Evaluation of Conventional Doppler Fetal Cardiac Function Parameters: E/A Ratios, Outflow Tracts, and Myocardial Performance Index

Abstract

Structural evaluation of the fetal heart is well established. Functional evaluation using pulsed-wave Doppler may also be performed. E/A ratios express the relationship between the maximal velocities of the E and A waveforms of ventricular filling. In normal fetuses, E/A ratios are usually <1 but show a constant increment during gestation, mainly related to the increment of the E wave. In intrauterine growth restriction (IUGR) fetuses, E/A ratios are lower compared to values in normally grown fetuses at the same gestational age. Cardiac outflows provide information on the time-velocity integral that, combined with the vessel area, allows calculation of the left and right cardiac outputs. In normal fetuses there is a predominance of the right ventricle (55–60%) in contributing to the combined cardiac output. In IUGR fetuses this predominance shifts to the left ventricle in order to increase the flow to the upper part of the fetal body and brain. The myocardial performance index (MPI) also provides information on systolic and diastolic cardiac function. The MPI is an early and consistent marker of cardiac dysfunction which becomes altered in early stages of chronic hypoxia or in cases with cardiac overload such as in twin-to-twin transfusion syndrome.

The (Pulsed-Wave) Doppler Fetal Myocardial Performance Index: Technical Challenges, Clinical Applications and Future Research

“…As the heart's primary function is ejection of blood to deliver adequate tissue perfusion, Doppler ultrasound is commonly used to evaluate cardiac function through either assessing blood flow or cardiac time periods [4]. One quantitative measurement is the myocardial performance index (MPI), a pulsed-wave Doppler-derived index reflecting global myocardial function [5] which has been shown to be a highly sensitive measure of dysfunction [6,7].…”

Applicability and technical aspects of two-dimensional ultrasonography for assessment of fetal heart function

“…In most cases, diastolic changes precede systolic changes. Therefore, Doppler echocardiographic parameters that assess diastolic function or combined systolic and diastolic function, as well as the myocardial performance index (MPI), may contribute to the early treatment of fetuses with cardiac dysfunction [8].…”

“…After the ninth week of pregnancy, the E and A waves can be measured; the E/A ratio is always lower than 1.0 until term, as the fetal heart is more rigid owing to its higher collagen content. For accurate measurement of E and A waves, either mitral or tricuspid, the sample volume of pulsed Doppler (2-3 mm) should be positioned in each ventricle immediately distal to the atrioventricular valves at an insonation angle smaller than 20° [8].…”

The development of, and future for, fetal functional cardiac imaging techniques

“…The basis of many of the novel indices of fetal cardiac function include techniques familiar to most fetal medicine practitioners and cardiologists such as pulsed wave, 5 M‐mode, 6 and tissue Doppler 7 as well as the relatively new technique of speckle tracking 8 . Traditionally, cardiologists have been trained in, and fetal medicine practitioners have shied away from M‐mode though it is a very sensitive tool for cardiac measurements.…”