WFDB Applications Guide - PhysioNet

GQRS(1) WFDB Applications Guide GQRS(1)
NAME
gqrs, gqpost − QRS detector and post-processor
SYNOPSIS
gqrs -r record [ options ... ]
gqpost -r record [ options ... ]
DESCRIPTION
gqrs attempts to locate QRS complexes inanECG 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new and as yet unpublished.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) inwhich
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. Itdoes this
by copying its input annotation file, changing N annotations into artifact ("|") annotations if they are likely
to be erroneous.
Aconfiguration 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. Asample configuration
file is available (see SOURCES, below); it contains details about all configurable parameters.
Options include:
-a annotator
[gqpost only] Read annotations from the specified annotator (default: qrs).
-c file Initialize parameters based on the specified (text) configuration file. See the example configuration
file, gqrs.conf, for details.
-f time Begin at the specified time in record (default: the beginning of record).
-h Print a usage summary.
-H Read the signal files in high-resolution mode (default: standard mode).
-m threshold
Specify the threshold (default: 1.0) for detection [qqrs] or acceptance [gqpost]. Use higher values
to reduce false detections, or lower values to reduce the number of missed beats.
-n name
[gqrs only] Save the filtered signals in a new record with the specified record name.
-o name
[gqpost only] write annotations to an annotation file with the specified annotator name.
-s signal
[gqrs only] Specify the signal to be used for QRS detection (default: 0). Note that signals may be
specified by number or name.
-t time Process until the specified time in record (default: the end of the record).
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.
ENVIRONMENT
It may be necessary to set and export the shell variable WFDB (see setwfdb(1)).
EXAMPLES
To mark QRS complexes inrecord 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
30 21 July 2013 WFDB 10.5.19