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Myocardial revascularization can be achieved through 2 different methods: coronary artery bypass grafting (CABG) and percutaneous coronary intervention (PCI). Clinical trials comparing PCI and CABG generally use the composite end points of death, stroke, myocardial infarction and target vessel revascularization to determine superiority. Other effects of these interventions, including the preservation of normal coronary physiology, the response of the coronary tree to stressors and the response of the vessel wall to the revascularization intervention, are not routinely considered, but these may have significant implications for patients in the medium and long term. For PCI, relatively small differences in clinical outcomes have been reported between bare metal and drug-eluting stents, and the latter seems to have inconsistent and somewhat unpredictable effects on the vascular biology of the coronary arteries. In coronary bypass, the use of arterial conduits is associated with superior clinical outcomes, better long-term patency and the preservation of essentially normal coronary function after intervention. This review assembles the clinical, physiological, angiographic and pathological literature currently available and attempts to provide a more complete picture of the effects of CABG and PCI on coronary arteries.

Purpose of Review: The publication of the NOBLE and EXCEL trials, with seemingly conflicting results, brought into question whether percutaneous coronary intervention (PCI) or coronary artery bypass grafting (CABG) is better for low-risk patients with left main coronary artery stenosis (LMCAS). This review appraises the methods and results of NOBLE and EXCEL, contextualizes them within the literature, and determines how they may affect clinical practice., Recent Findings: We appraised the trials and describe differences in methodology and results. NOBLE recruited primarily isolated LMCAS, and found that CABG was superior to PCI. EXCEL's population included patients LMCAS in the context of multivessel CAD, and found PCI and CABG were comparable. Both trials enrolled young patients with few comorbidities, and there was more protocol-mandated consistency in the procedural techniques and medical therapy of patients receiving PCI., Summary: The generalizability of these trials is limited by the use of young, healthy patients at highly skilled centres that rarely reflect typical clinical practice. If these studies are to maintain relevance, trialists must address the lack of protocolization of surgical interventions and inconsistent medical therapies. Unfortunately, the limitations of NOBLE and EXCEL mean that we are no closer to answering the question of what is the optimal treatment for patients with LMCAS.

Objectives: Bilateral internal thoracic artery (BITA) bypass provides long-term survival benefits over strategies that use single internal mammary arteries during coronary artery bypass grafting (CABG). However, the rate of adoption of this strategy remains very low. Moreover, optimal BITA configuration and the use of cardiopulmonary bypass still remain a matter of debate. We investigated the long-term results of a coronary revascularization strategy, utilising exclusively BITA-Y composite grafts using off-pump platform and sequential anastomoses., Methods: From March 2000 to November 2010, all isolated CABGs (n = 2057 patients) were performed using an off-pump platform. Of these, 1240 patients had three-vessel coronary disease (60.3%), with severe coronary disease defined as >70% stenosis and three-vessel disease defined as the presence of 3 vessels with >70% stenosis, of which 784 (63.2%) were treated with two internal thoracic artery grafts in a composite fashion with a no-touch technique avoiding any manipulation of the ascending aorta. The primary end-point was the long-term survival and freedom from major adverse cerebral and cardiovascular events (MACCEs). The follow-up was completed using the annual anniversary method., Results: The mean number of anastomoses per patient was 4.0. Hospital mortality occurred in 8 patients (1%). Ninety-day stroke, myocardial infarction and repeat revascularization rates were respectively 0.7, 0.6 and 0.3%. The mean follow-up was 6.6 ± 3.2 years and was obtained for 99% of the patients. The 5- and 10-year survival rates were 93.1 ± 1.6 and 83.8 ± 3.2%, respectively. Freedom from major adverse cardiac and cardiovascular event (MACCE) at 5 and 10 years was: cardiovascular event: 98.7 ± 1.6 and 96.1 ± 1.7%, documented ischaemia: 90.5 ± 2 and 80.2 ± 3.8%, revascularization: 94.0 ± 1.5 and 89.7 ± 2.5%, infarction: 98.1 ± 0.8 and 96.0 ± 1.6%. The patency of left and right internal thoracic artery in a BITA-Y configuration was 91.1 and 88.8% at 5 ± 3 years, respectively., Conclusion: Performance of an exclusive composite BITA off-pump revascularization strategy optimal and sustained long-term protection from MACCE., (© The Author 2016. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.)

Objectives: Recent studies have demonstrated the superiority of bilateral internal mammary arteries (BIMAs) as conduit material for coronary artery bypass grafting (CABG) surgery. However, there is limited research on the effects of other graft conduits used in patients who require additional bypasses. The goal of this study was to evaluate the impact of the radial artery (RA) when used in conjunction with the BIMAs., Methods: From the beginning of 2000 to the end of 2013, 4370 patients underwent CABG for three or more vessels at our institution. There were 568 and 183 patients who received BIMA + saphenous vein graft (SVG) and BIMA + radial ± SVG, respectively. Propensity matching was used to create a balanced cohort from these patients, which resulted in two groups of 183 patients. Thirty-day outcomes and long-term survival were compared between the two groups. Long-term follow-up was generated using the Social Security Death Index., Results: There were no significant differences in preoperative characteristics. For 30-day outcomes, the BIMA + radial ± SVG group had more postoperative atrial fibrillation (24.6 vs 12.0%; P = 0.001) and a longer median postoperative length of stay (6 vs 5 days; interquartile range = 2; P = 0.016) than BIMA + SVG patients. There was no significant difference in long-term survival between the two groups over the 14-year period. However, before year 10, the BIMA + SVG group had a trend towards higher survival, whereas on follow-up after 10 years, there was a trend that favoured the BIMA + radial ± SVG patients. Cox regression analysis using a time-dependent covariate demonstrated that when the groups were split at 10 years, there was a statistically significant improvement in survival of the BIMA + radial ± SVG group [adjusted hazard ratio 0.254 95% confidence interval (CI) 0.062-0.977; P = 0.048] over BIMA + SVG patients between 10 and 14 years., Conclusions: Overall, there were no statistically significant differences in survival between the BIMA + SVG and BIMA + radial ± SVG groups over the 14 years. However, further analysis demonstrated that while the BIMA + radial ± SVG group had a trend towards decreased survival before 10 years, use of the RA in conjunction with BIMAs was associated with significantly increased survival in the later years. A larger cohort of patients with longer follow-up is needed to assess the outcomes of CABG using BIMA + radial ± SVG., (© The Author 2015. Published by Oxford University Press on behalf of the European Association for Cardio-Thoracic Surgery. All rights reserved.)

Objective: Previous studies have demonstrated that bilateral internal mammary artery (BIMA) grafts lead to superior outcomes compared with single internal mammary artery grafts. This study examines whether cardiopulmonary bypass affects conduit-dependent outcomes of coronary artery bypass grafting (CABG) surgery., Methods: From 1994 to 2013, a total of 6666 patients underwent isolated CABG surgery at our institution. Of these procedures, 3548 (53.2%) were performed off pump. A BIMA-saphenous vein graft (SVG) was used in 1544, and 5122 had left internal mammary artery-SVGs. These 2 conduit groups differed significantly in baseline characteristics. Propensity matching based on 22 preoperative variables and using a nearest-neighbor matching algorithm was used to make balanced cohorts, resulting in 2 groups of 1006. To account for the influence of pump status on conduit selection, a second propensity score was developed for pump use. These cases were matched to create 4 patient cohorts of 353 patients each (a total of 1412), balanced for both conduit use and pump status. Late mortality was determined using the Social Security Death Index., Results: No difference was found in survival between patients receiving BIMA-SVGs on or off pump (78.9% vs 79.1%). BIMA-SVGs outperformed the left internal mammary artery-SVGs regardless of whether the procedure was performed off pump (73.9%) or on pump (69.9%)., Conclusions: This study demonstrates that the use of cardiopulmonary bypass does not significantly affect the long-term outcomes in these patients as long as full revascularization is achieved. In addition, these results are consistent with prior research showing that the use of BIMAs produces better outcomes than use of a single internal mammary artery when performing CABG., (Copyright © 2015 The American Association for Thoracic Surgery. Published by Elsevier Inc. All rights reserved.)

Background: ASCERT (American College of Cardiology Foundation and the Society of Thoracic Surgeons Collaboration on the Comparative Effectiveness of Revascularization Strategies) was a large observational study designed to compare the long-term effectiveness of coronary artery bypass graft (CABG) and percutaneous coronary intervention (PCI) to treat coronary artery disease (CAD) over 4 to 5 years., Objectives: This study examined the cost-effectiveness of CABG versus PCI for stable ischemic heart disease., Methods: The Society of Thoracic Surgeons and American College of Cardiology Foundation databases were linked to the Centers for Medicare and Medicaid Services claims data. Costs for the index and observation period (2004 to 2008) hospitalizations were assessed by diagnosis-related group Medicare reimbursement rates; costs beyond the observation period were estimated from average Medicare participant per capita expenditure. Effectiveness was measured via mortality and life-expectancy data. Cost and effectiveness comparisons were adjusted using propensity score matching with the incremental cost-effectiveness ratio expressed as cost per quality-adjusted life-year gained., Results: CABG patients (n = 86,244) and PCI patients (n = 103,549) were at least 65 years old with 2- or 3-vessel coronary artery disease. Adjusted costs were higher for CABG for the index hospitalization, study period, and lifetime by $10,670, $8,145, and $11,575, respectively. Patients undergoing CABG gained an adjusted average of 0.2525 and 0.3801 life-years relative to PCI over the observation period and lifetime, respectively. The life-time incremental cost-effectiveness ratio of CABG compared to PCI was $30,454/QALY gained., Conclusions: Over a period of 4 years or longer, patients undergoing CABG had better outcomes but at higher costs than those undergoing PCI., (Copyright © 2015 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Background: Recent observational studies show that patients with multivessel coronary disease have a long-term survival advantage with coronary artery bypass grafting (CABG) compared with percutaneous coronary intervention (PCI). Important nonfatal outcomes may also affect optimal treatment recommendation., Methods: CABG was compared with percutaneous catheter intervention by using a composite of death, myocardial infarction (MI), or stroke. Medicare patients undergoing revascularization for stable multivessel coronary disease from 2004 through 2008 were identified in national registries. Short-term clinical information from the registries was linked to Medicare data to obtain long-term follow-up out to 4 years from the time of the procedure. Propensity scoring with inverse probability weighting was used to adjust for baseline risk factors., Results: There were 86,244 CABG and 103,549 PCI patients. The mean age was 74 years, with a median 2.67 years of follow-up. At 4 years, the propensity-adjusted adjusted cumulative incidence of MI was 3.2% in CABG compared with 6.6% in PCI (risk ratio, 0.49; 95% confidence interval, 0.45 to 0.53). At 4 years, the cumulative incidence of stroke was 4.5% in CABG compared with 3.1% in PCI patients (risk ratio, 1.43; 95% confidence interval, 1.31 to 1.54). This difference was primarily due to the higher 30-day stroke rate for CABG (1.55% vs 0.37%). For the composite of death, MI, or stroke, the 4-year adjusted cumulative incidence was 21.6% for CABG and 26.7% for PCI (risk ratio, 0.81; 95% confidence interval, 0.78 to 0.83)., Conclusions: The 4-year composite event rate of death, MI, and stroke favored CABG, whereas the risk of stroke alone favored PCI., (Copyright © 2014 The Society of Thoracic Surgeons. Published by Elsevier Inc. All rights reserved.)

Clopidogrel is an oral antiplatelet pro-drug prescribed to 40 million patients worldwide who are at risk for thrombotic events or receiving percutaneous coronary intervention (PCI). However about a fifth of patients treated with clopidogrel do not respond adequately to the drug. From a cohort of 105 patients on whom we had functional data on clopidogrel response, we used ultra-high throughput sequencing to assay mutations in CYP2C19 and ABCB1, the two genes genetically linked to respond. Testing for mutations in CYP2C19, as recommended by the FDA, only correctly predicted if a patient would respond to clopidogrel 52.4% of the time. Similarly, testing of the ABCB1 gene only correctly foretold response in 51 (48.6%) patients. These results are clinically relevant and suggest that until additional genetic factors are discovered that predict response more completely, functional assays are more appropriate for clinical use., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Background: Questions persist concerning the comparative effectiveness of percutaneous coronary intervention (PCI) and coronary-artery bypass grafting (CABG). The American College of Cardiology Foundation (ACCF) and the Society of Thoracic Surgeons (STS) collaborated to compare the rates of long-term survival after PCI and CABG., Methods: We linked the ACCF National Cardiovascular Data Registry and the STS Adult Cardiac Surgery Database to claims data from the Centers for Medicare and Medicaid Services for the years 2004 through 2008. Outcomes were compared with the use of propensity scores and inverse-probability-weighting adjustment to reduce treatment-selection bias., Results: Among patients 65 years of age or older who had two-vessel or three-vessel coronary artery disease without acute myocardial infarction, 86,244 underwent CABG and 103,549 underwent PCI. The median follow-up period was 2.67 years. At 1 year, there was no significant difference in adjusted mortality between the groups (6.24% in the CABG group as compared with 6.55% in the PCI group; risk ratio, 0.95; 95% confidence interval [CI], 0.90 to 1.00). At 4 years, there was lower mortality with CABG than with PCI (16.4% vs. 20.8%; risk ratio, 0.79; 95% CI, 0.76 to 0.82). Similar results were noted in multiple subgroups and with the use of several different analytic methods. Residual confounding was assessed by means of a sensitivity analysis., Conclusions: In this observational study, we found that, among older patients with multivessel coronary disease that did not require emergency treatment, there was a long-term survival advantage among patients who underwent CABG as compared with patients who underwent PCI. (Funded by the National Heart, Lung, and Blood Institute.).

Background: Most survival prediction models for coronary artery bypass grafting surgery are limited to in-hospital or 30-day end points. We estimate a long-term survival model using data from the Society of Thoracic Surgeons Adult Cardiac Surgery Database and Centers for Medicare and Medicaid Services., Methods and Results: The final study cohort included 348 341 isolated coronary artery bypass grafting patients aged ≥65 years, discharged between January 1, 2002, and December 31, 2007, from 917 Society of Thoracic Surgeons-participating hospitals, randomly divided into training (n=174 506) and validation (n=173 835) samples. Through linkage with Centers for Medicare and Medicaid Services claims data, we ascertained vital status from date of surgery through December 31, 2008 (1- to 6-year follow-up). Because the proportional hazards assumption was violated, we fit 4 Cox regression models conditional on being alive at the beginning of the following intervals: 0 to 30 days, 31 to 180 days, 181 days to 2 years, and >2 years. Kaplan-Meier-estimated mortality was 3.2% at 30 days, 6.4% at 180 days, 8.1% at 1 year, and 23.3% at 3 years of follow-up. Harrell's C statistic for predicting overall survival time was 0.732. Some risk factors (eg, emergency status, shock, reoperation) were strong predictors of short-term outcome but, for early survivors, became nonsignificant within 2 years. The adverse impact of some other risk factors (eg, dialysis-dependent renal failure, insulin-dependent diabetes mellitus) continued to increase., Conclusions: Using clinical registry data and longitudinal claims data, we developed a long-term survival prediction model for isolated coronary artery bypass grafting. This provides valuable information for shared decision making, comparative effectiveness research, quality improvement, and provider profiling.

Objectives: We sought to determine how practice patterns for unprotected left main stenosis have changed with the advent of drug-eluting stents (DES)., Background: Percutaneous coronary intervention (PCI) of unprotected left main coronary stenosis has been controversial., Methods: We analyzed data submitted to the American College of Cardiology-National Cardiovascular Data Registry (ACC-NCDR) between January 1, 2002 and December 31, 2004 from 1,276,582 cardiac catheterizations at 417 institutions. Of these, 53,548 (4.2%) had left main stenosis >50% and no prior CABG. After excluding the unrevascularized, the patient sample (N = 32,562) was analyzed for PCI vs. CABG. Data was stratified by year/quarter, bare metal stent vs. DES, elective vs. urgent/emergent situations, LVEF < or > or =40%, and %left main and RCA stenosis., Results: Of unprotected left main revascularizations from 2002 to 2004, PCI increased from 17.0% to 21.9%, while CABG decreased from 83.0% to 78.1% (P < 0.0001). In 2002, bare metal stents were used for all PCIs; in 2004, bare metal stent use was only 25.5%, while DES use was 74.5% (P < 0.0001). Of elective procedures, PCI rose from 19.1% to 27.5% while CABG fell from 80.9% to 72.5% (P < 0.0001). Similar trends, all significant, were seen in every clinical situation., Conclusions: In the era of DES, the rate of PCI for unprotected left main stenosis has risen, while CABG has declined. These findings are seen across varying clinical situations, including elective procedures. DES have rapidly and largely replaced bare metal stents for PCI of unprotected left mains. However, PCI is still chosen less frequently than CABG for unprotected left main revascularization.

Limited data are available on the off-label use of drug-eluting stents (DESs) in clinical practice. We used data from the American College of Cardiology National Cardiovascular Data Registry to describe the rates and outcomes of DES use in 4 common off-label situations: ST-elevation myocardial infarction, in-stent restenosis, coronary artery bypass grafts, and chronic total occlusions. The rates of in-hospital adverse events for each off-label situation were determined and compared with the expected rates calculated from a validated model. From approval of DESs to the end of 2004, a total of 408,033 procedures involved placement of a DES. The use of DESs increased from 19.7% at the start of the study to 78.2% by the end of fourth quarter of 2004. Off-label use of DESs occurred in 24.1% of procedures. The rates of in-hospital adverse events with DES use in ST-elevation myocardial infarction, in-stent restenosis, coronary artery bypass grafting, and chronic total occlusions were lower than expected from the validated model. In conclusion, off-label use of DESs is common and is associated with a low rate of short-term adverse events. Randomized clinical trials are needed to confirm the efficacy of DESs in these clinical and angiographic settings. These data also highlight the importance of multicenter registries in tracking new technologies.

Background: Blood transfusions are a common and costly intervention for cardiac surgery patients. Evidence suggests that a more restrictive transfusion strategy may reduce costs and transfusion-related complications without increasing perioperative morbidity and mortality.Study Design and Methods: A transfusion-limiting protocol was developed and implemented in a cardiovascular surgery unit. Over a 5-year period, data were collected on patient characteristics, procedures, utilization of blood products, morbidity, and mortality, and these were compared before and after the protocol was implemented.Results: After the protocol was put in place, fewer patients required transfusions (38.2% vs. 45.5%, p = 0.004), with the greatest reduction observed in postoperative blood use (29.1% vs. 37.2%, p = 0.001). In-hospital morbidity and mortality did not increase. When patients who received transfusions were stratified by procedure, the protocol was most effective in reducing transfusions for patients undergoing isolated coronary artery bypass grafting (CABG; 4.09 units vs. 2.51 units, p = 0.009) and CABG plus valve surgery (10.32 units vs. 4.77 units, p = 0.014). A small group of patients were disproportionate recipients of transfusions, with approximately 6% of all patients receiving approximately half of the blood products.Conclusion: A protocol to limit transfusions decreased the proportion of cardiothoracic surgery patients who received blood products. A very small group of patients received a large number of transfusions, and within that group the observed mortality was significantly higher than in the general patient population. Current protocols cannot possibly account for these patients, and this should be considered when analyzing the performance of protocols designed to reduce unnecessary transfusions. [ABSTRACT FROM AUTHOR]

Background: Stroke remains an important complication after coronary artery bypass graft surgery (CABG). We sought to determine the frequency and death-related incidence of stroke after on-pump and off-pump CABG. Methods: We analyzed 4,869 consecutive isolated CABG performed in our institution. Of these, 3,490 (71.7%) were off-pump and 1,379 (28.3%) were on-pump. Propensity matched samples of 1,379 off-pump and 1,379 on-pump were compared on clinical presentation and The Society of Thoracic Surgeons (STS) predicted scores for risk of postoperative mortality and stroke. Univariate analyses were used to compare the relationship of off-pump and on-pump groups to postoperative mortality and stroke. Multivariate logistic regression was used to determine the unique association between all variables and occurrence of mortality after stroke. Results: No differences were found for sex, diabetes mellitus, history of renal failure, prior stroke, or timing of surgery. Postoperative mortality occurred in 75 patients (2.7%) and stroke in 47 (1.7%). The off-pump patients had a lower rate of stroke (1.0% versus 2.4%; p < 0.01) compared with on-pump patients. Mortality after stroke occurred in 14 patients, with a lower rate occurring in the off-pump group (14.3% versus 36.4%; p = 0.07). Multivariate analyses controlling for the effect of preoperative risk factors and STS mortality risk demonstrated that off-pump status was independently associated with an 84% decrease in the risk of death after stroke (adjusted odds ratio 0.157, 95% confidence interval: 0.035 to 0.711, p = 0.016). Conclusions: Off-pump CABG is associated with lower stroke rates and stroke-related mortality. It may be useful to consider off-pump CABG for patients who are at higher risk for postoperative stroke. [Copyright &y& Elsevier]

: ObjectivesWe sought to develop and evaluate a risk adjustment model for in-hospital mortality following percutaneous coronary intervention (PCI) procedures using data from a large, multi-center registry.: BackgroundThe 1998–2000 American College of Cardiology–National Cardiovascular Data Registry (ACC–NCDR) dataset was used to overcome limitations of prior risk-adjustment analyses.: MethodsData on 100,253 PCI procedures collected at the ACC–NCDR between January 1, 1998, and September 30, 2000, were analyzed. A training set/test set approach was used. Separate models were developed for presentation with and without acute myocardial infarction (MI) within 24 h.: ResultsFactors associated with increased risk of PCI mortality (with odds ratios in parentheses) included cardiogenic shock (8.49), increasing age (2.61 to 11.25), salvage (13.38) urgent (1.78) or emergent PCI (5.75), pre-procedure intra-aortic balloon pump insertion (1.68), decreasing left ventricular ejection fraction (0.87 to 3.93), presentation with acute MI (1.31), diabetes (1.41), renal failure (3.04), chronic lung disease (1.33); treatment approaches including thrombolytic therapy (1.39) and non-stent devices (1.64); and lesion characteristics including left main (2.04), proximal left anterior descending disease (1.97) and Society for Cardiac Angiography and Interventions lesion classification (1.64 to 2.11). Overall, excellent discrimination was achieved (C-index = 0.89) and application of the model to high-risk patient groups demonstrated C-indexes exceeding 0.80. Patient factors were more predictive in the MI model, while lesion and procedural factors were more predictive in the analysis of non-MI patients.: ConclusionsA risk adjustment model for in-hospital mortality after PCI was successfully developed using a contemporary multi-center registry. This model is an important tool for valid comparison of in-hospital mortality after PCI. [Copyright &y& Elsevier]

OBJECTIVES Bilateral internal mammary arteries (BIMA) remains widely underutilized in coronary artery bypass grafting (CABG). Although prior research has demonstrated a long-term benefit of the use of BIMA over left internal mammary artery (LIMA)-only, validation of these results is lacking in a contemporary surgical experience. We compared complications and survival at 17-year follow-up in a large series of consecutive CABG patients from a single institution that underwent BIMA grafting with a propensity-matched group where LIMA only was used. METHODS Propensity scores representing the estimated probabilities of patients receiving either BIMA or LIMA alone were developed based on 22 observed baseline covariates in a logistic regression model with procedure group as the dependent variable. The nearest-neighbour-matching algorithm with Greedy 5-1 Digit Matching was used to produce two patient cohorts of 928 patients each balanced for baseline factors. We compared 30-day morbidity and mortality, as well as long-term survival at 5-year intervals up to 17-year follow-up. RESULTS In-hospital and 30-day mortality was 0.8% for the BIMA group and 1.1% for the LIMA-saphenous vein grafting (SVG). No significant difference was found in complications, mortality and/or length-of-stay between these two groups. Off-pump was done in 48.9% of BIMA cases and 51.3% of LIMA cases. Regardless of the types of grafts used, on-pump patients were more likely to have postoperative permanent strokes and longer postoperative lengths of stay. Use of the BIMA over LIMA-only had a statistically significant impact conferring a 10% survival advantage at 10-year and 18% at 15-year follow-up. The Kaplan–Meier survival curves comparing off-/on-pump BIMA and off-/on-pump LIMA-SVG patients demonstrated a 22% survival advantage for off-pump BIMA patients when compared with on-pump LIMA-SVG patients at 15-year follow-up. CONCLUSIONS Perioperative complications do not increase with the use of BIMAs. Long-term survival is optimized with off-pump CABG and BIMA grafting. The low morbidity and mortality rates in this series are likely due to the continuous evolution of technology and the adoption of less invasive options for CABG patients. A more widespread use of BIMAs in CABG patients would continue to improve the overall excellent short- and long-term results of this operation. [ABSTRACT FROM AUTHOR]