Welch Allyn Means ECG Physicians Manual for CP Series Electrocardiographs - User Manual - Manual (Page 32)

MEANS Physicians Manual
Welch Allyn
32
3 Rhythm analysis
3.1 Introduction
In this section of the algorithm a wide range of diagnoses is offered. There are six basic
processing steps:
1 The first aim of the algorithm is to detect artificial pacemaker spikes. If these are found,
the program will issue an appropriate statement and stop. Contour analysis is performed if
there are enough unpaced complexes.
2 If no artificial pacemaker spikes are detected, the program will try to find QRS complexes
which do not conform to the dominant complexes in the ECG. These non-dominant
complexes are analyzed, classified and discarded so that further rhythm analysis can be
performed on sequences of complexes of the dominant type.
3 After this procedure, with only one type of QRS complexes left to analyze, the program
will look for flutter waves. Finding no flutter waves does not automatically mean that the
diagnosis of atrial flutter cannot be made. This precaution has been built in because it is
not always possible for the computer to detect flutter waves.
4 For the actual rhythm analysis, a division is made between regular and irregular rhythms.
A rhythm is judged to be regular if the difference between the maximum and minimum RR
interval is less than 20% of the average RR interval. If there are RR intervals falling
outside this range, the rhythm is categorized as irregular.
5 Subsequently, the algorithm checks which relationship exists between the dominant QRS
complexes and P waves. There are several possibilities:

There are no P waves found. The analyzed ECG falls into this category if fewer than
15% of the QRS complexes are preceded by P waves. This criterion has been built in
to make allowance for the program detecting P waves by mistake.

Some QRS complexes are preceded by P waves, but others are not. This category
will be chosen if 15-90% of the QRS complexes are preceded by P waves.

Each QRS complex is preceded by one and only one P wave. This category will be
chosen if 90-100% of the QRS complexes is preceded by a P wave. This criterion was
so formulated because it is possible that the program will incidentally miss a P wave.

Some or all QRS complexes are preceded by more than one P wave. This implies that
the number of P waves is larger than that of the QRS complexes.
6 A final distinction between the diagnostic groups is the constancy of the PR intervals. With
difference between the largest PR interval and the shortest PR interval of less than 30 ms
the interval is said to be constant.