Session P72.7

Post-Extrasystolic Changes of the Vectorcardiographic T Loop in Healthy Subjects

VN Batchvarov, II Christov, G Bortolan*, II Simova, AJ Camm

ISIB-CNR
Padova, Italy

Visible changes in the T (or T-U) wave of the first sinus beat following a ventricular premature beat (VPB) are sometimes observed both in healthy subjects and patients with various cardiac diseases. Their mechanism has been linked to cardiac memory. In this study, we hypothesised that ventricular repolarisation of the post-VPB beat can be significantly modulated even in the absence of visible T wave changes. We analysed digitally recorded 12-lead ECGs (10 seconds length, 500 Hz, 12 bit A/D). Seven healthy subjects were included in the study (3 men, 4 women, age 23-48, mean 35.3 +/-7.9 years). Five to seven consecutive recordings at rest were analysed for each subject. Each ECG contained at least 1 VPB with no visible T-U wave changes in the 1st post-VPB beat. The spatial T loop of each sinus beat was reconstructed in orthogonal XYZ Frank leads derived from the 12-lead ECG and was characterised by the following parameters: maximum angle between QRS and T loop axes (MA), T axis elevation and azimuth angle difference (DEA), ratio of maximum to mean T vector magnitudes (RMMV), angle of the T loop in the frontal (TF) and horizontal (TH) plane, with the zero point chosen between the 2 points of the loop with maximum distance. For each subject and each parameter, the 1st post-VPB complex was compared with the average of the 2nd and 3rd pre-VPB complexes (unpaired t-test). In 6 out of 7 subjects 1 to 3 of the T loop parameters were significantly modified. The number of subjects (n) with significant change and the average change (in %) for each of the T loop parameters are: MA (n=3, – 18.5 +/-6.8%); DEA (1, 16%); RMMV (2, -18.9 +/-6.6%); TF (3, 3.6 +/-9.4%); TH (1, 30.1%).
Conclusions: In healthy subjects, ventricular repolarisation heterogeneity of the first post-extrasystolic sinus beat can be evaluated and significantly obtained (p<0.05) even in the absence of visible T-U wave changes.

(Abstract Control Number: 1)