Method and device for processing a cardiac signal

A subcutaneous active implantable medical device comprising:

• a housing;
• a subcutaneous implantable lead connected to the housing and comprising one or more sensing electrodes configured to capture cardiac rhythms subcutaneously;
• and
• a control circuit configured to:
• provide a number n of different threshold levels Ni, with i=1 to n, and n being greater than or equal to three;
• detect, from a given time T and for each of the different threshold levels Ni, at least two successive intersections of a cardiac signal with each of the different threshold levels Ni, wherein each of the at least two successive intersections indicate to a crossing of a threshold level Ni due to an increasing or decreasing value of the cardiac signal;
• determine at least one statistical parameter for the cardiac signal from the at least two successive intersections of the cardiac signal with the different threshold levels Ni, wherein the determination of the at least one statistical parameter comprises determining a period of the cardiac signal, and wherein the at least one statistical parameter is indicative of an arrhythmia;
• and
• provide, based on the at least one statistical parameter, a defibrillation shock to a patient.