pediatrics
Ventricular Septal Defect (VSD)
Classification
Most ventricular septal defects are classified by location: Perimembranous (also called conoventricular) Trabecular muscular Subpulmonary outlet (supracristal, conoseptal, doubly committed subarterial) Inlet (atrioventricular septal type, atrioventricular canal type) Perimembranous defects (70 to 80%) are defects in the membranous septum adjacent to the tricuspid valve and they extend into a variable amount of surrounding muscular tissue; the most common type of this defect occurs immediately below the aortic valve. Trabecular muscular defects (5 to 20%) are completely surrounded by muscular tissue and may occur anywhere in the septum. Subpulmonary outlet defects (5 to 7% in the United States; about 30% in Far Eastern countries) occur in the ventricular septum immediately under the pulmonary valve. These defects are often referred to as supracristal, conoseptal, or doubly committed subarterial defects and are frequently associated with aortic leaflet prolapse into the defect, causing aortic regurgitation. Inlet defects (5 to 8%) are bordered superiorly by the tricuspid annulus and are located posterior to the membranous septum. These defects are sometimes referred to as atrioventricular septal-type defects. Malalignment type ventricular septal defects are characterized by displacement of the conal or outlet septum. When the conal septum is malaligned anteriorly, it protrudes into the right ventricular outflow tract often resulting in obstruction, as occurs in Tetralogy of Fallot . When the conal septum is malaligned posteriorly, there may be left ventricular outflow tract obstruction. These VSDs occur in the same location as perimembranous VSDs but represent an important subset with different physiology related to this outflow tract obstruction. 