EXPLORING ASSOCIATIONS BETWEEN HEART RATE VARIABILITY AND EXERCISE TOLERANCE IN INDIVIDUALS WITH PERIPHERAL ARTERY DISEASE

Abstract

Objective: Lower-extremity artery disease (LEAD) characterized by a progressive atherosclerotic build-up in leg arteries affects more than 200 million people worldwide. LEAD is often associated with autonomic dysfunction as evidenced by a reduced heart rate variability (HRV). We aimed to investigate whether the autonomic function is associated with ambulatory capacity and exercise capacity in patients with LEAD. Design and method: Thirty-four patients (age > 17 years) diagnosed with LEAD (ABI < 0.9 and/or 20% decrease after a maximal treadmill test) suffering from intermittent claudication (Rutherford I-III) were recruited in the PROSECO-IC trial. Patients were grouped based on beta-blocker medication (B-blocker and non-B-blocker). Intervals between R waves (i-RR) obtained by heart rate (HR) signal were acquired beat-to-beat (Polar®H10) during 15 min of supine rest and were used for 5-minute HRV analysis. Time-domain indexes (mean i-RR, SDDD)and frequency domains (high-frequency band (HF), low frequency (LF, very LF (VLF)), and the ratio (LF/HF). Ambulatory capacity was assessed by a submaximal treadmill test, graded maximal treadmill test using Gardner protocol (GTM), and 6 minutes walking test (6MWT); exercise capacity was assessed by graded maximal cardiopulmonary exercise test (HR, blood pressure (BP) and peak oxygen uptake (VO2peak)) at resting, 2 minutes and the peak of exercise. Results: Pearson test showed that sympathetic modulation indexes were moderately associated with pain-free distance in GTM (LF/HF: r = 0.52, p = 0.04) and pain-free time in 6MWT (LFlog: r = -0.62, p = 0.01; VLF: r = -0.52, p = 0.04), respectively, in patients without B-blocker. Similar HR associations with HRV (time and frequency domain) were observed during the submaximal treadmill test and cardiopulmonary exercise test (p < 0.05). Test-t demonstrated a significantly increased response intra-groups in HR and BP during both tests (p < 0.05). Average BP was positive associated with the earlier stages of the cardiopulmonary test (resting to 2 min) with LFlog (r = 0.70, p = < 0.001) in B-blocker while non-B-blocker were associated from 2 min to peak with LFabs (r = 0.67, p = < 0.001) and LF/HF (r = 0.52, p = 0.03). Conclusions: Sympathetic modulation was correlated with a longer pain-free walking capacity in non-B-blockers. Yet, individuals treated by -B-blockers showed an earlier sympathetic modulation through exercise pressor response during the first stages of cardiopulmonary exercise compared to non-B-blockers.