a semi - automatic atrial defibrillation system monitors activity of a heart , detects atrial fibrillation , and cardioverts detected af . the system includes an implantable atrial defibrillator capable of communicating with an external portable device that can further communicate with a remote service center . the implantable atrial defibrillator is capable of detecting af , automatically sending warning signal and diagnostic data to an external portable device after detection of af , receiving commands from the external portable device , and cardioverting af . the external portable device is capable of sending commands to the implantable atrial defibrillator , receiving data from the implantable atrial defibrillator , providing patient discernable warning signal and brief diagnostic information after detection of af , and transmitting diagnostic information to the remote service center . the external portable device is operable by the patient , who may self - control the delivery of atrial cardioversion therapy after receiving the af warning message , or may contact the remote service center for physician &# 39 ; s advice before taking any action .