.TH SQRS 1 "22 October 1996" "MIT DB software 9.6" "DB applications"
.SH NAME
sqrs \- single-channel QRS detector
.SH SYNOPSIS
\fBsqrs -r \fIrecord\fR [ \fIoptions\fR ... ] ]
\fBsqrs125 -r \fIrecord\fR [ \fIoptions\fR ... ] ]
.SH DESCRIPTION
.PP
\fIsqrs\fR attempts to locate QRS complexes in an ECG signal in the specified
\fIrecord\fR.  The detector algorithm is based on example 10 in the \fIECG
Database Programmer's Guide\fR, which in turn is based on a Pascal program
written by W.A.H. Engelse and C. Zeelenberg, ``A single scan algorithm for
QRS-detection and feature extraction'', \fIComputers in Cardiology\fB
6\fR:37-42 (1979).  \fIsqrs\fP does not include the feature extraction
capability of the Pascal program.  The output of \fIsqrs\fR is an annotation
file (with annotator name \fIqrs\fR) in which all detected beats are labelled
normal; the annotation file may also contain `artifact' annotations at
locations that \fIsqrs\fR believes are noise-corrupted.
.PP
\fIsqrs\fR can process records containing any number of signals, but it uses
only one signal for QRS detection (signal 0 by default;  this can be changed
using the \fB-s\fR option, see below).  For best results on adult human ECGs,
use \fIxform\fR to resample the input signal at 250 Hz if a different sampling
frequency was used originally (or use \fIsqrs125\fR, a variant of \fIsqrs\fR
designed for signals sampled at 125 Hz). For other ECGs, it may be necessary to
experiment with the input sampling frequency and the time constants indicated
in the source file.
.PP
This program is provided as an example only, and is not intended for any
clinical application.  At the time the algorithm was originally published,
its performance was typical of state-of-the-art QRS detectors.  Recent designs,
particularly those that can analyze two or more input signals, may exhibit
significantly better performance.
.PP
\fIOptions\fR include:
.TP
\fB-f\fI time\fR
Begin at the specified \fItime\fR in \fIrecord\fR (default: the beginning of
\fIrecord\fR).
.TP
\fB-m\fI threshold\fR
Specify the detection \fIthreshold\fR (default: 500 units);  use higher values
to reduce false detections, or lower values to reduce the number of missed
beats.
.TP
\fB-s\fI signal\fR
Specify the \fIsignal\fR to be used for QRS detection (default: 0).
.TP
\fB-t\fI time\fR
Process until the specified \fItime\fR in \fIrecord\fR (default: the end of the
\fIrecord\fR).
.PP
The shell variable \fBDB\fR should be set and exported (see \fIsetdb\fR(1)).
.SH EXAMPLES
.PP
To mark 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:
.br
\fBsqrs -r 100 -f 5:0 -t 10:35 -s 1\fR
.br
The output annotations may be read using (for example):
.br
\fBrdann -a qrs -r 100\fR
.PP
To evaluate the performance of this program, run it on the entire record, by:
.br
\fBsqrs -r 100\fR
.br
and then compare its output with the reference annotations by:
.br
\fBbxb -r 100 -a atruth qrs\fR
.SH SEE ALSO
bxb(1), rdann(1), setdb(1), xform(1)