Most Common Type of Ventricular Septal Defect
Perimembranous VSD (Type 2) is the most common type, accounting for approximately 80% of all ventricular septal defects. 1, 2
VSD Classification by Frequency
The ventricular septum can be divided into four anatomic regions, each giving rise to a distinct type of VSD with different prevalence rates:
Type 2: Perimembranous VSD (Most Common)
- Accounts for 80% of all VSDs 1, 2
- Located in the membranous septum, adjacent to the septal leaflet of the tricuspid valve 1
- On the left ventricular side, the defect sits adjacent to the aortic valve 1
- The tricuspid valve septal leaflet can become adherent to the defect, forming a pouch or "aneurysm" of the ventricular septum that may limit left-to-right shunting and result in partial or complete spontaneous closure 1
Type 4: Muscular VSD (Second Most Common)
- Accounts for 5% to 20% of all VSDs 1
- Can be located centrally (mid-muscular), apically, or at the margin of the septum and right ventricular free wall 1
- May be multiple in number ("Swiss cheese" septum) 1
- High rate of spontaneous closure - symptoms usually abate with medical treatment as the defect size decreases in absolute terms or relative to increasing body size 1, 2
Type 3: Inlet VSD
- Accounts for 5% of all VSDs 1
- Located in the lower part of the right ventricle, adjacent to the tricuspid valve 1
- Typically occur in patients with Down syndrome 1, 2
Type 1: Supracristal/Subarterial VSD (Least Common in Most Populations)
- Accounts for fewer than 5% of all defects in non-Asian populations 1
- However, incidence is 15% to 20% in Asian populations (up to 33% in some Asian cohorts) 1, 2
- Located in the outflow portion of the right ventricle 1
- Spontaneous closure is uncommon 1, 2
Clinical Significance of Perimembranous VSDs
Important caveat: While perimembranous VSDs are the most common type overall, their clinical behavior differs significantly from muscular VSDs:
- Perimembranous defects have variable rates of spontaneous closure depending on the presence of septal aneurysm formation 1
- When a membranous septal aneurysm forms, approximately 75% of defects will have a small or no left-to-right shunt at long-term follow-up, though only 5% achieve complete spontaneous closure 3
- Surgical closure remains safe and effective for hemodynamically significant perimembranous VSDs and is considered the therapeutic option of choice in neonates, infants, and children under 3 years of age 1