Learning Curve of Cardiac Surgery Residents in Transit-Time Flow Measurement and High-Resolution Epicardial Ultrasonography During Coronary Surgery

<b>Objectives</b>: This study aimed to define the learning curve required for cardiac surgery residents to acquire basic technical and interpretive skills in transit-time flow measurement (TTFM) and high-resolution epicardial ultrasonography (HRUS) during coronary artery bypass grafting (CABG). <b>Methods</b>: Prospective, observational, single-center study evaluating performance using a novel scoring system combining functional (TTFM) and anatomical (HRUS) assessment criteria. This study was registered on ClinicalTrials.gov (Identifier: NCT06589323). Nine cardiac surgery residents without prior hands-on experience in TTFM or HRUS were enrolled. Twenty-seven elective CABG patients (67 grafts) were analyzed. Each measurement was compared with those obtained by an expert benchmark surgeon (N.T.) under standardized hemodynamic conditions. <b>Results</b>: Residents achieved the predefined primary endpoint (combined TTFM + HRUS score/number of grafts ≥ 11) after a median of 3 cases (IQR 2-4) and 7 anastomoses (IQR 7-10). Kaplan-Meier analysis showed a progressive increase in the probability of success, with a sharp rise after the seventh anastomosis. A shorter interval between attempts (<30 days) was significantly associated with earlier achievement of the endpoint (<i>p</i> < 0.05). Median acquisition time for TTFM was 25 s, with <10% inter-observer variability across all flow parameters. HRUS images of adequate quality were obtained within 60 s in >90% of cases, though slightly lower success rates were observed for lateral and inferior wall targets. No resident- or procedure-related variable was independently associated with performance improvement. <b>Conclusions</b>: Mastery of basic TTFM and HRUS skills requires only a few cases and anastomoses, demonstrating a short and attainable learning curve. These findings challenge the perception of a steep learning process and support the routine use of intraoperative graft verification techniques in all CABG procedures.