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Our teacher gave us a homework. He says first find an ecg signal, then take FFT of that signal?

Why do we need to take FFT of an ecg signal? Is it that we can cancel noise only if we know the frequency spectrum of the signal?

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  • $\begingroup$ Ask yourself the opposite question: why wouldnt' you? $\endgroup$
    – Peter K.
    Feb 24, 2016 at 0:02

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I'm not a doctor, I'm an engineer. However, I think I see the point of this.

An electrocardiograph is used as a diagnostic tool to assess the state of the heart and cardiovascular system. Several signals are measured, each of which can be used to make judgements about the health of the patient. Most of the signals measured in an ECG are periodic (in other words, they occur at a given frequency). The DFT/FFT is basically a way of analyzing the frequency content of a signal. So, it follows that by taking the DFT/FFT of an ECG, you can easily see those frequency components.

From the Wikipedia article on ECGs, here are some common components of an ECG and their associated frequencies:

P Wave: 0.08s, 12.5Hz

QRS Complex 0.09s, 11Hz

T Wave: 0.16s, 6.25Hz

I don't actually know the medical meaning of those features, but in any case, they're periodic, meaning you can analyze them using spectral analysis.

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