Mainardi Luca, Sassi Roberto
Dipartimento di Bioingegneria, Politecnico di Milano, Italy.
J Electrocardiol. 2011 Mar-Apr;44(2):119-25. doi: 10.1016/j.jelectrocard.2010.11.017.
The dominant T wave (DTW) reflects the derivative of the repolarization phase of the transmembrane potential of myocytes. T-wave alternans (TWA) is defined as an alteration of this repolarization that repeats every other beat. We investigate if the DTW can offer new insight on TWA. We first proved that the DTW estimate obtained through singular value decomposition is optimal, because it minimizes the norm of the residuals. Then we suggested an optimal estimate of the vector of lead factors, in the case in which the DTW is given. Finally, we derived a mathematical relationship between observable TWA on electrocardiogram and DTW morphology. The relationship depends on the slope of the repolarization phase of the myocytes' transmembrane potentials and on the dispersion of the repolarization times. Based on this finding, a new index meant to quantify TWA was defined and termed amplitude of dominant T-wave alternans (ADTWA). A preliminary validation of the index was performed using the synthetic records contained in the Computers in Cardiology 2008 data set. They were obtained from 5 electrocardiogram models to which TWA was added at different extents. We found a linear relationship between the TWA amplitude and the ADTWA metric (R(2) = 0.9898 ± 0.100 across all models). Moreover, the root mean square error between actual and estimated TWA amplitudes was 10.9 μV (ADTWA) vs 12.9 μV obtained with the classical spectral method.
主导T波（DTW）反映了心肌细胞跨膜电位复极化阶段的导数。T波交替（TWA）被定义为这种复极化的交替变化，每隔一个搏动重复一次。我们研究DTW是否能为TWA提供新的见解。我们首先证明了通过奇异值分解获得的DTW估计是最优的，因为它使残差的范数最小化。然后，在给定DTW的情况下，我们提出了导联因子向量的最优估计。最后，我们推导了心电图上可观察到的TWA与DTW形态之间的数学关系。这种关系取决于心肌细胞跨膜电位复极化阶段的斜率和复极化时间的离散度。基于这一发现，定义了一个用于量化TWA的新指标，称为主导T波交替幅度（ADTWA）。使用2008年心脏病学计算机数据集中包含的合成记录对该指标进行了初步验证。这些记录来自5个心电图模型，在不同程度上添加了TWA。我们发现TWA幅度与ADTWA指标之间存在线性关系（所有模型的R(2) = 0.9898 ± 0.100）。此外，实际和估计的TWA幅度之间的均方根误差为10.9 μV（ADTWA），而经典频谱方法得到的误差为12.9 μV。
