Quantification of T wave shape changes following exercise.

T wave shape is increasingly used to provide insights into cardiac repolarization and, although shape is known to change as heart rate changes, there are no published quantitative clinical data. The aim of this study was to quantify these changes. Heart rate (HR), T wave amplitude, and two measures of T wave symmetry (SRarea--ratio of areas about the peak, SRtime--ratio of centrality of peak), were quantified over a period of 360 seconds following exercise in 20 healthy human subjects. As HR decreased, in all subjects the T wave became more asymmetrical (SRarea 20/20, SRtime 20/20, P < 0.0001). Resting reference HR and symmetry ratios were (mean +/- SD), HR 63 +/- 10 beat/min, SRarea 1.68 +/- 0.25, and SRtime 2.13 +/- 0.39. Fifty seconds postexercise, HR was significantly higher than reference at 92 +/- 11 beat/min (P < 0.0001), and symmetry ratios were significantly less at SRarea 1.04 +/- 0.15, SRtime 1.24 +/- 0.36 (P < 0.0001). Significant differences in HR and both symmetry ratios remained at 300 seconds postexercise. Amplitude increases had returned to their reference values at 300 seconds. T wave shape was significantly more symmetrical at higher HRs. These findings confirm qualitative reports of shape changes.