Characterization of atrial morphology and sinus node morphology in heterotaxy syndrome: an autopsy-based study of 41...

Heterotaxy syndrome affects the sidedness of heart, lungs, and abdominal viscera, and is associated with complex congenital heart disease. Cardiac sidedness is defined by the position of the morphological right atrium and may be normal, mirror-image, or isomeric. The sinus node has been reported to be present bilaterally in right isomerism and absent bilaterally in left isomerism, although exceptions may occur.

Our aim was to evaluate bilaterally the presence or absence of sinus node tissue in autopsy-derived hearts from patients with heterotaxy and to correlate the findings with the sidedness of the two atria.

Autopsy and clinical records were reviewed from 41 cases with heterotaxy. From the cardiac specimens, tissue was collected bilaterally from expected sinus node sites. Sinus node tissue was categorized microscopically as normal, hypoplastic, indeterminate, or absent.

In hearts thought to show right atrial isomerism, sinus node tissue was detected bilaterally in 54%, was absent on one side in 43%, and was absent on both sides in 3%. For cases with apparent left atrial isomerism, a single sinus node was present in the left-sided atrium in 75% of cases and was absent bilaterally in 25%.

Bilateral sinus nodes were observed in only 54% of cases with right isomerism, and bilateral absence of sinus nodes was documented in only 25% of cases with left isomerism. Thus, our findings indicate that the sinus node is not a morphologically right-sided structure, and its presence therefore is not consistently related to the sidedness of the atria.