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--- a +++ b/mit-bih-arrhythmia-database-1.0.0/mitdbdir/intro.htm @@ -0,0 +1,336 @@ +<html> +<head> +<title>MIT-BIH Arrhythmia Database Directory (Introduction)</title> +</head> +<body bgcolor="#FFFFFF"> + +<a href="mitdbdir.htm"><h1 align=center>MIT-BIH Arrhythmia Database Directory +</h1></a> + +<p> +<b>Next:</b> <a href="records.htm">Records</a> +<b>Up:</b> <a href="mitdbdir.htm#toc">Contents</a> +<b>Previous:</b> <a href="foreword.htm">Foreword</a> + +<a name="intro"><h1>Introduction</h1></a> +<p> +This introduction describes how the database records were +obtained, and discusses the characteristics of the recorded signals. +Following these notes are annotated ``full disclosure'' plots of the entire +database. These can be useful for obtaining an overall +impression of the contents of individual records. Following the +``full disclosure'' plots are sample ECG strips. These strips +were chosen to illustrate the salient features of each record. +Next are notes on the important features of each record. +These notes also include background information on the subjects, +including their medications. +At the end of the book are tables of rhythms and annotations, which +summarize the contents of the database. +These tables can be helpful in finding a record with a specific +set of characteristics. + +<a name="selection"><h2>Selection criteria</h2> +<p> +The source of the ECGs included in the MIT-BIH Arrhythmia Database is a +set of over 4000 long-term Holter recordings that were obtained +by the Beth Israel Hospital Arrhythmia Laboratory between 1975 and 1979. +Approximately 60% of these recordings were obtained from inpatients. +The database contains 23 records +(numbered from 100 to 124 inclusive with some numbers missing) +chosen at random from this set, and 25 records +(numbered from 200 to 234 inclusive, again with some numbers missing) +selected from the same set to include a variety of rare but clinically +important phenomena that would not be well-represented +by a small random sample of Holter recordings. +Each of the 48 records is slightly over 30 minutes long. +<p> +The first group is intended to serve as a representative sample of the +variety of waveforms and artifact that an arrhythmia detector might +encounter in routine clinical use. A table of random numbers was used +to select tapes, and then to select half-hour segments of them. +Segments selected in this way were excluded only if neither of the two +ECG signals was of adequate quality for analysis by human experts. +<p> +Records in the second group were chosen to +include complex ventricular, junctional, +and supraventricular arrhythmias and conduction abnormalities. Several +of these records were selected because features of the rhythm, QRS +morphology variation, or signal quality may be expected to present +significant difficulty to arrhythmia detectors; these records have +gained considerable notoriety among database users. +<p> +The subjects were 25 men aged 32 to 89 years, and 22 women aged 23 to 89 +years. (Records 201 and 202 came from the same male subject.) + +<a name="leads"><h2>ECG lead configuration</h2></a> +<p> +In most records, the upper signal is a modified limb lead II (MLII), +obtained by placing the electrodes on the chest. The lower signal is +usually a modified lead V1 (occasionally V2 or V5, and in one instance V4); +as for the upper signal, the electrodes are also placed on the chest. +This configuration is routinely used by the BIH Arrhythmia Laboratory. +Normal QRS complexes are usually prominent in the upper signal. +The lead axis for the lower signal may be nearly orthogonal to the mean +cardiac electrical axis, however (i.e., normal beats are usually +biphasic and may be nearly isoelectric). +Thus normal beats are frequently difficult to discern in the lower signal, +although ectopic beats will often be more prominent (see, for example, record +106). +A notable exception is record 114, for which the signals were reversed. +Since this happens occasionally in clinical practice, arrhythmia detectors +should be equipped to deal with this situation. +In records 102 and 104, it was not possible to use modified lead II because of +surgical dressings on the patients; +modified lead V5 was used for the upper signal in these records. + +<a name="analog"><h2>Analog recording and playback</h2></a> +<p> +The original analog recordings were made using nine Del Mar Avionics +model 445 two-channel recorders, designated <i>A</i> through <i>I</i>: +<table border> +<tr><th><i>Recorder</i></th><th><i>Records</i></th></tr> +<tr><td align=center><i>A</i></td><td>102, 107, 111, 115, 121</td></tr> +<tr><td align=center><i>B</i></td><td>212</td></tr> +<tr><td align=center><i>C</i></td><td>203</td></tr> +<tr><td align=center><i>D</i></td><td>118, 124, 217</td></tr> +<tr><td align=center><i>E</i></td> + <td>101, 103, 106, 108, 112, 117, 119, 122, 209, 219, 220, 223, 233</td></tr> +<tr><td align=center><i>F</i></td> + <td>104, 109, 123, 205, 207, 210, 215, 221</td></tr> +<tr><td align=center><i>G</i></td> + <td>100, 105, 114, 116, 213, 214, 222, 228</td></tr> +<tr><td align=center><i>H</i></td><td>113, 201, 202, 231</td></tr> +<tr><td align=center><i>I</i></td><td>200, 230, 232, 234</td></tr> +</table> +<br> +(It is not known which recorder was used for record 208.) +<p> +During the digitization process, the analog recordings were played back +on a Del Mar Avionics model 660 unit. The analog tapes used for records +112, 115 through 124, 205, 220, 223, and 230 through 234 were played back +and digitized at twice real time; the rest were played back at real time +using a specially constructed capstan for the model 660 unit. +Skew between the two signals was found to be as great as 40 +milliseconds for some of the analog recorders. +In addition to the fixed skew that results from extremely small differences +in the orientations of the tape heads on the recorder and the playback unit, +microscopic vertical wobbling of the tape, either during recording or playback, +introduces a variable skew, which may be comparable in magnitude to the fixed +skew. +This problem (which also +occurs on the AHA database) may present difficulties for certain two-channel +analysis methods designed for real-time applications. +<p> +Minor tape speed variations should not pose problems for typical arrhythmia +detectors. It is difficult to avoid tape sticking or slippage during low-speed +playback, and several episodes of tape slippage were noted and marked with +comment annotations. Wow and flutter should be studied carefully in the +context of heart-rate variability studies, since flutter compensation +was not possible in these recordings. A number of frequency-domain artifacts +have been identified and related to specific mechanical components of the +recorders and the playback unit: +<table border> +<tr><th><i>Frequency (Hz)</i></th><th><i>Source</i></th></tr> +<tr><td align=center>0.042</td><td>Recorder pressure wheel</td></tr> +<tr><td align=center>0.083</td><td>Playback unit capstan (for twice real-time playback)</td></tr> +<tr><td align=center>0.090</td><td>Recorder capstan</td></tr> +<tr><td align=center>0.167</td> + <td>Playback unit capstan (for real-time playback)</td></tr> +<tr><td align=center>0.18-0.10</td> + <td>Takeup reel (frequency decreases over time)</td></tr> +<tr><td align=center>0.20-0.36</td> + <td>Supply reel (frequency increases over time)</td></tr> +</table> +<br> +The most significant of these artifacts by far is the 0.167 Hz artifact on +recordings that were played back at real time. The next largest is the +0.090 Hz artifact; the 0.083 Hz artifact on recordings that were played back +at twice real-time is of roughly the same magnitude as the 0.090 Hz artifact. +The 0.042 Hz artifact is of much lower magnitude. Other frequencies +related to the drive train (at 0.42 Hz, 1.96 Hz, 9.1 Hz, and +42 Hz) do not appear as noticeable artifacts. +The frequencies of the last two artifacts listed in the table depend on +how much tape is on the supply and takeup reels; the supply reel causes +a much more noticeable artifact than does the takeup reel. Other +frequency-domain artifacts generated by the supply reel appear in the +0.10-0.18 Hz and 0.30-0.54 Hz bands. +<p> +Four of the 48 records (102, 104, 107, and 217) include paced beats. +The original analog recordings do not represent the pacemaker artifacts +with sufficient fidelity to permit them to be recognized by pulse amplitude +(or slew rate) and duration alone, the method commonly used for real-time +processing. The database records reproduce the analog recordings with +sufficient fidelity to permit use of pacemaker artifact detectors designed for +tape analysis, however. + +<a name="digitization"><h2>Digitization</h2></a> +<p> +The analog outputs of the playback unit +were filtered to limit analog-to-digital converter (ADC) +saturation and for anti-aliasing, +using a passband from 0.1 to 100 Hz relative to real time, well +beyond the lowest and highest frequencies recoverable from the recordings. +The bandpass-filtered signals were +digitized at 360 Hz per signal relative to real time +using hardware constructed at the MIT Biomedical Engineering Center and +at the BIH Biomedical Engineering Laboratory. +The sampling frequency was chosen to facilitate implementations of 60 Hz +(mains frequency) digital notch filters in arrhythmia detectors. +Since the recorders were battery-powered, most of the 60 Hz noise present +in the database arose during playback. +In those records that were digitized at twice real time, this noise appears +at 30 Hz (and multiples of 30 Hz) relative to real time. +<p> +Samples were acquired from each signal almost simultaneously (the intersignal +sampling skew was on the order of a few microseconds). As noted above, analog +tape skew was several orders of magnitude larger. The ADCs were +unipolar, with 11-bit resolution over a ±5 mV range. Sample values thus +range from 0 to 2047 inclusive, with a value of 1024 corresponding to zero +volts. +<p> +The 11-bit samples were originally recorded in 8-bit first difference format +(this was necessary because of limited mass storage capacity). Given the +sampling frequency and the resolution of the ADC, the difference encoding +implies a maximum recordable slew rate of ±225 mV/s. In practice, this +limit was exceeded by the input signals very infrequently, only during severe +noise on a small number of records. The effect on the quality of the recorded +signals is totally negligible. On this CD-ROM, the samples have been +reconstructed from the first differences and stored as pairs of 12-bit +amplitudes packed in triplets of consecutive bytes (for details on the storage +format, see <a href="/physiotools/wag/signal-5.htm">signal(5)</a>). + +<a name="annotations"><h2>Annotations</h2></a> +<p> +An initial set of beat labels was produced by a simple slope-sensitive +QRS detector, which marked each detected event as a normal beat. Two +identical 150-foot chart recordings were printed for each 30-minute record, +with these initial beat labels in the margin. +For each record, the two charts were given to two cardiologists, who worked +on them independently. The cardiologists added additional beat labels +where the detector missed beats, deleted false detections as necessary, +and changed the labels for all abnormal beats. They also added rhythm +labels, signal quality labels, and comments. +<p> +The annotations were transcribed from the paper chart recordings. +Once both sets of cardiologists' annotations for a given record +had been transcribed and verified, they were automatically compared +beat-by-beat, and another chart recording was printed. This chart showed +the cardiologists' annotations in the margin, with all discrepancies +highlighted. Each discrepancy was reviewed and resolved by consensus. +The corrections were transcribed, and the annotations were then analyzed +by an auditing program, which checked them for consistency and which +located the ten longest and shortest R-R intervals in each record (to +identify possible missing or falsely detected beats). +<p> +In early copies of the database, most beat labels were placed +at the R-wave peak, but manually inserted labels were not always +located precisely at the peak. +In copies of the database made since 1983, the beat labels have been shifted +from their original locations. +The ECG (usually the upper signal) was digitally bandpass-filtered to +emphasize the QRS complexes, and each beat label was moved to the major local +extremum, after correction for phase shift in the filter. +A few noisy beats were manually realigned. +This process was applied to all records except record 117 in 1983; the +beat labels for record 117 were not realigned until March 1998, however. +The result is that annotations generally appear at the R-wave peak, and +are located with sufficient accuracy to make the reference annotation +files usable for studies requiring waveform averaging and for +heart rate variability studies (but note the comments +with respect to analog tape wow and flutter above). +In the annotated ECG plots produced by <tt>psfd</tt> and <tt>pschart</tt>, +and in printed copies of this directory, each label is placed so that the +fiducial mark for the annotation corresponds to the left edge of the label. +<p> +The database contains approximately 109,000 beat labels. Sixteen +were corrected in the first seven years after the database was released in 1980 +(in records 104, 108, 114, 203, 207, 217, and 222); in addition, +all of the left bundle branch block beats in record 214 were originally +labelled as normal beats. The rhythm labels +have been more substantially revised and now include notations for paced +rhythm, bigeminy, and trigeminy, which were missing in early copies. +<p> +In October 1998, a rhythm label in record 203 was corrected. In +October 2001, a seventeenth error in the beat labels was discovered +and corrected (in record 209). In April 2003, 26 PVC annotations in +record 119 were manually realigned by small amounts (up to 74 ms). In +May 2003, an eighteenth error in the beat labels was discovered and +corrected (in record 214). In April 2005, many of the episodes +previously labelled as atrial fibrillation in record 222 were +partially or completely relabelled as atrial flutter. In April 2008, +three beat labels were corrected (two in record 108, and one in record +215). In June 2010, the 22nd and 23rd errors in the beat labels were +found and corrected (both in record 203). Thanks to Bob Bruce, Pat +Hamilton, Yin Dengfeng, Roger Mark, Sebastian Vasquez, and Mariano +Llamedo Soria for finding and reporting these errors. + +<hr> + +<a name="symbols"><h1>Symbols used in plots</h1></a> + +<p> +[An expanded and updated version of the table below can be found at +<a href="/physiobank/annotations.shtml"> +<tt>http://www.physionet.org/physiobank/annotations.shtml</tt></a>.] + +<p> +<table border> +<tr><th><i>Symbol</i></th><th><i>Meaning</i></th></tr> +<tr><td><b>·</b> <i>or</i> N</td><td>Normal beat</td></tr> +<tr><td>L</td><td>Left bundle branch block beat</td></tr> +<tr><td>R</td><td>Right bundle branch block beat</td></tr> +<tr><td>A</td><td>Atrial premature beat</td></tr> +<tr><td>a</td><td>Aberrated atrial premature beat</td></tr> +<tr><td>J</td><td>Nodal (junctional) premature beat</td></tr> +<tr><td>S</td><td>Supraventricular premature beat</td></tr> +<tr><td>V</td><td>Premature ventricular contraction</td></tr> +<tr><td>F</td><td>Fusion of ventricular and normal beat</td></tr> +<tr><td>[</td><td>Start of ventricular flutter/fibrillation</td></tr> +<tr><td>!</td><td>Ventricular flutter wave</td></tr> +<tr><td>]</td><td>End of ventricular flutter/fibrillation</td></tr> +<tr><td>e</td><td>Atrial escape beat</td></tr> +<tr><td>j</td><td>Nodal (junctional) escape beat</td></tr> +<tr><td>E</td><td>Ventricular escape beat</td></tr> +<tr><td>/</td><td>Paced beat</td></tr> +<tr><td>f</td><td>Fusion of paced and normal beat</td></tr> +<tr><td>x</td><td>Non-conducted P-wave (blocked APB)</td></tr> +<tr><td>Q</td><td>Unclassifiable beat</td></tr> +<tr><td>|</td><td>Isolated QRS-like artifact</td></tr> +<tr><td colspan=2 align=center>Rhythm annotations appear <i>below</i> the +level used for beat annotations:</td></tr> +<tr><td>(AB</td><td>Atrial bigeminy</td></tr> +<tr><td>(AFIB</td><td>Atrial fibrillation</td></tr> +<tr><td>(AFL</td><td>Atrial flutter</td></tr> +<tr><td>(B</td><td>Ventricular bigeminy</td></tr> +<tr><td>(BII</td><td>2° heart block</td></tr> +<tr><td>(IVR</td><td>Idioventricular rhythm</td></tr> +<tr><td>(N</td><td>Normal sinus rhythm</td></tr> +<tr><td>(NOD</td><td>Nodal (A-V junctional) rhythm</td></tr> +<tr><td>(P</td><td>Paced rhythm</td></tr> +<tr><td>(PREX</td><td>Pre-excitation (WPW)</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>(VFL</td><td>Ventricular flutter</td></tr> +<tr><td>(VT</td><td>Ventricular tachycardia</td></tr> +<tr><td colspan=2 align=center>Signal quality and comment annotations appear <i>above</i> +the level used for beat annotations:</td></tr> +<tr><td><i>qq</i></td> +<td> +Signal quality change: the first character (`c' or `n') indicates the quality +of the upper signal (clean or noisy), and the second character indicates the +quality of the lower signal</td></tr> +<tr><td>U</td><td>Extreme noise or signal loss in both signals: ECG is unreadable</td></tr> +<tr><td>M (<i>or</i> MISSB)</td><td>Missed beat</td></tr> +<tr><td>P (<i>or</i> PSE)</td><td>Pause</td></tr> +<tr><td>T (<i>or</i> TS)</td><td>Tape slippage</td></tr> +</table> + +<HR> +<P><ADDRESS> +<I><A HREF="mailto:george@mit.edu">George B. Moody (<tt>george@mit.edu</tt>)</A></ADDRESS></I><BR> +24 May 1997 +<br> +<i>Revised 24 June 2010</i> +</body> +</html>