Heterotaxy is a term used to describe two groupings of congenital heart defects that generally involve a looping defect, dextrocardia. In addition to several anomalies in the heart, the liver of a person with heterotaxy is generally midline, instead of placed on one side of the body. The most significant indicator of heterotaxy is the presence of a number of small spleens, polysplenia, or the total absence of a spleen, asplenia. Heterotaxy is split into two types, left atrial isomerism and right atrial isomerism, sometimes called Ivemark’s Syndrome.
Left atrial isomerism is generally associated with polysplenia. This form of heterotaxy is less severe than Ivemark’s because these multiple tiny spleens tend to do some of the work of a regular spleen. Often, ventricular septal defects and pulmonary stenosis are present, but these two conditions, unless severe, can usually be repaired in one surgery.
Surgical repairs for left atrial isomerism are usually not necessary right after birth. Surgeons generally elect to repair the heart’s defects during the first five years of life. Diagnosis of dextrocardia is usually made during routine sonograms, but prior to birth it is difficult to determine whether a spleen or multiple spleens exist, because they cannot be visualized easily. After birth, a blood test can determine splenic function to confirm diagnosis of polysplenia associated with heterotaxy.
Right atrial isomerism is one of the more difficult heart anomalies to treat. This form of heterotaxy is marked by multiple defects in addition to asplenia. The most prominent defect is complete atrioventricular canal defect. The septum between the ventricles usually has a large hole, allowing blood to mix. Additionally, the septum between the atria may never have formed, and the atria are generally undersized.
Extreme pulmonary stenosis and transposition of the arteries may also be present. As well, the pulmonary veins may drain on the wrong side, 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 a spleen means a much greater risk of post-operative infection. A child with this form of heterotaxy will require daily antibiotics for life, which may cause problems later.
If right atrial isomerism requires staged operations that can alleviate but not fix the heart defects, then at some point the child will probably need to undergo a heart transplant. Key to successful transplantation is the ability to fight off infections. However, long-term use of antibiotics builds resistance, so the available types of antibiotics after a heart transplant may be slim for the child with heterotaxy.
Despite the risks of surgery, and the need for daily prophylactic antibiotics, present surgical techniques are improving the survival rate of these children. Fortunately too, heterotaxy is one of the rarest forms of congenital heart defects, and a child is much more likely to have dextrocardia with abnormal heart than either right or left atrial isomerism. Research suggests that unlike most heart defects, heterotaxy may have a genetic cause. Scientists have found a gene in mice that they believe may be responsible for heterotaxy. However, the same gene has not yet been found in humans.
