Intraoperative graft assessment and imaging of native coronary arteries
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The evaluation of native coronary arteries in cardiac surgery represents a useful tool to detect coronary artery stenosis, identify the target artery, and choose the best anastomotic site. Intraoperative graft assessment is a fundamental step of coronary artery bypass grafting. It is able to reduce graft failure related to technical error, improving both short- and long-term outcome of patients submitted to surgical myocardial revascularization. Herein procedures of graft assessment are described, reporting their strengths and limitations.
KeywordsIntraoperative graft verification Transit-time flow measurement High-resolution epicardial ultrasonography
High resolution imaging for native coronary arteries evaluation
The use of high resolution ultrasonography (HR-ECUS) in the evaluation of native coronary arteries is a well-known method from the 1980s when for the first time. Sahn et al. used HR-ECUS in coronary evaluation in patients submitted to valvular surgery with negative angiography (normal coronaries) and in patients with severe coronary disease .
They demonstrated a high correlation between angiographic findings and intraoperative imaging with an R-value of 0.91. They were the first to report the potential use of this method to select the best site for coronary artery bypass graft (CABG) anastomosis and to evaluate the presence of severe stenosis in chronic vessel occlusion where angiography gives less information. The dimension of the probe used by Sahn et al. was 7 × 6 × 5 cm, and the frequency of the signal was 9 MHz.
In 1986, McPherson et al. validated the use of epicardial echocardiography for the measurement of wall thickness and vessel lumen of coronary artery measured with ultrasonography in animal studies and autopsy compared with histologic measurements . They demonstrated a good correlation between the two methods suggesting that epicardial coronary echography could be a useful tool for in vivo coronary artery evaluation in patients.
One of the major issues in the evaluation of coronary arteries is the dimension of the probe that should be put on the epicardial surface of the heart. In 2008, the introduction of a smaller probe with a wide range of frequencies from 8 up to 18 MHz for HR-ECUS (Medistim, Oslo, Norway) extended the usefulness of this method in the field of coronary surgery simplifying the evaluation of the coronary arteries, arterial graft, aorta, and coronary anastomosis.
Concerning the role of HR-ECUS in the evaluation of native coronary arteries, we started to use it in 2009, and we reported three cases of HR-ECUS guided coronary revascularization on the left anterior descending artery (LAD) in patients submitted to surgery without preoperative angiography for different reasons . In all three cases, we decided to revascularize the LAD because we demonstrated a severe stenosis in the proximal part of the LAD. In these patients’ transit-time flow measurement (TTFM) of the coronary graft confirmed the presence of a severe stenosis in the native vessel.
With the improved confidence with the method, we routinely perform native coronary arteries scan from the left main coronary artery to the proximal part of the LAD and circumflex (LCx) arteries.
Another use of HR-ECUS is the localization of the best anastomotic point or the vessel itself in case of intramyocardial course especially in off-pump CABG.
Technique for left coronary artery evaluation (Video 1)
The left main can be easily scanned from its origin to the bifurcation and the proximal part of the LAD and LCx. The probe should be held between the index and middle finger and passed between the left auricle and the pulmonary trunk to reach the transverse sinus and the top of left main coronary artery. To obtain a more reliable imaging, the pericardial sac should be filled with warm water.
With the use of 2-D and color flow mapping (CFM), imaging the extent of plaque, lumen reduction, and flow acceleration can be easily assessed. Moreover, there is the chance to measure the diameter of the residual lumen calculating the percentage of stenosis. To avoid over or underestimation of the stenosis, it is important to not compress the vessel below the probe.
Technique for right coronary artery evaluation
The probe should be positioned at the level of the origin of the right coronary artery from the aorta moving towards the right atrio-ventricular groove overtaking the acute margin of the heart up to the crux cordis. The right coronary artery can be viewed in cross section and longitudinal scans with or without color flow mapping.
Theory of intraoperative graft assessment with TTFM and HR-ECUS
Reported cut-offs for TTFM parameters in different experiences
Kim et al. 
MGF < 15 ml/min—PI > 3 (LCA) or PI > 5 (RCA) PI > 5
Di Giammarco et al. 
MGF ≤ 15 ml/min—PI ≥ 3
Tokuda, et al. 
MGF ≤ 15 ml/min—PI ≥ 5.1 (LCA)
MGF ≤ 20 ml/min—PI ≥ 4.7 (RCA)
Kieser et al. 
PI > 5
Procedural aspects of intraoperative graft verification
The flow chart of intraoperative graft assessment
We developed a flow chart of intraoperative verification to guide the surgeon through the entire procedure of graft assessment . The first step of intraoperative graft verification procedure is the check with HR-ECUS of the arterial conduit. Subsequently, after the completion of the distal anastomosis, the second step is the morphological verification with HR-ECUS. In case of stenosis, the anastomosis should be redone immediately. The third step is the functional verification of the graft with TTFM. Repeated measures should be obtained as indicated in the previous section. There are three possible scenarios. The first (low MGF, low PI, and BF between 0 and 3) indicates a graft with a poor run-off. If the parameters will improve after dobutamine test, we can argue that the graft will have a good fate, conversely the risk of graft failure is high (Fig. 4). The second scenario (low MGF, high PI, and high BF) is a situation of competition of flow. This situation can occur in case of a graft put on a vessel with a moderate stenosis or more commonly in case of composite arterial conduits when the stenoses of the native vessels are unbalanced. If the parameter values will improve after dobutamine test, the graft will have a good prognosis, conversely especially for composite grafts; conduit configuration should be rearranged.
The third scenario is characterized by normal TTFM parameters (MGF > 15, PI < 3, and BF between 0 and 3) conferring to the graft a good chance to be patent at mid-term follow-up.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
Informed consent and ethical committee approval
Not applicable as the manuscript is a review paper.
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