Background: The first Ventilatory Threshold (VT1) has been shown to assess exercise tolerance and help in the exercise rehabilitation prescription of Chronic Heart Failure patients (CHF). However, VT1 cannot always be detected in CHF by classical methods. Previous investigations revealed that the assessment from Heart Rate Variability (HRV) analysis gives an accurate estimation of VT1 in trained subjects.
Objectives: This study proposed to examine whether HRV analysis could help in VT1 determination in CHF.
Methods: 18 CHF patients (12 males and 6 females, age: 62 ± 13 years, weight: 73 ± 17 kg, left ventricular ejection fraction: 0.32 ± 0.7, VO2peak: 1.3 ± 0.4 L.min-1) performed a Cycle Incremental Exercise (CPX testing). Beatto- beat RR interval, Oxygen Uptake (VO2), carbon production (VCO2) and minute ventilation (VE) were collected during the test. VT1 corresponded to the last point before a first non-linear increase in both VE and VE/VO2. Time (RMSSD) and time-frequency (HFp) domain indices, both extrapolated from the RR time series were calculated.
Results: A marked RMSSD and HFp deflection points were found in the region of VT1, and were identified as Variability Heart Rate Thresholds (HRVT). No significant difference was found between VT1 and both HRVT (p<0.05) in terms of VO2, heart rate values and exercise intensity. Correlations between the different measures ranged from 0.97 to 0.99 providing a strong agreement between all methods (Bland and Altman’s method).
Conclusions: These data reveal that HRV analysis using time-frequency indices during CPX testing can provide a useful alternative to the classical VT1 determination in CHF patients.