Post-extrasystolic changes of the vectorcardiographic T loop in healthy subjects

Visible T wave changes of the 1^st sinus beat following a ventricular premature beat (VPB) are sometimes observed in the electrocardiograms (ECG) of both healthy subjects and cardiac patients. We hypothesized that ventricular repolarization of the post-VPB beat can be modulated even without visible T wave changes. We analyzed 12-lead ECGs acquired in 7 healthy subjects, with at least 1 VPB/ECG with no visible changes of the 1^st post-VPB beat. The spatial T loop of each sinus beat was reconstructed in derived XYZ leads and was characterized by 5 parameters. The 1^st post-VPB beat was compared with the 2^nd and 3^rd pre-VPB beats. In 6 subjects, 1 to 3 T-loop parameters were significantly modified with an average change from -18.9% to 30.1% signifying increased repolarization heterogeneity. In conclusion, heterogeneity of the post-VPB sinus beat can be increased in the absence of visible T wave changes.