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Published on: November 24, 2014
Blood flow assessment by transit time flow measurement and its prognostic impact in coronary bypass surgery
Lars Niclauss1,2, Pier-Giorgio Masci3, Anna G Pavon3
1Division of Cardiovascular Surgery, Cardiovascular Department, University Hospital of Lausanne (CHUV), Lausanne, Switzerland - lars.niclauss@chuv.ch.
Insights
Competitive coronary flow impacts arterial grafts but not venous grafts. Vein grafts to small coronary arteries risk occlusion, and borderline flow in arterial grafts warrants careful evaluation.
Area of Science:
- Cardiovascular Surgery
- Medical Imaging
- Hemodynamics
Background:
- Coronary artery bypass graft (CABG) patency is influenced by competitive coronary flow and stenosis severity.
- Intraoperative graft assessment uses Transit Time Flow Measurement (TTFM).
- Cardiac magnetic resonance (MRI) facilitates graft evaluation during follow-up.
Purpose of the Study:
- To investigate the impact of competitive coronary flow and target vessel diameter on coronary graft patency.
- To correlate intraoperative TTFM findings with long-term graft outcomes assessed by cardiac MRI.
Main Methods:
- 35 patients undergoing off-pump CABG were analyzed for competitive flow and target vessel diameter.
- TTFM was used for intraoperative graft evaluation.
- Cardiac MRI assessed cardiac function, ischemia, and graft flow during follow-up.
Main Results:
- Competitive flow reduced mean graft flow (MGF) and increased pulsatility index (PI) in arterial grafts, but not in veins.
- Grafting to smaller coronary arteries (<1.5 mm) led to reduced MGF and increased PI/shortened diastolic flow fraction (DF) in veins.
- Borderline TTFM values, particularly in arterial grafts, required careful consideration of native coronary flow and target vessel characteristics.
Conclusions:
- Competitive flow differentially affects arterial versus venous grafts.
- Venous grafts are susceptible to occlusion when anastomosed to small target coronary arteries.
- Borderline arterial graft flow, especially without clear physiological explanation, may indicate a risk for graft failure.
Background:
The competitive coronary flow is influenced by the severity of the stenosis and may affect graft patency. Transit time flow measurement (TTFM) enables intraoperative graft evaluation and cardiac magnetic resonance (MRI) allows for graft evaluation during follow-up.
Methods:
Competitive flow and target vessel diameters were determined in 35 patients undergoing off-pump coronary bypass graft surgery (CABG) and correlated to TTFM. Cardiac function, ischemia, and graft flow were evaluated using cardiac MRI during the follow-up period to determine the impact of above-mentioned parameters on graft patency.
Results:
Competitive flow led to reduced mean graft flow (MGF) and increased pulsatility index (PI) in arterial grafts. This effect to was not observed in veins. Smaller target coronary arteries (<1.5 mm) were associated with reduced MGF, more pronounced in veins, which presented increased PI and shortened diastolic flow fraction (DF). No death and no re-hospitalization for acute coronary syndrome occurred. Borderline values of TTFM (mean MGF 13±4 mL/min; PI 3.8±1) in left internal mammary artery (LIMA) were mainly observed due to increased native anterior descending artery (LAD) flow. These LAD's collateralized occluded right coronaries (RCA). The corresponding LIMA to LAD grafts showed a bypass flow increase at cardiac MRI follow-up. Two graft occlusions occurred: one in LIMA-to-LAD bypass with borderline TTFM, which did not collateralize the RCA and one in a vein graft with borderline TTFM bypassed on a narrow vascular target.
Conclusions:
Competitive flow has an impact on arteries contrary to veins. Veins are at risk for occlusion when grafted to smaller targets. Borderline LIMA flow should be considered as potentially dangerous, if satisfactory explanations are missing, e.g. in the absence of a large coronary target without flow competition.
