Residency · Residency · Cardiothoracic Surgery
Atrial and Ventricular Septal Defects
Overview
Atrial septal defects (ASDs) and ventricular septal defects (VSDs) are among the most common congenital heart defects. VSDs are the most common congenital heart defect overall (excluding bicuspid aortic valve), while ASDs are the most common congenital heart defect presenting in adulthood. The hemodynamic significance of these defects depends on their size, location, and associated lesions. Both surgical and device closure options exist, with indications guided by anatomy and hemodynamics.
Atrial Septal Defects
Embryology and Classification
Secundum ASD (75%)
The secundum ASD is a defect in the fossa ovalis region resulting from deficiency of the septum primum. It is the most common ASD type and is amenable to both surgical and device closure, provided adequate rims are present (especially the aortic rim).
Primum ASD (15-20%)
The primum ASD is a defect in the inferior atrial septum adjacent to the aV valves and falls within the atrioventricular septal defect (AVSD) spectrum. It is associated with a cleft anterior mitral valve leaflet and mitral regurgitation and is not amenable to device closure, requiring surgical repair. There is a well-known association with Down syndrome.
Sinus Venosus ASD (5-10%)
The superior type occurs near the SVC-RA junction and is almost always associated with partial anomalous pulmonary venous return (PAPVR) of the right upper pulmonary vein(s). The inferior type is rare and occurs near the IVC-RA junction. Neither type is amenable to device closure; surgical repair with a baffle to redirect pulmonary venous return is required.
Coronary Sinus ASD (< 1%)
This defect involves the wall of the coronary sinus ("unroofed coronary sinus") and is associated with a persistent left SVC draining to the left atrium. It requires surgical repair.
ASD Types Summary
| Type | Frequency | Location | Device Closure | Key Association |
|---|---|---|---|---|
| Secundum | 75% | Fossa ovalis | Yes (with adequate rims) | Most common; Amplatzer Septal Occluder |
| Primum | 15-20% | Inferior septum, near AV valves | No | Cleft mitral valve; Down syndrome |
| Sinus venosus (superior) | 5-10% | SVC-RA junction | No | PAPVR of right upper pulmonary vein(s) |
| Sinus venosus (inferior) | Rare | IVC-RA junction | No | Rare; requires baffle repair |
| Coronary sinus | < 1% | Coronary sinus wall | No | Persistent left SVC to LA |
Hemodynamics
The ASD creates a left-to-right shunt because left atrial pressure exceeds right atrial pressure. This produces chronic volume overload of the right atrium and right ventricle. Pulmonary overcirculation eventually leads to pulmonary vascular changes. The Qp:Qs ratio quantifies the shunt magnitude. If pulmonary hypertension becomes irreversible and the shunt reverses to right-to-left (Eisenmenger syndrome), closure is contraindicated.
Clinical Presentation
ASDs are often asymptomatic in childhood and present in adulthood with dyspnea on exertion, fatigue, atrial arrhythmias (atrial fibrillation and flutter, which increase with age), right heart failure, or paradoxical embolism causing stroke. On physical examination, fixed splitting of the second heart sound and a systolic flow murmur at the pulmonic area (resulting from increased pulmonary flow, not from the ASD itself) are characteristic findings.
Indications for Closure
Closure is indicated for a hemodynamically significant shunt with a Qp:Qs of 1.5:1 or greater, right atrial and right ventricular enlargement on echocardiography, symptoms attributable to the shunt, or paradoxical embolism. Closure is contraindicated in patients with Eisenmenger physiology (irreversible pulmonary hypertension with a net right-to-left shunt) or severely elevated pulmonary vascular resistance greater than 8 Wood units that does not respond to vasodilator testing.
Device Closure (Percutaneous)
Device closure is indicated for secundum ASDs with adequate rims of at least 5 mm from surrounding structures. The Amplatzer Septal Occluder is the most widely used device. Sufficient rim tissue is required along the posterior, inferior, superior, and IVC margins, though a deficient aortic rim may be acceptable. The maximum defect size for device closure is generally 38-40 mm. Advantages include avoidance of sternotomy and shorter recovery. Complications are uncommon but include device erosion (rare but serious), device embolization, residual shunt, and arrhythmia.
Surgical Repair
The standard approach uses median sternotomy with cardiopulmonary bypass and right atriotomy. Minimally invasive options include right mini-thoracotomy and robotic-assisted approaches. Small defects (less than 2 cm) with adequate tissue can be closed by direct suture, while larger defects require patch closure using a pericardial patch (autologous or bovine) or Gore-Tex patch. Sinus venosus ASDs are repaired using the Warden procedure, which involves SVC transection with SVC-to-right atrial appendage anastomosis and an intra-atrial baffle redirecting anomalous pulmonary veins to the left atrium. Primum ASD repair requires patch closure combined with repair of the cleft mitral valve through suture closure of the cleft.
<image>Classification of atrial septal defects showing secundum (fossa ovalis), primum (inferior septum near AV valves), sinus venosus (SVC junction), and coronary sinus types</image>
Ventricular Septal Defects
Classification
Perimembranous (Membranous) VSD (80%)
The perimembranous VSD is located in the membranous septum beneath the aortic valve, adjacent to the septal leaflet of the tricuspid valve. The bundle of His passes along the posteroinferior rim, making the conduction system closely proximate. There may be associated malalignment, override of the aorta, or tricuspid valve tissue forming an "aneurysm of the membranous septum" that provides partial closure. This is the most common VSD type overall.
Muscular VSD (5-20%)
Muscular VSDs are defects entirely surrounded by muscle that can be single or multiple ("Swiss cheese" septum). Small defects may close spontaneously. Surgical access can be challenging for apical or anterior muscular VSDs, making device closure a preferred option for complex cases.
Outlet (Supracristal, Doubly Committed Subarterial) VSD (5-7%)
Outlet VSDs are located below both semilunar valves (aortic and pulmonary) and result from absence of the muscular outlet septum. They carry a risk of aortic valve cusp prolapse and progressive aortic regurgitation, so surgical closure is recommended even for small defects. They rarely close spontaneously. The incidence is higher in Asian populations.
Inlet (AV Canal-type) VSD (5-8%)
Inlet VSDs are located in the posterior septum beneath the septal leaflet of the tricuspid valve. They are associated with the AVSD spectrum, and the bundle of His runs along the posteroinferior margin.
VSD Types Summary
| Type | Frequency | Location | Conduction Risk | Spontaneous Closure | Special Concern |
|---|---|---|---|---|---|
| Perimembranous | 80% | Membranous septum, beneath aortic valve | Bundle of His along posteroinferior rim | 30-40% | Most common overall |
| Muscular | 5-20% | Entirely within muscular septum | Low (remote from conduction) | 80-90% (small defects) | May be multiple ("Swiss cheese") |
| Outlet (supracristal) | 5-7% | Below both semilunar valves | Remote | Rarely | Aortic cusp prolapse → progressive AR |
| Inlet (AV canal-type) | 5-8% | Posterior septum, beneath tricuspid septal leaflet | Bundle of His along posteroinferior margin | Rarely | AVSD spectrum |
Hemodynamics
The magnitude of the left-to-right shunt is determined by defect size and pulmonary vascular resistance. A restrictive VSD is a small defect with a large pressure gradient, minimal shunt, and is often well-tolerated. A non-restrictive VSD is a large defect with equalized ventricular pressures and a significant left-to-right shunt. Chronic overcirculation leads to pulmonary vascular disease, and untreated, Eisenmenger syndrome develops with irreversible pulmonary hypertension and cyanosis.
Indications for Closure
Closure is indicated for a hemodynamically significant VSD with a Qp:Qs of 2:1 or greater and LV volume overload, symptoms such as heart failure, failure to thrive in infants, or dyspnea, outlet VSDs with aortic valve prolapse or aortic regurgitation (regardless of shunt size), and before progression of pulmonary vascular disease occurs. Eisenmenger syndrome with irreversible pulmonary hypertension is a contraindication to closure.
Surgical Repair
The standard approach uses median sternotomy, cardiopulmonary bypass, and moderate hypothermia. Access is typically through a right atriotomy with a trans-tricuspid approach for perimembranous and inlet VSDs. Right ventriculotomy is rarely used due to the risk of ventricular dysfunction and arrhythmia. The transpulmonary approach through the pulmonary valve is used for outlet/supracristal VSDs, and left ventriculotomy is reserved for certain apical muscular VSDs. Patch closure uses a Dacron or Gore-Tex patch with interrupted pledgeted sutures, with sutures placed on the RV side of the septum along the inferoposterior rim (away from the bundle of His) to avoid heart block. Direct suture closure is reserved for very small muscular VSDs. Device closure using Amplatzer devices is an option for select muscular VSDs, especially those with difficult surgical access.
<image>Ventricular septal defect types (perimembranous, muscular, outlet/supracristal, inlet) shown from the right ventricular aspect with relationship to the conduction system</image>
Conduction System Protection
Anatomy Relevant to VSD Repair
The bundle of His traverses the posteroinferior rim of perimembranous VSDs and passes on the left ventricular side of the septum. In inlet VSDs, the conduction runs along the posteroinferior rim. In outlet VSDs, the conduction system is generally remote from the defect.
Avoiding Heart Block
To protect the conduction system, sutures should be placed on the RV side of the septum posteroinferiorly, staying at least 3-5 mm from the crest of the septum at the posteroinferior margin. Suture bites should be superficial in the area of the conduction tissue, and pledgets are used to distribute force and avoid deep bites. Continuous intraoperative monitoring for conduction disturbances is essential. The complete heart block rate should be less than 1% in modern series (historically 1-3%). Transient heart block may recover within 7-10 days, but a permanent pacemaker is required if it persists.
<image>Surgical view of perimembranous VSD repair through right atriotomy showing patch placement with sutures placed away from the bundle of His at the posteroinferior margin</image>
Special Considerations
Spontaneous Closure
Small muscular VSDs close spontaneously in 80-90% of cases by age 2. Small perimembranous VSDs close or diminish in 30-40% of cases through tricuspid valve tissue aneurysm formation. Outlet VSDs rarely close spontaneously.
VSD with Aortic Regurgitation
In outlet (supracristal) VSDs, the right coronary cusp prolapses into the defect, and progressive aortic regurgitation develops if the VSD is not closed. Surgical closure is therefore recommended even for small outlet VSDs to prevent AR progression, and concurrent aortic valve repair may be needed if significant AR is already present.
Multiple VSDs
A "Swiss cheese" septum with multiple muscular VSDs presents a technically challenging surgical closure. A combined surgical and device approach may be required. Pulmonary artery banding serves as interim palliation in infants with uncontrollable heart failure.
Adults with VSDs
Residual or previously unrepaired VSDs may present in adulthood with risk of endocarditis, progressive AR, arrhythmia, and pulmonary hypertension. Surgical or device closure depends on anatomy, and pulmonary vascular resistance must be assessed before closure, as elevated PVR may preclude repair.
Clinical Pearls
The conduction system is the key vulnerability in VSD repair, and understanding its relationship to each defect type is essential to avoid heart block. Sinus venosus ASDs are almost always associated with anomalous pulmonary venous return, so PAPVR should always be sought on preoperative imaging. Primum ASDs require cleft mitral valve repair in addition to ASD patch closure -- this is not a simple ASD closure. Outlet VSDs require closure even when small and hemodynamically insignificant to prevent progressive aortic regurgitation. For perimembranous VSD patch closure, the golden rule is to stay on the right ventricular side of the septum posteroinferiorly to protect the bundle of His. Device closure is an excellent option for secundum ASDs with adequate rims and for muscular VSDs with difficult surgical access. Eisenmenger physiology must always be assessed before planning closure, as closing a defect in the presence of fixed elevated PVR can be fatal.
References
- Baumgartner H et al. "2020 ESC Guidelines for the management of adult congenital heart disease." Eur Heart J. 2021.
- Stout KK et al. "2018 AHA/ACC Guideline for the Management of Adults With Congenital Heart Disease." Circulation. 2019.
- Jacobs JP et al. "Congenital Heart Surgery Nomenclature and Database Project." Ann Thorac Surg. 2000.
- Butera G et al. "Transcatheter closure of perimembranous ventricular septal defects." JACC Cardiovasc Interv. 2007.
- Anderson RH et al. "The surgical anatomy of ventricular septal defects." J Card Surg. 2005.
