Remove Lower Frequencies from ECG Signal Sample

Hello guys,

I want to remove lower frequencies from ECG signal sample that I got from physionet.org.

After surfing the internet, I got this tutorial from youtube: ECG Signal Processing in MATLAB - Detecting R-Peaks: Full

He give the source code too. But I need extra explanation from the source code that he gave in remove lower frequencies segment.

 fresult=fft(ecg);
 fresult(1 : round(length(fresult)*5/samplingrate))=0;
 fresult(end - round(length(fresult)*5/samplingrate) : end)=0;
 corrected=real(ifft(fresult));

I know how fft works but can someone here give explanation about this code?

 fresult(1 : round(length(fresult)*5/samplingrate))=0;
 fresult(end - round(length(fresult)*5/samplingrate) : end)=0;

And why he use 1000 for samplingrate variable?

Thanks in advance :)