Pre- and Post-Protamine Administration Graft Flow with Intraoperative Transit Time Flow Measurement – a Pilot Study to Asses a New Parameter

Introduction: Intraoperative graft assessment is imperative for quality control in coronary artery bypass grafting (CABG). When performed with Transit Time Flow Measurements (TTFM), assessment relies on mean graft flow (MGF), pulsatility index (PI), diastolic filling (DF) and backflow (BF). Despite endorsement by the 2018 European guidelines for myocardial revascularization, graft assessment has yet to receive wide diffusion. This can possibly be attributed to a lack of clear cut-off values and varying sensitivity/specificity to predict graft patency. Based on observations noting a post-protamine MGF reduction, we investigated the variation of TTFM parameters before and after protamine administration to identify new parameters for graft quality assessment.

Metirials and Methods: The database of the REQUEST (“REgistry for QUality AssESsmenT with Ultrasound Imaging and TTFM in Cardiac Bypass Surgery”) study was retrospectively reviewed to quantify the average change in flow parameters before and after the administration of protamine. A per graft analysis was performed.

Grafts (arterial or venous) with both pre- and post-protamine TTFM variables recorded and both pre- and post-protamine acoustical coupling index (ACI) > 30% were included. Grafts with incomplete data and mixed grafts (arterio-venous) were excluded. Non-normality was verified with Shapiro-Wilk test and Wilcoxon signed-rank test was used for paired comparisons.

Results and disscusion: MGF increased post- protamine for venous grafts from 32 to 35 ml/min, but remained unchanged for arterial grafts. PI decreased for both venous (2.3 to 2.0) and arterial grafts (2.3 to 2.1). DF decreased as well for both venous (62% to 61%) and arterial grafts (71% to 70%).

Conclusion: Comparing pre- and post-protamine measurements, we found no clinically significant changes in TTFM parameters. We therefore suggest further inspection, if not revision, of a graft when a significant drop in MGF is noted post protamine even if the flow parameters are within normal range.