Ventricular septal defects

Congenital

• Ventricular septal defects (VSDs) are usually developmental congenital conditions. No definite cause is known. In families with a strong history of congenital cardiovascular malformations, the incidence of VSD is increased. Certain genetic abnormalities have a high incidence of associated VSD, the most common being Down syndrome, which is associated with congenital cardiovascular malformations in one third to one half of cases.[14]Freeman SB, Taft LF, Dooley KJ, et al. Population-based study of congenital heart defects in Down syndrome. Am J Med Genet. 1998 Nov 16;80(3):213-7. http://www.ncbi.nlm.nih.gov/pubmed/9843040?tool=bestpractice.com [15]Freeman SB, Bean LH, Allen EG, et al. Ethnicity, sex, and the incidence of congenital heart defects: a report from the National Down Syndrome Project. Genet Med. 2008 Mar;10(3):173-80. https://www.gimjournal.org/article/S1098-3600(21)02177-8/fulltext http://www.ncbi.nlm.nih.gov/pubmed/18344706?tool=bestpractice.com ​​

Acquired

• In rare cases, a VSD can occur as a result of acute myocardial infarction (MI). This usually occurs 2 to 5 days after the infarction and is marked by the onset of acute left-heart failure, chest pain, low cardiac output and shock.[6]Birnbaum Y, Fishbein MC, Blanche C, et al. Ventricular septal defect after acute myocardial infarction. New Engl J Med. 2002 Oct 31;347(18):1426-32. http://www.ncbi.nlm.nih.gov/pubmed/12409546?tool=bestpractice.com VSD also occurs as a result of penetrating or, rarely, blunt trauma.

The pathophysiologies of all VSDs are essentially the same, regardless of location. Two factors determine the hemodynamic effects of a VSD: the size of the defect and the pulmonary vascular resistance. If the defect is able to limit the transmission of pressure from the left to the right side of the heart, it is called a restrictive defect.

A small restrictive defect (pulmonary to systemic blood flow ratio [Qp:Qs] <1.5:1) leads to minimal left-to-right shunting across the ventricles, and is not associated with any increase in pulmonary vascular resistance or with any symptoms. If found in infancy there is a high likelihood of spontaneous closure; however, it has a good prognosis, even if it persists into adulthood.

A moderate restrictive defect (Qp:Qs 1.5:1 to 2.5:1) will lead to left-to-right shunting and a variable amount of pulmonary hypertension. Initially, there is reactive pulmonary hypertension (pulmonary hypertension that is reversible with pulmonary vasodilators) with left-to-right shunting. Gradually, the pulmonary vascular resistance rises, resulting in decreased shunting. Persistent pulmonary hypertension eventually becomes "fixed" pulmonary hypertension, produced by permanent irreversible remodeling of the pulmonary vasculature. Pulmonary hypertension increases the back pressure on the heart, causing dilatation of the cardiac chambers and, eventually, heart failure.

In larger defects (Qp:Qs >2.5:1) and in late stages, significant pulmonary hypertension occurs and pulmonary vascular resistance rises to the point that the shunt reverses (Eisenmenger syndrome). Shunt reversal alludes to blood flowing from the right to the left ventricle, effectively "reversing" the flow seen through most VSDs. It results in unoxygenated blood from the systemic venous return passing directly into the systemic arterial circulation without going through the lungs to be oxygenated. Oxygen saturation in the systemic arterial circulation therefore falls, resulting in cyanosis. The VSD becomes inoperable at this point.

In infancy, the mechanism of pulmonary hypertension is different from in adults, and is primarily due to increased pulmonary blood flow rather than increased pulmonary vascular resistance. However, the sequelae are the same. Reduced systemic perfusion is still seen in infants, resulting in heart failure.

An acute VSD resulting from an acute MI will usually result in acute left-heart failure with pulmonary edema and shock.[6]Birnbaum Y, Fishbein MC, Blanche C, et al. Ventricular septal defect after acute myocardial infarction. New Engl J Med. 2002 Oct 31;347(18):1426-32. http://www.ncbi.nlm.nih.gov/pubmed/12409546?tool=bestpractice.com

Additional problems can arise with certain types of VSD. With type 1 defects, accompanying aortic regurgitation is common, produced by prolapse of the anterior aortic valve leaflet. With type 3 defects, there is often involvement of the atrioventricular valves and the atrial septum.

Classification according to location[1]Warnes CA, Williams RG, Bashore TM, et al. ACC/AHA 2008 guidelines for the management of adults with congenital heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines (Writing Committee to Develop Guidelines on the Management of Adults With Congenital Heart Disease). Developed in collaboration with the American Society of Echocardiography, Heart Rhythm Society, International Society for Adult Congenital Heart Disease, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons. J Am Coll Cardiol. 2008 Dec 2;52(23):e143-263. https://www.sciencedirect.com/science/article/pii/S0735109708033044 http://www.ncbi.nlm.nih.gov/pubmed/19038677?tool=bestpractice.com

VSDs are classified according to their location. There are 4 main types, 3 of which are known by several synonyms.

Type 1

• 6% of isolated VSDs in non-Asian populations, but up to 33% in Asian populations

• Synonyms: conal defect, conal septal hypoplasia, sub-pulmonary defect, infundibular defect, supracristal defect, doubly committed juxta-arterial defect

• Location: lies beneath the semilunar valves in the conal or outlet septum

• Often associated with aortic regurgitation produced by prolapse of the anterior aortic valve leaflet

Type 2

• Synonyms: perimembranous defect, paramembranous defect, conoventricular defect

• Location: confluent with the membranous septum, bordered by an atrioventricular (AV) valve

Type 3

• Synonyms: peri-inlet defect, AV canal type defect, AV septal defect, endocardial cushion defect

• Location: involves the inlet of the ventricular septum immediately inferior to the AV valve apparatus

• Typically occur in patients with Down syndrome

Type 4

• Up to 20% of VSDs in infants. Adult incidence is much lower

• Synonym: muscular defect

• Location: completely surrounded by muscle; multiple defects may be present, producing a "Swiss cheese" appearance of the septum

•  Spontaneous closure may occur[Figure caption and citation for the preceding image starts]: Simplified diagram of the left ventricular septum showing the anatomical locations of the ventricular septal defectsFrom the collection of Dr Zuhdi Lababidi [Citation ends].

Classification by etiology

Congenital

• Most VSDs are the result of a developmental defect

Acquired

• Rare

• Necrosis of the septum following MI can produce a VSD

• Penetrating trauma (e.g., a stab wound) or, very rarely, blunt trauma can produce a VSD

Classification by size[2]Stout KS, Daniels CJ, Aboulhosn JA, et al. 2018 AHA/ACC guideline for the management of adults with congenital heart disease: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. Circulation. 2019 Apr 2;139(14):e698-800. https://www.ahajournals.org/doi/10.1161/CIR.0000000000000603 http://www.ncbi.nlm.nih.gov/pubmed/30586767?tool=bestpractice.com

VSDs can be divided into small, moderate, and large defects according to size. The magnitude of the shunt produced by a VSD is described by the Qp:Qs ratio.

The 2018 American Heart Association/American College of Cardiology guideline includes the following classification:

• Small restrictive defects. The pulmonary vascular resistance is not significantly elevated and the left-to-right shunt is small (Qp:Qs <1.5:1).

• Large nonrestrictive defects in cyanotic patients who have developed Eisenmenger syndrome, with pulmonary vascular resistance at systemic levels and shunt reversal (right-to-left).

• Patients with moderately restrictive defects (Qp:Qs ≥1.5:1 and <2:1) who have not undergone closure for some reason. These patients often have mild-to-moderate pulmonary arterial hypertension.

• Patients who have had their defects closed in childhood. These patients may have VSD patch leaks.

International Society for Nomenclature of Paediatric and Congenital Heart Disease classification scheme for VSD[3]Lopez L, Houyel L, Colan SD, et al. Classification of ventricular septal defects for the eleventh iteration of the International Classification of Diseases-Striving for Consensus: a report from the International Society for Nomenclature of Paediatric and Congenital Heart Disease. Ann Thorac Surg. 2018 Nov;106(5):1578-89. http://www.ncbi.nlm.nih.gov/pubmed/30031844?tool=bestpractice.com

Alternate classification of VSD

• Perimembranous central VSD

• Inlet VSD without a common AV junction

  • Inlet perimembranous VSD without AV septal malalignment and without a common AV junction

  • Inlet perimembranous VSD with AV septal malalignment and without a common AV junction

  • Inlet muscular VSD

• Trabecular muscular VSD

  • Trabecular muscular VSD: midseptal

  • Trabecular muscular VSD: apical

  • Trabecular muscular VSD: postero-inferior

  • Trabecular muscular VSD: anterosuperior

  • Trabecular muscular VSD: multiple (“Swiss cheese” septum)

• Outlet VSD

  • Outlet VSD without malalignment

    • Outlet muscular VSD without malalignment

    • Doubly committed juxta-arterial VSD without malalignment

      • Doubly committed juxta-arterial VSD without malalignment and with a muscular postero-inferior rim

      • Doubly committed juxta-arterial VSD without malalignment and with a fibrous postero-inferior rim (perimembranous extension)

  • Outlet VSD with anteriorly malaligned outlet septum

    • Outlet muscular VSD with anteriorly malaligned outlet septum

    • Outlet perimembranous VSD with anteriorly malaligned outlet septum

    • Doubly committed juxta-arterial VSD with anteriorly malaligned fibrous outlet septum

      • Doubly committed juxta-arterial VSD with anteriorly malaligned fibrous outlet septum and a muscular postero-inferior rim

      • Doubly committed juxta-arterial VSD with anteriorly malaligned fibrous outlet septum and a fibrous postero-inferior rim (perimembranous extension)

  • Outlet VSD with posteriorly malaligned outlet septum

    • Outlet muscular VSD with posteriorly malaligned outlet septum

    • Outlet perimembranous VSD with posteriorly malaligned outlet septum

    • Doubly committed juxta-arterial VSD with posteriorly malaligned fibrous outlet septum

      • Doubly committed juxta-arterial VSD with posteriorly malaligned fibrous outlet septum and a muscular postero-inferior rim

      • Doubly committed juxta-arterial VSD with posteriorly malaligned fibrous outlet septum and a fibrous postero-inferior rim (perimembranous extension)

International Classification of Diseases, 11th revision (ICD-11)[4]World Health Organization. International classification of diseases 11th revision (ICD-11). Jan 2022 [internet publication]. https://www.who.int/standards/classifications/classification-of-diseases

In ICD-11, VSDs are contained within the “Developmental anomalies” chapter and are defined as a congenital cardiac malformation in which there is a hole or pathway between the ventricular chambers. They are further subclassified as follows.

Trabecular muscular ventricular septal defect

• A congenital cardiac malformation in which there is a ventricular septal defect within the trabeculated component of the ventricular septum.

Perimembranous central ventricular septal defect

• A congenital cardiovascular malformation in which there is a ventricular septal defect that:

  • occupies the space that is usually closed by the interventricular part of the membranous septum

  • is usually adjacent to the area of fibrous continuity between the leaflets of an atrioventricular valve and an arterial valve

  • is adjacent to an area of mitral-tricuspid fibrous continuity

  • is located at the center of the base of the ventricular mass.

Ventricular septal defect hemodynamically insignificant

• A congenital cardiac malformation in which there is one or more small, clinically insignificant ventricular septal defect(s) in the absence of flow-related cardiac chamber dilation or abnormal elevation of pulmonary arterial pressure.