title: Determinants of the total cosine of the spatial angle between the QRS complex and the T wave (TCRT): implications for distinguishing primary from secondary T-wave abnormalities.
abstract: BACKGROUND
  Contrary to intuitive expectations and dissimilar from that which occurs in the atria, left ventricular (LV) depolarization and repolarization proceed in opposite directions, creating a concordance of the spatial QRS complex and T-wave angles (QRS-T). By defining the determinants of QRS-T, it might be possible to distinguish a primary (caused by an abnormality of repolarization) from a secondary (caused by a delay in ventricular depolarization) T-wave abnormality.
  
  
  RESULTS
  From a near-consecutive series of 154 patients (age, 60 +/- 16 years; 81 females) in sinus rhythm, Doppler echocardiographic and 12-lead electrocardiogram (ECG) findings were related to the total cosine of the angle subtended by the spatial QRS complex and T wave (TCRT). Using the QRS complex and T-wave angles in the frontal and horizontal planes, TCRT was obtained from the table cited in the article of Helm and Fowler (Am Heart J 1953;45:835). TCRT correlated negatively with age, QRS duration (QRS), interventricular septal thickness (IVS) and posterior wall thickness, LV mass, LV cross-sectional area (CSA), LV relative wall thickness (RWT), left atrial dimension, and atrial velocity time integral (all, P < .001), but it was not related to LV diastolic dimension or systolic function. In multivariate analyses of the entire cohort or of patients without a left bundle branch block, QRS, CSA, RWT, and atrial velocity time integral emerged as independent variables (all, P < .001). When patients with right bundle branch block were also excluded, IVS, instead of CSA and RWT, was significant (P < .001). Overall, TCRT distinguished normal patients from those with heart disease, and patients with diabetes mellitus and hypertension from those not having these conditions. However, residuals of regression, TCRT = (-1.6IVS [cm]) + (-0.01QRS [milliseconds]) + 3, distinguished patients with coronary disease, but not other disorders, from normals, and diabetics, but not patients with hypertension or hyperlipidemia, from those not having these conditions (the regression having adjusted for secondary QRS-T discordance).
  
  
  CONCLUSIONS
  The determinants of TCRT can be quantified and expressed as a regression that may be used to distinguish primary from secondary T-wave abnormalities.
authors.affiliation: Division of Cardiology, Department of Medicine, New York University School of Medicine, New York, NY, USA. howard.friedman@med.nyu.edu
authors.forename: Howard S
authors.initials: HS
authors.lastname: Friedman
mesh_terms: D001145:Arrhythmias, Cardiac / Q000175:diagnosis*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity