Clinical value of different QRS-T angle expressions

Figure 1. Comparisons of QRT-T angle measurements. Panels A–C show the differences between the different methods for QRS-T angle calculation obtained for individual subjects and patients (see the text for details). Panel D shows the relationship of the differences between the TCRT and MRT methods in dependency on the QRS complex duration which is used as a surrogate of QRS loop abnormality. Panel E shows the cumulative distributions of the TCRT assessment of the QRS-T angle in different populations. Note that in panels A–C, the trapezoidal shape of the graphs is determined by the fixed range of all measurements between 0 and 180° (e.g. the maximum difference of 180° between two measurements can only exist if one measurement is 0 and the other 180°). The red, blue, yellow, and brown marks and lines correspond to healthy females, healthy males, survivors of acute myocardial infarction, and recipients of implantable defibrillators (ICD), respectively. (Note that panel D shows the data for the ICD recipients.) MRT, maximum R to T; ART, area R to T; TCRT, total cosine R to T; ICD, implantable cardioverter defibrillators (see the text for explanations).

Figure 2. Reproducibility of QRT-T angle measurements in healthy subjects. Intra-subject standard deviations of repeated QRS-T angle measurements in healthy subjects repeated for different heart rate bands around intra-subject heart rate medians (see the text for details). The graph shows population means ± standard errors of means. The diamonds, squares, and circles correspond to maximum R to T, area R to T, and total cosine R to T measurements, respectively. The red, blue, and violet marks correspond to females, males, and the complete pooled population of healthy subjects, respectively.

Figure 3. Prediction of outcome in survivors of acute myocardial infarction. The figure shows receiver operator characteristics for the prediction of outcome events among survivors of acute myocardial infarction based on increased values of the spatial QRS-T angle. The graphs show the median curvatures and their 90% confidence bands obtained by bootstrap (see the text for details). The top, middle, and bottom row correspond to the prediction of all-cause mortality, cardiac death, and sudden cardiac death, respectively. The left, middle, and right column correspond to the prediction based on the maximum R to T (MRT), area R to T (ART), and total cosine R to T (TCRT) calculations, respectively. Numerical values of the areas under the characteristics (AUC) and of their 90% confidence intervals (CI) are shown in each panel (see also Table 2).

Figure 4. Probabilities of follow-up events among survivors of acute myocardial infarction. The figure shows Kaplan–Meier curves of the probabilities of follow-up events among survivors of acute myocardial infarction stratified according to the spatial QRS-T angle. For each graph, the P-value of the χ2 test comparison of the probabilities is also shown. The blue, violet, and red curves correspond to patients with QRS-T angles within the smallest, middle, and largest tertile of the measurements, respectively. The top, middle, and bottom row correspond to the prediction of all-cause mortality, cardiac death, and sudden cardiac death, respectively. The left, middle, and right column correspond to the prediction based on the maximum R to T (MRT), area R to T (ART), and total cosine R to T (TCRT) calculations, respectively.

Figure 5. Probabilities of death during follow-up of ICD recipients. Kaplan–Meier curves show the probability of death during follow-up among the recipients of implantable defibrillators stratified according to the spatial QRS-T angle. For each graph, the P-value of the χ2 (top row) and log-rank (bottom row) test comparison of the probabilities is also shown. The top and bottom rows correspond to the complete population and to patients with QRS complex width > 120 ms. In the top row, the blue, violet, and red curves correspond to patients with QRS-T angles within the smallest, middle, and largest tertile of the measurements. In the bottom row, the blue and red curves correspond to patients with the QRS-T angles within the smallest and the two larger tertiles of the measurements, respectively. The left, middle, and right column correspond to the prediction based on the maximum R to T (MRT), area R to T (ART), and total cosine R to T (TCRT) calculations, respectively.