A medical device is provided that comprises a lead assembly. The lead assembly includes at least one intra-cardiac (IC) electrode, an extra-cardiac (EC) electrode and a subcutaneous remote-cardiac (RC) electrode. The IC electrode is configured to be located within the heart. The EC electrode is configured to be positioned proximate to at least one of a superior vena cava (SVC) and a left ventricle (LV) of a heart. The RC electrode is configured to be located remote from the heart. An extra-cardiac impedance (ECI) module is configured to measure extra-cardiac impedance along an ECI vector between the EC and RC electrodes to obtain ECI measurements. An arrhythmia monitoring module is configured to declare a potential atrial arrhythmia to be an atrial arrhythmia based on the hemodynamic performance determined from the ECI measurements. The hemodynamic performance assessment module is further enabled to compare a current ECI pattern with a prior baseline ECI waveform.