Variable,Description 
subject_id,An identifier for the subject which aligns across the MIMIC-IV database
study_id,An identifier for the study which the diagnostic ECG is associated with
cart_id,An identifier specific to the ECG cart used to collect the diagnostic ECG waveform 
ecg_time,The date that the diagnostic ECG was collected on
report_#,A text based cardiology report generated by the ECG machine. A variable number of report #'s are expected and can be separated by blank rows.
bandwidth,The bandwidth of the ECG machine
filtering,An indicator for the filter setting
rr_interval,Time between successive R-waves (msec)
p_onset,Time at the onset of the P-wave (msec)
p_end,Time at the end of the P-wave (msec)
qrs_onset,Time at the beginning of the QRS complex (msec)
qrs_end,Time at the end of the QRS complex (msec)
t_end,Time at the end of the T-wave (msec)
p_axis,The electrical axis of the P-wave (degrees)
qrs_axis,The electrical axis of the QRS complex (degrees)
t_axis,The electrical axis of the T-wave (degrees)