'Cor placentale': placental intervillus/intravillus blood flow mismatch isthe pathophysiological mechanism in severe intrauterine growth restrictiondue to uteroplacental disease

The underlying pathophysiology in most cases of severe intrauterine growth restriction and pre-eclampsia is thought to be abnormal and inadequate conv ersion of the branches of the uterine arteries into low resistance uteropla cental vessels, due to poor extravillous trophoblastic invasion, leading to reduced intervillous blood flow. Since, in most vascular beds the main sit e of flow resistance is at the level of the small arteries/arterioles rathe r than the capillary bed itself it is likely that in cases of intrauterine growth restriction due to uteroplacental dysfunction with abnormal fetal um bilical artery flow velocity waveforms, the underlying pathological mechani sm is primarily an initial reduction in intervillus flow leading to relativ e local hypoxia of some villus territories. This results initially in autoc rine/paracrine mediated localized stem artery vasoconstriction to minimize intervillus/intravillus flow mismatch which, when widespread, will result i n abnormal umbilical artery Doppler waveforms due to the globally increased resistance to fetoplacental flow. Since, a small reduction in vessel radiu s will result in an exponential increase in flow resistance and reduction i n flow, the magnitude of stem vessel constriction need only be small to res ult in large changes in fetoplacental vascular haemodynamics. Thus, the und erlying progressive pathology in this condition may be cardiac failure, sec ondary to chronic stem vessel vasoconstriction caused by abnormalities in o xygenation of the fetal respiratory system hence the term 'cor placentale' is proposed. (C) 2001 Harcourt Publishers Ltd.