Deceleration Capacity as a Marker of Autonomic Cardiac Modulation in Prodromal and Manifest Parkinson's Disease, Multiple System Atrophy, and Progressive Supranuclear Palsy.

BACKGROUND: Degenerative parkinsonian syndromes, including the alpha-synucleinopathies (aSYN) Parkinson's disease (PD), and multiple system atrophy (MSA), and the tauopathy progressive supranuclear palsy (PSP), are characterized by motor and non-motor symptoms. The later subsume autonomic dysfunction, which may appear early or progress with the disease. Cardiac dysfunction varies by syndrome and can also occur in isolated REM sleep behavior disorder (iRBD), a prodromal stage of aSYN. Overlapping motor features make early differentiation challenging. Heart rate variability (HRV) analysis is a noninvasive tool for evaluating cardiac autonomic function, with deceleration capacity (DC) as a sensitive parasympathetic marker. This study compares HRV and DC across parkinsonian syndromes to assess their potential in early diagnosis and differentiation.

METHODS: Using standardized 30-min resting ECG recordings in the early morning, we analyzed HRV parameters in five groups: iRBD (n = 10), PD (n = 10), MSA (n = 10), PSP (n = 9), and healthy controls (HC, n = 10). Evaluated HRV parameters included HRV index (HRVI), reflecting overall variability, and DC.

RESULTS: As expected, DC was significantly lower in MSA (3.82 ± 1.38) and unexpectedly even lower in PSP (3.19 ± 2.77), compared to HC (9.66 ± 4.67) and PD (7.55 ± 2.48). These findings are novel for PSP. HRVI was significantly reduced in PSP, while other HRV parameters showed no significant differences.

CONCLUSIONS: Deceleration capacity (DC) reduction in MSA and PSP suggests pronounced cardiac parasympathetic dysfunction. DC may support differentiation between PD and atypical syndromes, but larger studies are needed for validation. Given the impact of autonomic dysfunction on quality of life and mortality, comprehensive autonomic testing should be included in the diagnostic workup.