Perioperative observation and study of blood flow of different bypass form in right coronary artery bypass grafting


 Background: With the aging of China's population, the incidence and mortality of coronary atherosclerotic heart disease (CAD) are increasing year by year, which brings a heavy burden to the family and society [1]. To analyse the strategy of Coronary artery bypass grafting(CABG) in right coronary artery. To compare hemodynamic characteristics of the sequential grafts with those of single grafts and observe the patency rate of those grafts for one week after-operation.Methods: A total of 242 patients (178 male, mean age 62.6±8.8 years ) underment the right coronary artery bypass grafting in our hospital from October 2016 to January 2019 were collected. The blood flow (Q, ml/min) and pulsatility index (PI) and related parameters of grafts are measured and recorded by TTFM in CABG.The patency of grafts were evaluated by coronary computed tomography(CT) for one week after operation.Results: The most common material of graft in right coronary system of CABG is great saphenous vein(92.3%), followed by the radial artery and internal mammary artery. The highest frequency target of right coronary artery is posterior descending artery (PDA)(47.6%),followed by the Right main coronary artery (RCA )(29.1%) and Posterior branch of left ventricle (PL)(23.3%).The proportion of single graft is the largest in right coronary artery in CABG(178 cases，67.9%),followed by the proportion of the graft of PDA-PL (42cases，16.0%) and other sequential grafts among the different coronary artery system (including the system of Left anterior descending artery (LAD) and Left Circumflex (LCX)).The research shows that whether the sequential grafts of PDA-PL or with other sequential grafts among the different system of coronary artery the instantaneous flow of group of sequential grafts is higher than that of single graft, and the difference has statistical significance (P < 0.01) .But there was no statistical difference of the flow between groups of sequential grafts (P = 0.410).Diastolic flow (DF) in the group of sequential grafts of right coronary system is better than that in non-sequential group (P < 0.001), and the difference has statistical significance. There was no statistical difference between the DF of groups of other system of sequential grafts and that of right coronary sequential grafts .Coronary artery CT suggests that there was 11 cases existing poor development grafts or stenosis and occlusion in week after operation,and those phenomenon mainly occurred in the group of a single graft.There was only one case which be occluded in the group of other systems of sequential grafts, and statistically significant difference existed between two groups (P < 0.01).Conclusions: The most common form of CABG in right coronary artery system is non-sequential vein bridge to PDA in our center. Whether the sequential grafts of PDA-PL or other sequential grafts among the different coronary artery system the instantaneous flow of group of sequential grafts is higher than that of single graft. DF in the group of sequential grafts of right coronary system is better than that in non-sequential group.

occurred in the group of a single graft.There was only one case which be occluded in the group of other systems of sequential grafts, and statistically significant difference existed between two groups (P < 0.01).
Conclusions: The most common form of CABG in right coronary artery system is non-sequential vein bridge to PDA in our center. Whether the sequential grafts of PDA-PL or other sequential grafts among the different coronary artery system the instantaneous flow of group of sequential grafts is higher than that of single graft. DF in the group of sequential grafts of right coronary system is better than that in non-sequential group.

Background
With the aging of China's population, the incidence and mortality of CAD are increasing year by year, which brings a heavy burden to the family and society [1].CABG has been recognized as one of the accepted standard protocols for the treatment of complex, multivessel coronary vasculopathy since it was first introduced in the 1970s [2,3].
The surgical strategies of the right coronary system (including the right main trunk, the posterior descending branch, and the left ventricle branch) have been significantly individualized and differentiated [4], especially in the selection of target vessel sites, which depending on the surgeon's clinical experience and his own habits, causing that there is no recognized, immobilized model for the bypass or surgical strategy of the right coronary system. The purpose of this study was to observe and analyze the surgical strategy of the right coronary artery bypass graft in the conventional CABG population in our center. The hemodynamic characteristics of the sequential bypass and nonsequential bypass vessels were compared and the patency rate of one week after the operation was observed. Coronary CT examination was performed one week after the operation to observe the patency of the right coronary artery. All patients were routinely taking aspirin 100 mg/day to the day before surgery, and routinely taking aspirin 100 mg/day and Plavix 75 mg/day after offline extubation.

Methods 1.2.1 Research methods
TTFM was used to measure and record related parameters such as mean graft flow (MGF) and pulsatility index (PI value). Coronary CT examination was performed on the above population one week after surgery. Inclusion criteria: 1, the first simple CABG patients; 2, the right coronary system for coronary artery bypass grafting; exclusion criteria: 1, patients with minimally invasive small incision single and / or multiple coronary artery bypass grafts; 2, Patients, for various reasons, was not performed TTFM examination in operation 3, patients who, one week after surgery, was not performed coronary CT examination for various reasons; all CABG operations are completed by three surgeons, the seniority is more than the deputy chief physician, and the independent completion of CABG surgery exceeds 700. example / person.

Surgical methods
All patients underwent endotracheal intubation combined with general anesthesia. All patients underwent routine mid-opening. Under direct vision, the low-frequency electrosurgical detached left (right) lateral mammary artery and/or brachial artery, and obtained under endoscope or direct vision.
Saphenous vein, coronary artery bypass grafting after cardio-hepatic cardiopulmonary bypass or nonstop jumping.

Instruments and methods
The transient blood flow meter (TTFM) used during the surgery is the Medidist VQ2011 model. After the anastomosis of all the bypass vessels is completed, the protamine is neutralized and stabilized according to the diameter of the bypass. The ultrasonic probe is selected according to the diameter of the bypass, and the bypass vessel is placed in the probe near the anastomosis for direct measurement [5]. Parameters obtained during surgery: 1. MGF is the average blood flow per minute in the graft bypass blood vessels, and the unit is ml/min.Some studies have suggested that MGF < maximum blood flow and the minimum blood flow difference to the mean flow rate [PI=( Q max − Q min)/Qm] in the graft vessel. It is one of the most commonly used indicators of graft function, used to evaluate CABG during intraoperative TTFM. Excessive PI values represent functional defects in transplanted blood vessels [7]. Different studies have different definitions of cut-off values for PI. It is generally considered that greater than 5 is considered to be an independent risk factor for graft vascular dysfunction [6]. 3. DF is the ratio of the diastolic blood flow to the sum of systolic and diastolic blood flow [DF = Q diastole /(Q systole + Q diastole)], which is a good indicator for evaluating the function of CABG graft. It is generally believed that DF > 50% is one of the indicators of good graft function [8].

Intraoperative determination of flow satisfaction criteria
The coupling degree is satisfactory when measuring the graft bypass vessel (> 50% or more); 2. The TTFM shows that the blood flow waveform is stable and reproducible; 3. The average flow red line is recorded after the plateau period is stable; 4. According to the previous study Display PI value < 5, flow rate > 15 ml/min is a satisfactory bypass blood flow parameter.

Postoperative coronary CT evaluation method
The vascular patency or restenosis was evaluated by two senior radiologists. The diameter of the bypass was measured in the cross section of the bypass vessel. The mean value of the vascular diameter of the stenosis was not used as a reference. According to the Fitzgibbon bypass vascular grading criteria [9]: Grade A, bypass vessel no stenosis or stenosis < 50%; grade B, vascular stenosis ≥ 50%, but not completely occluded; grade O, complete occlusion of the bypass vessel. In this study, we will classify the grade A into the patency group, classify the grade B and grade O into the stenosis group, and classify the poorly developed ones into the stenosis group.

Statistical analysis
All recovered data was created using EpiDate3.1 software, and data was entered in parallel twice, and the input data was logically checked, collated, and analyzed for abnormal values to form a final analysis database. Correlation analysis was performed using the SPSS 20.0 statistical software package.
All descriptive measurement data were expressed by mean ± standard deviation, normal distribution data mean comparison using variance analysis, and non-normal distribution data mean comparison using nonparametric test (rank sum test). The comparison between the groups was performed using a chi-square test.

Results
A total of 242 patients were included in the study, including 178 males and 64 females. The average age was 62.6 ± 8.8 years, and the average number of bypass was 3.22 ± 0.803. The specific results are shown in Table 1. This study showed that the proportion of non-sequential single-branched bypass in the right coronary system was the largest (178 cases, 67.9%), followed by the sequential between the right posterior descending branch and the left ventricle posterior (42 cases, 16.0%). The rest are mostly sequential bypass between the right crown system and the non-right crown system (including the front descending branch system and the gyroscopic branch system) (see Table 2). In total 262 100.0 *In the operation, the right crown system only has a single bypass. **In the operation, right coronary system separately set up two bypass Considering the convenience of subsequent statistics on single-branched bypass and sequential bypass, combined with clinical features, we grouped the intraoperative bypass conditions as follows: the single-nodes of the right-crown system were respectively single-bypassd to the single-group (group A), the sequential bypass of the right coronary system and the convoluted and/or anterior descending branch system is attributed to other systematic sequential groups (group C), while the right coronary system Y-bypass is attributed to the PDA-PL right coronary sequential group (group B).
The differences in flow, pulsation index and DF parameters between the three groups were compared.
Considering that the single crown of the right crown system and one other system have a sequential influence on the flow distribution, this part of the data is ignored (2 cases / 0.7%)(see Table 3). In total 12 * The hybrid bypass is the posterior branch anastomosis after the right internal mammary artery is connected to the saphenous vein; ** Of the 11 cases, 4 were poorly developed, 4 were occluded (grade O), 1 was moderate to severe stenosis (grade B), and 2 were moderately stenotic (grade B).
This study showed that the bypass material used in the right coronary system of our center was mainly the saphenous vein (286 cases, 92.3%), followed by the radial artery and the internal mammary artery, and the utilization rate of the arterial bypass was low. In the choice of target vessel sites in the right coronary system, we prefer to choose the posterior descending artery for bypass (47.6%), followed by the right coronary trunk (29.1%) and the left ventricle posterior branch (23.3%).
One week after the surgery coronary CT examination, 11 cases of bypass vessels had different degrees of poor development or stenosis and occlusion, and mainly occurred in single bypass vessels (11 cases, 91.7%), of which only one was sequential bypass blood vessels with other systems. The difference between the above groups was statistically significant (P < 0.01)(see Table 3).
In this study, the instantaneous flow of the vascular in both the right coronary sequential group and the other system sequential group was higher than that of the single group and the above difference was statistically significant (P < 0.01). However, there was no statistical difference in instantaneous bypass flow between the two sequential groups (P = 0.410). There was no significant difference in the pulsatility index between the three groups (P > 0.05). In the diastolic blood supply ratio, the right coronary sequential group was superior to the single-group (P < 0.001), and the difference was statistically significant, while there was no statistical difference between the right coronary sequential group and other systematic sequential groups(see Table 4 and 5).

Discussion
The development of CABG surgical strategy is one of the important factors for the success of surgery, of which the selection of target blood vessel sites is the most important strategy. Previous studies have shown that preestablished CABG surgical strategies based on coronary angiography are somewhat different from actual surgical strategies and are not related to the surgeon's seniority [4]. Regardless of whether he is a low-grade or highgrade doctor, compared with the left coronary artery system, the actual coincidence rate of the selection strategy of the target right ventricle in the right coronary system is the lowest, and also shows to some extent that the right coronary revascularization strategy is still controversial. This study shows that the choice of right coronary target vascular sites in our center prefers the posterior descending branch (47.6%). Of course, this may be related to the patient's own coronary lesions, but, on the other hand, may also because that, in off-pump surgery (63.5%), PDA is more convenient to expose and the intraoperative safety is relatively higher (compared to the right coronary trunk, less arrhythmia induced by bleeding) and other factors.
In recent years, the call of CABG of multiple arterial bypass and whole arterial bypass has become higher and higher, and a large number of studies have confirmed that they have better mid-and long-term patency rates compared with veins [10,11]. This study shows that the selection of bypass material for the right coronary system has a large proportion of the great saphenous vein (92.3%), which may be related to its recent safety, relatively simple acquisition, relatively sufficient material, more plasticity and other factors. For the selection of multiple arterial bypass, in addition to strengthening awareness, more clinical practice is still needed.
In this study, the flow rate of the comparison between the other system sequential group (group C), the right coronary system sequential group (group B) and the single-group (group A) group gradually decreased, especially in the sequential group and the non-sequential groups the difference were statistically significant (P < 0.05). To some extent, the viewpoint that the sequential bypass flow was better than the single-bypass flow was verified(as the number of anastomoses increased, the flow rate gradually increased). In addition, in the non-sequential single-bypass, the peak flow of the right coronary target vessel was the largest (37.0 ± 21.6 ml / min), and compared with the posterior descending branch (24.7 ± 15.5. ml / min) and the left ventricle posterior branch (26.9 ± 23.3 ml/min) had a statistically significant difference (P < 0.05). However, unlike the previous research results [12][13][14], this study shows that the left ventricular posterior tributary flow is higher than the posterior descending branch, which is inconsistent with the classical vascular bed theory. It may be related to the number of cases, causing certain Bias.
Previous studies have shown that due to the larger number of anastomotic ports and relatively larger vascular beds, the sequential bypass have a larger flow rate than the single-branched bypass, and the high flow rate will delay the proliferation of the intima to a certain extent, making the bypass vessels better with long-term patency rate [12,14]. One week after coronary CT in the study, 11 patients in the non-sequential group had different degrees of stenosis or unclear visualization, but only one case in the sequential group. Although not necessarily caused by intimal hyperplasia, it also proves to some extent that high-flow sequential bypass have better postoperative short-term patency [15].
In this study, coronary CT showed that poorly developed vascular vessels were more in the radial artery bypass (4 cases). Although the relevant parameters such as intraoperative bypass flow were satisfactory, poor CT results also made Surgeons, who intent to do multi-arterial or all-arterial CABG, have concerns, including what is the cause and the long-term patency still require long-term observation. This study did not include the analysis of the location and stenosis of the right coronary vasculature, which may have an impact on the surgical strategy and blood flow results. In addition, this study is a single-center study, and the overall sample size is small, which needs further confirmation by large-scale clinical research.

Limitations
Our study had several limitations. Due to its retrospective design, we were unable to certify that all potential confounding factors had been record. Our single center experience may not be applicable to other institutes.

Conclusion
The most common form of CABG in right coronary artery system is non-sequential SV to PDA in our center.
Whether the sequential grafts of PDA-PL or other sequential grafts among the different coronary artery system the instantaneous flow of group of sequential grafts is higher than that of single graft. DF in the group of sequential grafts of right coronary system is better than that in non-sequential group.