Ventricular Septal Defects

An opening of the ventricular septum causing communication between the two ventricles.

Ventricular septal defects (VSDs) are the most common cardiac malformation. As an isolated finding it is found in 30% of babies born with CHD. As an associated finding it is obligatory part in some CHD but also occasionally found in other CHD. This group accounts for at least additional 30% of CHD cases.

The development of the ventricular septum takes a long time during cardiac embryogenesis and many cardiac and extracardiac disturbances can lead to a deficient closure of the septum. Intracardiac cell necrosis events, flow disturbances, apoptosis abnormalities and others can be responsible for it. Therefore a VSD can be found in almost all anomalies and syndromes.

Since VSD is a common defect the etiology is also aspecific. Many genetic diseases including numerical aberrations as Trisomy 21,18,13 and others can cause a VSD. Environmental factors and teratogenic exposure as infections, maternal diabetes mellitus, anticonvulsant drugs and others can be responsible for a VSD as well. Most cases however are multifactorial.

There are 4 types of VSDs based on where they are located in the ventricular septum:

• Muscular or trabecular defects occur in the muscular portion of the septum
• Perimembranous defects involve the membranous septum below the aortic valve and extend to variable degrees into the adjacent portion of the muscular septum.
• Inlet defects occur in the inlet septum, close to the insertion of the atrioventricular valves.
• Subpulmonary defects are on the inflow tract of the right entricle and thus affect the implantation of the septal chordae of the tricuspid valve.

VSDs can be isolated or associated with other cardiac defects. VSD defects associated with conotruncal defects are usually associated with malalignment of the ventricular and infundibular septa and are commonly referred to as malalignment VSDs. In postnatal series of isolated VSDs, perimembraneous defects are the most frequent, but in the largest antenatal series available muscular VSDs were predominant (87% of cases.)¹ This discrepancy is probably the consequence of a high rate of spontaneous closure of the muscular defects compared to the other types. VSDs do not cause significant hemodynamic compromise in utero. Even a large interventricular communication probably only gives rise to small shunts in the fetus, as during intrauterine life the right and left ventricular pressure are very similar. The vast majority of infants are not symptomatic in the neonatal period. Rare exceptions are represented by very large defects causing massive left to right shunt, that can indeed be associated with congestive heart failure soon after birth.

VSD is commonly an isolated defect but in the fetus its detection is often related to the detection of an associated cardiac or extracardiac abnormality. It can be found in association with almost every other kind of structural cardiac defect and extracardiac anomaly. Extracardiac anomalies associated with VSD are not specific. The combination of a VSD with an extracardiac abnormality increases the risk for the presence of a syndrome or chromosomal aberration. The association of isolated VSSs with aneuploidies is controversial in the recent literature. Some studies report a high probability of chromosomal aberrations includingtrisomy 21 and 18, but this is probably the consequence of a selection bias. In general, muscular defects have a lower risk than perimembranous types.^2-4 The largest available series thus far suggests hat in truly isolated cases the risk is very low (1/248). In particular, no chromosomal aberrations were found in 216 muscular VSDs.¹ In another series, no chromosomal aberrations were found in cases with a reassuring first trimester screening and without associated anomalies.⁵ Clearly, the differences in the available fetal studies largely depends upon the recent technological advances in ultrasound equipment that permit the diagnosis of very small fetal VSDs, that are likely to have no clinical implications.⁶

VSDs tends to have a high recurrence rate.

VSDs can be visualized on 2D ultrasound as they appear as an absence of ventricular septal tissue. In general VSDs need to be larger than 2-3 mm to be detected during a comprehensive cardiac scan. Small defects may not be easily seen and the use of Color Doppler has made it possible to visualize small defects. Especially in the mucular septum, Color Doppler shows the bidirectional shunting across the septum. The best approach is a perpendicular insonation of the the septum with the demonstration of the communication. Often on 2D the borders of the VSD appear echogenic due to the covering of the defect with endocardium. The confirmation of a VSD should be achieved with color Doppler with a typical shunting. Pulsed Doppler interrogation of the shunting confirms the bidirectional flow and rejects possible artifacts. Inlet VSDs are difficult to detect and they are found at the septum under the atrioventricular valves. Muscular VSD are often found in the apical half of the muscular septum. Perimembranous VSD can be visualized in the left ventricular outflow tract, in the five chamber view or a parasagittal long axis view, as aninterruption of the continuity between interventricular septum and ascending aorta.^{1-3, 5}

Once a VSD is suspected there are two major differential diagnoses to be addressed the false positive and the incomplete diagnosis: Most common false positive diagnosis of a VSD is a drop out artefact, primarily in the perimembraneous region of the septum typically by transabdominal ultrasound before 20 weeks gestation. Such false positive diagnosis of a VSD is more common when the interventricular septum is scanned apically. The lateral visualization of the septum combined with the use of sensitive color Doppler help in confirming or rejecting the diagnosis. A VSD can be accurately detected but additional cardiac findings can be not recognized. Therefore a comprehensive cardiac examination should be performed once such defect is found.

Once a VSD is detected a sequential segmental examination of the heart should be perfomed to rule out the presence of additional cardiac malformations. Comprehensive fetal examination should be also performed to rule out the presence of additional extracardiac anomalies or soft marker for typical or rare chromosomal aberrations or genetic disorders. The large majority of accidentally detected muscular VSD are isolated findings.

On screening ultrasound a VSD can be detected during the cardiac examination once the heart is magnified on 2D.

Prognosis of VSD is excellent, provided it is an isolated finding in the fetus. Muscular VSD generally close within the first two years of life. Less frequently they close in utero during the third trimester.1 Small perimembranous VSD occasionally can close spontaneously, but larger one need to be operated to avoid a chronic volume overload in the right venticle due to the left to right shunt.1-3, 5 In one series, 13% of muscular VSDs recognized in utero required surgical correction compared to 50% of perimembraneous defects.5 Inlet and subpulmonary ventricular septal defects, as well as large muscular and perimembranous ventricular septal defects patent at birth usually require surgical closure in the first year or two of life at low surgical risk with few long term sequelae.2, 3, 5 The vast majority of patents will have a normal life span and a normal level of activity. Ventricular septal defects associated with other structural cardiac defects may have a less favorable prognosis.

No specific management is needed during gestation, apart from a careful search for associated anomalies, intracardiac and extracardiac as well. Determination of fetal karyotype should be considered. A follow up control fetal echocardiogram can be offered to rule out possible association with other minor cardiac abnormalities. Prompt cardiologic evaluation after birth is however recommended.

1. Gomez O, Martinez JM, Olivella A, Bennasar M, Crispi F, Masoller N, Bartrons J, Puerto B, Gratacos E. Isolated ventricular septal defects in the era of advanced fetal echocardiography: risk of chromosomal anomalies and spontaneous closure rate from diagnosis to age of 1 year. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2014 Jan;43(1):65-71. PubMed PMID: 23733584.

2. Axt-Fliedner R, Schwarze A, Smrcek J, Germer U, Krapp M, Gembruch U. Isolated ventricular septal defects detected by color Doppler imaging: evolution during fetal and first year of postnatal life. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2006 Mar;27(3):266-73. PubMed PMID: 16485323.

3. Paladini D, Palmieri S, Lamberti A, Teodoro A, Martinelli P, Nappi C. Characterization and natural history of ventricular septal defects in the fetus. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2000 Aug;16(2):118-22. PubMed PMID: 11117079.

4. Paladini D, Tartaglione A, Agangi A, Teodoro A, Forleo F, Borghese A, Martinelli P. The association between congenital heart disease and Down syndrome in prenatal life. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2000 Feb;15(2):104-8. PubMed PMID: 10775990.

5. Mosimann B, Zidere V, Simpson JM, Allan LD. Outcome and requirement for surgical repair following prenatal diagnosis of ventricular septal defect. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2014 Jul;44(1):76-81. PubMed PMID: 24357326.

6. Allan L. Re: Isolated ventricular septal defects in the era of advanced fetal echocardiography: risk of chromosomal anomalies and spontaneous closure rate from diagnosis to age of 1 year. O. Gomez, J. M. Martinez, A. Olivella, M. Bennasar, F. Crispi, N. Masoller,J. Bartrons, B. Puerto, E. Gratacos. Ultrasound Obstet Gynecol 2014; 43: 65-71. Ultrasound in obstetrics & gynecology : the official journal of the International Society of Ultrasound in Obstetrics and Gynecology. 2014 Jan;43(1):12. PubMed PMID: 24395687.

This article should be cited as: Chaoui R. Pilu G: Ventricular sepetal defects. Visual Encyclopedia of Ultrasound in Obstetrics and Gynecology. www.isuog.org, August 2014

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