The Effect of On-pump and Off-pump Coronary Artery Bypass Surgery on Intraoperative Graft Flow Parameters by Transit-time Flowmetry
Sanaz Amin, Jr.1, Raphael S. Werner2, George Krasopoulos1, David P. Taggart1.
1University of Oxford, Oxford, United Kingdom, 2University of Zurich, Zurich, United Kingdom.
OBJECTIVE: Transit Time Flowmetry (TTFM) is the most commonly applied technique for assessing graft patency during coronary artery bypass graft (CABG) surgery. TTFM measures four pertinent flow parameters: MGF, mean graft flow; PI, pulsatility index; %DF, diastolic filling and %BF, backward flow. Previous studies have only addressed the effect of on-pump and off-pump CABG on MGF and PI, with conflicting results. Crucially, most of these consisted of small sample sizes. Two studies with adequate sample sizes did however find higher MGF and lower PI in on-pump vs. off-pump grafts, hypothesizing that these findings were probably a result of vasodilatation resulting from cardiopulmonary bypass and reactive hyperemia resulting from a period of ischemia. The aim of this study is to assess all TTFM parameters in on-pump and off-pump CABG in both venous and arterial conduits in the left and the right coronary territory.
This study was designed as a prospective 2-surgeon single centre non-randomized observational study of surgeonsí standard practices between July 2015 and April 2017. A total of 659 conduits (patients: n=268) were included in this study. Transit Time flowmetry was prospectively recorded in all internal mammary arteries, radial and saphenous vein grafts in patients undergoing on-pump or off-pump CABG (with or without additional valve replacement/repair). All measurements were performed with the VeriQC device (Medistim ASA, Oslo, Norway).
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CONCLUSIONS: In conflict with current literature, we did not find any significant difference in PI between the groups. A significant difference in MGF was found between arterial grafts (on-pump vs. off-pump in the left and the right coronary territory) but not for venous grafts. This is most probably due to the fact that veins are less susceptible to competitive flow. Competitive flow arises during on-pump CABG as the native coronary vessels are relaxed due to cardiopulmonary bypass and reactive hyperemia resulting from a period of ischemia. This allows increased blood flow through the native coronary system and hereby result in what we call; "iatrogenic competitive flow".
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