Multicenter Implementation and Validation of the Structured 3 × 3 CASSEAL Framework for Second-Trimester Assessment of the Extended Fetal Cardiovascular System.

OBJECTIVES: To evaluate the feasibility, transferability, and implementation performance of the cardiovascular system sonographic evaluation algorithm (CASSEAL), a structured 3 × 3 sequential framework for second-trimester ultrasound assessment of the extended fetal cardiovascular system, in a multicenter screening setting. METHODS: This prospective multicenter observational study included unselected singleton and twin pregnancies examined between 18 and 22+6 weeks' gestation. After standardized training, operators completed an initial implementation phase (first 30 examinations) followed by a validation phase (≥50 additional examinations). The CASSEAL algorithm consists of sequential acquisition of 9 axial planes organized into infracardiac, cardiac, and supracardiac territories within a structured 3 × 3 framework. The primary outcome was complete visualization of all 9 views. Secondary outcomes included examination time, factors associated with incomplete visualization, and exploratory screening performance using absence of normality in ≥1 axial view as the screening criterion. RESULTS: A total of 1494 fetal examinations performed by 15 operators across 7 centers were analyzed. Complete visualization of all 9 views increased from 78% in the implementation phase to 84% in the validation phase (p = .01). Mean examination time decreased significantly after completion of the learning phase (8.0 ± 6.4 versus 5.8 ± 3.9 minutes; p < .001). In multivariable analysis, the validation phase independently reduced the likelihood of incomplete visualization (adjusted OR, 0.65; p < .01), whereas higher maternal body mass index (adjusted OR, 1.06 per kg/m2; p < .001) and anterior fetal spine position (adjusted OR, 3.95; p < .001) increased this risk. Thirty-six fetuses (2.4%) had confirmed cardiovascular anomalies, vascular variants, or relevant ultrasound markers. Exploratory screening performance estimates based on available prenatal and postnatal follow-up suggested high specificity and negative predictive value, although sensitivity estimates should be interpreted cautiously because systematic postnatal echocardiography was not available. CONCLUSIONS: The CASSEAL algorithm demonstrates high feasibility, a short learning curve, and robust multicenter reproducibility for structured second-trimester evaluation of the extended fetal cardiovascular system. The integrated 3 × 3 sequential framework may facilitate standardized assessment of supracardiac, cardiac, and infracardiac territories in routine multicenter screening practice.