Dextrocardia in patients with Poland syndrome: Phenotypic characterization provides insight into the pathogenesis

Objective: Poland syndrome is a rare congenital anomaly characterized by complete or partial agenesis of the pectoralis major muscle variably associated with other thoracic malformations, upper limb malformations, or both. More than 20 patients with dextrocardia and left-sided Poland syndrome have been previously described. The association between these 2 rare anomalies suggests a causal relationship, but the etiopathogenetic mechanism has not been clarified yet. We studied the clinical correlation between these 2 anomalies, and we tried to elucidate whether dextrocardia or Poland syndrome comes first. Methods: This is a multicentric multidisciplinary study conducted over the last 5 years. We identified 122 patients with Poland syndrome, and we investigated heart position through different imaging techniques. Logistic regression statistical analyses were carried out. Results: We observed dextrocardia in 14 (11.5%) patients, which was never associated with situs inversus. All of them presented with left-sided Poland syndrome and partial agenesis of 2 or more ribs. Conversely, all patients with Poland syndrome with partial agenesis of 2 or more ribs presented with dextrocardia, whereas dextrocardia was never associated with partial agenesis of a single rib. Three patients with dextrocardia presented with simple congenital heart defects. Conclusions: These findings suggest that mechanical factors during embryonic life could explain the strong association between left-sided Poland syndrome and dextrocardia. According to this hypothesis, partial agenesis of 2 or more ribs is needed to displace the heart toward the right side. The peculiar features of dextrocardia when associated with Poland syndrome (neither associated with situs inversus nor complex intracardiac anomalies) support our hypothesis.