Time–frequency analysis of the QRS complex in patients with ischemic cardiomyopathy and myocardial infarction

Abstract

Background

Time–frequency analysis of the electrocardiographic QRS complex (QRS) has not been uniformly accepted. We investigated this new method of analysis and evaluated its clinical significance in patients with ischemic cardiomyopathy (ICM) and with myocardial infarction (MI).

Methods

The study population included 71 consecutive patients with MI, 32 with ICM, and 40 healthy individuals. We recorded 12-lead electrocardiograms through a band pass filter (0.15–300 Hz) and applied a continuous wavelet transform (CWT) to measure the time–frequency power within the QRS in leads V₁ or II. Integrated time–frequency power (ITFP) between QRS complexes was measured to quantify the wavelet-transformed ECG signals (WT-ECG signal), which were classified into three frequency zones: low-frequency QRS (LF-QRS, 5–15 Hz), mid-frequency QRS (MF-QRS, 15–80 Hz) and high-frequency (HF-QRS, 150–250 Hz). In addition, we explored the relationship between the frequency power within the QRS and the density of fibroblasts using a computer simulation.

Results

The ITFP values were lower in MF-QRS band in patients with anterior or inferior MI, but were significantly greater in LF-QRS and HF-QRS bands of ICM patients than in other groups. In the simulation study, the ITFP values from pseudo-QRS increased in the HF and LF zones if the fibroblast–myocyte ratio (r) was between 1.0 and 2.5.

Conclusions

The QRS frequency profile was characterized by an increase in HF-QRS in ICM, which might be due to the generation of micro-fibrous tissues in local areas of the cardiac ventricles.