Ventricular septal defect

A ventricular septal defect (VSD) is a defect in the interventricular septum allowing a haemodynamic communication between the right and left ventricles. It typically results in a left to right shunt.

Epidemiology

They represent one of the most common congenital cardiac anomalies and may be associated with up to 40% of such anomalies ¹.  The estimated incidence is at ~ 1 in 400 births ⁶.

Pathology

Classification according to location

• membranous / perimembranous (most common : ~ 80 - 90%)
• inlet
• outlet
• muscular / trabecular 

Associations

A VSD can occur on its own but frequently tends to occur with other cardiovascular associations. 

• cardiovascular associations
  • tetralogy of Fallot
  • truncus arteriosus
  • double outlet right ventricle - including Taussig-Bing malformation
  • aortic coarctation
  • tricuspid atresia
  • aortic regurgitation
  • pulmonary stenosis
• extra cardiac associations
  • aneuploidic / chromosomal anomalies
    • trisomy 21
    • trisomy 18
    • trisomy 13
    other syndromic anomalies : there are several and include
    • Holt-Oram syndrome

Radiographic features

Plain film

CXR can be normal with a small VSD. Larger VSDs may show cardiomegaly (particularly left atrial enlargement although the right and left ventricle can also be enlarged). A large VSD may also show features of pulmonary oedema, pleural effusion or / and increased pulmonary vascular markings. 

Ultrasound - echocardiography

Allows direct visualisation of the septal defect which can be easily seen in the four chamber view. A perimembranous VSD can seen as a septal dropout in the area adjacent to the tricuspid septal leaflet and below the right border of the aortic annulus. Small isolated VSD's can be difficult to detect prenatally.

CT

Allows direct visualisation of the defect on contrast CT.

MRI

May also show added functional information (e.g. quantifiation / shunt severity) in addition to anatomy. Some muscular defects can give a "Swiss cheese" appearance owing to their complexity.

Complications

• Eisenmenger phenomenon with shunt reversal ( i.e. L > R becomes R > L )
• cardiac failure

Prognosis

The prognosis is good for small VSDs which show a high spontaneous intra-uterine or post-natal closure rate. VSD's usually do not cause any haemodynamic compromise in utero due to right and left ventricular pressures being very similar during that period.