Normal limits of the spatial QRS-T angle and ventricular gradient in 12-lead electrocardiograms of young adults: dependence on sex and heart rate.

Background And Purpose: Normal limits of the spatial QRS-T angle and spatial ventricular gradient (SVG) are only available from Frank vectorcardiograms (VCGs) of male subjects. We determined normal limits for these variables derived from standard 12-lead electrocardiograms (ECGs) of 660 male and female students aged 18 to 29 years.

Methods: A computer algorithm was used that constructed approximated VCG leads by inverse Dower matrix transformation of the 12-lead ECG and subsequently calculated the spatial QRS-T angle, SVG magnitude, and orientation.

Results: In female subjects, the QRS-T angle was more acute (females, 66 degrees +/- 23 degrees; normal, 20 degrees-116 degrees; males, 80 degrees +/- 24 degrees; normal, 30 degrees-130 degrees; P < .001), and the SVG magnitude was smaller (females, 81 +/- 23 mV x ms; normal, 39-143 mV x ms; males, 110 +/- 29 mV x ms; normal, 59-187 mV x ms; P < .001) than in male subjects. The male SVG magnitude in our study was larger than that computed in Frank VCGs (79 +/- 28 mV.ms; P < .001).

Conclusions: The spatial QRS-T angle and SVG depend strongly on sex. Furthermore, normal limits of SVG derived from Frank VCGs differ markedly from those derived from VCGs synthesized from the standard ECG. As nowadays, VCGs are usually synthesized from the 12-lead ECG; normal limits derived from the standard ECG should preferably be used.