Researchers from the University Medical Center Groningen performed a validation of the ECG from participants at 1A visit 1 and 2A visit 1. Additionally, derivative variables have been created. (sections: physical state (ECG) and secondary & linked variables)).

The heart rate variability (HRV) variables will be available soon in the Lifelines catalogue or by email (data@lifelines.nl).

For participants 13 years or older, 10 second single 12 –lead resting electrocardiogram ECG was recorded using Cardioperfect software (Welch Allyn DT100 recorder, Welch Allyn, Skaneateles Falls, NY). To calculate heart rate variability (HRV), ECG signals were extracted from the Lifelines ECG database. Lifelines cardiologistst inspected all the ECG signals to determine whether the ECG could be used or not. ECG signals were retrieved from the Lifelines ECG database using an in-house software developed by Dr. van Roon from Department of Vascular Medicine (UMCG) in collaboration with Prof. Snieder at Department of Epidemiology (UMCG). This software semi-automatically calculates the HRV indices. All ECG recordings with arrhythmia, pacemaker, and triggering failure were excluded.

Using the ECG recordings that passed the validation stage, some derivative variables were calculated:

1. new HRV indices corrected for the effect of mean interbeat interval using coefficient of variation
2. ln-transformation of HRV indices (because of skewed distribution)
3. identification of outliers (value above/below 5SDs from the mean)

Additionally, a correction has been performed in case two ECG measurements were available for one participant: the measurement with the lowest mean interbeat interval was excluded.