Atrial Septal Defect

The atrial septal defect (ASD) is the most common congenital heart defect encountered in adults, accounting for up to 15% of all adult CHD (Fig. 1). It results from the failure of proper embryologic development of the atrial septum. There are many different types of ASD (Fig. 2), the most common of which is the secundum ASD, in which the defect occurs in the middle of the atrial septum.

Figure 1 Atrial septal defect (ASD).

An ASD is the most common congenital heart defect encountered in adults, accounting for up to 15% of all adult congenital heart disease.

Figure 2 Types of atrial septal defect.

The flow of blood across the defect (shunt) is determined by the size of the defect and the compliance of the atria. ASD should be suspected whenever right heart enlargement is present without an alternative explanation. Occasionally, patients present late in life with ASD-related symptoms when the left atrial pressure increases because of a stiff left ventricle and diastolic dysfunction, usually the result of long-standing hypertension or coronary artery disease, resulting in increased shunt.

The larger the left-to-right shunt is in patients with ASD, the greater is the risk for long-term complications, such as atrial fibrillation and pulmonary hypertension. The latter condition affects up to 15% of adults with ASD and, if it remains uncorrected, it can result in Eisenmenger’s syndrome (see later). Another condition associated with ASD is stroke, which presumably results from paradoxical embolization—blood clots forming in the extremities and reaching the cerebral circulation by passing through the ASD.

Other, less-common variations of ASD include the sinus venosus ASD, in which there is abnormal fusion of the vena cava (superior or inferior) to the left atrium. This defect is almost always associated with partial anomalous return of the pulmonary veins (right superior or both right pulmonary veins drain into the right atrium). The primum ASD involves the lower portion of the atrial septum and typically affects the ventricular septum as well (the atrioventricular [AV] canal defect). Both AV valves are structurally abnormal, and the mitral valve is typically cleft. The least common form of ASD involves unroofing of the coronary sinus, which results in shunting into the left atrium. At this time, only the secundum ASD has been successfully occluded through percutaneous means.

Ventricular Septal Defect

Ventricular septal defect (VSD) is the most common congenital heart defect seen in children (Fig. 3). Defects can occur at various locations in the septum but most commonly occur in the membranous (Fig. 4) or muscular portions. Small defects often close spontaneously during childhood. One type of defect, the outflow (or supracristal) VSD, can be spontaneously occluded by one of the aortic leaflets prolapsing into it. This can result in the development of significant aortic insufficiency.

Figure 3 Types of ventricular septal defect (VSD).

VSD is the most common congenital heart defect seen in children.

Figure 4 Membranous ventricular septal defect.

Defects can occur at various locations in the septum, but they most commonly occur in membranous or muscular portions.

Small VSDs are usually asymptomatic, whereas larger defects are more likely to manifest during childhood with heart failure. VSD is the most common cause of Eisenmenger’s syndrome.

Patent Ductus Arteriosus

Patent ductus arteriosus (PDA; Fig. 5) is the second most common congenital heart defect seen in adults (approximately 10%-15% of all CHD in adults). PDA is present as an isolated lesion in most adults, unlike in children, in whom it is often seen with more complex heart defects. The ductus connects the descending aorta at the level of the subclavian artery to the proximal left pulmonary artery. As in VSD, patients with a large uncorrected PDA can develop pulmonary hypertension.

Figure 5 Patent ductus arteriosus.

This is the second most common congenital heart defect seen in adults.

Pulmonary Stenosis

Pulmonary stenosis is the most common congenital valve lesion that requires therapy in adults (Fig. 6). Gradients across the pulmonary outflow tract usually occur at the valvular level, but it can also involve the infundibulum (right ventricular outflow tract), peripheral pulmonary arteries, or both. Complications of pulmonary stenosis include right ventricular hypertrophy and eventually failure, as well as arrhythmias.

Figure 6 Pulmonary valve stenosis.

Excluding mitral valve prolapse and bicuspid aortic valve, this is the most common congenital valve lesion requiring therapy in adults.

Coarctation of the Aorta

Coarctation of the aorta (CoA) is a common congenital heart defect (Fig. 7) accounting for approximately 8% of all congenital defects. It probably results from extraneous ductal tissue that contracts following birth. Anatomically, it can occur before, at the level of, or after the ductus arteriosus, although adults with previously undiagnosed CoA almost always have postductal lesions. The most common way it is identified in adults is fortuitous discovery during secondary workup for systemic hypertension. Lower extremity and renal hypoperfusion lead to a hyper-renin state that might not abate, even after coarctation repair. In most patients, there is upper extremity hypertension and the development of collateral vessels around the coarctation to the lower extremity.

Figure 7 Coarctation of the aorta.

This common congenital heart defect accounts for approximately 8% of all congenital defects.

Transposition of the Great Arteries

Transposition of the great arteries (TGA; Fig. 8) refers to an abnormality in the developmental separation of the great vessels, which results in the aorta emanating from the venous ventricle and the pulmonary artery coming off the systemic ventricle (ventriculoarterial discordance). Two varieties are most commonly seen in adults. The first type is dextrotransposition of the great arteries (D-TGA), with “dextro” initially meant to describe the location of the aorta in respect to the pulmonary artery. In this condition, the right ventricle gives rise to the aorta and the left ventricle gives rise to the pulmonary artery, but both atria are appropriately connected to their respective ventricles (AV concordance). This condition is not compatible with life unless there is a naturally occurring shunt (ASD, VSD, or PDA) or surgically created shunt. Often, these patients have undergone repair during childhood with a Senning or Mustard procedure, in which blood is baffled from the venae cavae to the left atrium and from the pulmonary veins to the right atrium (Fig. 9). The primary long-term concern in these patients is that the right ventricle is ill prepared to serve as the systemic ventricle. It can weaken and fail over time (usually when the patient enters the third or fourth decade), and these patients also develop significant systemic AV regurgitation, with the tricuspid valve in the mitral position.

Figure 8 Transposition of the great arteries (TGA).

This refers to an abnormality in the developmental separation of the great vessels, which results in the aorta emanating from the venous ventricle and the pulmonary artery coming off the systemic ventricle (ventriculoarterial discordance). In D-TGA, the ventricles are located in their normal anatomic positions (atrioventricular concordance), and in L-TGA, the ventricles are also discordant with the atria.

Figure 9 Mustard procedure for dextrotransposition of the great arteries.

In this procedure, blood is baffled from the venae cavae to the left atrium and from the pulmonary veins to the right atrium.

The other type of TGA is the congenitally (naturally) corrected lesion, levotransposition of the great arteries (L-TGA). In this case, the ventricles are also inverted (both AV and ventriculoarterial discordance are present). This variation (see Fig. 8) results in a circulation in which blood flows from vena cava to right atrium to left ventricle to pulmonary artery to pulmonary veins to left atrium to right ventricle to aorta. Again, the problem remains a right ventricle pumping into the systemic circulation. This condition is also associated with about a one in three lifetime prevalence of complete heart block.

Tetralogy of Fallot

Tetralogy of Fallot (TOF), a conotruncal abnormality, is a constellation of four findings: an aorta that overrides the right ventricular outflow tract; right ventricular outflow obstruction; a large subaortic VSD; and hypertrophy of the right ventricle (Fig. 10). The frequent coexistence of an ASD can make for a pentalogy. Occasionally, patients with unrepaired TOF only present in adulthood because of a remarkable balance between the pulmonic obstruction and the VSD, which limits cyanosis.

Figure 10 Tetralogy of Fallot.

This conotruncal abnormality is the constellation of four findings: an aorta that overrides the right ventricular outflow tract, right ventricular outflow obstruction, a large subaortic ventricular septal defect, and hypertrophy of the right ventricle.

Early palliation with a systemic-to-arterial shunt (e.g., Blalock-Taussig), which connects the subclavian and pulmonary arteries (Fig. 11), facilitates growth of the pulmonary arteries and is a precursor to definitive surgical repair in the young child. Definitive repair often involves complete removal of the pulmonic valve (Fig. 12) and therefore results in wide open pulmonic regurgitation. Although the repair is tolerated for several years, the right ventricle eventually succumbs to volume overload and progressively increases in size.

Figure 11 Blalock-Taussig shunt.

This connects the subclavian and pulmonary arteries.

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