The atria and ventricles of the right and left hearts are each separated by a wall. A hole in these septums can cause serious impairment of cardiovascular function. You can read more about what exactly a cardiac septal defect is, how to recognize it, and what to do in such a case here.
What is a cardiac septal defect?
The cardiac septum, which can reach several millimeters in thickness, separates the cavities of the right heart from those of the left. Here, the right atrium and right ventricle are part of the so-called low-pressure system in the circulation, through which oxygen-depleted venous blood flows to the heart and, after passing through the atrium and ventricle, is pumped into the pulmonary circulation.
After saturation with oxygen in the lungs, the now oxygen-rich, bright red blood flows into the arterial high-pressure system fed by the left heart. Consequently, the cardiac septa also represent interfaces between two systems with different pressure ratios. A fact that is important for understanding the sequelae of septal defects is that cardiac septal defects are nothing more than holes of different sizes between the atria or ventricles that create short-circuit connections for blood flow between the high-pressure and low-pressure systems.
Causes of cardiac septal defects
In the vast majority of cases, genetic causes underlie cardiac septal defects. During the early developmental period of the unborn child in the womb, this genetic damage leads to a wide variety of malformations of the heart, some of which also result in cardiac septal defects. In rare cases, cardiac septal defects are also acquired later in life, with a major myocardial infarction usually being responsible for the defect.
Forms of cardiac septal defect.
Cardiac septal defects appear either as isolated cardiac defects or in association with other complex malformations of the heart and the great vessels near the heart. Depending on the localization, a distinction is made between
- Defects of the atrial septum (ASD = atrial septal defect); the third most common congenital heart defect in adolescents and adults.
- Defects of the ventricular septum
Atrial septal defect
Due to higher pressures in the left atrium, a hole in the atrial septum causes blood flow to pass directly from the left atrium to the right atrium – the amount depends on the size of the defect, among other factors. As a result of this short circuit, some of the already oxygen-saturated blood flows directly back to the right heart and thus to the small circulation, without being able to contribute to the perfusion of the organs in the large circulation. This means, above all, that a higher pressure is created in the pulmonary circulation due to the increased blood volume.
Ultimately, the size of the defect in the septum is decisive for the resulting load of the small circulation with a disproportionate amount of blood. Particularly small holes in the cardiac septum can last a lifetime without causing any problems. In the case of large defects, increased stress on the right heart and pulmonary circulation, which have to cope with the additional blood flow via the defect in the septum, must be expected already in childhood. In the longer term, there is a risk of myocardial weakness of the right ventricle, which is overtaxed, as well as pulmonary hypertension, which in turn increases the burden on the right heart.
Ventricular septal defect
The pressure differences between the left and right ventricles are even more pronounced than at the atrial level, so a markedly developed ventricular septal defect results in even greater blood flow from left to right and even greater stress on the right heart than in the atrial septal defect.
In particularly large ventricular septal defects, shunt reversal may occur. In this case, the resistance in the small circuit and the pressure in the right heart increase so much due to the constant additional load that the pressure in the right eventually exceeds the pressure in the left heart. Under these conditions, the blood flow changes direction and now flows from right to left. This means that it is insufficiently oxygenated.
Once shunt reversal has occurred, it marks an extremely unfavorable turning point in the course of the disease, since from this point on heart surgery no longer has any chance of success.
