Rate dependence of ventricular extrasystoles: computer identification and quantitative analysis

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Abstract
A new computer program was designed to identify and quantify the rate dependence of arrhythmias using 24 hour Holter tape recordings. The program was used in 10 untreated apparently heatlhy patients with fixed, coupled, isolated monomorphic ventricular extrasystoles. The second cycles of two consecutive sinus cycles were grouped according to whether or not they were followed by a ventricular extrasystole. Each of these sinus cycles was further analysed by cycle length during successive one hour periods. From the number of cycles in each cycle length class, identification and quantification of an upper or lower limit, or both, of cycle length beyond which ventricular extrasystoles disappeared were possible. Upper and lower limit were observed in 10 and eight of the 10 patients respectively. An upper and a lower limit were identifiable (mean(SD) 9.3(5.1) and 8.4(5.8) times per recording respectively). Values of both types of limits varied throughout tape recording. A positive significant correlation was found between the values of upper and lower limits and the mean sinus cycle length during the corresponding hour in nine of the 10 and eight of the eight patients respectively. The type of relation observed suggests that heart rate directly alters limits or that heart rate and limits are under the same influence of the autonomic nervous system. It is concluded (a) that identification and quantification of the rate dependence of arrhythmias is possible using this computer program; and (b) that, in patients with ventricular extrasystoles and apparently normal hearts, upper and lower limits vary and are related to heart rate.