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Heterotaxy is a rare congenital heart defect that involves dextrocardia and abnormalities in the heart and spleen. It is divided into left and right atrial isomerism, with left being less severe. Surgical repairs may be needed, but right atrial isomerism is more difficult to treat and may require a heart transplant. Antibiotic prophylaxis is necessary for life, and research suggests a genetic cause.
Heterotaxy is a term used to describe two groups of congenital heart defects that generally involve a loop defect, dextrocardia. In addition to several abnormalities in the heart, the liver of a person with heterotaxy is usually in the midline, instead of being located on one side of the body. The most significant indicator of heterotaxy is the presence of a number of small spleens, polysplenia, or the complete absence of one spleen, asplenia. Heterotaxy is divided into two types, left atrial isomerism and right atrial isomerism, sometimes called Ivemark syndrome.
Left atrial isomerism is usually associated with polysplenia. This form of heterotaxy is less severe than Ivemark’s because these small multiple spleens tend to do some of the work of a normal spleen. Ventricular septal defects and pulmonic stenosis are often present, but these two conditions, unless serious, can usually be repaired with surgery.
Surgical repairs for left atrial isomerism are usually not needed soon after birth. Surgeons generally choose to repair heart defects during the first five years of life. The diagnosis of dextrocardia is usually made during routine ultrasound scans, but before birth it is difficult to determine whether a spleen or multiple spleens exist, because they cannot be seen easily. After birth, a blood test can determine splenic function to confirm the diagnosis of polysplenia associated with heterotaxis.
Right atrial isomerism is one of the most difficult cardiac anomalies to treat. This form of heterotaxy is characterized by multiple defects in addition to asplenia. The most important defect is the complete defect of the atrioventricular canal. The septum between the ventricles usually has a large hole, which allows blood to mix. Also, the septum between the atria may never have formed, and the atria are usually undersized.
Extreme pulmonic stenosis and transposition of the arteries may also be present. Also, the pulmonary veins can drain out the wrong way, depriving the heart of oxygen-rich blood. These multiple defects usually require surgery soon after birth, and generally the surgery must be done in stages, as with the Fontan procedure.
Surgery to correct right atrial isomerism is complicated by asplenia. Lack of spleen means a much greater risk of postoperative infection. A child with this form of heterotaxy will require daily antibiotics for life, which could cause problems later on.
If right atrial isomerism requires gradual operations that can relieve but not correct the heart defects, then your child will likely need a heart transplant at some point. The key to successful transplantation is the ability to fight infection. However, long-term use of antibiotics creates resistance, so the types of antibiotics available after a heart transplant may be in short supply for the child with heterotaxy.
Despite the risks of surgery and the need for daily antibiotic prophylaxis, current surgical techniques are improving the survival rate of these children. Fortunately, heterotaxy is also one of the rarest forms of congenital heart defects, and a child is much more likely to have dextrocardia with an abnormal heart than right or left atrial isomerism. Research suggests that, unlike most heart defects, heterotaxis may have a genetic cause. Scientists have found a gene in mice that they believe may be responsible for the heterotaxis. However, the same gene has not yet been found in humans.
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