Implications of Turbulence Slope Variations in Different Approaches

Both heart rate variability (HRV) and heart rate turbulence (HRT) are established tools to study cardiac autonomic activity. Short-term studies of HRV had been reported to be stable for autonomic function assessment. However, there is little information on whether short-term HRT assessment is comparable to 24 h assessment. The aim of the study is to identify the relationship of HRT values between the 24 h and isolated tachogram measurements. We collected 24 h Holter recordings from 116 patients attending the outpatient department. HRT parameters were assessed for 24 h. Using the conventional method, HRT parameters were calculated using the average of tachograms over long-term recordings. In an alternative method, HRT parameters were obtained from each tachogram. We calculated a mean value for each subject by averaging the whole HRT data of every tachogram. Correlation analysis between the two groups of HRT values was performed. The results showed a high correlation between the two methods in turbulence slope (TS) (P<0.001; r=0.84) and an extremely significant correlation in turbulence onset (TO) (P<0.001; r=0.99). The values of TS were increased when assessed by separate tachogram. The variations became prominent when TS values calculated by the conventional method were low. HRT is as useful by separate tachogram assessment as by the standard Holter recordings. However, the TS values should be redefined. In subjects with abnormal turbulence slope (<2.5) calculated by averaging long-term recordings, the possibility of TS values blunted by diverse regression slope sequences in separate tachograms should be taken into consideration.