Vinet Alain, Dubé Bruno, Nadeau Réginald, Mahiddine Omar, Jacquemet Vincent
Faculty of Medicine, Department of pharmacology and physiology, Université de Montréal, Montréal, QC, Canada. Centre de Recherche, Hôpital du Sacré-Cœur, Montréal, QC, Canada. Institut de Génie Biomédical, Université de Montréal, Montréal, QC, Canada.
Physiol Meas. 2017 Mar;38(3):397-419. doi: 10.1088/1361-6579/aa57b4. Epub 2017 Jan 9.
Correction of the QT interval in the ECG for changes in heart rate (RR interval) is needed to compare groups of patients and assess the risk of sudden cardiac death. The QTc represents the QT interval at 60 bpm, although most patients typically have a faster heart rate, thus requiring extrapolation of the QT-RR relationship.
This paper investigates the ability of QT-RR models with increasing number of parameters to fit beat-to-beat variations in the QT interval and provide a reliable estimate of the QTc.
One-, two- and three-parameter functions generalising the Bazett and Fridericia formulas were used in combination with hysteresis reduction (memory) obtained by time-averaging the history of RR intervals with exponentially-decaying weights. In normal men and women datasets of Holter recordings in normal subjects (24 h monitoring), two measures were computed for each model: the root mean square error (RMSE) of fitting and the difference between the estimated QTc and a reference QTc obtained by collecting data points around RR = 1000 ms.
The two- and three-parameter functions all gave similar low RMSE with uncorrelated residues. An optimal memory parameter was found that still minimized the RMSE and could be used for all functions and subjects. This reduction in RMSE resulted from changes in the parameters linked to the increased steepness of the QT-RR relation after hysteresis reduction. At optimal memory, the two and three-parameter models provided poorer prediction of the QTc as compared to the Fridericia's model in subjects with fast heart rates, since accurate representation of the steeper QT-RR relation worsened the extrapolation that was then needed to determine the QTc.
As a result, among all models investigated, the Fridericia formulation offered the best trade-off for QTc prediction robust to memory and fast heart rates.
为了比较患者组并评估心源性猝死风险，需要根据心率变化（RR间期）校正心电图中的QT间期。QTc代表心率为60次/分时的QT间期，尽管大多数患者的心率通常较快，因此需要外推QT-RR关系。
本文研究了参数数量不断增加的QT-RR模型拟合QT间期逐搏变化并提供可靠QTc估计值的能力。
将推广Bazett和Fridericia公式的一参数、二参数和三参数函数与通过对RR间期历史进行指数加权时间平均获得的滞后减少（记忆）相结合。在正常受试者动态心电图记录的正常男性和女性数据集中（24小时监测），为每个模型计算了两个指标：拟合的均方根误差（RMSE）以及通过收集RR = 1000 ms附近的数据点获得的估计QTc与参考QTc之间的差异。
二参数和三参数函数均给出了相似的低RMSE，且残差不相关。发现了一个最优记忆参数，该参数仍能使RMSE最小化，并且可用于所有函数和受试者。RMSE的降低是由于滞后减少后与QT-RR关系陡度增加相关的参数变化所致。在最优记忆时，与Fridericia模型相比，二参数和三参数模型在心率较快的受试者中对QTc的预测较差，因为更陡峭的QT-RR关系的准确表示会使随后确定QTc所需的外推变差。
因此，在所有研究的模型中，Fridericia公式在对记忆和快速心率具有鲁棒性的QTc预测方面提供了最佳权衡。
