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

## TL;DR

This study shows that cardiac surgery residents can quickly learn to use transit-time flow measurement and high-resolution epicardial ultrasonography during coronary surgery.

## Contribution

The study quantifies a short and attainable learning curve for residents acquiring TTFM and HRUS skills during CABG procedures.

## Key findings

- Residents achieved the primary endpoint after a median of 3 cases and 7 anastomoses.
- A shorter interval between attempts was associated with faster skill acquisition.
- TTFM acquisition time was 25 seconds with low inter-observer variability.

## Abstract

Objectives: 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). Methods: 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. Results: 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 (p < 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. Conclusions: 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.