Definition

A ventricular septal defect (VSD) is a hole or a defect in the septum that divides the 2 lower chambers of the heart and that results in a communication between the ventricular cavities. The defect may occur as a primary anomaly with or without additional major associated cardiac defects.

At 4-8 weeks’ gestation, the single ventricular chamber is effectively divided into two. This division is accomplished with the fusion of the membranous portion of the ventricular septum, the endocardial cushions, and the bulbous cordis (proximal portion of the truncus arteriosus).

Frequency

In the United States, ventricular septal defects affect 2-7% of live births.

The patient’s area of residence may influence the prevalence of known ventricular septal defects. For example, small muscular ventricular septal defects are most likely to be identified in urban locations possibly because of ready access to sophisticated healthcare in these locations.

An echocardiographic study revealed a high incidence of 5-50 ventricular septal defects per 1000 newborns. The defects in this study were small restrictive muscular ventricular septal defects, which typically spontaneously close in the first year of life.

Ventricular septal defects are the most common lesion in many chromosomal syndromes, including trisomy 13, trisomy 18, trisomy 21, and relatively rare syndromes. However, in more than 95% of patients with ventricular septal defects, the defects are not associated with a chromosomal abnormality.

Classification

Many classifications of ventricular septal defects have been proposed. An underlying classification that is surgically and clinically useful is described below.

  1. Perimembranous (infracristal, conoventricular) ventricular septal defects lie in the LV outflow tract just below the aortic valve. Because they occur in the membranous septum with defects in the adjacent muscular portion of the septum, they are subclassified as perimembranous inlet, perimembranous outlet, or perimembranous muscular. These are the most common types of ventricular septal defects and account for 80% of such defects. Perimembranous ventricular septal defects are associated with pouches or aneurysms of the septal leaflet of the tricuspid valve, which can partially or completely close the defect. In addition, an LV-to-RA shunt may be associated with this defect.
  2. Supracristal (conal septal, infundibular, subpulmonic, subarterial, subarterial doubly committed, outlet) ventricular septal defects account for 5-8% of isolated ventricular septal defects in the United States but 30% of isolated ventricular septal defects in Japan. These defects lie beneath the pulmonic valve and communicate with the RV outflow tract above the supraventricular crest and are associated with aortic regurgitation secondary to the prolapse of the right aortic cusp.
  3. Muscular ventricular septal defects (trabecular) are entirely bounded by the muscular septum and are often multiple. The term Swiss-cheese septum has been used to describe multiple muscular ventricular septal defects. Other subclassifications depend on the location and include central muscular or midmuscular, apical, or marginal when the defect is along the RV-septal junction. These ventricular septal defects account for 5-20% of all defects. Any single defect observed from the LV aspect may have several openings on the RV aspect.
  4. Posterior (canal-type, endocardial cushion–type, AV septum–type, inlet, juxtatricuspid) ventricular septal defects lie posterior to the septal leaflet of the tricuspid valve. Although locations of posterior ventricular septal defects are similar to those of ventricular septal defect observed with AV septal defects, they are not associated with defects of the AV valves. About 8-10% of ventricular septal defects are of this type.

Other anatomic considerations

The relationship of the AV conduction pathways to the defect is important to surgical repair. The AV node occupies the apex of the triangle of Koch that is limited posteriorly by the tendon of Todaro, inferiorly by the os of the coronary sinus and superiorly by the tricuspid valve annulus. The bundle of His arises from the AV node. In perimembranous defects, the bundle of His lies in a subendocardial position as it courses along the posterior-inferior margin of the defect. In inlet defects, the bundle of His passes anterosuperiorly to the defect. In muscular ventricular septal defects and outlet defects, the risk of heart block is minimal because the bundle is remote from the defect.

Patients with subpulmonary conal defects usually have deficiency of muscular or fibrous support below the aortic valve with subsequent herniation of the right aortic leaflet. However, in patients with perimembranous ventricular septal defects with aortic insufficiency, it may be the right or the noncoronary cusp that prolapses.

Classification of congenital malformations – Phenotype

For purposes of etiologic analysis, clustering defects by potential pathogenic mechanisms is beneficial. The following pathologic classification allows for comparison of similar defects.

  1. Subarterial ventricular septal defect can be classified as abnormalities of ectomesenchymal tissue migration.
  2. Perimembranous ventricular septal defect can be classified as abnormal intracardiac blood flow.
  3. Muscular ventricular septal defect can be classified as abnormalities in cell death.
  4. Type III in-flow ventricular septal defect can be classified as abnormalities of the extracellular matrix and defects in the endocardial cushion.

Natural history

The natural history has a wide spectrum, ranging from spontaneous closure to congestive heart failure (CHF) to death in early infancy.

Spontaneous closure frequently occurs in children, usually occurs by age 2 years. Closure is uncommon after age 4 years. Closure is most frequently observed in muscular defects (80%), followed by perimembranous defects (35-40%). Outlet ventricular septal defects have a low incidence of spontaneous closure, and inlet ventricular septal defects do not close.

Closure may occur by means of hypertrophy of the septum, formation of fibrous tissue, subaortic tags, apposition of the septal leaflet of tricuspid valve, or (in rare cases) prolapse of a leaflet of the aortic valve. When perimembranous ventricular septal defects close because of development of fibrous tissue or the apposition of the tricuspid valve, an aneurysm of the interventricular septum may appear.

A small ventricular septal defect that does not spontaneously close is generally associated with a good prognosis. Patients are at risk for infective endocarditis, but small muscular ventricular septal defects pose no other adverse possibilities. However, small perimembranous VSD are associated with an increased risk of prolapse of the aortic cusp over time.

Source: eMedicine