gms | German Medical Science

Purposes: The frequency analysis with wavelet transform (WT) is better than fast Fourier transform for analyzing the time-frequency characteristics to know the electrophysiological and pathophysiological changes in hearts. There is no report about the change in the frequency profile of QRS according to the age with or without cardiac remodeling induced by hypertension. So we analyzed this subject.

Methods: Normotensive Wistar-Kyoto male rats (WKYIzm), 10-12 weeks (young, n=9) and 20-22 weeks (adult, n=8) of age and age-matched spontaneously hypertensive male rats (SHRIzm) were used in this study. Limb leads (II) electrocardiograms (ECGs) of rats were recorded under anesthesia, with the condition of filter off and sampling rate at 10KHz. ECGs were inputted into the personal computer (PC). Time-frequency power by WT with 40 scales bands from 70 to 1000Hz was calculated. The integral values of the time-frequency power between QRS were calculated every frequency band that were summed up all and averaged in each group. The percentage change in each adult rat was compared with that in each young rat. The remodeling was evaluated by histological studies, Sirius Red stain and Masson stain, and by molecular technique, quantitative real-time RT-PCR analysis.

Results: Compared with the young rat, the different aging shift of frequency distribution in QRS in WKY and SHR was observed. The most significant increasing change in signal power was recorded near 600Hz in WKY, while around 300Hz in SHR. The significant fibrosis was observed in hearts of adult SHR, compared with WKY and young SHR. The mRNA expression levels of collagen type III and connexin 43 were also more prominent in SHR.

Conclusion: The present study provides the evidence that different aging shifts of frequency distribution in QRS with WT are observed in between WKY and SHR, which may be related to the progression of cardiac remodeling such as fibrosis and/or the alterations of gap junctions.