Prediction of Graft Flow Impairment by Intraoperative Transit Time Flow Measurement in Off-Pump Coronary Artery Bypass Using Arterial Grafts

Effect of patent complete revascularization on the akinetic myocardial segments

OBJECTIVES

The aims of the study were (i) to examine the changes in echocardiographic parameters and (ii) to compare the fate of myocardial segments with akinesia and without akinesia on preoperative echocardiography after coronary artery bypass grafting.

METHODS

One hundred one patients who underwent complete revascularization, who were assessed by preoperative, before discharge, postoperative 3- and 12-month echocardiographic examinations, and who showed all patent grafts at postoperative 1-year angiograms were included. Echocardiographic left ventricular ejection fraction was assessed, and a 16-segment model was adopted for regional analysis of the left ventricle. A total of 1616 segments were analysed based on a 6-point scale: 1 = normal (N = 1083), 2 = mild hypokinesia (N = 2), 3 = moderate hypokinesia (N = 74), 4 = severe hypokinesia (N = 150), 5 = akinesia without thinning (N = 259) and 6 = akinesia with thinning (N = 48).

RESULTS

The serial left ventricular ejection fraction measured preoperatively, before discharge, at postoperative 3- and 12-months were 0.48 ± 0.14, 0.49 ± 0.12, 0.49 ± 0.10 and 0.54 ± 0.10, respectively. The left ventricular ejection fraction significantly increased over time during the postoperative 12 months (P < 0.001). Wall motion scores tended to decrease over time in both segment groups with akinesia and without akinesia (P < 0.001), and improvement of the wall motion was significantly higher in the segment group with akinesia than in the segment group without akinesia (P < 0.001).

CONCLUSIONS

The left ventricular ejection fraction and regional wall motion improved over time during the postoperative 12 months, regardless of the presence of an akinetic segment. Complete revascularization including akinetic myocardium should be considered when performing coronary artery bypass grafting.

Changes in Internal Thoracic Artery Blood Flow According to the Degree of Stenosis of the Anterior Descending Branch of the Left Coronary Artery

PURPOSE

Computational fluid dynamics has enabled the evaluation of coronary flow reserve. The purpose of this study was to clarify the hemodynamic variation and reserve potential of the left internal thoracic artery (LITA).

METHODS

Four patients were selected on the basis of various native coronary stenosis patterns and graft design. The wall shear stress and oscillatory shear index were measured, and one patient was selected. Next, we created three hypothetical lesions with 75%, 90%, and 99% stenosis in front of the graft anastomosis, and compared the changes in LITA blood flow and coronary flow distribution.

RESULTS

In the 75% to 90% stenosis model, blood flow was significantly higher in the native coronary flow proximal to the coronary artery bypass anastomosis regardless of time phase. In the 99% stenosis model, blood flow from the LITA was significantly dominant compared to native coronary flow at the proximal site of anastomosis. The range of LITA flow variability was the largest at 99% stenosis, with a difference of 70 ml/min.

CONCLUSION

The 99% stenosis model showed the highest LITA flow. The range of LITA flow variability is large, suggesting that it may vary according to the rate of native coronary stenosis.

Transit Time Flow Measurement in Robotic Totally Endoscopic Coronary Artery Bypass: What Do the Numbers Mean?

Objective

Transit time flow measurement (TTFM) is valuable for assessing intraoperative graft patency in coronary artery bypass surgery (CAB). The significance of competitive native coronary flow on patency, as predicted by percentage of backflow (%BF) on TTFM, is unknown. This study aims to evaluate intraoperative TTFM parameters, and specifically %BF, in predicting graft patency in robotic totally endoscopic CAB (TECAB).

Methods

We reviewed TTFM parameters in 311 patients undergoing robotic off-pump TECAB at our institution between February 2016 and January 2020. Patients with sequential or Y grafts were excluded, leaving 277 patients with a total of 387 isolated end-to-side grafts (248 left internal mammary artery [LIMA], 149 right IMA [RIMA]). Mean graft flow, diastolic flow, pulsatility index, and %BF were measured intraoperatively. Early postoperative angiograms were obtained in 83 patients undergoing percutaneous coronary intervention for hybrid revascularization, with a total of 125 grafts. Angiograms were independently analyzed and separated into 2 groups based on IMA graft patency, which were patent (FitzGibbon A/B) and nonpatent (FitzGibbon O) groups.

Results

Early angiographic patency at a median of 31.0 days after surgery showed 123 (97.1%) patent grafts and 3 (2.9%) occluded grafts in both LIMA and RIMA grafts to both left anterior descending (LAD) and non-LAD targets. Mean graft flow was 77.4 ± 41.6 mL/min. There was no difference in mean flow, pulsatility index, or %BF between the patent and occluded grafts.

Conclusions

Excellent intraoperative flow parameters and early angiographic patency can be obtained via robotic, off-pump TECAB. Our data did not demonstrate an association between intraoperative TTFM evidence of competitive native coronary flow and early angiographic graft outcomes.

The Use of Intraoperative Transit Time Flow Measurement for Coronary Artery Bypass Surgery: Systematic Review of the Evidence and Expert Opinion Statements

Transit time flow measurement (TTFM) allows quality control in coronary artery bypass grafting but remains largely underused, probably because of limited information and the lack of standardization. We performed a systematic review of the evidence on TTFM and other methods for quality control in coronary artery bypass grafting following PRISMA standards and elaborated expert recommendations by using a structured process. A panel of 19 experts took part in the consensus process using a 3-step modified Delphi method that consisted of 2 rounds of electronic voting and a final face-to-face virtual meeting. Eighty percent agreement was required for acceptance of the statements. A 2-level scale (strong, moderate) was used to grade the statements based on the perceived likelihood of a clinical benefit. The existing evidence supports an association between TTFM readings and graft patency and postoperative clinical outcomes, although there is high methodological heterogeneity among the published series. The evidence is more robust for arterial, rather than venous, grafts and for grafts to the left anterior descending artery. Although TTFM use increases the duration and the cost of surgery, there are no data to quantify this effect. Based on the systematic review, 10 expert statements for TTFM use in clinical practice were formulated. Six were approved at the first round of voting, 3 at the second round, and 1 at the virtual meeting. In conclusion, although TTFM use may increase the costs and duration of the procedure and requires a learning curve, its cost/benefit ratio seems largely favorable, in view of the potential clinical consequences of graft dysfunction. These consensus statements will help to standardize the use of TTFM in clinical practice and provide guidance in clinical decision-making.

Reopening of the occluded saphenous vein composite grafts after coronary artery bypass grafting

BACKGROUND

We have observed reopening of the occluded "no-touch" saphenous vein (NT SV) composite grafts on follow-up angiograms in patients who underwent coronary artery bypass graftings (CABGs).

METHODS

Between 2008 and 2018, 1283 patients received NT SV conduits without or with surrounding pedicle tissue as composite grafts based on the in situ left internal thoracic artery (ITA) for CABG and underwent early postoperative angiographies. Among the 1283 patients, 53 patients showed 55 occluded SV conduit anastomoses, and 46 patients who had 48 occluded SV anastomoses were re-evaluated by 1-year postoperative angiographies.

RESULTS

Early postoperative angiographies in 1283 patients demonstrated overall occlusion rates of 1.2% (56/4518); occlusion rates of the ITA and SV were 0.08% (1/1259) and 1.7% (55/3260), respectively. One-year angiograms demonstrated that 14 occluded SV anastomoses (29.2% [14/48 occluded SV]) of 14 patients became patent. Reopening of occluded SV conduits occurred more frequently in NT SV with pedicle tissue than in NT SV without pedicle tissue (45.0% [9/20] vs. 17.9% [5/28]; p = .057). When we examined the preoperative and 1-year postoperative angiograms, reopening of the occluded SV conduits was not related with progression (p = .258) or preoperative reversibility score (p = .115) of native target coronary artery disease.

CONCLUSIONS

More than a quarter of the occluded SV composite grafts on early postoperative angiograms were patent in the 1-year angiograms. The reopening rates were higher in patients who had received NT SV conduits with pedicle tissue than those who had received NT SV conduits without pedicle tissue.

Coronary Artery Bypass Grafting Transit Time Flow Measurement: Graft Patency and Clinical Outcomes

BACKGROUND

This subanalysis of the Randomized On-Off Bypass (ROOBY) trial examined transit time flow measurement (TTFM) use and its impact on graft patency and long-term clinical outcomes after coronary artery bypass graft surgery.

METHODS

Use of TTFM for ROOBY centers and surgeons was assessed. Comparative patient outcomes based on TTFM use included 1-year graft patency and 1-year and 5-year major adverse cardiac events: all-cause mortality, nonfatal myocardial infarction, and revascularization (percutaneous coronary intervention or repeat coronary artery bypass graft surgery).

RESULTS

Transit time flow measurement was used in 1067 patients (TTFM group) and not used in 501 patients (non-TTFM group); of the TTFM group, median percentage TTFM use was 79% (interquartile range, 41% to 98%) among 18 Veterans Affairs Medical Centers, and 74% (interquartile range, 13% to 98%) among 48 surgeons. Patients were comparable in age (63 ± 8.5 years TTFM vs 62 ± 8 years non-TTFM, P = .30) and estimated 30-day mortality risk (1.8 ± 1.7 TTFM vs 1.9 non-TTFM, P = .53). One-year FitzGibbon A patency was 83% (1600 of 1988 grafts) for TTFM assessed grafts and 78% (629 of 803) for non-TTFM assessed grafts (P < .01). Fewer TTFM patients had an occluded graft (29%, vs 38% non-TTFM; P = .01). Comparing TTFM patients with non-TTFM patients, 5-year major adverse cardiac event rates were 30% vs 25% (P = .06). Individual component rates were 14% vs 11% for death (P = .06), 12% vs 8.8% for myocardial infarction (P = .07), and 13% vs 12% for revascularization (P = .62).

CONCLUSIONS

The association of TTFM use with graft patency and clinical outcome is uncertain. Future randomized studies that account for patient risk factors and practice variation would help address this knowledge gap.

The relationship between epicardial fat tissue thickness and transit time flow measurement values of coronary artery bypass grafts

Introduction: Epicardial fat tissue, the true visceral adipose depot of the heart, has been associated with changes in both cardiac function and morphology. This study aimed to show the relationship between epicardial fat tissue (EFT) thickness and graft flow dynamics in arterial and venous grafts in coronary artery bypass graft surgery (CABG). Methods: Patients underwent transthoracic echocardiography before surgery and epicardial fat thickness were evaluated. The patients were divided into two groups as EFT value <5.5 (group 1) mm and ≥5.5 (group 2) mm. One hundred eighty-one patients with a total of 434 grafts (162 arterial and272 venous) underwent isolated coronary artery bypass grafting surgery. All grafts were examined by transit time flow meter intraoperatively. Results: The mean epicardial fat tissue thickness values were 4.9±0.8 mm and 6.1±1.3 mm, respectively.Mean graft flow values of left internal mammary artery was 44.21±23.2 mL/min in group 1 and39.65 ± 19.2 mL/min in group 2 (P = 0.041). Similarly, mean graft flow values were higher in group1 in all venous grafts regardless of which vessel bypass was performed. There is a significant negative correlation between epicardial fat thickness and mean graft flow. Conclusion: Epicardial fat thickness measurement preoperatively might provide additional data for the faith of the graft.

Improving coronary artery bypass grafting: a systematic review and meta-analysis on the impact of adopting transit-time flow measurement

Despite there being numerous studies of intraoperative graft flow assessment by transit-time flow measurement (TTFM) on outcomes after coronary artery bypass grafting (CABG), the adoption of contemporary TTFM is low. Therefore, on 31 January 2018, a systematic literature search was performed to identify articles that reported (i) the amount of grafts classified as abnormal or which were revised or (ii) an association between TTFM and outcomes during follow-up. Random-effects models were used to create pooled estimates with 95% confidence intervals (CI) of (i) the rate of graft revision per patient, (ii) the rate of graft revision per graft and (iii) the rate of graft revision among grafts deemed abnormal based on TTFM parameters. The search yielded 242 articles, and 66 original articles were included in the systematic review. Of those articles, 35 studies reported on abnormal grafts or graft revisions (8943 patients, 15 673 grafts) and were included in the meta-analysis. In 4.3% of patients (95% CI 3.3–5.7%, I² = 73.9) a revision was required and 2.0% of grafts (95% CI 1.5–2.5%; I²=66.0) were revised. The pooled rate of graft revisions among abnormal grafts was 25.1% (95% CI 15.5–37.9%; I²=80.2). Studies reported sensitivity ranging from 0.250 to 0.457 and the specificity from 0.939 to 0.984. Reported negative predictive values ranged from 0.719 to 0.980 and reported positive predictive values ranged from 0.100 to 0.840. This systematic review and meta-analysis showed that TTFM could improve CABG procedures. However, due to heterogeneous data, drawing uniform conclusions appeared challenging. Future studies should focus on determining the optimal use of TTFM and assessing its diagnostic accuracy.

Initial Experience with Epicardial Ultrasound Scanning in Coronary Artery Bypass Grafting

BACKGROUND

The benefits of epicardial ultrasound scanning (EUS) in coronary artery bypass grafting (CABG) have not yet been established. The aim of this study was to evaluate the usefulness of EUS in CABG, including in the assessment of the quality of distal anastomoses, the identification of epicardial target vessels, and the evaluation of any graft issues other than the distal anastomoses.

METHODS

Fifty-three patients undergoing CABG were enrolled between March 2018 and February 2019. Intraoperative EUS was performed along with transit-time flow measurement (TTFM). Graft evaluations were performed early (shortly after surgery) and 1 year after surgery for 53 (100%) and 47 (88.7%) patients, respectively.

RESULTS

EUS was applied to assess the quality of all distal anastomoses, 32 target vessels, and 2 conduit trunks. Insufficient TTFM findings were obtained for 18 grafts. However, graft revision was performed for only 3 distal anastomoses; based on the EUS findings, the remaining 15 sites were not revised. The early and 1-year overall graft patency rates were 100% (141 anastomoses) and 96.1% (122 of 127 anastomoses), respectively. All 15 of the distal anastomoses that were not revised despite insufficient TTFM results were patent at the 1-year mark.

CONCLUSION

The routine application of EUS in CABG could be beneficial by confirming the quality of surgery and reducing unnecessary procedures.

The predictive value of intraoperative transit-time flow measurement parameters for early graft failure in different target territories

BACKGROUND

Early graft failure can affect the short- and long-term outcomes of patients undergoing coronary bypass grafting surgery (CABG). The aim of our study was to explore the predictive value of transit-time flow measurement (TTFM) parameters for early graft failure (before discharge) after CABG in different coronary territories and calculate the TTFM cut-off values.

METHODS

We analyzed a total of 761 grafts (360 patients) that were evaluated by intraoperative TTFM and computed tomography angiography prior to discharge. Logistic model was established to detect the parameters of TTFM to predict early graft failure and receiver operating characteristic curve analysis was used to calculate the cut-off values.

RESULTS

The overall early graft failure was 3.5%. The results demonstrated that compared with off-pump CABG, mean graft flow volume was higher (28.0 vs 21.0 mL/min, p = 0.000), but pulse index (PI) (2.3 vs 2.5, p = 0.049) and diastolic flow fraction (DF) (68.0% vs 71.0%, p = 0.001) were lower in on-pump CABGs. DF (73.0% vs 65.5%, p = 0.000) of arterial grafts was higher than that of venous grafts. DF (72.0% vs 62.0%, p = 0.000) in left was higher than that in the right coronary artery territories. The results of multivariate logistic analysis showed that not only in the overall (OR 1.18, 95% CI 1.07-1.30, p = 0.001), but also the left (OR 1.21, 95% CI 1.03-1.41, p = 0.017) and right (OR 1.15, 95% CI 1.03-1.29, p = 0.017) coronary artery target territories, PI was a risk factor for early graft failure and the cut-off value was 3.4, 3.4, and 3.6, respectively. For grafts in left target territories, the results showed that DF (OR 0.94, 95% CI 0.91-0.97, p = 0.000) just in the univariate analysis was a risk factor that affected graft failure.

CONCLUSIONS

The overall early graft failure was about 3.5%. High PI value is a risk factor for early graft failure in not only overall grafts but in grafts of different target territories. DF might be more useful for the quality evaluation of grafts in left than in right target territories.

[Effect of the degree of stenosis of the right coronary artery on remote results of bypass grafting]

AIM

The purpose of this study was to assess the long-term results of right coronary artery bypass grafting and identify predictors of coronary artery bypass graft occlusion.

PATIENTS AND METHODS

Our retrospective single-centre study included a total of 245 patients subjected to isolated coronary artery bypass graft operations during the follow up period from 2010 to 2015. All patients endured bypass grafting of the right coronary artery (RCA) with either autovenous or autoarterial conduits. Control coronary bypass angiography was performed in all patients in connection with a relapse of angina pectoris. The duration of the follow up period amounted to 43.7±20.2 months. The patients were divided into two groups depending on the type of the conduit used to bypass the RCA. Group One patients (n=106) endured bypass grafting of the RCA and its branches using the internal thoracic artery. Group Two patients (n=139) underwent autovenous coronary artery bypass grafting of the RCA basin. By the main clinical, demographic and intraoperative parameters the groups were statistically homogeneous (p>0.05). The effect of the degree of proximal stenosis, the diameter of the grafted artery on the viability of bypass grafts was assessed.

RESULTS

During the follow-up period up to 84 months, 19 (17.9%) occluded arterial and 29 (20.9%) venous conduits were revealed. The Kaplan-Meier analysis showed that the probability of the absence of venous graft occlusion during the follow-up period up to 84 months was significantly lower than that of arterial grafts (log rank=0.012). The Cox regression analysis results revealed that shunt occlusion was influenced by the degree of proximal stenosis and the diameter of the shunted artery.

CONCLUSION

When shunting a moderate stenosis of the RCA (up to 70%), an advantage of autovenous conduits was revealed. When shunting the RCA with a critical stenosis and occlusion, advantages were revealed for the internal thoracic artery.

The influence of hemodynamics on graft patency prediction model based on support vector machine

In the existing patency prediction model of coronary artery bypass grafting (CABG), the characteristics are based on graft flow, but no researchers selected hemodynamic factors as the characteristics. The purpose of this paper is to study whether the introduction of hemodynamic factors will affect the performance of the prediction model. Transit time flow-meter (TTFM) waveforms and 1-year postoperative patency results were obtained from 50 internal mammary arterial grafts (LIMA) and 82 saphenous venous grafts (SVG) in 60 patients. Taking TTFM waveforms as the boundary conditions, the CABG ideal models were constructed to obtain hemodynamic factors in grafts. Based on clinical characteristics and combination of clinical and hemodynamic characteristics, patency prediction models based on support vector machine (SVM) were constructed respectively. For LIMA, after the introduction of hemodynamic factors, the accuracy, sensitivity and specificity of the prediction model increased from 70.35%, 50% and 74.17% to 78.02%, 70% and 78.89%, respectively. For SVG, the accuracy, sensitivity and specificity of the prediction model increased from 63.24%, 40% and 76.91% to 74.41%, 60.1% and 82.73%, respectively. The performance of the prediction model can be improved by introducing hemodynamic factors into the characteristics of the model. The accuracy, sensitivity and specificity of the prediction results are higher with the addition of hemodynamic characteristics.

Enhancement of flow measurement for graft verification

Background

We aimed to evaluate multiple transit-time flow measurements during coronary artery bypass grafting.

Methods

Transit-time flow measurements were performed first on the arrested heart both with and without a proximal snare on the target coronary artery, second, after weaning from cardiopulmonary bypass, and third, before chest closure.

Results

Among the 214 grafts considered, 9 (4.2%) were patent and 6 (2.8%) were failing. In the failed grafts, an abnormal transit-time flow was found during the first measurement, in 5 (2.3%) cases with a proximal snare and in one (0.47%) without a snare. In these cases, technical errors with the distal anastomoses were found and immediately corrected. A problem with the proximal anastomosis was found in one graft during the second measurement and corrected right away. Bending due to excessive length was found in 2 (0.93%) grafts during the third measurement, and graft repositioning was performed. The first transit-time flow measurement showed that mean graft flow was significantly decreased with a proximal snare compared to without a proximal snare, throughout the entire coronary territory. Pulsatility index during the first transit-time flow measurement was higher with a proximal snare than without one.

Conclusions

The 3-time transit-time flow measurement strategy makes it possible to verify and immediately correct technical problems with coronary bypass grafts.

Twenty-Year Experience With Off-Pump Coronary Artery Bypass Grafting and Early Postoperative Angiography

BACKGROUND

We have performed off-pump coronary artery bypass grafting and also performed early postoperative angiography to assess anastomosis accuracy and patency in most of our patients requiring surgical revascularization.

METHODS

Of 3083 patients who underwent isolated coronary artery bypass grafting between 1998 and 2017, 2919 patients (94.7%) underwent off-pump coronary artery bypass grafting. Conduits for distal anastomoses were left internal thoracic artery (n = 2764), right internal thoracic artery (n = 866), right gastroepiploic artery (n = 997), radial artery (n = 16), and saphenous vein (n = 1505). Since the introduction of transit-time flow measurement in 2000, we revised abnormal grafts intraoperatively. Early (≤7 days) angiography was performed in 2820 patients (96.6%) at 1.5 ± 1.2 postoperative days, and surgical intervention was performed based on angiographic findings.

RESULTS

Operative mortality was 1.1% (32 of 2919). Average number of distal anastomoses was 3.2 ± 1.0. Intraoperative flowmetry-guided revision for distal anastomosis failures was performed in 109 of 8585 distal anastomoses (1.3%). Angiography showed an overall patency of 98.2% (8836 of 9001): 99.0% (5484 of 5540) for arterial and 96.9% (3352 of 3461) for venous conduits (P < .001). Patency of venous conduits was 87.2% (231 of 265) for free grafts and 97.7% (3121 of 3196) for composite grafts (P = .001). After the introduction of transit-time flow measurement, patency of arterial conduits became significantly higher (97.2% vs 99.2%; P = .038); however, patency of free venous conduits was not significantly improved (86.0% vs 91.4%; P = .181). Early re-intervention according to angiographic findings was performed in 76 patients (2.7%). Reevaluation of graft patency before discharge in 31 who underwent revision of distal anastomoses showed improved patency (65.1% [56 of 86] vs 95.3% [82 of 86]; P < .001).

CONCLUSIONS

Intraoperative flowmetry and revision of abnormal grafts improved early arterial graft patency, and reoperation based on early angiographic findings may further improve graft patency at the time of discharge.

Comparison of blood flow in single and sequential vein grafts during off-pump coronary artery bypass

Background

The use of sequential anastomoses in coronary artery bypass grafting (CABG) is still controversial. This study aimed to evaluate the mean blood flow (MBF) rate and pulsatility index (PI) of single and sequential saphenous vein grafts to the posterior descending artery (PDA) in the same patient during off-pump CABG (OPCABG).

Methods

Sequential saphenous vein grafts were used to bypass the diagonal artery (Diagonal) (side-by-side), obtuse marginal artery (OM) (side-by-side) and PDA (end-to-side). The anastomoses of Diagonal and OM were temporarily occluded with bulldog clamps, making the sequential graft a "single" graft to PDA. The MBF and PI of this "single" graft to PDA were measured with transit-time flow measurement (TTFM). Then the bulldog clamps were removed and the MBF and PI of sequential graft to PDA were measured again and compared to those of the "single" graft in the same patient. Anastomoses were evaluated with coronary CT angiogram at 6 months.

Results

A total of 128 patients with triple vessel disease were enrolled (96 men; mean age, 66.0±8.0 years; range, 54-80 years). The MBF of the "single" vs. sequential graft to PDA was 20.6±9.1 vs. 21.4±10.1 mL/min (P=0.472). The PI of 'single graft' vs. sequential graft to PDA was 1.7±0.6 vs. 1.7±0.5 (P=0.941). The patency of all grafts was good in all patients after 6 months of follow-up.

Conclusions

There were no hydrodynamic differences between single and sequential grafts to PDA in OPCABG.

Intraoperative graft assessment and imaging of native coronary arteries

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.

Influence of coronary territory on flow profiles of saphenous vein grafts

Background

Differing perfusion of the left and right ventricular coronary territory may influence flow-profiles of saphenous vein grafts (SVGs). We compared flow parameters, measured by transit-time flowmetry (TTFM), in left- and right-sided SVGs during coronary artery by-pass grafting (CABG).

Methods

Routine TTFM measurements were obtained in 167 SVGs to the left territory (55%) and 134 SVGs to the right territory (total of 301 SVGs in 207 patients). The four standard TTFM parameters, [mean graft flow (MGF), pulsatility index (PI), percentage diastolic filling (%DF), and percentage backward flow (%BF)] were compared. Differences in flow parameters were also examined according to surgical technique (on- vs. off-pump).

Results

No significant difference between coronary territories was found for MGF, PI and %BF. However, a higher %DF was noted in left-sided SVGs in the overall cohort as well as in the on-pump (both p < 0.001) and the off-pump cohorts (p = 0.07). Further, a significantly higher %BF was found in SVGs performed off-pump to the left territory (1.2 ± 2.5 vs. 2.3 ± 3.0, p = 0.023). In a multivariate regression analysis, anastomosing a SVG to the left territory was weakly associated with higher PI (OR = 0.36, p = 0.026) and strongly associated with higher %DF (OR = 5.1, p < 0.001). No significant association was found for MGF, PI, %DF or %BF in either the on-pump nor the off-pump cohorts.

Conclusions

Although statistically significant, the established differences in TTFM parameters between left- and right-sided vein grafts were small and unlikely to be of clinical relevance.

Physiological insights of recent clinical diagnostic and therapeutic technologies for cardiovascular diseases

Diagnostic and therapeutic methods for cardiovascular diseases continue to be developed in the 21st century. Clinicians should consider the physiological characteristics of the cardiovascular system to ensure successful diagnosis and treatment. In this review, we focus on the roles of cardiovascular physiology in recent diagnostic and therapeutic technologies for cardiovascular diseases. In the first section, we discuss how to evaluate and utilize left ventricular arterial coupling in the clinical settings. In the second section, we review unique characteristics of pulmonary circulation in the diagnosis and treatment of pulmonary hypertension. In the third section, we discuss physiological and anatomical factors associated with graft patency after coronary artery bypass grafting. In the last section, we discuss the usefulness of mechanical ventricular unloading after acute myocardial infarction. Clinical development of diagnostic methods and therapies for cardiovascular diseases should be based on physiological insights of the cardiovascular system.

Intraoperative graft verification in coronary surgery

Transit-time flow measurement (TTFM) is a reliable method to check the graft function intraoperatively in coronary surgery. The given parameters are: Mean Graft Flow (MGF); Pulsatility Index (PI) and Insufficiency Ratio (%BF). Some cutoffs of these parameters have been identified as predictors for unfair 1-y clinical outcome: mean graft flow (MGF) less than 20 ml/min and high pulsatility index greater than 5. Other cutoffs have been found as related to postoperative angiography: MGF 15 ml/min or less and pulsatility index at least 3 (sensitivity 94%; specificity 61%); MGF less than 15 ml/min and pulsatility index greater than 3 for left coronary artery or pulsatility index greater than 5 for right coronary artery (sensitivity 96%; specificity 77%); MGF 15 ml/min or less and pulsatility index at least 5.1 left coronary artery (sensitivity 98%; specificity 26%). Hence, with the need to improve the diagnostic accuracy of TTFM, high-resolution epicardic coronary ultrasound module has been added to graft flow evaluation providing 2D ultrasound imaging (either in short-axis or long-axis) and color-flow mapping, allowing an accurate morphological evaluation of body graft and anastomosis. An intraoperative method aimed to verify coronary grafts should be easy to handle, not time consuming, minimally invasive, easily meaningful and relatively cheap; in addition, it should offer objective parameters more than qualitative criteria. We herein report the results of our experience with intraoperative graft verification with TTFM and high-resolution imaging along with a systematic review of the literature in this field with the aim to provide a road map to be followed.

False Positive Transit Time Flowmetry Graft Failure in Multivessel Coronary Spasm following Off-Pump Coronary Artery Bypass Grafting

Intraoperative Transit Time Flowmetry is currently recommended to assess graft patency during coronary artery bypass grafting (CABG), especially in presence of haemodynamic instability or inability to wean the patient from cardiopulmonary bypass, new regional wall motion abnormalities, or significant ventricular arrhythmias. The VeriQ™ system is one of the currently available systems, which detects imperfections that may be corrected by graft revision. In this case report, multivessel coronary spasm (CS) post-CABG interferes with these intraoperative parameters misleading initially into false results. Cardiac surgeons should bear in mind the limit of VeriQ in distinguishing between graft failure and CS. Angiography may be considered in patients with decreased graft flow despite revision of anastomosis and vasodilatory treatment for the definitive diagnosis.

Techniques for intraoperative graft assessment in coronary artery bypass surgery

Early graft patency is a major determinant of morbidity and mortality following coronary artery bypass surgery. Long-term graft failure is caused by intimal hyperplasia and atherosclerosis, while early failure, especially in the first year, has been attributed, in part, to surgical error. The need for intraoperative graft evaluation is paramount to determine need for revision and ensure future functioning grafts. Transit time flowmetry (TTFM) is the most commonly used intraoperative modality, however, only about 20% of cardiac surgeons in North America use TTFM. When combined with high resolution epicardial ultrasonography, TTFM provides high diagnostic yield. Fluorescence imaging can provide excellent visualization of the coronary and graft vasculature; however, data on this subject is limited. We herein examine the literature and discuss the available techniques for graft assessment along with their limitations.

On the relationship between competitive flow and FFT analysis of the flow waves in the left internal mammary artery graft in the process of CABG

BACKGROUND

During coronary artery bypass grafting (CABG), the ratio of powers of the fundamental frequency and its first harmonic (F0/H1) in fast Fourier transformation (FFT) analysis of the graft's flow waves has been used in the field of evaluation of the patency in anastomosis. But there is no report about using the FFT method to evaluate the magnitude of competitive flow. This study is aiming at exploring the relationship between competitive flow and FFT analysis of the flow waves in left internal mammary artery (LIMA) graft, and finding a new method to evaluate the magnitude of competitive flow.

METHODS

At first, establishing the CABG multiscale models of different stenosis in left anterior descending artery (LAD) to get different magnitude of competitive flows. Then, calculating the models by ANSYS-CFX and getting the flow waves in LIMA. Finally, analyzing the flow waves by FFT method and comparing the FFT results with the magnitude of competitive flow.

RESULTS

There is no relationship between competitive flow and F0/H1. As for F0/H2 and F0/H3, they both increase with the reduction of the stenosis in LAD. But the increase of F0/H3 is not obviously enough and it can't identify the significant competitive flow clearly, so it can't be used as the evaluation index. It is found that F0/H2 increases obviously with the increase of the competitive flow and can identify the significant competitive flow.

CONCLUSION

The FFT method can be used in the evaluation of competitive flow and the F0/H2 is the ideal index. High F0/H2 refers to the significant competitive flow. This method can be used during CABG to avoid the risk of competitive flow.

Predictors of early graft failure after coronary artery bypass grafting for chronic total occlusion

OBJECTIVES

Little is known regarding the transit-time flow measurement (TTFM) variables in grafts anastomosed to chronically totally occluded vessels (CTOs). We aimed to establish the TTFM cut-off values for detecting graft failure in bypass grafts anastomosed to chronically totally occluded arteries and clarify the relationship between early graft failure and the grade of collateral circulation/regional wall motion of the CTO territory.

METHODS

Among 491 patients who underwent isolated coronary artery bypass grafting (CABG) from 2009 to 2015, 196 cases with CTOs underwent postoperative coronary angiography within 1 month after CABG. Two hundred and forty-one CTOs in all patients were examined. Thirty-two CTOs (13%) were not bypassed and 214 conduits were anastomosed to CTOs and underwent intraoperative TTFM. Arterial conduits and saphenous vein grafts (SVGs) were used in 102 and 112 cases, respectively. Among the arterial conduit procedures that were performed, 78 involved the left internal thoracic artery (LITA), 10 involved the right internal thoracic artery (RITA) and 14 involved the right gastroepiploic artery (rGEA). Any graft showing Fitzgibbon type B or O lesions on angiography was considered to be a failing graft.

RESULTS

The insufficiency rates for LITA, RITA, rGEA and SVG procedures were 5.1, 10, 14.3 and 7.1%, respectively. The TTFM variables recorded in failing grafts had a significantly lower mean flow (Qmean) and higher pulsatility index (PI) compared with patent grafts. Furthermore, akinetic or dyskinetic wall motion in the territory of bypassed CTOs was observed at a significantly higher rate in failing grafts. A multivariable regression analysis and receiver operating characteristic analysis revealed good predictors of early graft failure as follows: a Qmean value of < 11.5 ml/min for arterial conduits, a PI value of >5.85 and akinetic/dyskinetic wall motion in the CTO territory for SVGs. The Rentrop collateral grade was not associated with early graft failure.

CONCLUSIONS

The Qmean value and PI value by the TTFM are useful to detect early graft failure in conduits anastomosed to CTOs. The collateral grade is not associated with graft failure; however, bypass grafting to CTOs with akinetic/dyskinetic wall motion should be carefully considered.

Relationship of Intraoperative Transit Time Flowmetry Findings to Angiographic Graft Patency at Follow-Up

Early and late graft occlusion remains a significant complication of coronary artery bypass grafting. Transit time flowmetry is the most commonly used imaging technique to assess graft patency intraoperatively. Although the value of transit time flowmetry for intraoperative quality control of coronary anastomosis is well established, its standard variables for predicting eventual graft failure remain controversial. This review readdresses the issue of intraoperative transit time flowmetry, with a particular emphasis on defining cutoff values for standard variables and correlating them with the ability to predict midterm and long-term graft patency for arterial and venous conduits. Further research is warranted to support clinically useful recommendations on the intraoperative application and interpretation of transit time flowmetry.

Intraoperative graft assessment during coronary artery bypass surgery

Coronary artery bypass grafting (CABG) is an established revascularization method for treating multivessel coronary artery disease. The goal of CABG is to achieve complete revascularization with a durable, patent graft without reintervention. However, early graft failure, including that associated with technical errors, has been reported. This makes intraoperative verification of graft patency one of the most important ways in which surgeons can reduce the rate of early graft failure. Conventional angiography is considered the gold standard for graft assessment. However, because it is invasive and inconvenient, several alternatives to intraoperative graft assessment have become available that help reduce early graft failure by allowing revision of the anastomosis intraoperatively. The aim of this article is to review the advantages and disadvantages of several intraoperative graft assessment methods for CABG.

Real-time graft flow assessment using epigraftic ultrasonography during coronary artery bypass grafting

OBJECTIVES

Real-time graft flow assessment in the operative field has been performed to ascertain the patency in coronary artery bypass grafting (CABG). This study aims to evaluate the efficacy of graft flow assessment by epigraftic ultrasonography.

METHODS

CABG was performed in 135 patients from January 2010 to December 2012. One hundred and ten patients (81.4%) underwent both real-time graft flow measurement using epigraftic ultrasonography and coronary angiography (CAG) with a total of 249 grafts. Parameters were obtained from flow velocity curves in all grafts. The grafts were divided into two groups: patent grafts (Group A) and failing grafts (Group B). All parameters were compared in these two groups. Logistic regression analysis was performed to detect the predictors of graft failure and receiver operating characteristic (ROC) curve analysis was used to calculate the optimal cut-off value of the predictors of graft failure.

RESULTS

The overall patency as measured by CAG of the grafts was 97.2% (242/249). Logistic regression analysis revealed that the percentage of systolic and diastolic reverse flow (%sRF, %dRF) as well as the pulsatility index (PI) were predictors of early postoperative graft failure. ROC curve analysis revealed that mean velocity <12.5 cm/s, %sRF >9.3%, %dRF >4.1% and PI >4.4 were predictors of early graft failure.

CONCLUSIONS

In this series, epigraftic ultrasonography depicted graft flow clearly. Epigraftic ultrasonography is a useful tool to predict graft failure during CABG. This technique is easily performed using a conventional linear ultrasound transducer.

The Accuracy of Transit Time Flow Measurement in Predicting Graft Patency after Coronary Artery Bypass Grafting

Objective

Transit time flow measurement (TTFM) is a method used to assess intraoperative blood flow after vascular anastomoses. Angiography represents the criterion standard for the assessment of graft patency after coronary artery bypass grafting (CABG). The purpose of this study was to compare flow measurements from TTFM to diagnostic angiography.

Methods

From October 9, 2009, to April 30, 2012, a total of 259 patients underwent robotic-assisted CABG procedures at a single institution. Of these, 160 patients had both TTFM and either intraoperative or postoperative angiography of the left internal mammary artery to the left anterior descending coronary artery graft. Transit time flow measurements were obtained after completion of the anastomosis and after administration of protamine before chest closure. Transit time flow measurement assessment included pulsatility index, diastolic fraction, and flow (milliliters per minute). Angiograms were graded according to the Fitzgibbon criteria. The patients were grouped according to angiographic findings, with perfect grafts defined as FitzGibbon A and problematic grafts defined as either Fitzgibbon B or O.

Results

Overall, there were 152 (95%) of 160 angiographically perfect grafts (FitzGibbon A). Of the eight problematic grafts, five were occluded (Fitzgibbon O) and three had significant flow-limiting lesions (FitzGibbon B). Two patients had intraoperative graft revision after completion angiography, one had redo CABG during the same hospitalization, and five were treated with percutaneous coronary intervention. A significant difference was seen in mean ± SD flow (34.3 ± 16.8 mL/min vs 23.9 ± 12.5 mL/min, P = 0.033) between patent and nonpatent grafts but not in pulsatility index (1.98 ± 0.76 vs 1.65 ± 0.48, P = 0.16) or diastolic fraction (73.5% ± 8.45% vs 70.9% ± 6.15%, P = 0.13).

Conclusions

Although TTFM can be a useful tool for graft assessment after CABG, false negatives can occur. Angiography remains the criterion standard to assess graft patency and quality of the anastomosis after CABG.

Conduits for Coronary Bypass: Arteries Other Than the Internal Thoracic Artery's

This is the third in a series on coronary artery bypass which reviews three alternative arterial conduits. The radial artery has become the most widely used of the three and accumulating experience demonstrates better patency at 10 years versus saphenous vein. Drawbacks are a long incision on the forearm, the propensity for spasm and persistent sensory disturbance in about 10%. The first is answered by endoscopic harvest which may yield a shorter conduit but reduces sensory nerve injury. Spasm is managed pharmacologically and by less harvest trauma. The gastroepiploic artery is used in situ and free and although the abdominal cavity is entered complications are minimal and patency compares favorably with the radial artery. Use of the inferior epigastric artery remains minimal and its similar length often requires composite use but limited patency data are supportive. Other arteries have had rare use and this is unlikely to change because the three presented here have significant advantages and acceptance.

Conduits for coronary bypass: internal thoracic artery

This second report in the series on coronary artery bypass presents the authors experience and personal views on the internal thoracic artery (ITA) which date to 1966. There has been a very gradual evolution in the acceptance of this conduit which was initially compared with the saphenous vein and viewed as an improbable alternative to it. As is common with concepts and techniques which are 'outside the box' there was skepticism and criticism of this new conduit which was more difficult and time consuming to harvest for the surgeon who had to do it all. It was viewed as small, fragile, spastic and its flow capacity was questioned. Only a few surgeons employed it because of these issues and some of them would frequently graft it to the diagonal artery as it was thought not to supply adequate flow for the left anterior descending unless it was small. After a decade, angiographic data revealed superior patency to vein grafts. Even this evidence and survival benefit reported a few years later did not convince many surgeons that their concerns about limitations justified its use. Thus widespread adaption of the ITA as the conduit of choice for the anterior descending required another decade and bilateral use is only now expanding to more than 5% of patients in the US and somewhat faster in other countries.

Anaortic, total-arterial, off-pump coronary artery bypass surgery: why bother?

Coronary artery bypass grafting (CABG) remains the standard of care for multi-vessel coronary disease. However, the increased rate of peri-operative stroke reported after surgery compared to percutaneous coronary intervention (PCI) remains of concern. Anaortic, total-arterial, off-pump coronary artery bypass (OPCAB) grafting is a technique that offers the main advantages of surgical revascularisation with a rate of stroke that is equivalent to that of PCI. Some recent trials comparing conventional on-pump CABG with OPCAB have questioned the efficacy of the off-pump technique - these are most often performed with manipulation of the ascending aorta. We review the potential benefits of the anaortic, total-arterial OPCAB technique to explain why it is being employed by an increasing number of surgeons.

Conduits for coronary bypass: vein grafts

The saphenous vein has been the principal conduit for coronary bypass grafting from the beginning, circa 1970. This report briefly traces this history and concomitantly presents one surgeons experience and personal views on use of the vein graft. As such it is not exhaustive but meant to be practical with a modest number of references. The focus is that of providing guidance and perspective which may be at variance with that of others and recognizing that there may be many ways to accomplish the task at hand. Hopefully the surgeon in training/early career may find this instructive on the journey to surgical maturity.