Indices of cardiac function during treatment with betamimetic drugs (fenoterol and hexoprenaline).

The limiting factor in the treatment of preterm labor by betamimetics is the effect of these drugs on heart rate and cardiac action. In this paper we compare these effects produced by hexoprenaline and fenoterol, which are both beta-sympathomimetic drugs now in clinical use. As indices of cardiac action we measured the pre-ejection period (PEP), the left ventricular ejection time (LVET) and their sum, namely total electromechanical systole (QS2) by thoracic impedance cardiography. In 20 individual tests, seven subjects were given both hexoprenaline and fenoterol on separate occasions in a dose relationship of 1 : 12.5. We found a relation between PEP/LVET on the one hand and the Heather-index (an impedance specific parameter of response to stress) on the other. Both parameters represent inotropic effects in cardiac action. With increasing betamimetic stimulation there was a decrease of PEP/LVET (-23% for hexoprenaline and -29% for fenoterol) and an increase in the Heather-index (+98% for hexoprenaline and +117% for fenoterol). These results are not statistically significantly different and so we cannot agree with Lipshitz [19 ]who reported less beta 1-stimulation with hexoprenaline.