Intracardiac Intermediate Diastolic Velocity in Response to Fetal Anemia: Using Hemoglobin Bart's Disease as a Study Model

Objective To compare intermediate diastolic velocity (IDV) measurements, as well as E/IDV and A/IDV ratios, between fetuses affected and unaffected by Hb Bart's disease. Methods Fetuses at risk of Hb Bart's disease between 17 and 22 weeks of gestation were off‐line and blindly assessed for IDV, E/IDV, and A/IDV ratios, along with parameters of cardiac function. Results A total of 418 fetuses were included, comprising 84 affected and 334 unaffected cases. The IDV in the right ventricle was significantly lower in the affected group (24.5 ± 5.76 vs. 26.66 ± 6.88; p = 0.010), while the IDV in the left ventricle was significantly higher (22.36 ± 5.79 vs. 20.54 ± 5.54; p = 0.008). The E/IDV and A/IDV ratios in the left ventricle were significantly lower in the affected group. Among the affected fetuses, right‐sided cardiac output and myocardial performance index (MPI) were significantly greater than those on the left side. Conclusion In the early stages of fetal anemia, the heart appears to enhance ventricular diastolic function, more prominently in the left ventricle. However, as the condition progresses, with increasing volume and pressure load due to chronic anemic hypoxia, the compensatory mechanisms are eventually overwhelmed, leading to a gradual deterioration of diastolic function, predominantly affecting the right ventricle.