Objectives: The objectives of this study were: (i) to assess the feasibility of a tissue Doppler imaging (TDI) evaluation in the fetus, (ii) to identify color-TDI patterns consistent with the various phases of the cardiac cycle; and (iii) to assess myocardial velocities and the myocardial velocity gradient.
Methods: Eighty-nine normal fetuses between the 17th and the 37th week of gestation were studied. Color-TDI was superimposed on an apical four-chamber view of the fetal heart and three cardiac cycles captured in cine-loop format. By reviewing the cine-loop strip, color patterns consistent with the various phases of the cardiac cycle were identified. The procedure was then repeated with a transverse four-chamber view. On each frame corresponding to mid-systole, early and late diastole, myocardial velocities were calculated at the subepicardial and subendocardial layer and regressed against gestational age. Statistics included correlation and regression analysis, calculation of the 95% confidence intervals and of the Cronbach's alpha reliability coefficient for repeated observations.
Results: TDI examination is acceptably reproducible in the fetus. We were able to identify color-TDI patterns depicting the systolic contraction wave, ventricular relaxation and atrial contraction. Statistical evaluation demonstrated that: all variables (systolic right and left subendocardial and subepicardial velocities, early diastolic right and left subendocardial and subepicardial velocities, end diastolic right and left subendocardial velocities, right subepicardial velocities) except end-diastolic right and left subepicardial velocities, showed a positive correlation with advancing gestational age; subendocardial velocities were higher than subepicardial ones throughout the cardiac cycle in both ventricles; systolic myocardial velocities were higher in the left ventricle whereas early diastolic velocities were higher in the right ventricle; and the ratio between early and late diastolic subendocardial velocities (EM/AM) was constantly < 1 and did not change 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. Quantitative evaluation of myocardial velocities has shown also in the fetus the existence of the myocardial velocity gradient found in postnatal life.