Reflex autonomic modulation of automatically measured repolarization parameters

Automatic recognition of repolarization abnormalities from the standard ele ctrocardiogram (ECG) is of considerable clinical importance. This study exa mined the autonomic variations in automatically measured repolarization par ameters, including maximum QT interval (QTmax), global QT dispersion (QTd), T area dispersion (T area D) and principal component analysis ratio 2 (PCA -2). Twelve-lead ECGs were recorded continuously in 40 healthy subjects dur ing supine, sitting and standing positions, and during the Valsalva maneuve r. With the exception of PCA-2, the other repolarization parameters correla ted either moderately or strongly during the steady-state supine position. QTmax, PCA-2, and T area D decreased significantly between supine and sitti ng position (P < 0.001, P < 0.001 and P < 0.01, respectively). QTmax, QTD, and T area D decreased significantly between sitting and standing (P < 0.00 1, P < 0.05 and P < 0.01, respectively). All parameters significantly decre ased between supine and standing position : QTmax (P < 0.001), QTD (P < 0.0 5), PCA-2 (P < 0.05) and T area D (P < 0.001). During Valsalva, only PCA-2 increased significantly (P < 0.001) between supine and standing position. T here were no significant changes in QT dispersion and dispersion of T wave area during Valsalva, compared to baseline, in both supine and standing pos itions. Automatic conventional measures of repolarization heterogeneity hav e limited practical value in detecting the effects of autonomic changes on ventricular repolarization. Newer concepts evaluating spatial and temporal irregularity of ventricular repolarization are still needed to reliably def ect the effects of autonomic activity on ventricular repolarization.