% find_Q_on.m - Find Q_on using gradients
% Copyright (C) 2006 Vaclav Chudacek
% This software is released under the terms of the GNU General
% Public License (http://www.gnu.org/copyleft/gpl.html).
function Q_on = find_Q_on(in_ECG)
ekg = slidingavg(in_ECG(1,1:150),5)+1000;
%%% Computation of gradients for Q-on detection
number_of_points = 0; previous_i = 0;
length_for_gradient = 150 - 10 -1;
for i = 1:length_for_gradient,
gradient2(i) = ekg(end-i-10)-ekg(end-i);
end
for i=2:length_for_gradient,
if ((gradient2(i-1)<0)&&(gradient2(i)>0))&&((gradient2(i)~=0)||(gradient2(i-1)~=0)),
number_of_points = number_of_points + 1;
points(number_of_points) = 147-i+3;
values(number_of_points) = ekg(points(number_of_points));
distance(number_of_points) = i - previous_i; previous_i = i;
elseif((gradient2(i-1)>0)&&(gradient2(i)<0))&&((gradient2(i)~=0)||(gradient2(i-1)~=0))
number_of_points = number_of_points + 1;
points(number_of_points) = 147-i+3;
values(number_of_points) = ekg(points(number_of_points));
distance(number_of_points) = i - previous_i; previous_i = i;
elseif (gradient2(i)==0)||(gradient2(i-1)==0)
%disp('Nulovy gradient');
end
end
%%% Q-on point selection
for i = 1:1%length(points)
if values(1)<ekg(150) %%% R-wave positive
%disp('Positive R => searching for neg/zero Q');
if values(2) < values(1)
if values(2)+100 > values(1)
Q_on = points(2);
else
Q_on = points(1);
end
elseif length(values)>2,
if (values(2) > values(1))&&(abs(values(2)-values(3))<150),
if values(2)- values(1)>100,
%disp('Q onset found.');
Q_on = points(2);
else
Q_on = points(1);
end
else
Q_on = points(3);
end
elseif length(values)>1,
if values(2)- values(1)>100,
Q_on = points(2);
else
Q_on = points(1);
end
else
Q_on = points(1);
end
%%% R-wave negative
else
%disp('Negative R => searching for neg/zero Q');
if length(values)>2,
if values(3) < values(2)
Q_on = points(2);
else
if (values(3) > values(2)),
if values(3)- values(2)>100,
% disp('Q onset found.');
Q_on = points(3);
else
Q_on = points(2);
end
end
end
elseif length(values)>1,
Q_on = points(2);
else
Q_on = points(1);
end
end
end