Illustration of ECG waves and values.

<p>(<b>a</b>) Illustration of standard ECG leads: The six extremity leads (I, II, III, aVL, aVR, aVF) record voltage differences by means of electrodes placed on the limbs (left panel). The triangle shows the spatial relationships of the extremity leads, which record electrical voltages onto the frontal plane of the body. The six chest leads (V1–V6) record voltage differences by means of electrodes placed on the chest wall (right panel). The oval indicates spatial relationships of the six chest leads, which record electrical voltages transmitted onto the horizontal plane. (<b>b</b>) Illustration of ECG amplitude parameters used in the present study (P-, R-, RS-, and T-waves, each wave is measured from each of the twelve ECG leads in each individual). Due to the absence of a Q-wave in some individuals at some leads, the R-wave is measured with regard to the iso-electric line. (<b>c</b>) Illustration of ECG amplitude parameters used to calculate values (indicated in red): R-wave of III (measured from the baseline preceding the P-wave), RS-complex of aVL, T-wave of aVL, and RS-complex of the chest lead with the maximal RS amplitude (usually V3 or V2). The upper panel shows averaged ECG cycles measured from a male subject with a high value (90th percentile of our study population), the lower panel shows averaged ECG cycles from a male subject with a low value (10th percentile of our study population). Both subjects had similar body height (184 vs. 185 cm), body weigt (70 vs. 72 kg), and normal QRS axis orientation (96.23 vs. 75.24). Note the smaller T-wave in aVL in relation to the RS-wave in aVL, and the smaller R-wave in III in relation to the RS-wave in V3, in the subject with low value (lower panel), compared to the subject with high value (upper panel). (<b>d</b>) Equation for computation of values. Computation of the ECG amplitude parameters shown in (<b>c</b>) leads to an value of 1.61 for the ECG shown in the upper, and an value of 0.17 for the ECG shown in the lower panel of (<b>c</b>) (for a better readability, values are scaled by a factor ). Abbrevations: : R-wave of lead III (measured from the baseline preceding the P-wave); : RS-complex of aVL; : RS-complex of the chest lead with the maximal RS amplitude; : T- wave of aVL.