[The frequency variation--a parameter in the evaluation of heart rhythm]

The duration of the pulse period shows under physiological conditions a though slight variation, which is regarded as the expression of the vegetative regulation of the heart. When this "irregularity" of the duration of the pulse period decreases or increases, it has pathological significance. A calculation algorithm of this parameter called variation of frequency is given. When it is between 2.5 and 10%, i.e. the length of the duration of the pulse period varies by this sum by the mean value, this can be regarded as physiological. At a variation of frequency below 2.5% one speaks of cardiac automatism. It has the same significance as the omission of the vegetative regulation of the heart and thus shows a bad prognosis for the patient. When the variation of frequency is more than 10%, a disturbance of the cardiac rhythm (of various form) is to be derived. At the same time the condition of the criterion of untimeliness can again be formulated. According to this an untimely beginning of beating of the heart (an extrasystole) is existing then, when it begins in an interval of less than 0.9-fold of a normal RR-interval.