The role of β-adrenergic stimulation in QT interval adaptation to heart rate during stress test

Figures

• 

  Fig 1. Main panel: dRR(n) time series, in seconds, from the analyzed ECG recording of a CAD patient. Insets: normalized pECG signals, ψ(t), computed from the simulated transmembrane potentials of the tissue fiber at two time instants.

• 

  Fig 2. Fitting of linear (red) and hyperbolic (black) regression models to a patient’s QT and RR data (“highCAD-4” in Table 1). The data clusters correspond to the different windows Wi, i ∈ 1, 2, 3. The residual εrms took values of 4.27 and 1.75 ms for the linear and hyperbolic fittings, respectively.

• 

  Fig 3. Time-varying pattern of Iso concentration during exercise and recovery, with time points n1, n2, n3 and n4 determined from the dQTi(n) and dQT(n) time series of an analyzed ECG recording from a CAD patient.

• 

  Fig 4. Left panels: QT adaptation delay between dQT(n) and dQTi(n) during exercise and recovery for a patient in the study. Middle panels: APD adaptation delay between dAPD(n) and dAPDi(n) during exercise and recovery in a simulated endocardial cell for constant β-adrenergic stimulation and the same HR as for the patient in the left. Right panels: APD adaptation delay between dAPD(n) and dAPDi(n) during exercise and recovery in a simulated endocardial cell for the proposed time-varying β-adrenergic stimulation. Top panels show results using the U estimation strategy, while bottom panels use the M estimation strategy. The red points correspond to ne, o, ne, e, nr, o and nr, e, calculated as described in section 2.6, which delimit the exercise and recovery ramps in dQTi(n) or dAPDi(n). The blue points were identified in dQT(n) or dAPD(n) as the nearest samples to the red points having QT or APD values within 2 ms of the corresponding red point value.

• 

  Fig 5. Left panels: QT adaptation delay between dQT(n) and dQTi(n) during exercise and recovery for a patient in the study. Middle panels: QT adaptation delay between dQT(n) and dQTi(n) during exercise and recovery in a simulated pECG for constant β-adrenergic stimulation and the same HR as for the patient in the left. Right panels: QT adaptation delay between dQT(n) and dQTi(n) during exercise and recovery in a simulated pECG for the proposed time-varying β-adrenergic stimulation. Top panels show results using the U estimation strategy, while bottom panels use the M estimation strategy. The red points correspond to ne, o, ne, e, nr, o and nr, e, calculated as described in section 2.6, which delimit the exercise and recovery ramps in dQTi(n). The blue points were identified in dQT(n) as the nearest samples to the red points having QT values within 2 ms of the corresponding red point value.

• 

  Fig 6. Distributions of the differences Λτ = τφ, s − τφ, p, φ ∈ {e, r}, between the QT adaptation delays calculated in the simulations, τφ, s, and the corresponding QT adaptation delays from the patients, τφ, p, both under constant (Iso-c) and time-varying (Iso-tv) β-adrenegic stimulation, for exercise (four most-left boxplots) and recovery (four most-right boxplots).

• 

  Fig 7. Relationship between the QT adaptation delays calculated using the U estimation strategy in patients (vertical axis, τφ, p, φ ∈ {e, r}) and in simulations (horizontal axis, τφ, s) for a constant (blue) or time-varying Iso level (red). Fitted lines are shown in the corresponding colors, while black lines show the diagonal. The left panel corresponds to the exercise phase and the right panel to the recovery phase.

• 

  Fig 8. Relationship between the QT adaptation delays calculated using the M estimation strategy in patients (vertical axis, τφ, p, φ ∈ {e, r}) and in simulations (horizontal axis, τφ, s) for a constant (blue) or time-varying Iso level (red). Fitted lines are shown in the corresponding colors. The black lines show the diagonal.