Abstract Introduction Heterotaxy syndrome, or situs ambiguous, is a rare congenital disorder of abnormal visceral lateralization characterized by complex cardiac malformations and variable abdominal organ arrangement. It is broadly classified into right isomerism (asplenia) and left isomerism (polysplenia), frequently associated with atrial and atrioventricular septal abnormalities. Common atrium represents one of the most severe forms of atrial septal defect, involving complete absence of the interatrial septum, often accompanied by atrioventricular valve regurgitation. Survival into adulthood without corrective intervention is extremely uncommon. Case Presentation We describe a 49-year-old female presenting with progressive dyspnea and melena. Past medical history was notable for severe pulmonary hypertension and chronic atrial fibrillation. Initial evaluation revealed hypotension, tachycardia, hemoglobin (6 g/dl), elevated BNP (12,000 pg/mL), and troponin (751 ng/L). Chest radiography demonstrated dextrocardia with massive cardiomegaly. Transthoracic echocardiography demonstrated a common atrium with severe regurgitation of both atrioventricular valves, while biventricular systolic function was normal. Cross-sectional imaging additionally identified a right-sided aortic arch, left-sided vena cava, situs inversus, and multiple splenic nodules consistent with polysplenia. These findings placed the patient on the spectrum of advanced left isomerism. Given severe structural disease, severe pulmonary hypertension, and multisystem compromise, surgical intervention was deemed futile; she was referred for combined heart-lung transplantation. Discussion Heterotaxy syndrome exhibits wide phenotypic variability, with outcomes largely dependent on the extent of cardiac involvement. While polysplenia can present incidentally in adulthood, common atrium associated with significant valvular insufficiency rarely progresses without early mortality. Chronic atrial arrhythmias, such as atrial fibrillation, are common in adult survivors, reflecting conduction system anomalies. Embryologically, heterotaxy results from disruption of left-right axis determination involving NODAL-LEFTY2-PITX2 signaling pathways. Adult cases with severe uncorrected defects are exceedingly rare; most patients either undergo early surgical palliation (e.g., Fontan procedure) or succumb during infancy. This report emphasizes the importance of comprehensive cardiac and abdominal imaging when heterotaxy is suspected, as although severe forms are uncommon in adulthood, late complications including arrhythmia, heart failure, and gastrointestinal manifestations warrant lifelong multidisciplinary surveillance. Early diagnosis and timely surgical intervention remain key prognostic determinants, and continued reporting of adult presentations is essential to improve understanding of heterotaxy’s natural history. (A) Transthoracic echocardiogram apical view demonstrating complete absence of the interatrial septum consistent with a common atrium.(B) Color Doppler imaging showing bilateral atrioventricular valve regurgitation.(C) Axial contrast-enhanced CT of the abdomen revealing multiple splenic nodules compatible with polysplenia. This abstract is funded by: None
Wasay et al. (Fri,) studied this question.