QRS loop folding phenomenon in vectorcardiogram of healthy individuals

Recently, we developed a novel approach to study the rapid and sudden changes in the direction of ventricular activation called folding phenomenon. In order to better understand this phenomenon, we were interested in studying the variation of the orientation of QRS_t for i=1... N where QRS_t represents the QRS vector at the i^th sample point. In this study, we described the orientation of the QRS vector and the rotation of its frame of reference in details in 81 healthy participants from the Intercity Digital Electrocardiogram Alliance (IDEAL) study using unit quaternions and Euler angles. We observed that the variance of the elevation of rotation axis u was significantly higher in men compared to women (1340±421 vs. 1063±381, P=0.003, respectively). Additionally, there was a significant negative correlation between the variance of the azimuth of u and height (CC=-0.26, P=0.019) while the elevation of u and height were significantly positively correlated (CC=0.24, P=0.034). Moreover, the elevation of u had a positive significant correlation with weight and body surface area (CC=0.22, P=0.045 and CC=0.26, P=0.020 respectively).