Effect of isoproterenol on the "early repolarization" syndrome.

A study has been carried out on a group of subjects with RS-T segment elevation, a normal variant of early repolarization. Following isoproterenol administration, the RS-T segment became isoelectric. In most cases this was accompanied by shorter QT and longer QTc intervals. The same effects were observed after physical exertion but not after atropine or amyl-nitrite. Propranolol administration exaggerated RS-T elevation. Considering the mechanism with which isoproterenol acts and some analogies with the electrocardiographic picture experimentally obtained by means of the unilateral stimulation of the stellate ganglions, the hypothesis is advanced that the normal variant of early repolarization is related to an enhanced activity of the right sympathetic nerves.