Session S31.6

Beat-to-Beat Variation of Three-Dimensional QRS-T Angle Measures during Exercise Test

M Karsikas*, K Noponen, M Tulppo, H Huikuri, T Seppänen

University of Oulu
Oulu, Finland

The relationship between the QRS complex and the T wave, expressed as an angle in three-dimensional space, has been a subject of interest during the last decade. Especially the parameter named ‘Total Cosine R-to-T’ (TCRT) has been shown to have a remarkable prognostic value as a predictor of the outcomes of the coronary artery disease. However, the dynamical beat-to-beat behavior of the QRS-T angle features is largely unknown.
In this study, an automatic beat-to-beat method for calculating the vectorcardiographic parameters from standard 12-lead ECG was developed, and the variability of three QRS-T angle measures during an incremental exercise on a bicycle ergometer was studied. Study groups consisted of coronary artery disease (CAD) patients (n=20) and healthy age-matched subjects (n=10). The automated analysis is based on digital filters, a derivative-based RR-detector, the removal of the extrasystoles, and the heart-rate normalized segmentation of the waveforms. The angle measures were the TCRT parameter, the cosine of the three-dimensional QRS-T angle (cos(QRS-T)), and the angle between the normal vectors of the QRS and T planes (P_Angle). The results show that an RSA-like modulation in the frequency band of the breathing occurs in all three angle measures during exercise. The trend of the TCRT during exercise was negative, and it was more negative in healthy subjects compared to CAD patients (p=0.01). The trends of the cos (QRS-T) and P_Angle were not statistically significant in either study group, however. The reason for the differing behavior of the TCRT measure is probably due to the sensitivity of the algorithm to the asymmetry of the QRS loop.
In conclusion, the QRS-T angle measures do not appear to behave similarly during the exercise test or at rest, and therefore, they should not be paralleled with each other. In addition, the breathing significantly affects the beat-to-beat variability of all the QRS-T-angle measures, which should be taken into account when considering the reliability of one-beat analyses of the angle measures.

(Abstract Control Number: 62)