Li Wenhai, Yang Cuiwei, Wang Yanlei, Wang Dexi, Chen Ying, Wu Zhong
Department of Electronic Engineering, Fudan University, Shanghai, 200433, China.
Key Laboratory of Medical Imaging Computing and Computer Assisted Intervention of Shanghai, Shanghai, 200433, China.
Biomed Eng Online. 2016 Apr 12;15:38. doi: 10.1186/s12938-016-0157-2.
Dominant frequency (DF) analysis of atrial electrograms has become an important method in characterizing atrial fibrillation (AF). As a classic method, Botteron's approach is widely used in the preprocessing of frequency analysis during AF. It includes three steps: (1) band-pass filtering at 40-250 Hz, (2) absolute value, and (3) low-pass filtering at 20 Hz. This paper aims to expound the necessity and adjustability of each step.
Unipolar epicardial mapping signals were recorded during AF from eight mongrel dogs with cholinergic AF model. Episodes of these data were randomly selected to evaluate the impact of different pass bands and the necessity of low-pass filtering with 20 Hz cutoff frequency. Each episode of AF signal is 5 s long with a sampling rate of 2 kHz. Simulated electrograms were adopted to discuss the role of taking absolute value. Furthermore, direct spectral analysis method (FFT et al.) is compared with Botteron's preprocessing approach. According to our statistical analysis, the pass band of 40-250 Hz was not the best, while 20-100 Hz presented the high accuracy rate of DF. From the comparing result of direct FFT without Botteron's approach we deduced that the rectification of absolute value was meaningful for the fundamental atrial frequency. The final step, 20 Hz low-pass filter can completely be omitted in DF analysis. In consideration of the demand for real-time distribution of DF in clinical or experimental situations, down-sampling method and the impact of ventricular artifacts on DF was also discussed.
In the actual application of the three preprocessing steps, the pass band selection of band-pass filter can be adjusted and the rectification of taking absolute value is important. Nevertheless, the final step of 20 Hz low-pass filter is totally unnecessary. In real-time signal processing situations, taking down-sampling method and ignoring the ventricular artifacts can also have high performance in DF analysis of atrial electrograms.
心房电图的主频（DF）分析已成为表征心房颤动（AF）的一种重要方法。作为一种经典方法，Botteron方法广泛应用于房颤期间频率分析的预处理。它包括三个步骤：（1）40 - 250Hz带通滤波，（2）取绝对值，（3）20Hz低通滤波。本文旨在阐述每个步骤的必要性和可调整性。
在房颤期间，从八只患有胆碱能性房颤模型的杂种犬记录单极心外膜标测信号。随机选取这些数据片段以评估不同通带的影响以及20Hz截止频率低通滤波的必要性。每个房颤信号片段时长5秒，采样率为2kHz。采用模拟心电图来讨论取绝对值的作用。此外，将直接频谱分析方法（快速傅里叶变换等）与Botteron预处理方法进行比较。根据我们的统计分析，40 - 250Hz的通带并非最佳，而20 - 100Hz的主频准确率较高。从未经Botteron方法处理的直接快速傅里叶变换比较结果来看，我们推断绝对值校正对于基本心房频率是有意义的。最后一步，在DF分析中可以完全省略20Hz低通滤波器。考虑到临床或实验情况下DF实时分布的需求，还讨论了下采样方法以及心室伪差对DF的影响。
在这三个预处理步骤的实际应用中，带通滤波器的通带选择可以调整，取绝对值的校正很重要。然而，20Hz低通滤波的最后一步完全没有必要。在实时信号处理情况下，采用下采样方法并忽略心室伪差在心房电图的DF分析中也能有较高性能。
