Shannon Entropy in Heart Rate Variability: A Unified Indicator of Electrical and Hemodynamic Cardiovascular Instability
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http://orcid.org/0000-0003-0823-4488
Abstract
Background: Autonomic dysregulation and progressive loss of physiological complexity are implicated in both atrial fibrillation and reflex (vasovagal) syncope.
Objective: To compile published data on the Shannon Entropy of RR (the interval between the R‑wave peaks of two consecutive heartbeats on the Electrocardiogram) and assess its validity as a symptom of reduced autonomic complexity in both atrial fibrillation and tilt-induced syncope.
Methods: Twenty-two studies have been reviewed, progressively listed with RR-interval dynamics and entropy-based metrics, harmonised preprocessing and entropy calculation parameters where feasible, and published summary results have been extracted (no new subject-level data were collected).
Results: Shannon Entropy has demonstrated a consistent pattern across the reviewed literature: it exhibited a gradual decline during tilt testing studies, transitioning from patients negative for the tilt test (control group) to those positive, and subsequently from baseline values (-10% compared to the control group) to pre-syncope values (-15-20%) and then to impending syncope values (-25-30%). Entropy has demonstrated a corresponding (both qualitative and quantitative) progressive deterioration in research on Atrial Fibrillation, transitioning from healthy sinus rhythm to paroxysmal, then to persistent, and finally to permanent fibrillation. Additionally, entropy assessments generally provided a significantly higher specificity than other HRV indices while maintaining the same sensitivity in both syncope and fibrillation studies.
Conclusions: The integrated evidence supports Shannon Entropy as a robust, scale‑insensitive indicator of loss of autonomic complexity that precedes both electrical (fibrillation) and mechanical (syncope) cardiovascular instability. Prospective, harmonized data collection and pooled reanalysis are recommended to validate effect sizes and clinical thresholds for monitoring applications.These findings support the use of Shannon Entropy as a practical, robust, and physiologically meaningful tool for early detection, monitoring, and risk stratification in both arrhythmic and syncopal disorders.
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