identify q, r, s peaks of a ecg in matlab

main.m
% Assuming you have loaded your ECG signal in a variable called ecg

% Find R peaks
[~,r_locs] = findpeaks(ecg, 'MinPeakHeight', max(ecg)*0.6, 'MinPeakDistance', 0.2*fs); % adjust thresholds as needed

% Find Q and S peaks by searching before and after each R peak
q_locs = zeros(size(r_locs));
s_locs = zeros(size(r_locs));

for i = 1:length(r_locs)
    [~,q_loc] = findpeaks(-ecg(max(1, r_locs(i)-0.08*fs):r_locs(i)), 'MinPeakDistance', 0.02*fs); % adjust thresholds as needed
    [~,s_loc] = findpeaks(-ecg(r_locs(i):min(length(ecg), r_locs(i)+0.08*fs)), 'MinPeakDistance', 0.02*fs); % adjust thresholds as needed

    q_locs(i) = q_loc + r_locs(i) - 0.08*fs;
    s_locs(i) = s_loc + r_locs(i) - 1;
end

% Plot ECG signal with identified QRS peaks
figure;
plot(ecg);
hold on;
plot(r_locs, ecg(r_locs), 'ro', 'MarkerSize', 10);
plot(q_locs, ecg(q_locs), 'g*', 'MarkerSize', 10);
plot(s_locs, ecg(s_locs), 'b*', 'MarkerSize', 10);
legend('ECG Signal', 'R Peaks', 'Q Peaks', 'S Peaks');
xlabel('Samples');
ylabel('Amplitude');
title('ECG Signal with QRS Peaks');
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