Hemodynamic changes
The pathophysiology of the defect is directly related to the presence of the abnormal opening. Basic blood flow disturbances develop in a specific sequence:
- Direction of shunting: initially, blood shunts from left to right—from the left atrium to the right atrium.
- Volume overload: the influx of additional blood into the right heart leads to hypervolemia of the pulmonary circulation.
- Morphological changes: the right atrium and right ventricle progressively enlarge (dilatation) and increase in muscle mass (hypertrophy).
- Long-term consequences: pulmonary hypertension develops over time. In late stages of the disease, the direction of the blood shunt can reverse completely—from right to left.
Clinical presentation and auscultation
Clinical manifestations are often associated with right heart overload. Patients complain of dyspnea and note poor exercise tolerance. Objective examination reveals signs of dilatation and hypertrophy of the right heart chambers.
The auscultatory findings are of utmost diagnostic value:
- Changes in S2: a fixed splitting of the second heart sound is heard. This is a highly specific sign, as the splitting does not vary with respiratory phases.
- Systolic murmur in the second intercostal space: heard over the pulmonary artery. Important nuance: its mechanism is not related to blood passing through the septal defect itself. The murmur occurs due to relative stenosis of the pulmonary outflow tract, as the right ventricle ejects a pathologically large volume of blood through it.
- Late manifestations: with progression of the defect and marked right ventricular dilatation, a systolic murmur of tricuspid regurgitation may appear.
Instrumental diagnostics
To confirm the diagnosis and assess the severity of hemodynamic disturbances, a set of instrumental examinations is used:
- Electrocardiography (ECG): registers right axis deviation (RAD) along with classic signs of right ventricular hypertrophy.
- Chest X-ray: visualizes enlargement of the right atrium and right ventricle. Vascular markings show dilatation of the main pulmonary artery and its branches.
- Echocardiography (EchoCG): directly visualizes enlargement of the right ventricle and pulmonary artery. A characteristic EchoCG sign is anterior systolic motion of the interventricular septum.
- Doppler ultrasonography: used for non-invasive confirmation of the diagnosis by visualizing pathological blood shunting (according to some diagnostic protocols, a right-to-left flow is recorded).
Briefly: answers to topical questions
What types of atrial septal defects are distinguished based on anatomical location?
Based on anatomical location, there are five main types of atrial septal defects. These include:
- Superior sinus venosus defect (Superior sinus venosus defect).
- Inferior sinus venosus defect (Inferior sinus venosus defect).
- Secundum ASD (Secundum ASD) — located in the region of the fossa ovalis.
- Primum ASD (Primum ASD) — located in the lower part of the septum, adjacent to the atrioventricular valves.
- Coronary sinus defect (Coronary sinus defect).
What is the name of the syndrome that develops when the shunt direction changes to right-to-left due to severe pulmonary hypertension?
The condition in which high pressure in the pulmonary artery leads to shunt reversal is called Eisenmenger syndrome. This syndrome develops as a complication of uncorrected congenital heart defects, including large atrial septal defects with a diameter of 2 cm or more. Pulmonary artery pressure exceeds systemic pressure, resulting in a change of the blood shunt direction to right-to-left or the formation of bidirectional shunting. Clinically, this is accompanied by the development of cyanosis and secondary erythrocytosis.
What echocardiographic (EchoCG) signs are detected in atrial septal defect?
Echocardiography reveals signs of dilatation and hypertrophy of the right heart chambers due to volume overload. The main instrumental EchoCG signs of atrial septal defect include:
- Visualization of right ventricular (RV) and pulmonary artery trunk enlargement.
- Presence of a dilated and hypertrophied right ventricle (RV).
- Systolic anterior motion of the interventricular septum.
- Visualization of abnormal blood shunting (flow from the right atrium to the left) during Doppler sonography.
For ASD auscultation, remember the "Two NOTs" rule: the systolic murmur does NOT occur due to the defect itself (but due to relative stenosis), and the splitting of the second heart sound does NOT depend on respiration (it is fixed).
Class and exam questions
Why is the murmur in ASD auscultated over the pulmonary artery rather than at the defect projection?
Blood flows through the defect without a significant pressure gradient, so the shunt itself is silent. The murmur occurs because a huge volume of blood entering the right ventricle rushes into the pulmonary artery, creating its relative stenosis.
How does blood shunting change in late stages?
Due to the development of severe pulmonary hypertension, the pressure in the right heart chambers may exceed the pressure in the left. At this point, the blood shunt changes direction and becomes right-to-left.
What ECG axis changes are characteristic of this defect?
Since the main load falls on the right ventricle, it hypertrophies. On the ECG, this manifests as a right axis deviation.
What else to study on this topic
- Mechanism of fixed splitting of the second heart sound
- Causes of relative pulmonary artery stenosis in hypervolemia
- Pathogenesis of shunt direction change in late stages
- EchoCG analysis: why the interventricular septum shifts anteriorly
- Differences between the tricuspid regurgitation murmur and the relative stenosis murmur
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