Abstract
BACKGROUND Brugada syndrome is a significant cause of sudden cardiac death (SCD), but the underlying mechanisms remain hypothetical. OBJECTIVES This study aimed to elucidate this knowledge gap through detailed ex vivo human heart studies. METHODS A heart was obtained from a 15-year-old adolescent boy with normal electrocardiogram who experienced SCD. Postmortem genotyping was performed, and clinical examinations were done on first-degree relatives. The right ventricle was optically mapped, followed by high-field magnetic resonance imaging and histology. Connexin-43 and Na V 1.5 were localized by immunofluorescence, and RNA and protein expression levels were studied. HEK-293 cell surface biotinylation assays were performed to examine Na V 1.5 trafficking. RESULTS A Brugada-related SCD diagnosis was established for the donor because of a SCN5A Brugada-related variant (p.D356N) inherited from his mother, together with a concomitant NKX2.5 variant of unknown significance. Optical mapping demonstrated a localized epicardial region of impaired conduction near the outflow tract, in the absence of repolarization alterations and microstructural defects, leading to conduction blocks and figure-of-8 patterns. Na V 1.5 and connexin-43 localizations were normal in this region, consistent with the finding that the p.D356N variant does not affect the trafficking, nor the expression of Na V 1.5. Trends of decreased Na V 1.5, connexin-43, and desmoglein-2 protein levels were noted; however, the RT-qPCR results suggested that the NKX2-5 variant was unlikely to be involved. CONCLUSIONS This study demonstrates for the first time that SCD associated with a Brugada-SCN5A variant can be caused by localized functionally, not structurally, impaired conduction.