All forms of congenital heart defects can be classified into one of the following three broad groups. Most common are congenital heart defects in the form of short circuits with left-to-right shunts – most notably, ventricular septal defect in nearly one-third of cases. Less common are congenital heart defects with right-to-left shunt. The following is an overview of forms of congenital heart defects. The approximate frequency in % is given in parentheses (according to the “Competence Network for Congenital Heart Defects”).
Heart defects without shunt
- Pulmonary stenosis (7%): narrowing of the heart valve connected between the right ventricle and the pulmonary artery. Depending on the degree of severity, pulmonary stenosis results in increased stress on the right ventricle, which must fight increased outlet resistance. The consequence of pulmonary stenosis can be myocardial weakness of the right heart.
- Aortic stenosis (3-6%): aortic stenosis is a narrowing of the heart valve that separates the left ventricle from the aorta. Aortic stenosis places increased demands on the performance of the left heart muscle, which can be overloaded in the long term.
- Aortic isthmic stenosis (aortic coarctation, CoA; 5-8%): high-grade narrowing to constriction in the descending part of the aorta. Aortic coarctation also predominantly affects the left heart and causes hypertension in the head and arms. Typically, blood pressure measured at the legs is strikingly lower than at the arms in aortic isthmic stenosis.
Cardiac defects with left-to-right shunt
In these heart defects, oxygen-rich blood flows from the left heart to the right heart, that is, from the systemic to the pulmonary circulation. As a result, the right heart experiences increased workload.
- Atrial septal defect (ASD; 7%): a hole in the septum of the heart that separates the two atria represents the atrial septal defect. Since under normal circumstances higher pressures prevail in the left heart than in the right, part of the blood flow that should actually supply the organism is directed back to the right heart via the atrial septal defect. This part of the blood flow then circulates again and again through the pulmonary circulation without being available to the organism as a whole. In the long term, an atrial septal defect can result in pulmonary circulation overload with pulmonary hypertension and right heart muscle weakness.
- Ventricular septal defect (VSD; 31%): ventricular septal defect is characterized by a hole in the cardiac septum between the right and left ventricles. As with the atrial septal defect, in the ventricular septal defect a varying proportion of the blood flow returns via the septal hole to the right heart, whose muscle strength is unable to cope with the new pressure conditions. Chronic overload usually results in myocardial weakness of the right ventricle from a ventricular septal defect.
- Endocardial cushion defects (atrioventricular septal defect, AVSD; 4.8%): inadequate connection of muscle and connective tissue structures at the junction between atrial septum and ventricular septum in varying degrees. In extreme cases, an endocardial cushion defect has an open channel extending from the atrial septum to the ventricular septum, resulting in massive blood flow from left to right with stress on the right heart and pulmonary circulation.
- Persistent ductus arteriosus (PDA; 7%): the ductus arteriosus botalli is a short-circuit connection between the pulmonary artery and the aorta, which has the important function for the unborn child in the womb to conduct blood from the right heart past the non-functioning lung directly into the great circulatory system (the oxygenation of the fetal blood takes place in this phase namely via the mother’s lungs). If this short-circuit connection continues after birth, it favors the flow of blood from the left to the right heart, leading to right heart strain.
Cardiac defects with right-to-left shunt
In these heart defects, deoxygenated blood flows from the right heart into the left heart. As a result, the left heart is subjected to increased stress, and the oxygen level in the blood of the great circulatory system decreases, which is manifested as blue discoloration (cyanosis) of the lips and nails. These heart defects can be coupled with complex vascular malformations, causing blood flow to be different than normal – which in turn can lead to increased rather than decreased pulmonary blood flow.Right-to-left shunt with decreased pulmonary blood flow
- Tetralogy of Fallot (TOF; 5.5%): the combination of the following four (= tetra) malformations: Pulmonary stenosis, defective course of the aorta, ventricular septal defect, and increase in muscle thickness of the right ventricle. Since pulmonary stenosis obstructs the regular flow of blood to the pulmonary circulation, some of the deoxygenated blood from the right heart flows alternatively to the left, lowering the oxygen level in the great circulation. Chronic oxygen deficiency of all organs is the result of tetralogy of Fallot.
- Pulmonary atresia or tricuspid atresia (1-3%): defective formation of the pulmonary valve and/or tricuspid valve (valve between the right atrium and right ventricle). In these anomalies, part of the oxygen-depleted blood from the right heart must be diverted to the left heart via either an atrial septal defect or a ventricular septal defect. In individual cases, this involves pulmonary circulation predominantly from the aorta via a persistent ductus arteriosus into the pulmonary artery. In this heart defect, severe impaired circulation and hypoxia of the organs must also be expected.
Right-to-left shunt with increased pulmonary circulation.
- Transposition of the great arteries (TGA; 4.5%): in this complex malformation, the aorta mistakenly arises from the right ventricle and the pulmonary artery from the left ventricle. Thus, the small and large circulations are not connected in series but in parallel; the right heart supplies blood to the large circulation, the left to the small circulation. This heart defect is compatible with life only if additional short-circuit connections at the atrial or ventricular level ensure an exchange between the two circuits. Since the right ventricle must provide the pressure of the large circuit, the right heart can be expected to fail soon.
- Total pulmonary vein malocclusion (TAPVC; < 1%): in this case, the pulmonary veins open into the right atrium instead of the left. The anomaly requires an additional short-circuit connection between the right and left hearts to allow exchange between the small and large circulations and stresses both the pulmonary circulation and the right heart.
- Double outlet right ventricle (DORV;1.2%): origin of both great arteries from the right ventricle): The left heart is involved in the circulation via a defect in the cardiac septum. Since the right heart must supply both circuits simultaneously, its overload with right heart failure is inevitable.
- Double inlet left ventricle (Singular ventricle, DIVM 1.5%): in this anomaly, instead of a right and left ventricle, only one ventricle exists, from which follow both problems of oxygen saturation of the blood and blood circulation with myocardial weakness.
- Hypoplastic left heart syndrome (HLHA; 3.8%): inadequately formed left ventricle that cannot perform its normal function. As a result, blood flow to the great circulation must come from the right heart via the ductus arteriosus. This very rare anomaly is not compatible with life under any circumstances.
