Maternal and fetal ECG alterations during and after infusion of fenoterol

The T/QRS ratio values in pregnancies complicated by threatened preterm labour treated with intravenous infusions of fenoterol

“…Foetal symptoms are usually less pronounced probably because of partial transplacental transfer of fenoterol from the mother to the foetus. Researchers report changes of foetal heart rate [13] . Moreover, transient changes in electrocardiograms were observed for several weeks after birth in newborns exposed in utero to prolonged tocolytic therapy.…”

“…Fenoterol binds almost selectively to the β 2 adrenergic receptors. Its therapeutic effect starts immediately after beginning intravenous infusion; however, peak plasma concentration is reached in 10 min and lasts for approximately 4 -8 h. The half-life is approximately 6 -7 h [13] . Transplacental transfer and pharmacokinetics of fenoterol in foetal compartment is unknown.…”

“…These symptoms are the result of altered depolarisation and repolarisation of the myocardium [13] . The concentration of cardiac troponin T, one of the most sensitive and specific indicators of myocardial necrosis, started to increase in pregnant women ' s blood from the first day of tocolytic therapy and was significantly higher from the third day.…”

“…The efficacy of betamimetics is comparable to other groups of tocolytics. Side effects affecting both the mother and the foetus which can limit their use are usually transient [1,2,9,13] . Despite that, betamimetics are still widely used in obstetric management especially in the acute phase of preterm labour in many European countries [24] .…”

“…That is being explained by immature sympathetic innervation of the foetal and newborn heart; therefore, betamimetics ' stimulating action is very low [14] . Some others suggest that they are transported though the placenta and have influence on the foetal heart resulting in lowering of the ST segment and/or flattening of T, which are caused by pharmacologic sympathetic-like influence on the cardiac nervous system and its function [13] , or in ischaemic changes in the electrocardiogram (ECG) observed after birth [9] . Their effect is less visible in the foetus than in the mother but can be observed even several weeks after birth [9] .…”