Session PB2.2

Vectorcardiographic Representation of Concordant and Discordant T-Wave Alternans

D Janusek*, Z Pawlowski, M Kania, S Karczmarewicz,
A Przybylski, R Maniewski

Institute of Biocybernetics and Biomed Engineering
Warsaw, Poland

Background: Two different modes of the T-wave alternans (TWA): concordant - relatively benign, and discordant – leading to fibrillation, were described. The effect of repolarization disturbance on the TWA is not fully explained and reliable methods of differentiation between both types of TWA in clinical studies are not established yet.
Methods: Study group consisted of 18 pts with coronary artery disease and ICD in whom TWA was detected using FFT algorithm. Control group consisted of 20 healthy volunteers. Recordings were carried out during pacing from ICD. Orthogonal XYZ lead configuration was used. Vectorcardiographic representation of electrocardiograms was analysed. The new orthogonal coordinate system was created by means of singular value decomposition where one axis was in direction of maximal vector of the T-loop and second one lied also in the T-loop plane. The magnitude of main T-loop vector and its deviation from the main axis were analysed. An angle Fi between T-loop vector projection on the plane perpendicular to the main vector and axis which is transversal to the T-loop was analysed.
Results: In the study group two types of vectorcardiographic changes correlated with TWA were found. The first one shows T-loops similar in shape in every beat and in general shape similar to that recorded in control group. T-wave alternans manifest as T-loop length changes from beat to beat. Probably, this type of TWA reflects concordant alternans. In the second group also main T-loop vector length is changing as well as the shape of even and odd T-loops changes. Angle Fi shows changes in the location of T-loop vector which have spiral track. Probable source of such changes could be re-entrant waves. This type of TWA may reflect discordant alternans.
Conclusions: Dispersion of repolarization process was assessed, which allows distinguishing between concordant and discordant T-wave alternans. T-loop vector magnitude changes its value, but the process is similar from beat to beat in the case of concordant alternans in contrast to the discordant alternans where changes of repolarization wave front propagation direction are very fast and may contribute to arrhythmia generation.

(Abstract Control Number: 14)