Evaluation of cardiac autonomic control during the 6-min walk test in women with systemic sclerosis

OBJECTIVE: To evaluate the association between sympathovagal balance and exercise performance, as measured by the 6-min walk test (6MWT), in women with systemic sclerosis (SSc) without cardiac involvement. RESULTS: This was a cross-sectional study in which 69 women with SSc [median age 51 (40–63 years)] without cardiac involvement underwent the 6MWT. Throughout the 6MWT, heart rate variability (HRV) was assessed using dedicated software. METHODS: The median 6-min walking distance (6MWD) was 451 (392–498) meters, and 29 (42%) participants did not achieve 80% of the predicted value for healthy adults. Desaturation during the 6MWT (SpO(2) ≤ 4%) was observed in 10.1% of participants. Significant correlations were observed between the 6MWD and the following HRV parameters: number of successive normal-to-normal RR interval differences > 50 ms (r(s)=-0.397, P = 0.013), low-frequency range (r(s)=0.374, P = 0.023), high-frequency range (r(s)=-0.372, P = 0.023), and parasympathetic nervous system index (r(s)=-0.342, P = 0.045). CONCLUSION: In women with SSc, there is an interrelationship of the 6MWD with both vagal withdrawal and sympathetic hyperactivation. This relationship between autonomic imbalance and worse exercise performance might increase cardiovascular risk, even in patients without apparent cardiac involvement. Control of the heart by the autonomic nervous system may be a potential target for treating patients with SSc.