Objectives The objectives of this study were: (i) to assess the feasibility
of a tissue Doppler imaging (TDI) evaluation in the fetus, (ii) to identif
y color-TDI patterns consistent with the various phases of the cardiac cycl
e; and (iii) to assess myocardial velocities and the myocardial velocity gr
adient.
Methods Eighty-nine normal fetuses between the 17th and the 37th week of ge
station were studied. Color-TDI was superimposed on an apical four-chamber
view of the fetal heart and three cardiac cycles captured in cine-loop form
at. By reviewing the cine-loop strip, color patterns consistent with the va
rious phases of the cardiac cycle were identified. The procedure was then r
epeated with a transverse four-chamber view. On each frame corresponding to
mid-systole, early and late diastole, myocardial velocities were calculate
d at the subepicardial and subendocardial layer and regressed against gesta
tional age. Statistics included correlation and regression analysis, calcul
ation of the 95% confidence intervals and of the Cronbach's alpha reliabili
ty coefficient for repeated observations.
Results TDI examination is acceptably reproducible in the fetus. We were ab
le to identify color-TDI patterns depicting the systolic contraction wave,
ventricular relaxation and atrial contraction. Statistical evaluation demon
strated that: all variables (systolic right and left subendocardial and sub
epicardial velocities, early diastolic right and left subendocardial and su
bepicardial velocities, end diastolic right and left subendocardial velocit
ies, right subepicardial velocities) except end-diastolic right and left su
bepicardial velocities, showed a positive correlation with advancing gestat
ional age; subendocardial velocities were higher than subepicardial ones th
roughout the cardiac cycle in both ventricles; systolic myocardial velociti
es were higher in the left ventricle whereas early diastolic velocities wer
e higher in the right ventricle; and the ratio between early and late diast
olic subendocardial velocities (E-M/A(M)) was constantly <1 and did not cha
nge with advancing gestational age.
Conclusions TDI evaluation of the fetal heart is feasible and reproducible.
Color-TDI is able to identify the various phases of the cardiac cycle. Qua
ntitative evaluation of myocardial velocities has shown also in the fetus t
he existence of the myocardial velocity gradient found in postnatal life.