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<p>

An initial set of beat labels was produced by a slope-sensitive QRS detector,

which marked each detected event as a normal beat.  Each two-hour, two-channel

ECG record was printed out in full disclosure format, each page two minutes

in duration, with the addition of QRS detection marks, trend plots of ST

segment displacement and T-wave amplitude (measured for each beat), and boxes

for checking annotation operations.  For each record, two cardiologists

(neither of whom was a member of the research group which had submitted the

record) were given copies of the full-disclosure printout, trend plots of

mean heart rate and ST-T parameters at 10-second intervals, and record-specific

transparent plastic rulers for measuring time intervals and ECG signal

displacements.  A heart rate scale and a two-channel

<a href=#reference-beat>reference QRST complex</a>

(taken from the first 30 seconds of each record) were printed on each ruler.</p>

<p>

Working independently, the cardiologist-annotators visually checked the

computer-generated beat labels on the full-disclosure printouts and manually

corrected them, and inserted annotations indicating changes in ST and T

morphology, rhythm, and signal quality.  Annotations from the two cardiologists

were compared and the differences were resolved by a cardiologist of the

coordinating group.  This method assumes that the third cardiologist is able

to make a more reliable judgement since he knows both sets of annotations.</p>

<h2>Definition of ST and T episodes</h2>

<p>

The cardiologists participating in the project jointly defined and followed

a set of rules for locating <i>ST episodes</i> and <i>T episodes</i> (i.e.,

intervals during which the ECG exhibits significant ST segment or T-wave

changes).  To identify and annotate an ST episode, these criteria were

applied:</p>

<ul>

<li> <i>ST segment deviations</i> are measured relative to a reference

waveform for each subject (usually selected from the first 30 seconds of

each record).  Measurements of ST segment deviation are taken 80 milliseconds

after the J point if the heart rate does not exceed 120 bpm, and 60

milliseconds after the J point otherwise.</li>

<li> <i>ST episodes</i> must contain an interval of at least 30 seconds during

which the absolute value of the ST deviation is no less than 0.1 millivolt

(mV).</li>

<li> The <i>beginning</i> of each ST episode is annotated.  The beginning is

located by searching backward from the time at which the absolute ST deviation

first exceeds 0.1 mV.  The search continues until a beat is found for which

the absolute ST deviation is less than 0.05 mV, and for which the absolute

ST deviation is less than 0.1 mV throughout the previous 30 seconds.  An

ST change annotation which indicates the beginning of the episode is placed

immediately following this beat.</li>

<li> The <i>peak</i> (i.e., the greatest deviation, positive or negative) of

each ST episode is annotated.  An ST change annotation is placed before the

beat judged to exhibit the greatest ST deviation;  this annotation contains

a manual measurement of the peak ST deviation.</li>

<li> The <i>end</i> of each ST episode is annotated.  The end is

located by searching forward from the time at which the absolute ST deviation

last exceeds 0.1 mV.  The search continues until a beat is found for which

the absolute ST deviation is less than 0.05 mV, and for which the absolute

ST deviation is less than 0.1 mV throughout the following 30 seconds.  An

ST change annotation which indicates the end of the episode is placed

immediately before this beat.</li>

</ul>

<p>To identify and annotate a T episode, similar criteria were applied:</p>

<ul>

<li> <i>T deviations</i> are measured relative to the same reference

waveform which is used for measuring ST deviations.  The quantity

<i>A<sub><font size=-1>T</font></sub></i> is defined as the amplitude

of the dominant phase of the T-wave, measured relative to baseline (at

the PQ junction); if the T-wave is inverted, or if the dominant phase

of a biphasic T-wave is below the baseline, <i>A<sub><font

size=-1>T</font></sub></i> is negative.  The T deviation is defined as

the difference (positive or negative) between the values of

<i>A<sub><font size=-1>T</font></sub></i> for the current waveform and

for the reference waveform.</li>

<li> <i>T episodes</i> must contain an interval of at least 30 seconds during

which the absolute value of the T deviation is no less than 0.2 mV.</li>

<li> The <i>beginning</i> of each T episode is annotated.  The beginning is

located by searching backward from the time at which the absolute T deviation

first exceeds 0.2 mV.  When an interval of at least 30 seconds is found in

which the absolute T deviation does not exceed 0.2 mV, the end of that interval

defines the beginning of the episode.  A T change annotation is placed before

the first beat of the episode.</li>

<li> The <i>peak</i> (i.e., the greatest deviation, positive or negative) of

each T episode is annotated.  A T change annotation is placed before the

beat judged to exhibit the greatest T deviation;  this annotation contains

a manual measurement of the peak T deviation.</li>

<li> The <i>end</i> of each T episode is annotated.  The end is

located by searching forward from the time at which the absolute T

deviation last exceeds 0.2 mV.  When an interval of at least 30

seconds is found in which the absolute T deviation does not exceed 0.2

mV, the beginning of that interval defines the end of the episode.  A

T change annotation is placed after the last beat of the episode.</li>

<li> Within T episodes which contain absolute T deviations exceeding 0.4 mV,

additional T change annotations are placed whenever the absolute T deviation

crosses the 0.4 mV threshold value which defines <i>extreme T deviations</i>.

These additional T change annotations indicate the beginning and end of each

such interval of extreme T deviation.</li>

</ul>

<p>

These rules were applied to each of the two signals independently;  for this

reason, each ST and T change annotation indicates the signal to which it

applies.</p>

<p>

Each ST and T change annotation contains a text field which describes its

significance.  The text field contains characters which identify the episode

type ('ST' or 'T'), the signal number ('0' or '1'), and the direction of the

deviation ('+' or '-';  extreme T deviations are signified by '++' and '--').

The text field of an annotation which marks the beginning of an episode

contains a '(' prefix.  For an annotation which marks the end of an episode,

there is a prefixed 'A' and an appended 3- or 4-digit decimal number which

expresses the magnitude of the peak deviation in microvolts.  An annotation

which marks the end of an episode has a ')' appended to the end of its text

field.  For example, an episode of ST depression in signal 0 with a peak

(absolute) deviation of 200 microvolts would be marked by three annotations,

with text fields of '(ST0-', 'AST0-200', and 'ST0-)'.</li>

<p>

In six records (e0161, e0509, e0601, e0611, e0613, and e0615), axis shifts

resulting from positional change give the appearance of real ST or T changes.

These axis shifts are annotated using comment annotations.  The text fields

of these annotations are constructed in the same way as for ST and T change

annotations, except that lower-case characters are used in order to make it

easier to distinguish these axis shift episodes from real ST or T change

episodes.  For example, an axis shift in signal 1 which gives the appearance

of a peak T deviation of 350 microvolts would be marked by three annotations,

with text fields of '(t1+', 'at1+350', and 't1+)'.</li>

<h3>Annotation types</h3>

<p>

The following types of annotations appear in the European ST-T Database

reference (<tt>.atr</tt>) annotation files.  The <b>Code</b> column shows

the symbols defined in

<a href="/physiotools/wfdb/lib/ecgcodes.h">ecgcodes.h</a>, and the

<b>Mnemonic</b> column indicates how these annotations are displayed by

WFDB applications such as <a href="/physiotools/dbag/wave-1.htm">WAVE</a>,

<a href="/physiotools/dbag/wview-1.htm">WVIEW</a>, and

<a href="/physiotools/dbag/pschar-1.htm">pschart</a>.</p>

<div class="edbtable">

<table>

<th class="headerrow">Code</th><th>Mnemonic</th>

 <th>Meaning</th></tr>

<tr><td>NORMAL</td><td>&#149; [bullet]</td><td>Normal beat</td></tr>

<tr><td>ABERR</td><td>a</td><td>Aberrated atrial premature beat</td></tr>

<tr><td>NPC</td><td>J</td><td>Nodal (junctional) premature beat</td></tr>

<tr><td>SVPB</td><td>S</td><td>Supraventricular premature or ectopic beat

 (atrial or nodal)</td></tr>

<tr><td>PVC</td><td>V</td><td>Premature ventricular contraction</td></tr>

<tr><td>FUSION</td><td>F</td><td>Fusion of ventricular and normal beat</td>

 </tr>

<tr><td>UNKNOWN</td><td>Q</td><td>Unclassifiable beat</td></tr>

<tr><td>ARFCT</td><td>|</td><td>Isolated QRS-like artifact</td></tr>

<tr><td valign=top>RHYTHM</td><td></td>

 <td>Rhythm change, specified by text field:<br>

 <table>

 <tr><td>(AB</td><td>Atrial bigeminy</td></tr>

 <tr><td>(AFIB</td><td>Atrial fibrillation</td></tr>

 <tr><td>(B</td><td>Ventricular bigeminy</td></tr>

 <tr><td>(B3</td><td>Third degree heart block</td></tr>

 <tr><td>(N</td><td>Normal sinus rhythm</td></tr>

 <tr><td>(SAB</td><td>Sino-atrial block</td></tr>

 <tr><td>(SBR</td><td>Sinus bradycardia</td></tr>

 <tr><td>(SVTA</td><td>Supraventricular tachyarrhythmia</td></tr>

 <tr><td>(T</td><td>Ventricular trigeminy</td></tr>

 <tr><td>(VT</td><td>Ventricular tachycardia</td></tr>

 </table></td></tr>

<tr><td valign=top>STCH</td><td></td>

 <td>ST change, specified by text field:<br>

 <table>

 <tr><td>(ST...</td><td>Beginning of ST episode</td></tr>

 <tr><td>AST...</td><td>Peak of ST episode</td></tr>

 <tr><td>ST...)</td><td>End of ST episode</td></tr>

 </table></td></tr>

<tr><td valign=top>TCH</td><td></td>

 <td>T change, specified by text field:<br>

 <table>

 <tr><td>(T...</td><td>Beginning of T episode</td></tr>

 <tr><td>AT...</td><td>Peak of T episode</td></tr>

 <tr><td>T...)</td><td>End of T episode</td></tr>

 </table></td></tr>

<tr><td valign=top>NOTE</td><td></td>

 <td>Comment annotation, specified by text field:<br>

 <table>

 <tr><td>(st...</td>

   <td>Beginning of ST deviation resulting from axis shift</td></tr>

 <tr><td>ast...</td>

   <td>Peak of ST deviation resulting from axis shift</td></tr>

 <tr><td>st...)</td>

   <td>End of ST deviation resulting from axis shift</td></tr>

 <tr><td>(t...</td>

   <td>Beginning of T deviation resulting from axis shift</td></tr>

 <tr><td>at...</td>

   <td>Peak of T deviation resulting from axis shift</td></tr>

 <tr><td>t...)</td>

   <td>End of T deviation resulting from axis shift</td></tr>

 <tr><td>BUTTON</td>

   <td>Patient-activated event button pressed</td></tr>

 <tr><td>TS</td>

   <td>Tape slippage</td></tr>

 </table></td></tr>

<tr><td valign=top>NOISE</td><td valign=top><i>qq</i></td>

 <td>Signal quality change:  the first character ('c', 'n', or 'u')

       indicates the quality of signal 0 (clean, noisy, or unreadable),

       and the second character indicates the quality of signal 1.

       The <tt>subtyp</tt> field of the annotation encodes these

       characters:<br>

 <table>

 <tr><td>0x00</td><td>cc</td>

 <tr><td>0x01</td><td>nc</td>

 <tr><td>0x02</td><td>cn</td>

 <tr><td>0x03</td><td>nn</td>

 <tr><td>0x11</td><td>uc</td>

 <tr><td>0x12</td><td>un</td>

 <tr><td>0x20</td><td>cu</td>

 <tr><td>0x21</td><td>nu</td>

 <tr><td>0x33</td><td>uu</td>

 </table></td></tr>

</table> 

</div> <!-- end edbtable -->

<h3 id="reference-beat">Which was the reference beat in each record?</h3>

<p>

As noted above, the expert annotators were given a clear plastic

template on which had been printed a reference waveform.  The position

of this waveform was not recorded, however, and the original plastic

templates no longer exist.  The only available information about the

choice of reference beat is that the waveform was taken from the first

30 seconds of the record being annotated.  One may assume that the

waveform was typical of those within the 30-second interval, and that

if the amount of noise varied significantly within the interval, the

reference was one of the cleaner waveforms.</p>

<p>

As a practical matter for evaluation of an algorithm for automated ST

analysis using this database, this question need not be an issue.

Some of the patients represented in the database had prior myocardial

infarctions with consequent fixed ST elevation or depression.  The ST

annotations in this database mark transient ST changes that are

superimposed on any fixed elevation or depression.  The important

point is that this database's annotations provide samples not of

the <em>ST level</em> function (the difference, for any given time,

between the ECG amplitudes of the nearest beat during the ST segment

and at the isoelectric point), but of the <em>ST deviation</em>

function (the difference between the ST level function measured at any

given time and during the first 30 seconds of the record).

Put another way, the ST level function is the sum of the fixed

elevation or depression (the reference ST level) and the transient

changes in ST level (the ST deviation function).</p>

<p>

To use this database to evaluate an ST analysis algorithm, the

algorithm needs to estimate the ST deviation function, a

task that requires determining its own reference ST level (using any

desired method;  a median of its ST level measurements made during the

first 30 seconds is a commonly used approach).  The algorithm's ST

deviation function is the difference between its ST level function and its

reference ST level.  See <a href="/physiotools/wag/epicmp-1.htm">epicmp</a>

for details on how to record an algorithm's ST deviation function in an

annotation file, and how to use standard software to measure how well

an algorithm's ST deviation measurements match those provided with the

database.</p>

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