Salivary Redox Biomarkers as a Non-Invasive Research Framework for Exploring Redox-Related Cardiac Electrical Vulnerability in Sudden Unexplained Cardiac Death: A Mechanistic and Narrative Review

Sudden unexplained cardiac death (SUCD) is unpredictable, causing major emotional, economic, and productivity loss. In young, apparently healthy individuals, it remains one of the most challenging causes of mortality to understand mechanistically, and no validated molecular biomarkers are currently available to support investigation of subclinical cardiac electrical vulnerability. Conventional clinical assessment tools such as electrocardiography, echocardiography, and genetic testing often fail to detect early molecular disturbances that precede electrical or structural cardiac abnormalities. Recent evidence suggests that oxidative stress and redox imbalance play a crucial mechanistic role in cardiac electrical instability, modulating ion channel function, calcium handling, mitochondrial signaling, and intercellular coupling. This literature review explores the emerging role of salivary redox biomarkers as a non-invasive research framework for exploring redox-related mechanisms relevant to cardiac electrophysiology, introducing the concept of a "Salivary Redoxome"-an integrated oxidative-antioxidative profile measurable in saliva that may reflect systemic redox homeostasis in an exploratory context, without implying myocardial specificity. Key antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx), together with oxidative damage indices such as malondialdehyde (MDA) and total antioxidant capacity (TAC), are discussed for their theoretical mechanistic relevance, biological plausibility, and current limitations. Methodological considerations, sources of pre-analytical variability, and challenges related to biomarker specificity and validation are also addressed to contextualize the current evidence base. At present, no direct clinical evidence links salivary oxidative stress markers to sudden unexplained cardiac death or to electrophysiological arrhythmic risk, and their proposed relevance is therefore exploratory and hypothesis-generating. This review positions salivary redox profiling as a research approach rather than a clinical screening, predictive, or preventive tool, and outlines a future research agenda aimed at systematic validation in well-designed prospective studies.