Power-Law Properties of Nocturnal Arrhythmia Avalanches: A Novel Marker for Incident Cardiovascular Events

Background Self-organised criticality, ubiquitous in nature, involves complex networks evolving autonomously to a critical state with scale-invariant events exhibiting a power-law distribution. Biologically, neural discharges' durations in the brain follow power-law distribution. The duration of non-sustained arrhythmia events during sleep can follow power-law distributions, analogous to neuronal avalanches. Objective We hypothesised that the durations of nocturnal arrhythmia avalanches (NAA) could follow a power-law, whose exponent could predict long-term clinical outcomes. Methods We defined NAA as any instance of a drop in ECG template-matched R-R intervals 30% of baseline, followed by a return to the baseline. We studied NAA in ECG recordings of 9176 participants in Sleep Heart Health Study (SHHS), Osteoporotic Fractures in Men Study (MrOS) Sleep and Multi-Ethnic Study of Atherosclerosis (MESA). The association of the NAA durations with a power-law distribution was evaluated, and the association of derived power-law exponents (α) with major cardiovascular outcomes was assessed with multivariable Cox regression. Results The arrhythmia distribution showed a power-law versus comparator distributions. (Positive log likelihood ratio of power-law vs. power-law vs. log-normal in MESA: 95%; SHHS: 35% and MrOS: 64%). In datasets evaluated, multivariable Cox regression, adjusting for conventional CV risk factors showed a significant association of the NAA power-law exponent (increased α) with adverse CV outcomes (CV mortality: SHHS (HR = 1.39 [1.07–1.79], p=0.012); MrOS (HR = 1.42 [1.02–1.94], p=0.039; CV events: MESA (HR = 3.46 [1.46–8.21], p=0.005)) (Figure). Conclusion Nocturnal arrhythmia avalanches follow power-law distribution and could conform principles of self-organised criticality. The exhibited power-law properties are associated with long-term CV events and mortality.