A system and method for confirming arrhythmias in an implantable cardiac stimulation device senses electrical events in an intracardiac signal and identifies a potential arrhythmia based on the electrical events. The electrical events may be depolarization events occurring in a heart, such as R-waves or P-waves. The electrical events are high pass filtered and analyzed to confirm or reject the electrical events. The confirmed electrical events are then analyzed to determine whether the electrical events indicate a heart arrhythmia. A therapy may then be applied to the heart for treating the arrhythmia.
