite adequate views of all parts of the interventricular septum. In addition, artifactual areas of hypoechogenicity in the septum during the apical four-chamber view may give the false impression of a VSD; therefore a true VSD is confirmed only when it is visible in at least two different planes (Romero et al., 1988). Color Doppler sonography may also be used to demonstrate flow across the area of defect (Figure 44-4) (Sanders et al., 1996).
The accuracy of prenatal sonographic screening for VSDs is poor. In a series of 7459 fetuses that were screened at 18 weeks of gestation, there were 53 VSDs, none of which were identified prenatally (Tegnander et al., 1995). In another series, only 5% of the 486 VSDs present in a single large population were detected prenatally (Montana et al., 1996). The accuracy of targeted fetal echocardiography for prenatal detection of isolated VSDs is also poor. In one series of targeted fetal echocardiograms, only 4 (31%) of 13 ASDs or VSDs were correctly identified (Benacerraf et al., 1987). In another series of fetal echocardiograms, there were 29 VSDs, 19 (66%) of which were correctly identified; the vast majority of these were associated with other more complex cardiac malformations (Crawford et al., 1988). In one further series, only 11 (44%) of 25 isolated VSDs were correctly identified prenatally, with small and moderate-sized VSDs the most likely to be missed (Kirk et al., 1997).
