Table 1.

Methods of determination or calculation of the electrocardiographic (ECG) variables used in the analysis of the 1,554 healthy volunteers aged 18 to 30 years with a body mass index (BMI) between 18.5 and 30.0 kg/m²

Variable	Description
Maximum P-wave duration (ms)	Longest P-wave duration sampled from all leads
P-wave balance in lead V1 (µV)	Difference between the upward and downward deflection of the P‑wave
P-wave dispersion (ms)	Difference between the longest minus the shortest P-wave duration from all leads
Total P-wave area in lead V1 (mm*ms)	Sum of the total area under and above the isoelectric line from onset to termination of the P‑wave [27]
PR interval (ms)	Beginning of the P‑wave until the beginning of the QRS complex
QRS duration (ms)	First deflection from the isoelectric line following the P‑wave until the J‑point
Heart axis (degrees)	Net vector of the R wave axis based on the extremity leads
Sokolow-Lyon voltage (mm)	Sum amplitude of the S wave in lead V1 and the amplitude of the R wave in lead V5 or V6 (whichever is larger) [28]
Cornell product (ms*mm)	Product of the QRS duration and the Cornell voltage [29]. Cornell voltage is the sum of the amplitude of the R wave in lead aVL and the amplitude of the S wave in lead V3 [29]
Maximum T‑wave duration (ms)	Longest T‑wave duration sampled from all leads
Minimum T‑wave duration (ms)	Shortest T‑wave duration sampled from all leads
T-wave dispersion (ms)	Difference between the longest and shortest T‑wave duration selected from all leads
QTcF duration (ms)	QTcF duration is calculated using the Fridericia formula, which divides the QT interval by the cube root of RR interval [30]. QT interval is the interval between the start of the Q wave and the end of the T wave. RR interval is the interval between the onset of one QRS complex to the onset of the next QRS complex, measured in seconds, derived from the heart rate (HR) as 60/HR

mV millivolt, µV microvolt, ms milliseconds, mm millimetres, QTcF corrected QT interval with the Fridericia formula