New descriptors of homogeneity of the propagation of ventricular repolarization

Available descriptors of irregularities of ventricular repolarization are o f limited clinical value. We studied the effect of autonomic variations on several new descriptors of the three-dimensional T loop. Twelve-lead digita l ECGs were recorded continuously in 40 healthy subjects at baseline in the supine position, during postural changes (supine --> sitting --> standing --> supine --> standing), and during Valsalva maneuver performed three time s in the supine and three times in the standing positions. A minimum dimens ional space was constructed from the 12-lead EGG, using singular value deco mposition, on the basis of median ECG beats constructed from 10-second cons ecutive ECG recordings. Temporal variations (TLA and FL, which measure the T loop area, and LD, the interlead relationship during repolarization) and wavefront direction descriptors (TCRT, the deviation between the QRS and T vectors) were calculated and expressed as normalized values. Values of TLA, FL, and TCRT were significantly low er in the sitting than in the supine p osition (-38139 +/- 9099 vs 47133 +/- 7511, -0.017 +/- 0.005 vs 0.033 +/- 0 .005 and -0.032 +/- 0.019 vs 0.071 +/- 0.015, respectively P < 0.001 for al l) and decreased further in the standing position (-88288 +/- 14468, -0.067 +/- 0.013, -0.198 +/- 0.025, respectively P < 0.001 for all). LD increased from supine to sitting (98.7 +/- 29.4 vs -87.5 +/- 15.2, P < 0.001) and in creased further, though nonsignificantly in the standing position (118.3 +/ - 35.2). TLA, FL, and TCRT decreased from baseline during Valsalva in the s upine (-34118 +/- 11424 vs 62234 +/- 12215, -0.038 +/- 0.014 vs 0.065 +/- 0 .010, -0.08 +/- 0.03 vs 0.10 +/- 0.02, respectively, P < 0.002 for all) and standing positions (-108263 +/- 21051 vs -68909 +/- 10271, -0.109 +/- 0.01 4 vs -0.048 +/- 0.009, -0.30 +/- 0.035 vs -015 +/- 0.016, respectively, P < 0.05 for all). LD was significantly increased by Valsalva in the supine po sition (13 +/- 46 vs -153 +/- 30 P < 0.001) and nonsignificantly in the sta nding position (99 +/- 50 vs 86 +/- 30, P = NS). There were significant cor relations among TLA, FL, and LD, and no significant correlation between TCR T and any of the temporal variation descriptors. These new temporal and wav efront direction descriptors are sensitive and rapid detectors of autonomic effects on ventricular repolarization.