The most common abnormalities that occur during development are those produced by a defect in the atrial and ventricular septa.
A defect in the interatrial septum allows blood to pass from one side of the heart to the other from the chamber with the higher pressure to the chamber with the lower pressure; this is clinically referred to as a shunt. An atrial septal defect (ASD) allows oxygenated blood to flow from the left atrium (higher pressure) across the ASD into the right atrium (lower pressure), resulting in a left to right shunt and volume overload in the right-sided circulation. Many patients with ASD are asymptomatic, but in some cases the ASD may cause symptoms and needs to be closed surgically or by endovascular devices. Occasionally, increased blood flow into the right atrium over many years leads to right atrial and right ventricular hypertrophy and enlargement of the pulmonary trunk, resulting in pulmonary arterial hypertension. In such cases, the patients can present with shortness of breath, increasing tiredness, palpitations, fainting episodes and heart failure. In ASD, the left ventricle is not enlarged as it is not affected by increased returning blood volume.
The most common of all congenital heart defects are those that occur in the ventricular septum—ventriculoseptal defect (VSD). These lesions are most frequent in the membranous portion of the septum and they allow blood to flow from the left ventricle (higher pressure) to the right ventricle (lower pressure), leading to an abnormal communication between the systemic and pulmonary circulation. This leads to right ventricular hypertrophy, increased pulmonary blood flow, elevated arterial pulmonary pressure, and increased blood volume returning to the left ventricle, causing its dilation. Increased pulmonary pressure in most severe cases may cause pulmonary edema. If large enough and left untreated, VSDs can produce marked clinical problems that might require surgery. VSD may be an isolated abnormality or part of a syndromic constellation, such as the tetralogy of Fallot.
The tetralogy of Fallot, the most common cyanotic congenital heart disorder diagnosed soon after birth, classically consists of four abnormalities: pulmonary stenosis, VSD, overriding aorta (originating to a varying degree from the right ventricle), and right ventricular hypertrophy. The underdevelopment of the right ventricle and pulmonary stenosis reduce blood flow to the lungs, leading to reduced volume of oxygenated blood returning to the heart. The defect in the interventricular septum causes mixing of oxygenated and nonoxygenated blood. The mixed blood is then delivered by the aorta to the major organs, resulting in poor oxygenation and cyanosis. Infants can present with cyanosis at birth or develop episodes of cyanosis while feeding or crying (tet spells). Most affected infants require surgical intervention. The advent of cardiopulmonary bypass was crucial in delivering highly satisfactory surgical results.
Occasionally, the ductus arteriosus, which connects the left branch of the pulmonary artery to the inferior aspect of the aortic arch, fails to close at birth. This is termed a patent or persistent ductus arteriosus (PDA). When this occurs, the oxygenated blood in the aortic arch (higher pressure) passes into the left branch of the pulmonary artery (lower pressure) and produces pulmonary hypertension and left atrial and ventricular enlargement. The prognosis in patients with isolated PDA is extremely good, as most do not have any major sequelae after surgical closure.
All of these defects produce a left-to-right shunt, indicating that oxygenated blood from the left side of the heart is being mixed with deoxygenated blood from the right side of the heart before being recirculated into the pulmonary circulation. These shunts are normally compatible with life, but surgery or endovascular treatment may be necessary.
Rarely, a shunt is right-to-left. In isolation, this is fatal; however, this type of shunt is often associated with other anomalies, so some deoxygenated blood is returned to the lungs and the systemic circulation.
In the clinic