Effects of isoproterenol and methoxamine on the electrocardiogram

The effects of isoproterenal (ISP) and methoxamine (MTX) infusion in 20 asymptomatic subjects with labile T wave were studied. In those treated with ISP the T wave showed an early negative trend and later became clearly positive in 5 subjects. In the majority of the subjects treated with MTX the T wave became positive. T wave changes match variations of both the ventricular gradient and, to a lesser degree, the QRS area. These changes were not related to heart rate or, in the subjects treated with MTX, to the baroreceptorial sensitivity deduced from the slope of the regression equation between R-R internal and systolic arterial pressure. The results of this study confirm the existence of a neurogenic mechanism affecting the electrocardiographic changes in T wave.