Comparisons of the Spatial QRS-T Angle With Intra-cardiac Markers of Depolarization and Repolarization

The spatial QRS-T angle (QRS-Ta), a non-invasive risk marker for arrhythmia and sudden cardiac death, captures information on the spatiotemporal dynamics of ventricular depolarization and repolarization. QRS-Ta peak is the angle between QRS and T-wave loop maximal amplitudes. We compared QRS-Ta peak with intra-cardiac unipolar electrocardiogram parameters simultaneously recorded in the right ventricle, left ventricle (LV) endocardium and LV epicardium (coronary sinus) in 10 patients with structurally normal hearts. S1S2 restitution protocols were performed by pacing from the LV at intervals decrementing from 1000 ms to the effective refractory period (ERP). Repolarization time (RT), activation time (AT) and activation-recovery interval (ARI), a standard surrogate for local action potential duration, were calculated using standard definitions. Decreasing cycle length (CL) correlated with an increase in QRS-Ta. Two phases were identified 1) A stable QRS-Ta between CLs 1000 to 400ms and 2) a subsequent rapid increase in QRS-Ta with further decrements and a small decrease in QRS-Ta just prior achieving ERP. When plotted against the pacing interval, the QRS-Ta distribution mirrored the repolarisation restitution curve. The QRS-Tangle inversely correlated with mean RT (-0.59, -0.81 / -0.34, P=0.023) and mean ARI (-0.72, -0.73 / -0.42, P<0.02).