Welch Allyn Cardioperfect Workstation, PEDMEANS ECG Interpretation Module - Physicians - User Manual - Manual (Page 6)

CardioPerfect Workstation
PEDMEANS ECG Interpretation Module Physicians Manual
DIR 80015051 Rev. C 6 / 55
1.2 Pattern recognition
This part deals with the analysis of the various waveforms. First of all the QRS complexes must be
detected. No other waves or artifacts should be labeled as such. The intervals between QRS
complexes are measured and stored. After all QRS complexes have been detected, they are
typified, i.e., a comparison is performed that gives rise to classes of similar QRS complexes. Often
there is only one
type. If there are more, the “ordinary,” “representative” or “dominant” one is
established; the others are “extraordinary” or “non-dominant”. Mostly, the number of dominant
complexes in a recording is larger than that of the non-dominant ones. In special cases this may not
be true. In bigeminy their number may be equal to that of the non-dominant complexes, or be one
less or one more, depending on when the recording starts and stops. If runs of tachycardia occur,
the unusual complexes in a recording may even outnumber the dominant ones.
The second step is to search for atrial activity. Both P waves and flutter waves can be detected,
when present. PP and PR intervals are also measured and stored for use in the rhythm analysis.
The third step is to mutually compare the ST-T segments of the dominant complexes. For the
calculation of the averaged complex only complexes are selected that have not only similar QRS,
but also similar ST-T. In this way, complexes that are disturbed by spikes or sudden baseline jumps
are discarded.
For the morphological analysis the selected dominant P-QRS-T complexes are averaged into one
complex. The main advantage of averaging is to improve the signal-to-noise ratio. Noise is random,
and in the averaging the positive and negative oscillations will cancel out. An additional advantage
is that the analysis now has to be performed only once, on a single representative complex. It may
occur that in the averaged complex a P wave appears which was not consistently detectable in the
rhythm analysis, or vice versa.
The final step in the pattern recognition process is the determination of the zero level in the
representative P-QRS-T complex and the identification of points of onset and offset of P, QRS, and
T. The zero level is determined for the averaged complex per lead in an interval preceding the
onset of the QRS complex. Onsets and offsets however are determined simultaneously over all
leads together.
1.3 Parameter extraction
After the onset and end points of P, QRS and T waves have been established, the relevant
parameters can be measured to provide the input for the diagnostic logic. Besides amplitudes and
durations, other measurements such as surface areas under the signal are derived. Most
measurements are made on the averaged complex in each lead separately (e.g., R amplitude, Q
duration), but some are derived taking all leads in account (e.g., overall QRS duration, PR interval).
These durations are generally longer than one would measure by hand in individual leads or lead
groups since the first onset in any lead and the last offset are taken into account.