Ventricular Topology in Visceral Isomerism:Novel Associations with Cardiovascular Phenotypes and Survival

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Background: Syndromes of visceral isomerism are frequently associated with complex congenital heart defects. While atrial morphology often displays symmetry in these conditions, the ventricular segment does not show morphologic isomerism but exhibits either D-hand or L-hand topology, the distribution of which is hypothesized to reflect underlying embryological mechanisms. This study aimed to determine the statistical distribution of ventricular D-hand and L-hand topology in a large cohort of patients with visceral isomerism and to identify associations with cardiovascular disorders and survival. Methods: This retrospective cross-sectional study included 192 patients with left visceral isomerism (LVI, n=115) or right visceral isomerism (RVI, n=77) diagnosed at a single centre between 2000 and 2023. Diagnosis was primarily based on echocardiography and confirmed by advanced imaging where available. Ventricular topology (D-hand or L-hand) was determined by expert review of imaging data. Data on demographics, mortality, congenital heart defects, and disorders of excitation and conduction were collected and statistically analyzed to assess proportions and associations. Results: The overall study population showed a bias towards ventricular D-hand topology (67%). This bias was statistically significant in the LVI subgroup (74% D-hand) but not in the RVI subgroup, which showed an almost equal distribution (57% D-hand, 43% L-hand). No significant associations were found between ventricular topology and major congenital heart defects. However, significant associations were observed between ventricular topology and the position of the cardiac apex, the direction of the p-wave axis, and aortic arch sidedness. Mortality was significantly higher in the RVI group. Interestingly, within the LVI subgroup, patients with ventricular L-hand topology had significantly lower mortality and better long-term survival compared to those with D-hand topology. Conclusions: The observed distribution patterns of ventricular topology in visceral isomerism do not fully support current embryological concepts of ventricular looping, which favor either purely intrinsic chiral forces or extrinsic mechanical constraints. The novel finding of a survival advantage for LVI patients with L-hand ventricular topology requires further investigation. This study also provides the first evidence of a statistically significant association between ventricular topology and aortic arch sidedness in visceral isomerism, suggesting a functional link between ventricular looping and the development of the aortic arch system.

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