| disease | Corrected Transposition of the Great Arteries |
Normally, the primitive heart tube bends to the right, hence called the D-loop, positioning the right ventricle on the right and anterior side, while the left ventricle is located on the left and posterior side. If during development the heart tube bends to the left instead of the right, known as the L-loop, the anatomical right ventricle is positioned on the left posterior side, becoming the ventricle of the arterial system, while the anatomical left ventricle is located on the right anterior side, becoming the ventricle of the venous system. In this case, the arterial trunk still undergoes septation and rotation but in an inverted position. As a result, the pulmonary artery is positioned on the right posterior side, and the ascending aorta is on the left anterior side. Despite the reversal of the great vessel positions, the pulmonary artery remains connected to the venous ventricle, and the aorta is connected to the arterial ventricle, physiologically correcting the blood flow direction. This condition is termed corrected transposition of the great arteries. The left and right branches of the atrioventricular conduction bundle still distribute to their respective anatomical ventricles, but due to the ventricular position inversion, the conduction bundle is also inverted.
bubble_chart Pathological Changes
The blood from the superior and inferior vena cava returns to the normal right atrium, enters the dextropositioned ventricle through the bicuspid atrioventricular valve, and is then pumped into the pulmonary stirred pulse. The blood from the pulmonary veins returns to the normal left atrium, enters the levopositioned ventricle through the tricuspid atrioventricular valve, and is then pumped into the aortic stirred pulse. The internal structure of the dextropositioned ventricle is the same as that of a normal left ventricle, while the internal structure of the levopositioned ventricle is the same as that of a normal right ventricle. Although the positions of the left and right ventricles are reversed, the direction of blood flow still meets the requirements of normal systemic and pulmonary circulation due to the corresponding misalignment of the great stirred pulse. If no other malformations are present, there may be no symptoms. However, most clinical cases are accompanied by other malformations, commonly including ventricular septal defects, pulmonary stirred pulse stenosis, insufficiency of the left atrioventricular valve, aortic stirred pulse orifice stenosis, pre-excitation syndrome, atrioventricular block, and paroxysmal tachycardia.
bubble_chart Clinical Manifestations
It mainly depends on the associated cardiac malformations. According to different malformations, the common clinical manifestations are:
1. Left-to-right shunt group: Accompanied by ventricular septal defect, often presenting with dyspnea, reduced activity, failure to thrive, pulmonary infections, and heart failure. Signs are similar to ventricular septal defect.
2. Right-to-left shunt group: Accompanied by pulmonary stenosis, commonly presenting with cyanosis and hypoxic episodes.
3. Left atrioventricular valve insufficiency group: With an intact ventricular septum, the murmur is loudest at the 4th intercostal space near the sternum rather than at the apex, often accompanied by arrhythmias.
bubble_chart Auxiliary Examination
Chest X-ray: There is a slightly oblique ascending aortic shadow at the upper left border of the heart, with absence of the pulmonary artery shadow. Abnormal cardiac positions are observed, such as dextrocardia with normal visceral situs, mesocardia, or levocardia with visceral inversion.
Electrocardiogram (ECG): Atrial arrhythmias and abnormal ventricular depolarization are the main features. Atrioventricular block accounts for about one-third of cases, along with atrioventricular dissociation, junctional arrhythmias, paroxysmal tachycardia, and ventricular premature beats.
Echocardiography: There is no connection between the posterior atrioventricular valve (tricuspid valve) and the semilunar valves. The semilunar valves are located in a left-anterior and right-posterior plane. Systolic time intervals may indicate that the anterior great artery connects to the systemic circulation, while the posterior great artery flows into the lungs.
Right heart catheterization and angiography: This can reveal the contours, positions, and interrelationships of the ventricles and great arteries, as well as shunt conditions, thereby confirming the diagnosis.bubble_chart Treatment Measures
(1) Medical Treatment The main focus is on controlling heart failure and arrhythmias, but the effectiveness is limited.
(2) Surgical Treatment The approach depends on the specific malformation and includes ventricular septal defect repair. In cases of severe cyanosis or hypoxic episodes, a systemic-pulmonary shunt may be performed. For isolated left atrioventricular valve insufficiency, valve repair or artificial valve replacement can be performed. Patients with second-degree atrioventricular block require a permanent pacemaker implantation.
1. The left-to-right shunt group is difficult to distinguish clinically from large ventricular septal defects, and the diagnosis mainly depends on echocardiography, right heart catheterization, and heart blood vessel angiography.
2. The right-to-left shunt group is similar to tetralogy of Fallot. Tetralogy of Fallot presents with obvious cyanosis and a boot-shaped heart. Right heart catheterization, heart blood vessel angiography, and Doppler echocardiography are used to confirm the diagnosis.
