The following heart signals will be measured by 
'Cardiac' or 'Heart' mode:
Heart Beat - bpm or bps 
       HRT - Heart Rate Turbulence 
        ST - ST Segment Analysis 
       QTc - QT Analysis 
     AC/DC - Acceleration and Deceleration Capacity 
       HRV - Heart Rate Variability 
       TWA - T-Wave Alternans