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gqrs attempts to locate QRS complexes in an ECG signal in the specified record. The detector algorithm is new and as yet unpublished. The output of gqrs is an annotation file (with annotator name qrs) in which all detected beats are labelled normal ("N"). The subtyp, chan, and num fields of each annotation respectively indicate the detection pass (0 or 1) during which the QRS complex was detected, the signal number on which it was detected, and the peak amplitude of the detector’s matched filter during the QRS complex.
As a QRS detector for research, gqrs has been optimized for sensitivity. gqpost can post-process gqrs’s output annotation file to improve positive predictivity, generally at a cost of reduced sensitivity. It does this by copying its input annotation file, changing N annotations into artifact ("|") annotations if they are likely to be erroneous.
A configuration file shared by gqrs and gqpost can be used to describe some of the expected characteristics of the ECG signal. This is unnecessary when processing adult human ECGs, but an appropriately constructed configuration file allows gqrs to analyze fetal, pediatric, and animal ECGs. A sample configuration file is available (see SOURCES, below); it contains details about all configurable parameters.
Note that gqpost always copies its entire input annotation file. The -f and -t options, if present, only define the interval during which gqpost may change annotations. Since gqpost can reprocess its own output, this feature allows multiple passes using different threshold values and processing intervals, if necessary.
It may be necessary to set and export the shell variable WFDB (see setwfdb(1) ).
QRS complexes in record 100 beginning 5 minutes from the start, ending
10 minutes and 35 seconds from the start, and using signal 1, use the command:
gqrs -r 100 -f 5:0 -t 10:35 -s 1
The output annotations may be read using (for example):
rdann -a qrs -r 100
To evaluate the performance of this program, run it on the entire record,
gqrs -r 100
and then compare its output with the reference annotations by:
bxb -r 100 -a atr qrs
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Updated 28 May 2015