in a subcutaneous implantable cardioverter / defibrillator , cardiac arrhythmias are detected to determine necessary therapeutic action . cardiac signal information is sensed from far field electrodes implanted in a patient . the sensed cardiac signal information is then amplified and filtered . parameters such as rate , qrs pulse width , cardiac qrs slew rate , amplitude and stability measures of these parameters from the filtered cardiac signal information are measured , processed and integrated to determine if the cardioverter / defibrillator needs to initiate therapeutic action .