Dextrocardia

Dextrocardia results from abnormalities in the embryological development of the heart. Around day 22 to 23 of normal embryogenesis, or the process by which a fertilized egg becomes an embryo, the heart begins to develop. A straight, primitive heart tube develops first. The heart tube then undergoes elongation and a process called cardiac looping, which is what determines the position of the heart ventricles in relation to the atria. During normal cardiac looping, the cranial aspect of the tube bends to the right, then the caudal aspect of the tube bends to the left until it occupies a normal left thoracic position. Dextrocardia occurs when the caudal portion of the heart tube loops to the right instead of the left, which causes the heart base to reside on the right side of the thorax rather than the left side. Dextrocardia may occur in isolation or accompanied by situs inversus totalis, which refers to the mirror-image reversal of the other thoracic and abdominal organs. 

While the circumstances leading to the abnormal looping of the heart during development are unclear, there is an association between dextrocardia and defects in ciliary motility (e.g., primary ciliary dysfunction). Kartagener syndrome is a primary ciliary dysfunction disorder characterized by a triad of chronic sinusitis, situs inversus, and bronchiectasis, a form of chronic obstructive pulmonary disease defined by the abnormal widening of bronchi. Heterotaxy is also a condition in which the thoracic and abdominal organs and vessels are positioned abnormally across the left-right axis of the body. Heterotaxy occurs secondary to a lateralization defect during embryonic development and may result in highly complex cardiac lesions or accompanied by other congenital disorders which can lead to intestinal malrotation, venous abnormalities, and asplenia. 

Dextrocardia is often an incidental diagnosis that occurs when an electrocardiogram (ECG) or chest x-ray is performed. ECG findings of dextrocardia can include inversion of lead I, positive R wave in aVR, right axis deviation, and absent R wave progression in the precordial leads. Dextrocardia can be confirmed on a chest X-ray demonstrating cardiac malposition. Echocardiography, MRI, and CT imaging of the chest may be used to further evaluate dextrocardia and identify any associated abnormalities. Similar imaging of the abdominal organs may be used to identify situs inversus totalis. 

Due to its association with primary ciliary dysfunction, individuals with dextrocardia may undergo nasal nitric oxide measurements or evaluation with video-microscopy to screen for Kartagener syndrome. In individuals with Kartagener syndrome, a CT scan of the chest may reveal bronchiectasis in addition to dextrocardia. Electron microscopy and genetic testing can be used to confirm primary ciliary dysfunction. 

Many individuals with isolated dextrocardia are asymptomatic and do not require intervention. However, since dextrocardia may be accompanied by congenital heart defects, invasive treatment like surgery may be necessary in some cases. When transposition of the great vessels, cardiac wall defects, atrial or ventricular septal defects, severe valvular abnormalities, or other forms of congenital heart disease are present, treatment may include surgical reconstruction or heart transplantation with venous reconstruction depending on the complexity of the defects. Pacemaker implantation may be necessary in cases where the electrical system of the heart is affected.  

In individuals with primary ciliary dysfunction, symptomatic treatment, and prevention of acute bronchiectasis exacerbations are the mainstay of treatment. Mucolytics may be used to aid respiratory clearance as well as antibiotics for the prevention and treatment of respiratory infections. In individuals with severe bronchiectasis, lung resection or transplantation may be considered.