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Figure 4 Effect of isoproterenol on the U-wave. In a representative subject, isoproterenol infusion produced a dose-dependent increase in U-wave amplitude in all subjects studied. The U-wave in this subject was present at baseline, but visibly increased in amplitude during low dose isoproterenol. As the infusion rate increased, the U-wave (tracked by arrows in the figure) merged with the T-wave forming a single T-wave complex. At higher doses of isoproterenol, the T-wave is characterized by a prolonged, flattened terminal downslope during isoproterenol. In contrast, these U-wave changes were not observed during exercise (not shown) or atropine infusion. The end of T-wave is indicated by a tick mark for each electrocardiogram complex.
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