DESCRIPTION OF THE LTST DATABASE ANNOTATION FILES
Here is updated description of the annotation files and ST annotation
codes (and related measurements) according to the annotation protocol
used for the records of the LTST DB.
Each record in the LTST database includes the following files:
(The format of the files is the MIT DB format.)
sXXXXX.dat Data file (Two channel ECG data sampled at 250 Hz.)
sXXXXX.hea Header file
sXXXXX.ari ARISTOTLE's file (QRS labels attached to each heart
beat, plus rhythm changes.)
sXXXXX.atr Atruth file (QRS labels as manually determined attached
to each heart beat, plus rhythm changes.)
sXXXXX.sta ST annotation atruth file (This is the ST ANNOTATION file.)
sXXXXX.16a ST measurement atruth file
(The ST measurements were derived from the AVERAGE heart
beats. These average heart beats are composed for each
single heart beat (those which passed the preprocessing
phase as clean) from the 16 second time window surounding each
heart beat. The ST measurements thus obtained are attached
back to single heart beats.)
XXXXX - the record number
1. sXXXXX.16a file: (What it contains):
First, we computed average heart beats in the time windows of 16 seconds
for each clean heart beat. Clean heart beats are those which passed
filtering in the KL space during preprocesing phase. After that, we
manually set the position of the point defining the isoelectric level
and J-point for these average heart beats. Not for all of them, but
very frequently, i.e., prior to ST episode, at the peak of ST episode,
after the ST episode, prior to axis shift, after the axis shift,
otherwise approximately every 20 minutes. This manual seting of the
two fiducial points is performed during dummy annotation phase. The
positions of the points defining the isoelectric level and J-points
for the rest of average beats were computed using linear interpolation.
After that, we computed a number of ST measurements for each average
beat. These ST measurements were attached back to each single heart
beat. So, each ST annotation in the file sXXXXX.16a is attached to a
heart beat and contains ST measurements obtained on the corresponding
average heart beat. Noisy heart beats are not attached with these
annotations. They were judged as noisy during the preprocessing phase.
Time index of each ST annotation: ARISTOTLEs fiducial point plus
16 mili seconds.
The format of ST annotation is:
[DMY]STx+-aaaa,+-aaaa,+-aaaa,+-aaaa,+-aaaa,+-aaaa,
(a) (b) (c) (d) (e) (f)
+-aaaa,+-aaaa,NNint,Jpoint,J8060,nleft,nright
(g) (h) (i) (j) (k) (l) (m)
(a) ST amp.at J+80(60)(*)
(b) ST amp.at J-point
(c) ST amp.at J+20
(d) ST amp.at J+40
(e) ST amp.at J+60
(f) ST amp.at J+80
(g) ST amp.at J+100
(h) ST amp.at J+120
(i) Position of isoelectric level (mili seconds prior to ARISTOTLE's
fiducial point)
(j) Position of J-point (mili seconds after the ARISTOTLE's fiducial
point)
(k) Position of the point of measurement (mili seconds after the
ARISTOTLE's fiducial point)
(l) Number of heart beats left of current heart beat included into
the average beat
(m) Number of heart beats right of current heart beat included into
the average beat (**)
(The ST amplitude measurements (isoelectric level, J+XX ms) were
obtained as means of five ECG samples (20 mili seconds) in the
average waveforms.)
x: Lead number
[DMY]: Whether or not the average beat corresponds with manually
obtained measurements
(none: Does not, the measurements were obtained according
to prior interpolation of the positions of the points
defining the isoelectric level and J-points
DMY: The average beat corresponds to manually determined
measurements. The positions of the point defining
the isoelectric level and J-point were determined
manually for this average heart beat.)
(*) These measurments were obtained at the J-point plus 80 (or 60ms).
The point of measurement was determined according to heart rate
by the following rule:
J+80 if HR < 100 bpm
J+72 if HR >= 100 bpm and HR < 110 bpm
J+64 if HR >= 110 bpm and HR < 120 bpm
J+60 if HR >= 120 bpm
These measurements (J+80(60)) also serve as a basis for the ST
LEVEL FUNCTION which was used for ST annotating regarding ST
episodes. These ST annotations are described below in item 2.
(**) Thus, nleft + nright + 1 equals total number of heart beats
included into this average.
2. sXXXXX.sta file (What it contains):
ST annotations in this file mark: global reference, local
reference, the beginning of an ST episode, its extrema, its end,
noise, axis shift, or change due to QRS conduction change.
The ST measurements, i.e., ST amplitudes at J+80(60) obtained on
average heart beats are the basis for the raw ST LEVEL FUNCTION.
The J+80(60) samples were then smoothed, resampled (0.5 Hz) and
smoothed (7 point moving average - window of 12 seconds) thus
forming smooth ST LEVEL FUNCTION (or just ST LEVEL FUNCTION).
Next, we set a global reference and many local reference
annotations in the ST LEVEL FUNCTION for each ECG lead throughout
the record. By inserting the local references we tracked the
ST REFERENCE FUNCTION of the ST segment level (reference ST
level). After that, we subtracted the ST REFERENCE FUNCTION
(piecewisely linearly approximated ST LEVEL FUNCTION from local
reference to local reference) from the ST LEVEL FUNCTION. Thus,
we ended in the ST DEVIATION FUNCTION (or subtracted function).
Next, we annotated ISCHEMIC and RATE-RELATED episodes in the ST
DEVIATION FUNCTION. We also annotated noises and unreadable
intervals. Previously, during tracking the ST REFERENCE
FUNCTIN, we annotated axis shifts and shifts due to QRS
conduction changes.
Description of annotation codes:
Time index: Index of sample in the ST DEVIATION FUNCTION.
ST annotation codes:
The annotations could be in lower or in upper case characters.
Upper case: Annotations were set with regard to global reference
in the ST LEVEL FUNCTION. (These annotations are
global reference and local references.)
Lower case: Annotations were set with regard to the ST REFERENCE
FUNCTION (reference ST level) in the ST DEVIATION
FUNCTION.
(These are annotations for ischemic episodes,
rate-related episodes, axis shifts, conduction
change shifts, noises and unreadable events.)
Code Meaning
GRST x Global reference
LRST x +- llll Local reference
s[cc]st x Significant ST shift
([rt]st x +- dddd Beginning of significant ST episode
a[rt]st x +- dddd Extrema of significant ST episode
[rt]st x +- dddd) End of significant ST episode
noi x +- dddd Noise
(und x Beginning of unreadable interval
und x ) Beginning of unreadable interval
Legend:
x: lead number (0 or 1 or 2)
+- llll: ST level in microV
+- dddd: ST deviation in microV
[cc]: type of ST shift
(none: axis shift
cc: conduction change)
[rt]: type of episode
(none: ischemic
rt: rate-related)
Critera for episodes:
1.An episode begins when the magnitude of the ST deviation
function first exceeds 50 uV;
2.The deviation must reach a magnitude of Vmin or more throughout
a continuous interval of at least Tmin;
3.The episode ends when the deviation becomes smaller than 50 uV,
provided that it does not exceed 50 uV in the following 30 seconds.
3. sXXXXX.stb file
Vmin = 100 uV, Tmin = 30 s
4. sXXXXX.stc file
Vmin = 100 uV, Tmin = 60 s
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