Additional estimation of incidence and prevalence of isomerism proves difficult due to failure to diagnose and underestimation of the disease by clinicians. Furthermore, right isomerism is much more easily recognized than left isomerism, contributing to the failure to diagnose.Situs ambiguus is a growing field of research with findings dating back to 1973. Signs and symptoms
There are a variety of clinical manifestations of situs ambiguus. Acute symptoms can be due to both cardiac and non-cardiac defects. Cyanosis or blue skin coloration, primarily affecting the lips and fingernails, can indicate a systemic or circulatory issue. Poor feeding, failure to thrive, and rapid shallow breathing may also be observed due to poor circulation. Upon examination, arrhythmia and heart murmur may raise further suspicion of a cardiac abnormality. Non-cardiac symptoms include impairments of the liver and gastrointestinal tract. Biliary atresia, or inflammation and destruction of the bile ducts, may lead to jaundice. Vomiting and swelling of the abdominal region are features that suggest improper positioning of the intestines. Poor positioning of the intestine also makes it more prone to blockage, which can result in numerous chronic health issues. Asplenia and polysplenia are also possible features of heterotaxy syndrome.Due to abnormal cardiac development, patients with situs ambiguus usually develop right atrial isomerism consisting of two bilaterally paired right atria, or left atrial isomerism consisting of two bilaterally paired left atria. Clinical features and symptoms can vary dependent upon assignment of left versus right atrial isomerism.
Heart failure is often a concern because the inferior vena cava is disrupted due to the inappropriate morphology of the left ventricle to support the vena cava. Conductive nodes and tissues
Abnormal development of the heart results in impaired doubles of conductive nodes, as well as faulty electrical fibers throughout the ventricles. Individuals with right atrial isomerism develop two sinoatrial nodes, as they have 2 mirrored right atria, whereas those with left atrial isomerism fail to develop a sinus node at all. Thus, patients with left atrial isomerism are more likely to experience atrial fibrillation, or irregular rapid heart beat, and abnormal heart rhythm, known as atrial flutter. Development of the atrioventricular node and bundle of His largely depends on physiological looping of the ventricles. Abnormal looping of the ventricles contributes to arrhythmia and heart block in fetuses. Bronchial tree and lungs
Isomerism of the bronchial tree is not typically damaging and presents no significant clinical complications. Pulmonary valve stenosis results in issues of blood flow to the lungs. Abdominal organs
Abdominal organs, including the liver, stomach, intestinal tract, and spleen may be randomly arranged throughout the left-right axis of the body. Distribution of these organs largely dictates treatment, clinical outcomes, and further evaluation. The liver is typically symmetrical across the left-right axis in patients with situs ambiguus, which is abnormal. A majority of left atrial isomeric patients have defects throughout the biliary tree, which is responsible for bile production, even when the gall bladder is functional and morphologically normal.