Welch Allyn Means ECG Physicians Manual for CP Series Electrocardiographs - User Manual - Manual (Page 6)

MEANS Physicians Manual
Welch Allyn
6
1.4 Diagnostic classification
The diagnostic logic operates on the parameters and produces both a rhythm classification
and a contour or morphology classification. The criteria used by the computer may differ from
the criteria used in the ECG textbooks. The basic reason is that a human observer is
inaccurate but flexible and creative, a computer precise and obedient but rigid in its operation.
There are several specific reasons why ECG criteria in the program may differ from the
conventional ones. First, there is no uniformity of criteria in the literature. Then, criteria may
be based on inaccurate measurement by eye. Also, ECG measurements may be “falsified” for
the ease of the reader: axis calculations are generally made from the amplitudes of QRS
complexes rather than from the surface areas under the QRS tracings as prescribed by
theory. Further, criteria are sometimes not quantitatively defined (How flat must a flat ST-T
be? How slurred is a slurred QRS upstroke?) or their measurement is not unequivocally
prescribed. For the computer program to work, a quantitative definition must somehow be
decided upon. Moreover, conventional criteria may have been based on measurements
produced by technically outdated instrumentation. The amplitudes of R waves have been
consistently underestimated, especially in children, due to filtering effects by too low
frequency response of the electrocardiographs. Finally, a human interpreter may deviate from
strict criteria as he sees fit: sometimes criteria have been made to meet a priori expectations.
In one respect, the computer is inferior to the human observer: although the computer can
measure very accurately, its powers of pattern recognition are inferior. For instance, it will
have great trouble in detecting a P wave buried in a ST segment which is easily seen by the
human eye.
1.5 Outline of the manual
The following of this manual consists of two main parts. One part describes the diagnostic
criteria that are employed in the contour classification of the Modular ECG Analysis System
(MEANS), the other describes the criteria used in the rhythm classification of MEANS. Each
part contains a brief introductory section, a description of the measurements that are used in
the diagnostic logic, and a comprehensive list of statements and corresponding diagnostic
criteria. Related statements have been grouped in sections, e.g., all statements related to
intraventricular conduction delay, left ventricular hypertrophy, etc. Finally, an index of the
statements that can be generated by the program is provided on page 55.
A general format is used to specify the diagnostic criteria. The statement is given first,
followed by one or more conditions that must be fulfilled for the statement to be issued by the
program. Multiple conditions are combined with the use of logical “and” and “or” connectives,
binding the (combinations of) conditions that have the same level of indentation. For example:
Say: “probable inferior infarct”
if: Q duration

40 ms and 0.2

Q/R ratio < 0.3 in aVF
or 30  Q duration < 40 ms and Q/R ratio  0.3 in aVF
or Q duration in aVF

20 ms
and Q duration

50 ms and Q amplitude > 300 µV in III