Differentiation of irregular rhythms by frequency distribution analysis.

Distinctive electrocardiographic patterns for atrial fibrillation, sinus rhythm and atrial extrasystoles, sinus arrhythmia and atrial flutter were found by analysing the frequency distribution of cycle lengths of the electrocardiogram. Frequency distribution analysis, demonstrated that atrial fibrillation is not completely irregular, but shows more long cycles than expected by chance and often a mode at the lower end of the distribution. Irregular atrial flutter is similar. Sinus arrhythmia has more variable organization, but usually there is a centrally situated mode with decreasing observations to the two extremities, and positive skewing. Examples of sinus rhythm and atrial extrasystoles usually have a mode at the upper end of the distribution with a secondary concentration of observations at the lower extremity. Ratios derived from the frequency distributions were of value in differentiating these arrhythmias. It is suggested that such information will improve computer identification of arrhythmia.