An implantable medical device and method for determining an atrial arrhythmia event, comprising: a cardiac sensing device including a housing containing circuitry, and a plurality of electrodes electrically coupled to circuitry for sensing cardiac signals And generating an initial detection of an atrial arrhythmia event according to the atrial arrhythmia threshold, determining whether or not a P wave is generated during the initial detection, determining an adaptive threshold according to the detection of the P wave, and determining an atrial according to the adaptive threshold An apparatus and method comprising: a processor configured to adjust an arrhythmia threshold and generate an initial detection of a subsequent atrial arrhythmia event using the adjusted atrial arrhythmia threshold. [Selection] Figure 11心房不整脈事象を判定するための埋込型医療装置および方法であって、回路機構を内蔵するハウジングを含む心臓用感知装置と、心臓信号を感知する回路機構に電気的に連結された複数の電極と、心房不整脈閾値に応じて心房不整脈事象の初期検出を生成し、初期検出中におけるP波発生の有無を判定し、P波の検出に応じて適応閾値を判定し、適応閾値に応じて心房不整脈閾値を調節し、調整後の心房不整脈閾値を使用して後続の心房不整脈事象の初期検出を生成するように構成されたプロセッサーとを含む装置および方法。【選択図】図11