how to make P wave and T wave flat in ECG signal

I have an ECG signal, called mySignal.mat; can be downloaded here:

https://www.dropbox.com/s/lijszlrz8cereb2/mySignal.mat?dl=0

it looks like this:

One guy states in his PhD thesis that QRS complex has frequncy range 10-40 hz :

I want to keep only QRS complex in my ECG signal and I want all other components flatten to iso-electric line. If I visualize, I want signal left side to become like signal on the right side in this picture:

I used this bandPass filter:

if true
  % my bandPass filter starts here
load('mySignal.mat')
% Design and apply the bandpass filter
fs=250;
order    = 4;
fcutlow  = 8;
fcuthigh = 42;
[b,a]    = butter(order,[fcutlow,fcuthigh]/(fs/2), 'bandpass');
x        = filter(b,a,mySignal);
  % my bandPass filter ends here
end

Result of this filter:

I would be happy if somebody teach me how to do it. Thank you Experts