Ventricular septal defect (VSD)
A ventricular septal defect (pronounced ven·tric·u·lar sep·tal de·fect) (VSD) is a birth defect of the heart in which there is a hole in the wall (septum) that separates the two lower chambers (ventricles) of the heart. This wall also is called the ventricular septum.
Congenital VSDs occur in various parts of the ventricular septum. Membranous and muscular septal defects may spontaneously close in childhood as the septum grows and hypertrophies. A left-to-right shunt is present, the degree depending on associated RV pressure. The smaller the defect, the greater the gradient from the LV to the RV and the louder the murmur.
The presentation in adults depends on the size of the shunt and whether there is associated pulmonic or subpulmonic stenosis that has protected the lung from the systemic pressure and volume.
Unprotected lungs with large shunts invariably lead to pulmonary vascular disease and severe pulmonary hypertension (Eisenmenger physiology). VSD sizes are defined by comparison to the aortic root size; a small or restrictive VSD diameter is less than 25% of the aortic root diameter, a moderately restrictive VSD diameter is 25–75% of the aorta, and an unrestricted VSD size is greater than 75% of the aortic diameter. The size can also be quantitated based on the Qp/Qs (left-to-right shunt), with a restrictive lesion being less than 1.5:1, moderately restrictive VSD being 1.5–2.2:1, and an unrestricted lesion being greater than 2.2:1.
Types of Ventricular Septal Defects
An infant with a ventricular septal defect can have one or more holes in different places of the septum. There are several names for these holes. Some common locations and names are
- Conoventricular Ventricular Septal Defect
In general, this is a hole where portions of the ventricular septum should meet just below the pulmonary and aortic valves.
- Perimembranous Ventricular Septal Defect
This is a hole in the upper section of the ventricular septum.
- Inlet Ventricular Septal Defect
This is a hole in the septum near to where the blood enters the ventricles through the tricuspid and mitral valves. This type of ventricular septal defect also might be part of another heart defect called an atrioventricular septal defect (AVSD).
- Muscular Ventricular Septal Defect
This is a hole in the lower, muscular part of the ventricular septum and is the most common type of ventricular septal defect.
Symptoms and Signs
The clinical features depend on the size of the defect and the presence or absence of RV outflow obstruction or increased PVR. Small shunts are associated with loud, harsh holosystolic murmurs in the left third and fourth interspaces along the sternum. A systolic thrill is common. Larger shunts may create both LV and RV volume and pressure overload.
If pulmonary hypertension occurs, high-pressure pulmonary valve regurgitation may result.
Right heart failure may gradually become evident late in the course, and the shunt will begin to balance or reverse as RV and LV systolic pressures equalize with the advent of pulmonary hypertension.
Cyanosis from a developing right-to-left shunt may then occur. Cyanosis with pulmonary hypertension and an intracardiac shunt define the Eisenmenger syndrome.
Echocardiography can demonstrate the size of the overloaded chambers and can usually define the defect anatomy. Doppler can qualitatively assess the magnitude of shunting by noting the gradient from LV to RV and, if some tricuspid regurgitation is present, the RV systolic pressure can be estimated. The septal leaflet of the tricuspid valve may be part of the VSD anatomy and the complex appears as a ventricular septal “aneurysm.” These membranous septal aneurysms resemble a “windsock” and may fenestrate and result in a VSD shunt being present or they may remain intact. Color flow Doppler helps delineate the shunt severity and the presence of valvular regurgitation. MRI and cardiac CT can often visualize the defect and describe any other anatomic abnormalities. MRI can provide quantitative shunt data as well.
Cardiac catheterization is usually reserved for those with at least moderate shunting, to quantitate the PVR and the degree of pulmonary hypertension. A PVR of greater than 7.0 absolute units or a PVR/systemic vascular resistance ratio or a systolic PA pressure/systolic aortic pressure ratio greater than 0.67 (two-thirds) generally means the patient’s VSD is inoperable. The vasoreactivity of the pulmonary circuit may be tested at catheterization using agents such as inhaled nitric oxide, and if the pulmonary pressures can be lowered enough that the above ratios fall below the two-thirds value, then repair is reasonable as long as the left-to-right VSD shunt is greater than 1.5:1.
ECG and Chest Radiography: The ECG may be normal or may show right, left, or biventricular hypertrophy, depending on the size of the defect and the PVR. With large shunts, the LV, the LA, and the pulmonary arteries are enlarged and pulmonary vascularity is increased on chest radiographs. The RV is often normal until late in the process. If an increased PVR (pulmonary hypertension) evolves, an enlarged PA with pruning of the distal pulmonary vascular bed is seen. In rare cases of a VSD high in the ventricular septum, an aortic cusp (right coronary cusp) may prolapse into the VSD and reduce the VSD shunt but result in acute aortic regurgitation and acute heart failure.
The ACC/AHA guidelines for the management of patients with VSD include the following:
- Medical management (class IIb recommendation [benefit exceeds risk and may be considered]): Pulmonary vasodilatory therapy is appropriate for adults with a VSD and severe pulmonary hypertension. The response to inhaled nitric oxide is used to guide which agent would be the best option (Level of evidence [LOE] C).
- Surgical management (class I recommendation; LOE B): Closure is indicated when the left-to-right shunt ratio is greater than 2.0 or there is clinical LV volume overload. In addition, closure is recommended if there has been a history of infective endocarditis.
- Surgical management (class IIb recommendation; LOE C): Closure is reasonable if the left-to-right shunt is greater than 1.5 and pulmonary systolic pressure or the PVR is less than two-thirds systemic values, or both. Closure is also reasonable if the shunt ratio is greater than 1.5 with evidence of LV dysfunction.
Small shunts (pulmonary-to-systemic flow ratio less than 1.5) in asymptomatic patients do not require surgery or other intervention. The presence of RV infundibular stenosis or pulmonary valve stenosis may protect the pulmonary circuit such that some patients, even with a large VSD, may still be surgical candidates as adults if there is no pulmonary hypertension.
Surgical repair of a VSD is generally a low-risk procedure unless there is significant Eisenmenger physiology. Devices for nonsurgical closure of muscular VSDs are approved and those for membranous VSDs are being implanted with promising results; however, conduction disturbance is a major complication. The percutaneous devices are also approved for closure of a VSD related to acute myocardial infarction, although the results in this very high-risk patient population have not been encouraging. The medications used to treat pulmonary hypertension secondary to VSD are similar to those used to treat idiopathic (“primary”) pulmonary hypertension and at times can be quite effective in relieving symptoms and cyanosis.