title: The spatial QRS-T angle in the Frank vectorcardiogram: accuracy of estimates derived from the 12-lead electrocardiogram.
abstract: OBJECTIVE
  The spatial QRS-T angle (SA), a predictor of sudden cardiac death, is a vectorcardiographic variable. Gold standard vertorcardiograms (VCGs) are recorded by using the Frank electrode positions. However, with the commonly available 12-lead ECG, VCGs must be synthesized by matrix multiplication (inverse Dower matrix/Kors matrix). Alternatively, Rautaharju proposed a method to calculate SA directly from the 12-lead ECG. Neither spatial angles computed by using the inverse Dower matrix (SA-D) nor by using the Kors matrix (SA-K) or by using Rautaharju's method (SA-R) have been validated with regard to the spatial angles as directly measured in the Frank VCG (SA-F). Our present study aimed to perform this essential validation.
  
  
  METHODS
  We analyzed SAs in 1220 simultaneously recorded 12-lead ECGs and VCGs, in all data, in SA-F-based tertiles, and after stratification according to pathology or sex.
  
  
  RESULTS
  Linear regression of SA-K, SA-D, and SA-R on SA-F yielded offsets of 0.01 degree, 20.3 degrees, and 28.3 degrees and slopes of 0.96, 0.86, and 0.79, respectively. The bias of SA-K with respect to SA-F (mean +/- SD, -3.2 degrees +/- 13.9 degrees) was significantly (P < .001) smaller than the bias of both SA-D and SA-R with respect to SA-F (8.0 degrees +/- 18.6 degrees and 9.8 degrees +/- 24.6 degrees, respectively); tertile analysis showed a much more homogeneous behavior of the bias in SA-K than of both the bias in SA-D and in SA-R. In pathologic ECGs, there was no significant bias in SA-K; bias in men and women did not differ.
  
  
  CONCLUSIONS
  SA-K resembled SA-F best. In general, when there is no specific reason either to synthesize VCGs with the inverse Dower matrix or to calculate the spatial QRS-T angle with Rautaharju's method, it seems prudent to use the Kors matrix.
authors.affiliation: Department of Cardiology, Leiden University Medical Center, The Netherlands.
authors.forename: Charlotte A
authors.initials: CA
authors.lastname: Schreurs
authors.forename: Annemijn M
authors.initials: AM
authors.lastname: Algra
authors.forename: Sum-Che
authors.initials: SC
authors.lastname: Man
authors.forename: Suzanne C
authors.initials: SC
authors.lastname: Cannegieter
authors.forename: Ernst E
authors.initials: EE
authors.lastname: van der Wall
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Schalij
authors.forename: Jan A
authors.initials: JA
authors.lastname: Kors
authors.forename: Cees A
authors.initials: CA
authors.lastname: Swenne
mesh_terms: D000465:Algorithms; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004566:Electrodes; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014672:Vectorcardiography / Q000295:instrumentation* / Q000379:methods*; D014693:Ventricular Fibrillation / Q000175:diagnosis*