Validation of the fetal myocardial performance index in the second and third trimesters of gestation

To test the validity of the myocardial performance index (MPI) and its components against the more conventional methods of fetal cardiac function assessment: the ejection fraction (EF) for systolic function and the E/A index (ratio of transmitral flow during early (E) ventricular filling to flow during atrial (A) contraction) for diastolic function, both in a normal population and in a population at risk for cardiac failure because of volume overload (recipient fetuses in cases of twin-twin transfusion syndrome (TTTS)).

The MPI was measured prospectively in addition to more commonly used indices of systolic (EF) and diastolic (E/A index) cardiac function in 117 healthy fetuses (gestational age range, 20-36 weeks) and in 14 fetuses suspected of cardiac failure because of the presence of TTTS. Nomograms were constructed for all variables, and correlations between the MPI, EF and E/A index were assessed. The time taken to obtain the measurements as well as the interobserver and intraobserver variability were determined for the MPI and EF.

In healthy fetuses, the MPI and EF were independent of gestational age, whereas the E/A index and isovolumetric relaxation time (IRT) increased with gestational age. The MPI correlated inversely with the EF (P<0.001). The IRT showed a trend towards an inverse correlation with the E/A index (P=0.10). The mean+/-SD time needed to measure the MPI and EF was 140+/-65 s and 185+/-187 s, respectively (P=0.43). Interobserver and intraobserver intraclass correlation coefficients for the MPI were 0.98 (95% CI, 0.85-0.99) and 0.82 (95% CI, 0.14-0.95), respectively; those for the EF were 0.58 (95% CI, -0.16 to 0.85) and 0.51 (95% CI, -0.46 to 0.83), respectively; and those for the E/A index were 0.97 (95% CI, 0.88-0.99) and 0.91 (95% CI, 0.66-0.98), respectively. All variables, except ejection time, were significantly different between normal fetuses and those with TTTS.

The MPI is an indicator of the systolic component of fetal left ventricular function that can be easily acquired and reproduced. The MPI is strongly correlated with the EF but shows less interobserver and intraobserver variability.