Etiology: heredity and teratogens
The development of vitium cordis congenitum is always viewed as the result of a complex interaction between genetic predispositions and aggressive environmental factors.
First, hereditary factors play a huge role. It has been proven that genetic mutations are of fundamental importance in the origin of atrial septal defects. Interestingly, for ventricular septal defects, the influence of genetics is not as straightforward and is significantly less pronounced.
Second, the teratogenic impact of external factors on the pregnant woman's body is of critical importance. The most dangerous triggers include:
- Infectious diseases contracted during gestation (viral agents pose a particular threat to embryonic heart development).
- Chronic intoxications associated with the mother's lifestyle: alcohol abuse, tobacco smoking, and drug use.
- Pharmacological aggression: the intake of certain specific pharmacological drugs that have a proven negative effect on the developing fetus.
Pathophysiology and clinical manifestations
The severity of the disease course and the prominence of the clinical presentation directly depend on the size of the anatomical defect.
If the defects are small, the disease may remain completely asymptomatic for a long time. Patients have no complaints, and hemodynamic disturbances are minimal and successfully compensated by the body.
A completely different picture is observed with large defects. In this case, pronounced circulatory disorders develop. The key pathophysiological mechanism is a massive left-to-right blood shunt. Due to constant volume and pressure hemodynamic overload, compensatory myocardial hypertrophy of both ventricles develops. Objectively, upon examination and auscultation of such a patient, the physician detects a harsh systolic murmur, which is often accompanied by a palpable thrill on the chest wall.
Atrial septal defects
Among all variants of structural integrity disruption of the septum dividing the right and left atria, defects localized in the middle and upper parts of this anatomical structure are most frequently encountered in clinical practice.
Transposition of the great arteries
This is a severe developmental defect, the essence of which lies in the incorrect, altered position of the main blood vessels relative to the heart chambers. Globally, two forms of the pathology are distinguished: corrected and uncorrected.
In uncorrected transposition, the great arteries are displaced in such a way that the systemic and pulmonary circulations are completely isolated from each other:
- The aorta anatomically arises from the right ventricle. As a result, it carries venous, oxygen-depleted blood into the systemic circulation.
- The pulmonary artery originates from the left ventricle. It directs arterial (already oxygen-saturated) blood back into the pulmonary circulation, i.e., into the lungs.
Such anatomy is incompatible with the newborn's life. Survival is possible exclusively if additional pathways for blood mixing (shunts between circulations) are present in the heart. Concomitant atrial or ventricular septal defects, as well as a patent ductus arteriosus, can serve as such lifesaving shunts.
Briefly: answers to topical questions
What forms of transposition of the great arteries exist and what is their anatomical essence?
There are two main forms of transposition of the great arteries: uncorrected and corrected.
- Uncorrected form — the aorta arises from the right ventricle containing venous blood, and the pulmonary artery originates from the left ventricle with arterial blood.
- Corrected form (CCTGA) — characterized by atrioventricular and ventriculoarterial discordance. The aorta arises from the right-sided ventricle containing arterial blood, and the pulmonary artery originates from the left-sided ventricle containing venous blood.
In the uncorrected form, a parallel circulation is formed that is incompatible with life without a shunt, whereas in the corrected form, blood circulation remains physiological.
Which specific maternal viral infections have a proven teratogenic effect on the fetal heart?
Rubella virus has a proven teratogenic effect on the fetal heart. When the mother is infected in the first trimester of pregnancy, this virus causes classic congenital rubella syndrome, which includes the triad of defects: cataract, deafness, and congenital heart defects. The most frequent cardiovascular anomalies in rubella include:
- Patent ductus arteriosus — persistence of the ductus arteriosus.
- Pulmonary trunk stenosis.
- Ventricular septal defects — the presence of communication between the ventricles.
In addition, in viral damage during the first trimester, the formation of areactive necroses in the endocardium and subendocardial layers has been described.
What anatomical variants of ventricular septal defects are distinguished depending on localization?
Depending on localization, two main anatomical variants of ventricular septal defects are distinguished: perimembranous and muscular.
- Perimembranous defects — the most frequent localization, accounting for about 80% of all cases. Many small defects in this area are capable of closing spontaneously.
- Muscular defects — located in the muscular part of the septum, which is anatomically divided into three parts:
- Inlet (inlet);
- Outlet, or subarterial (outlet);
- Mid-muscular (midmuscular) and apical.
Patient management tactics directly depend on the type and size of the identified defect.
What developmental anomalies are included in the classic tetralogy of Fallot?
The classic tetralogy of Fallot includes four anatomical components.
- Ventricular septal defect — usually a high septal defect.
- Dextroposition of the aorta — displacement of the aorta to the right ("overriding aorta"), in which it is located above the septal defect and receives blood simultaneously from both ventricles.
- Pulmonary stenosis — narrowing of the infundibulum or the outflow tract of the right ventricle.
- Right ventricular hypertrophy.
This symptom complex is the most frequent cyanotic heart defect and is accompanied by pronounced cyanosis, the presence of which depends on the degree of pulmonary outflow tract stenosis.
To understand the hemodynamics of uncorrected transposition, imagine two isolated loops: the right ventricle idly pumps dark venous blood through the body, and the left pumps bright red arterial blood through the lungs. Without a "bridge" (shunt defect), the system is doomed.
Class and exam questions
What is the role of genetics in the development of various cardiac septal defects?
Genetic factors have a primary, decisive role in the formation of atrial septal defects. At the same time, in ventricular septal defects, their influence is significantly weaker.
How does the size of the defect affect the clinical presentation of the anomaly?
Defect size is the main factor determining the severity of the condition. Small anomalies may not produce any clinical manifestations, whereas large ones lead to pronounced circulatory disorders, hypertrophy of both ventricles, the appearance of a systolic murmur, and a thrill.
What is the core mechanism of uncorrected transposition of the great arteries?
In this defect, the aorta arises from the right ventricle and carries venous blood to the organs, while the pulmonary artery arises from the left ventricle, returning arterial blood to the lungs. The circulations are completely separated.
What mechanism enables infant survival in uncorrected transposition of the great vessels?
The patient's life is possible only in the presence of additional shunting between the systemic and pulmonary circulations. This blood mixing occurs through concomitant atrial or ventricular septal defects, or through a patent ductus arteriosus.
What else to study on this topic
- Ventricular septal defects: features of pathogenesis
- Corrected form of transposition of the great arteries
- Classification of congenital heart defects
- Mechanisms of formation of systolic murmur and thrill
- The role of patent ductus arteriosus in hemodynamic compensation
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