A Computational Study on the Relation between Resting Heart Rate and Atrial Fibrillation Hemodynamics under Exercise

Figures

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  Fig 1. Rate parameter, γ, as a function of the mean RR interval. The Long-Term AF Database [29, 30] contains 84 long-term ECG recordings of subjects with paroxysmal or sustained AF. Record durations vary but cover typically 24 to 25 hours. Among the 84 recordings we focus on those with unimodal distributions having at maximum 10 minutes of other arrhythmias (e.g. sinus bradycardia, idioventricular rhythm, ventricular bigeminy, etc), thereby selecting 26 recordings. For each of these series, two windows of 10,000 beatings have been extracted, allowing the evaluation of 52 power spectrum density functions. It has been observed[31] that γ = S∞-1/2, where S∞ is the flat power spectrum density at the highest frequencies. The rate parameter, γ, has been here evaluated over the 100 highest frequencies for each of the 52 RR series selected. γ values are reported through open circles as function of the mean RR of each chosen window. A linear least squares fitting of the data is introduced (solid line) together with the coefficient of determination, R2 = 0.60. The resulting relation γ = -9.2RR + 14.6 is adopted to obtain γ values for the different HR targets (specific values are reported in Table…

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  Fig 2. Probability distribution functions of the RR beating for the different AF simulations. Mean, μ, standard deviation, σ, and rate parameter, γ, values of each configuration are reported in Table 3.

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  Fig 3. Variation comparative index (VCI) graphs for computed cardiovascular variables. (A) VCI4, (B) VCI6, (C) VCI8. In each plot the solid line intercepts VCI axis at 1, while the two dashed lines intercept VCI axis at 0.85 and 1.15 (pre-defined cut-off between relevant, i.e. VCI ≥ 1.15 and ≤ 0.85, and not relevant variations, i.e. 1.15 > VCI > 0.85); with respect to the corresponding 1 MET simulation value, black dot indicates that the variable increases both in SHR and HHR exercise simulations, white dot indicates that the variable decreases both in SHR and HHR exercise simulations, black/white dot indicates that the variable undergoes an increase in SHR exercise simulation and a decrease in HHR exercise simulation.

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  Fig 4. Mean values and VCIs for cardiac output (CO) and pulmonary venous pressure (Ppvn). (A) Mean CO as function of exercise intensity in SHR and HHR simulations. (B) Plot of the VCIs calculated for CO. (C) Mean Ppvn as function of exercise intensity in SRH and HHR simulations. (D) Plot of the VCIs calculated for Ppvn. In plot B and D, the solid line intercepts VCI axis at 1, while the two dashed lines intercept VCI axis at 0.85 and 1.15 (pre-defined cut-off between relevant, i.e. VCI ≥ 1.15 and ≤ 0.85, and not relevant variations, i.e. 1.15 > VCI > 0.85); with respect to 1 MET simulation value, black dot indicates that the variable increases both in SHR and HHR exercise simulations.