An implantable medical device for classifying arrhythmia events being connectable to at least one medical lead (20, 30) adapted to be placed at or within a heart of a patient, said medical lead (20, 30) including at least one electrode (22, 24, 26, 32, 34) adapted to sense electrical activity of said heart and to produce at least one signal representative of said electrical activity, wherein said implantable medical device comprises: an IEGM analyzing circuit adapted to receive, from electrodes (22, 24, 26, 32, 34) arranged in said at least one medical lead (20, 30), said signal representative of said electrical activity and to analyse intracardiac electrograms, IEGMs, of said heart to detect an arrhythmia event; a sensing circuit adapted to sense a respiratory pattern of said patient and to produce at least one signal representative of said respiratory pattern; and a respiratory parameter determining circuit adapted to determine at least one respiratory parameter reflecting characteristics of the respiratory pattern of said patient based on said sensed respiratory pattern, characterized in that said respiratory parameter determining circuit is adapted to determine a respiratory measure corresponding to a change of a rate of change of said at least one respiratory parameter, said implantable medical device further comprising: an arrhythmia classifying circuit adapted to classify the detected arrhythmia event based on said respiratory measure and to classify arrhythmia events that satisfy at least a first criterion as an arrhythmia event requiring therapy, said arrhythmia classifying circuit is adapted to determine said at least a first criterion to be satisfied if said respiratory measure is higher than a predetermined threshold value. an IEGM analyzing circuit adapted to receive, from electrodes (22, 24, 26, 32, 34) arranged in said at least one medical lead (20, 30), said signal representative of said electrical activity and to analyse intracardiac electrograms, IEGMs, of said heart to detect an arrhythmia event; a sensing circuit adapted to sense a respiratory pattern of said patient and to produce at least one signal representative of said respiratory pattern; and a respiratory parameter determining circuit adapted to determine at least one respiratory parameter reflecting characteristics of the respiratory pattern of said patient based on said sensed respiratory pattern, characterized in that said respiratory parameter determining circuit is adapted to determine a respiratory measure corresponding to a change of a rate of change of said at least one respiratory parameter, said implantable medical device further comprising: an arrhythmia classifying circuit adapted to classify the detected arrhythmia event based on said respiratory measure and to classify arrhythmia events that satisfy at least a first criterion as an arrhythmia event requiring therapy, said arrhythmia classifying circuit is adapted to determine said at least a first criterion to be satisfied if said respiratory measure is higher than a predetermined threshold value. an arrhythmia classifying circuit adapted to classify the detected arrhythmia event based on said respiratory measure and to classify arrhythmia events that satisfy at least a first criterion as an arrhythmia event requiring therapy, said arrhythmia classifying circuit is adapted to determine said at least a first criterion to be satisfied if said respiratory measure is higher than a predetermined threshold value.