Unique RR Interval Dynamics Preceding Sudden Cardiac Death

Sudden cardiac death (SCD) is often the first manifestation of underlying cardiac pathology, highlighting the importance of early detection using properties of the electrocardiogram (ECG).We investigated how dynamical RR interval (RRI) correlations differ between SCD and non-SCD subjects during a clinical exercise test.We analyzed RR intervals (RRIs) extracted from Mason-Likar modified 12-lead ECG recordings obtained during a clinical exercise test (N=3406) from the FINCAVAS database.Over a follow-up period of 8.6 years (IQR 6.7-10.6),86 subjects suffered SCD.We evaluated RRI correlations using dynamic detrended fluctuation analysis (DDFA).Eight confounding factors were assessed using a multivariable Fine-Gray subdistribution hazard model, with other deaths (N=445) treated as competing risks.DDFA scaling exponents revealed clear differences between the alive and SCD groups.The lowest univariate hazard ratio, 0.43 (95% CI 0.34-0.54,p = 3 10 -12 ), was observed at scale 8 and quantile heart rate (HR) 0-0.1, corresponding to a 2.4-fold increased risk of SCD with one standard deviation decrease in the scaling exponent.Similarly, the smallest multivariable hazard ratio was 0.52 (95% CI 0.40-0.69,p = 5 10 -6 ) for the corresponding scale and HR.In conclusion, SCD patients exhibited significantly decreased scaling exponents at low HRs.