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17 Annex - Rhythm Analysis Detector
According to IEC / EN60601-2-4 it is an essential performance requirement for a defibrillator to
"accurately differentiate between shockable and nonshockable rhythms". This is also defined in the
Requirements for RHYTHM RECOGNITION DETECTOR where the sensitivity of the device to
recognize VF at peak to peak amplitude of 200 µV or higher shall exceed 90% in the absence of
artefacts. For devices which detect VT, the sensitivity shall exceed 75%. The specificity of the detector
in correctly differentiating non-shockable rhythms shall exceed 95% in the absence of artefacts.
1. Test of the rhythm analysis detector
a. Test databank [Databank1]
For the tests of the VF/VT recognition algorithm, data was taken from the CU (Creighton University)
Ventricular Tachyarrhythmia databank. This database includes 35 eight-minute ECG recordings of
human subjects who experienced episodes of sustained ventricular tachycardia, ventricular flutter, and
ventricular fibrillation.
Record cu01 was obtained from a long-term ECG (Holter) recording (played back at real time for
digitization); the other records were digitized in real time from high-level (1 V/mV nominal) analog
signals from patient monitors. All signals were passed through an active second-order Bessel low-
pass filter with a cut-off of 70 Hz, and were digitized at 250 Hz with 12-bit resolution over a 10 V range
(10 mV nominal relative to the unamplified signals). Each record contains 127,232 samples (slightly
less than 8.5 minutes).
In episodes of cardiac failure, fibrillation is almost always preceded by a run of ventricular tachycardia,
which eventually gives way to the fibrillation itself. The onset of fibrillation is extremely difficult to
pinpoint in many cases. Any clinically useful detector should respond to the runs of tachycardia
preceding fibrillation, since medical intervention is needed at the earliest opportunity. Thus any
detector responding to the premonitory tachycardia can exhibit a negative "time to alarm" compared to
the onset of fibrillation as recorded in the reference annotation files. For this reason, the database is
defined as a tachyarrhythmia database rather than a fibrillation database.
In these records, the minimum number of non-VF beats prior to the onset of a VF episode is 61. The
mean time interval from the beginning of the record to the onset of VF is 5:47 (with a standard
deviation of 2:01). Repeated defibrillation attempts are visible in many records.
The reference annotation files supplied for this database have been included to aid users in locating
events of interest. They are in no sense definitive. All beats are labelled normal (although many are
ectopic). VF onset annotations mark only the approximate beginnings of VF episodes.
b. Rhythm selection criteria
The ECG data from the CU database was divided into two groups – "Shockable" and "Nonshockable"
rhythms. All ECG signals from the CU databank were divided into 20 second segments. The 20
second period was chosen to accommodate both pre and post rhythm analysis cycles (Voice prompt
delivery and analysis time). To avoid loss of signals, there is a 10 second overlap between two
segments (see Figure 1).
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