Key Points
Question
Is the use of the radial artery instead of the saphenous vein for coronary artery bypass surgery associated with a lower risk of adverse cardiac events in the long term?
Findings
In this individual participant data meta-analysis from 5 randomized clinical trials that included 1036 patients undergoing coronary artery bypass grafting, randomization to receive radial artery compared with saphenous vein graft was associated with an incidence of a composite of death, myocardial infarction, or repeat revascularization of 41 vs 47 events per 1000 person-years after a median follow-up of 10 years, a difference that was statistically significant.
Meaning
Over 10 years of follow-up, radial artery graft compared with saphenous vein graft was associated with a lower risk of a composite of cardiovascular outcomes.
Abstract
Importance
Observational studies have suggested that the use of radial artery grafts for coronary artery bypass grafting may improve clinical outcomes compared with the use of saphenous vein grafts, but this has not been confirmed in randomized trials.
Objective
To compare clinical outcomes between patients receiving radial artery vs saphenous vein grafts for coronary artery bypass grafting after long-term follow-up.
Design, Setting, and Participants
Patient-level pooled analysis comparing radial artery vs saphenous vein graft in adult patients undergoing isolated coronary artery bypass grafting from 5 countries (Australia, Italy, Serbia, South Korea, and the United Kingdom), with enrollment from 1997 to 2009 and follow-up completed in 2019.
Interventions
Patients were randomized to undergo either radial artery (n = 534) or saphenous vein (n = 502) grafts for coronary artery bypass grafting.
Main Outcomes and Measures
The primary outcome was a composite of death, myocardial infarction, or repeat revascularization and the secondary outcome was a composite of death or myocardial infarction.
Results
A total of 1036 patients were randomized (mean age, 66.6 years in the radial artery group vs 67.1 years in the saphenous vein group; 376 [70.4%] men in the radial artery group vs 351 [69.9%] in the saphenous vein group); 942 (90.9%) of the originally randomized patients completed 10 years of follow-up (510 in the radial artery group). At a median (interquartile range) follow-up of 10 (10-11) years, the use of the radial artery, compared with the saphenous vein, in coronary artery bypass grafting was associated with a statistically significant reduction in the incidence of the composite outcome of death, myocardial infarction, or repeat revascularization (220 vs 237 total events; 41 vs 47 events per 1000 patient-years; hazard ratio, 0.73 [95% CI, 0.61-0.88]; P < .001) and of the composite of death or myocardial infarction (188 vs 193 total events; 35 vs 38 events per 1000 patient-years; hazard ratio, 0.77 [95% CI, 0.63-0.94]; P = .01).
Conclusions and Relevance
In this individual participant data meta-analysis with a median follow-up of 10 years, among patients undergoing coronary artery bypass grafting, the use of the radial artery compared with the saphenous vein was associated with a lower risk of a composite of cardiovascular outcomes.
This meta-analysis uses individual participant data from clinical trials to estimate associations between radial artery vs saphenous vein grafting techniques and cardiovascular outcomes at 10 years among patients undergoing coronary artery bypass grafting (CABG).
Introduction
The long-term clinical consequences of using the radial artery instead of the saphenous vein for coronary artery bypass grafting (CABG) remain uncertain. Observational studies have suggested that the use of the radial artery is associated with better postoperative outcomes,1 but they are open to bias.2
The Radial Artery Database International Alliance, a pooled analysis of individual patient data from 5 randomized clinical trials (RCTs) comparing use of the radial artery and the saphenous vein for CABG, previously reported that the use of the radial artery was associated with a significantly lower incidence of the composite outcome of death, myocardial infarction, or repeat revascularization at 5-year follow-up.3 No statistically significant difference in survival was found and the composite outcome was driven by repeat revascularization.
Due to the low number of events in the initial 5 years after surgery, the power of the 5-year analysis was limited. Because saphenous vein graft failure accelerates 5 years after surgery,4 it might be anticipated that any potential clinical benefit of radial artery grafting would become more evident with a longer duration of follow-up.
In addition, because the majority of the trials included in the database mandated angiography over the first 5 years of follow-up, it is unclear to what extent the revascularization outcome may have been inflated due to incidental finding of asymptomatic graft failure. After 5 years, all but 1 of the trials did not mandate imaging control, and extension of follow-up is necessary to elucidate the effect of per-protocol angiography on the outcomes.
The objective of the current study was to compare long-term clinical outcomes between patients undergoing radial artery vs saphenous vein grafts for CABG, based on 10 years of follow-up.
Methods
Project
Ethics approval and oral participant consent for the study was obtained locally by each study team. The Weill Cornell Medicine Institutional Review Board waived the need for ethics approval for the pooled analysis.
Study Protocol
The protocol for the present analysis was published a priori, and the analytic plan and the outcomes were defined before the start of the analysis.5
Selection of the Trials
A systematic literature search was performed to identify RCTs that compared use of the radial artery and the saphenous vein in patients who underwent CABG. MEDLINE and Embase were searched in January 2019, and the search was updated in March 2020. The following keywords were combined with the Boolean operator or: radial artery, saphenous vein, and coronary artery bypass grafting. Study inclusion was assessed independently by 2 investigators (A.D. and I.H.). Disagreements were discussed and resolved by consensus. In addition, the bibliographies of all studies were searched to identify additional publications. Details of the search strategy are provided in the Supplement.3 The PRISMA flowchart6 and the Cochrane Collaboration’s tool for assessing the risk of bias for the included RCTs are provided in eFigures 1 and 2 in the Supplement.
Follow-up
Clinical follow-up to 10 years or to the maximal possible follow-up for each patient was requested from the individual trial teams. Follow-up was performed by telephone interview for the study by Nasso et al,7 the Radial Artery Patency and Clinical Outcome (RAPCO) trial,8 and the study by Petrovic et al.9 For the Radial Artery vs Saphenous Vein Patency (RSVP) trial,10 follow-up data were obtained from the Royal Brompton & Harefield NHS Foundation Trust electronic patient record database and from questionnaires sent to general practitioners. For the Song et al11 trial, the Statistic Korea database as well as telephone interviews were used to obtain follow-up data. No central verification of data sources was performed. In the Song et al,11 Petrovic et al,9 and RSVP10 trials, the assessors of the clinical outcomes were blinded to the treatment assignment. For the Nasso et al7 and RAPCO8 trials, no formal blinding protocol was adopted, but assessors were not involved in the study.
Data Collection and Merging
An electronic preformatted data collection form containing core minimum data requirements was sent to each trial team. De-identified data were received by the coordinating center at Weill Cornell Medicine and checked for quality, completion, and consistency with both the 5-year analysis and previous publications. Discrepancies were resolved through direct consultation with the individual trial teams. Data elements were then consolidated into a master database. All variable definitions were similar to those used in the 5-year analysis.3
Outcomes
The primary outcome was a composite of major adverse cardiac events defined as death from any cause, myocardial infarction, or repeat revascularization. The secondary outcome was a composite of death from any cause or myocardial infarction. For all the events, individual trial definitions were used. Each component of the composite outcomes was analyzed separately but not formally tested, with the exception of mortality, which was tested as a post hoc exploratory outcome. Prespecified subgroup analyses were performed by age, sex, diabetes status, preoperative history of myocardial infarction, left ventricular ejection fraction, preoperative kidney function, and radial artery target vessel.
Statistical Analysis
Baseline and intraoperative characteristics in the 2 groups were reported as numbers and percentages for categorical variables and as means and SDs or medians and interquartile ranges for continuous variables. Parametric or nonparametric tests were used to compare the 2 groups, as appropriate. A comparison of baseline characteristics between patients who were lost to follow-up and those included in the analysis was performed to ensure that patients with follow-up data were representative of the parent cohorts.
Outcomes were reported as frequencies, cumulative incidence, and linearized event rates per 1000 patient-years to account for different follow-up duration across individual trials. The cumulative incidence of nonfatal events was determined with death as a competing risk. In the primary analysis, patients were analyzed according to their randomization group.
Association between treatment and outcomes were estimated using a mixed-effect Cox regression model, with treatment allocation included as fixed effect and trial identifiers included as random effect. Treatment effects were presented as hazard ratios (HRs) and 95% CIs. The proportional hazards assumption was verified using Schoenfeld residuals. For nonfatal events, competing risks regression analysis was based on the Fine and Gray proportional subhazards model.
The following effect modifiers on the primary end point were tested using subgroup analysis: age, sex, diabetes status, prior myocardial infarction, left ventricular ejection fraction less than 50%, kidney insufficiency,12 and radial artery target vessel. The results were displayed as a forest plot.
Multiple sensitivity analyses were performed. To investigate the effect of protocol-mandated angiography on the difference in the outcomes between the groups, separate analyses of repeat revascularization and death and of the primary and secondary composite end points were performed for the period before and after the fifth year of follow-up. Association between treatment and the primary outcome was re-estimated according to the conduit received.
The primary analysis was repeated using a 2-stage approach where a β coefficient with a relative standard error for the association between treatment and outcomes was obtained for each individual trial using a Cox regression model. Estimates of the association between treatment and outcomes across individual trials were then pooled in a second step using the generic inverse variance method with a random-effect model. Trial-level and pooled estimates were reported as HRs and 95% CIs; risk distribution was presented using forest plots with weighting according to a random-effect model. Heterogeneity across trials was assessed using I2 statistics. I2values less than 25% defined low heterogeneity; 25% to 50%, moderate heterogeneity; and greater than 50%, high heterogeneity. Leave-1-out analysis was used to assess the influence of individual trials on the final estimate.
To account for potential confounders and postrandomization imbalance between groups, the analysis for the primary end point and for mortality was repeated using a fully adjusted mixed-effect Cox model. To account for the loss to follow-up, 2 sensitivity analyses were performed for the primary outcome. In the first analysis, drop-outs were treated as nonevents and assigned 10 years follow-up in both groups. In the second analysis, varying scenarios for the event rate in each group of patients lost to follow-up were calculated, to the extreme case in which all patients lost to follow-up in the saphenous vein group were considered nonevents and assigned 10 years follow-up and all patients lost to follow-up in the radial artery group were considered dead at 10 years of follow-up (tipping point analysis). In addition, an analysis limited only to the studies at lowest risk of bias based on the Cochrane Collaboration’s tool for assessing risk of bias was performed.
The saphenous vein group was used as the reference in all analyses. A fixed-order sequential testing method was used with the primary outcome tested first at an α level of .05 and the secondary outcome tested at the same level if the primary outcome was statistically significant. All P values were 2-sided, and P values less than .05 were deemed statistically significant. No significance testing was done for subgroup analyses or for the individual components of the composite outcomes, except mortality. For these analyses, only estimates of the association between treatment and outcomes and corresponding 95% CIs were provided. Because of the lack of adjustment for multiple comparisons and the potential for type I error, the results of the secondary, subgroup, and post hoc analyses should be interpreted as exploratory. Statistical analyses were performed using R, version 3.6.1, and the following packages: coxme, meta, prodlim, Publish, and riskRegression.
Results
Study Population
A total of 774 studies were identified from the literature search, and 38 were included for full-text review. Five trials met the inclusion criteria.7,8,9,10,11 The principal investigators of all the trials were contacted and all agreed to extend the follow-up and share the data.
Two of the included trials (Nasso et al7 and RAPCO8) compared CABG with the radial artery vs either the saphenous vein or the right internal thoracic artery in separate comparisons. For those trials, only the radial artery and saphenous vein groups were included. Details of the individual trials are provided in Table 1.7,8,9,10,11
Table 1. Details of the Trials Included in a Study of the Association of Radial Artery vs Saphenous Vein Graft With Cardiovascular Outcomes Among Patients Undergoing Coronary Artery Bypass Grafting.
| Characteristic | Petrovic et al9 | RAPCO8 | RSVP10 | Nasso et al7 | Song et al11 |
|---|---|---|---|---|---|
| Study period (enrollment) | 2001-2003 | 1997-2004 | 1998-2000 | 2003-2006 | 2008-2009 |
| Country of origin | Serbia | Australia | United Kingdom | Italy | South Korea |
| Institution | Belgrade University School of Medicine, Belgrade, Serbia | University of Melbourne, Victoria, Australia | Royal Brompton Hospital, London, United Kingdom | Italy (multicenter) | Yonsei University Health System, Seoul, South Korea |
| No. of patients | 200 | 225 | 142 | 409 | 60 |
| Radial artery group | 100 | 113 | 82 | 204 | 35 |
| Saphenous vein group | 100 | 112 | 60 | 205 | 25 |
| Age, mean (SD), y | |||||
| Radial artery group | 56.3 (6.1) | 72.9 (62.3-83.5) | 58.0 (6.0) | 70.5 (3.1) | 72.7 (3.2) |
| Saphenous vein group | 57.1 (6.5) | 73.2 (64.0-82.4) | 59.0 (7.0) | 69.7 (3.5) | 74.6 (3.8) |
| Men, No. (%) | |||||
| Radial artery group | 73 (73) | 91 (81) | 79 (96) | 117 (57) | 17 (49) |
| Saphenous vein group | 73 (73) | 91 (81) | 58 (97) | 121 (59) | 14 (56) |
| Women, No. (%) | |||||
| Radial artery group | 27 (27) | 22 (19) | 3 (4) | 87 (43) | 18 (51) |
| Saphenous vein group | 27 (27) | 21 (19) | 2 (3) | 84 (41) | 11 (44) |
| LVEF | Mean (SD), % | All patients had LVEF >35% (per inclusion criteria) | All patients had LVEF ≥25% (per inclusion criteria) | Patients with LVEF <30%, % | Patients with LVEF <35%, % |
| Radial artery group | 48.8 (10.7) | 14.8 | 10.0 | ||
| Saphenous vein group | 48.0 (10.8) | 13.9 | 13.0 | ||
| Chronic pulmonary disease, No. (%) | |||||
| Radial artery group | 9 (9) | NR | NR | 57 (28.2) | NR |
| Saphenous vein group | 8 (8) | NR | NR | 56 (27.7) | NR |
| Diabetes, No. (%) | |||||
| Radial artery group | 39 (39) | 50 (44) | 15 (18) | 73 (36) | 15 (43) |
| Saphenous vein group | 43 (43) | 52 (46) | 10 (17) | 77 (38) | 13 (52) |
| Radial artery target vessel stenosis, % | >80 | >70 | >70 | >70 | NR |
| Radial artery grafts to the circumflex coronary artery, % | 83 | 100 | 100 | 47 | 98 |
| Crossover rate, % | |||||
| Radial artery group | 0 | 5.3 | 0 | 3.4 | 0 |
| Saphenous vein group | 0 | 1.8 | 0 | 4.9 | 0 |
| CPB details | NR | All on pump | All on pump | All on pump | All off pump |
| Details of postoperative medical therapy | Any CCB for 1 y, statins, β blockers, and aspirin | Amlodipine for 6 mo and aspirin | Diltiazem for 6 wk and aspirin | Diltiazem for 6 mo, statins, and aspirin | Diltiazem indefinitely, statins, β blockers, and aspirin |
Abbreviations: CCB, chronic calcium channel blocker therapy; CPB, cardiopulmonary bypass; LVEF, left ventricular ejection fraction; NR, not reported; RAPCO, Radial Artery Patency and Clinical Outcome Trial; RSVP, Radial Artery vs Saphenous Vein Patency Study.
Overall, 1036 patients (534 patients randomized to the radial artery group and 502 to saphenous vein group) were included. Baseline characteristics of the patients are summarized in Table 2. There were no statistically significant differences in any of the explored variables between the groups. The radial artery and saphenous vein groups were similar in terms of demographics (mean age, 66.6 vs 67.1 years; 70.4% vs 69.9% men), cardiovascular risk factors (33.9% vs 35.3% patients with diabetes), left ventricular ejection fraction, target vessel distribution, and number of grafts received. There was no significant difference in baseline characteristics between patients lost to follow-up and those included in the analysis (eTable 1 in the Supplement).
Table 2. Baseline Characteristics of Patients in a Study of the Association of Radial Artery vs Saphenous Vein Graft With Cardiovascular Outcomes Among Patients Undergoing Coronary Artery Bypass Grafting.
| Characteristic | No. (%) | Absolute difference (95% CI) | |
|---|---|---|---|
| Radial artery group (n = 534) | Saphenous vein group (n = 502) | ||
| Age, mean (SD), y | 66.6 (9.3) | 67.1 (9.8) | 0 (−1.16 to 1.16) |
| Men | 376 (70.4) | 351 (69.9) | 0.49 (–5.06 to 6.06) |
| Women | 158 (29.6) | 151 (30.1) | 0.40 (–3.90 to 4.48) |
| Diabetes | 181 (33.9) | 177 (35.3) | 1.36 (–4.41 to 7.14) |
| Prior myocardial infarction | 164 (30.7) | 160 (31.9) | 1.16 (–4.47 to 6.80) |
| Elective admission | 469 (87.8) | 456 (90.8) | 3.01 (–0.78 to 6.78) |
| Kidney insufficiencya | 45 (8.4) | 46 (9.2) | 0.36 (–3.77 to 4.45) |
| Left ventricular ejection fraction <50% | 70 (13.1) | 64 (12.7) | 0.36 (–3.77 to 4.45) |
| Target vessel | 4.21 (–1.02 to 9.43) | ||
| Left circumflex coronary artery | 415 (77.7) | 369 (73.5) | |
| Right coronary artery | 119 (22.3) | 133 (26.5) | |
| No. of grafts, mean (SD) | 3.1 (0.7) | 3.1 (0.6) | 0 (−8.00 to 8.00) |
| Proximal anastomosis site | 2.85 (–0.29 to 6.00) | ||
| Ascending aorta | 489 (91.5) | 474 (94.4) | |
| Internal thoracic artery | 45 (8.5) | 28 (5.6) | |
Kidney insufficiency was defined as preoperative serum creatinine greater than 1.5 mg/dL.12
The median (interquartile range) follow-up was 10 (10-11) years in both groups; 942 of 1036 patients (90.9%) had a follow-up of at least 10 years (details on patients lost to follow-up are reported in eFigure 3 in the Supplement). All patients with follow-up data had information available for each of the included outcomes. The proportional hazards assumption was met for all of the explored outcomes (eFigure 4 in the Supplement).
Risk of Bias
The risk of bias in the included trials was rated as low to moderate (eFigure 2 in the Supplement).
Main Outcomes
The main outcomes are reported in Table 3. The use of the radial artery for CABG, compared with the saphenous vein, was associated with a significantly lower incidence of the composite primary end point of death, myocardial infarction, or repeat revascularization (220 vs 237 events; 41 vs 47 events per 1000 patient-years; HR, 0.73 [95% CI, 0.61-0.88]; P < .001; Figure 1A). The use of the radial artery was associated with a significantly lower incidence of the composite secondary end point of death or myocardial infarction compared with the saphenous vein (188 vs 193 events; 35 vs 38 events per 1000 patient-years; HR, 0.77 [95% CI, 0.63-0.94]; P = .01; Figure 1B). In a post hoc analysis, the use of the radial artery was also associated with a significantly lower incidence of death (128 vs 134 events; 24 vs 27 events per 1000 patient-years; HR, 0.73 [95% CI, 0.57-0.93]; P = .01; Table 4 and eFigure 5 in the Supplement).
Table 3. Main Outcomes in a Study of the Association of Radial Artery vs Saphenous Vein Graft With Cardiovascular Outcomes Among Patients Undergoing Coronary Artery Bypass Grafting.
| Outcome | Radial artery group (n = 534) | Saphenous vein group (n = 502) | Treatment effecta | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Events, No. (%) | Events per 1000 patient-years | Cumulative incidence at 10 y (95% CI) | Cumulative incidence at 15 y (95% CI) | Events, No. (%) | Events per 1000 patient-years | Cumulative incidence at 10 y (95% CI) | Cumulative incidence at 15 y (95% CI) | Hazard ratio (95% CI) | P value | |
| Death, myocardial infarction, or repeat revascularization | 220 (41.2) | 41 | 31.0 (27.0-34.9) | 52.5 (46.1-58.9) | 237 (47.2) | 47 | 41.6 (37.2-46.0) | 61.5 (54.5-68.6) | 0.73 (0.61-0.88) | <.001 |
| Death or myocardial infarction | 188 (35.2) | 35 | 25.4 (21.6-29.1) | 47.8 (41.2-54.5) | 193 (38.4) | 38 | 33.0 (28.8-37.3) | 57.1 (49.5-64.7) | 0.77 (0.63-0.94) | .01 |
Results from mixed-effect Cox regression model with individual trials included as a random effect (saphenous vein graft group is the reference group).
Figure 1. Cumulative Incidence of Primary and Secondary Composite Outcomes in a Study of the Association of Radial Artery vs Saphenous Vein Graft With Cardiovascular Outcomes Among Patients Undergoing Coronary Artery Bypass Grafting.
A, Cumulative incidence of the composite outcome of death, myocardial infarction, or repeat revascularization. Median (interquartile range) observation time: 10.0 (8.5-11.4) years in the radial artery group vs 10.0 (6.1-10.2) years in the saphenous vein group. B, Cumulative incidence of the outcome of death or myocardial infarction. Median (interquartile range) observation time: 10.0 (9.2-12.1) years in the radial artery group vs 10.0 (7.0-10.4) years in the saphenous vein group (patients analyzed according to their randomization group).
Table 4. Post Hoc Outcomes in a Study of the Association of Radial Artery vs Saphenous Vein Graft With Cardiovascular Outcomes Among Patients Undergoing Coronary Artery Bypass Grafting.
| Outcome | Radial artery group (n = 534) | Saphenous vein group (n = 502) | Treatment effecta | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Events, No. (%) | Events per 1000 patient-years | Cumulative incidence at 10 y (95% CI) | Cumulative incidence at 15 y (95% CI) | Events, No. (%) | Events per 1000 patient-years | Cumulative incidence at 10 y (95% CI) | Cumulative incidence at 15 y (95% CI) | Hazard ratio (95% CI) | P value | |
| Death | 128 (24.0) | 24 | 14.0 (11.1-17.0) | 34.6 (28.2-41.0) | 134 (26.7) | 27 | 19.8 (16.2-23.4) | 47.1 (38.9-55.3) | 0.73 (0.57-0.93) | .01 |
| Myocardial infarction | 72 (13.5) | 13 | 12.0 (9.2-14.7) | 15.2 (11.6-18.7) | 81 (16.1) | 16 | 15.6 (12.3-18.8) | 19.3 (14.8-23.8) | 0.74 (0.54-1.02) | |
| Repeat revascularization | 63 (11.8) | 12 | 11.3 (8.6-14.0) | 11.8 (8.9-14.6) | 86 (17.1) | 17 | 16.4 (13.2-19.7) | 18.2 (14.4-22.0) | 0.62 (0.45-0.86) | |
Results from mixed-effect Cox regression model with individual trials included as a random effect (saphenous vein graft group is the reference group).
The incidence of myocardial infarction was 72 events in the radial artery group and 81 events in the saphenous vein group (13 vs 16 events per 1000 patient-years; HR, 0.74 [95% CI, 0.54-1.02]). The incidence of repeat revascularization was 63 events in the radial artery group and 86 events in the saphenous vein group (12 vs 17 events per 1000 patient-years; HR, 0.62 [95% CI, 0.45-0.86]) (Table 4 and eFigure 5 in the Supplement).
The HR for the primary outcome was similar during and after the first 5 years of follow-up (0.71 [95% CI, 0.52-0.95] vs 0.75 [95% CI, 0.59-0.94]; eFigure 6 in the Supplement). The analysis of outcomes in the first 5 years of follow-up and after the fifth year of follow-up is provided in eFigures 6 to 9 in the Supplement.
The results of the analysis based on the conduit used were consistent with the main analysis (eFigure 10 in the Supplement). The results of the 2-stage analysis for the primary end point were consistent with the main analysis (HR, 0.72 [95% CI, 0.58-0.88]; Figure 2 and eFigure 11 in the Supplement), with no statistically significant heterogeneity across trials (I2 = 3%). The adjusted HR for the primary outcome (0.73 [95% CI, 0.61-0.88]) was similar to the unadjusted HR.
Figure 2. Forest Plot of the Meta-analytic Estimate for the Composite Primary End Point of Death, Myocardial Infarction, or Revascularization in a Study of the Association of Radial Artery vs Saphenous Vein Graft With Cardiovascular Outcomes Among Patients Undergoing Coronary Artery Bypass Grafting.
The results of the sensitivity analyses to account for the loss to follow-up were consistent with the main analysis (eTable 2 and eFigures 12-13 in the Supplement). In particular, when all patients lost to follow-up in the saphenous vein group were considered as nonevents and assigned 10 years follow-up and all patients lost to follow-up in the radial artery group were considered dead at 10 years of follow-up, the HR for the primary outcome was 0.81 (95% CI, 0.68-0.97) (eFigure 14 in the Supplement).
The event rates by trial are shown in eFigure 15 and eTables 3 to 5 in the Supplement. Results of an analysis limited only to the studies at the lowest risk of bias (RSVP and RAPCO) were consistent with the main analysis (HR, 0.79 [95% CI, 0.58-1.09] for the primary outcome; eFigure 2 in the Supplement). Results of subgroup analyses are shown in Figure 3.
Figure 3. Subgroup Analysis for the Primary Composite Outcome in a Study of the Association of Radial Artery vs Saphenous Vein Graft With Cardiovascular Outcomes Among Patients Undergoing Coronary Artery Bypass Grafting.
Subgroup analysis for the primary composite outcome of death, myocardial infarction, or repeat revascularization. Kidney insufficiency was defined as preoperative serum creatinine greater than 1.5 mg/dL.12 LVEF indicates left ventricular ejection fraction.
Discussion
In this patient-level analysis of 5 RCTs including a total of 1036 patients with a median follow-up of 10 years, the use of the radial artery for CABG was associated with a statistically significant lower incidence of the composite outcomes of death, myocardial infarction, or repeat revascularization and of death or myocardial infarction compared with the use of the saphenous vein.
Observational studies have found that postoperative survival is longer when the radial artery is used as a second conduit for CABG compared with the saphenous vein.1 A meta-analysis of 14 adjusted observational comparative series (20 931 patients) found that at a mean follow-up of 6.6 years, mortality was 24.5% in the radial artery group vs 34.2% in the saphenous vein group (incidence rate ratio, 0.74 [95% CI, 0.63-0.87]).1 However, observational comparative CABG studies are susceptible to treatment allocation and confounding bias, which could account for the reported difference.2
Previous randomized comparisons between use of the radial artery and the saphenous vein for CABG were underpowered to detect statistically significant differences in clinical outcomes, and even the previous report from this database at 5-year follow-up had limited power.3 In addition, in the 5-year analysis, the use of per-protocol angiography by the majority of the trials mandated caution in the interpretation of the reported differences.
The only large RCT on the use of single vs multiple arterial grafts for CABG is the Arterial Revascularization Trial (ART),13 which compared single and bilateral internal mammary artery grafting in 3102 patients. In ART,13 there was no statistically significant difference in survival (HR, 0.96 [95% CI, 0.82-1.12]) or event-free survival (HR, 0.90 [95% CI, 0.79-1.03]) at 10 years.
The results of ART differ from the results of the present analysis, in which a lower risk of cardiac events at the 10-year follow-up was found in patients in the radial artery group compared with the saphenous vein group. A significant reduction in the incidence of death was also found in the radial artery group, but this was a post hoc analysis and the results must be considered hypothesis-generating.
One of the potential explanations for the discrepant results between ART and the current study is that the crossover rate from the bilateral to single arterial group in ART was relatively high (13.9%). Crossover, especially from the experimental to the control group, is known to dilute the treatment effect.14 In the present study, the crossover rate was low (2.4%) and it is possible that better deliverability of the intervention, and not biologic differences between the radial artery and the internal thoracic artery, explains the difference between the 2 analyses. The use of bilateral internal thoracic arteries is technically more complex than the use of the radial artery and it has been shown that experience of the surgeon plays a key role in the former, but not the latter, procedure.15 In addition, the use of the radial artery in 21.8% of the patients assigned to the control group in ART may have further diluted the association between treatment and outcomes and contributed to the null results.
Currently, the Randomized Comparison of the Outcome of Single vs Multiple Arterial Grafts (ROMA) trial (ClinicalTrials.gov 1703018094) is testing the multiple arterial graft hypothesis, including an effect on mortality, in a sample of 4300 patients.16 In ROMA, the second arterial graft can be either the radial artery or an internal thoracic artery, and the results are expected after 2025.
Limitations
This study has several limitations. First, there was a lack of standardized outcomes definitions, a central adjudicating committee, and data source verification. Second, the surgical procedures were performed more than a decade ago and the operative and postoperative protocols may not reflect the current practice. Third, the trials were performed in different countries and there were differences in surgical techniques and postoperative protocols. Fourth, the trials had different sample sizes and contributed differently to the result of the pooled analysis, with larger trials having a larger contribution to the final estimate. However, there was no heterogeneity in the association between treatment and outcomes among the trials, and the results remained robust in the sensitivity analyses. Fifth, the number of patients lost to follow-up was higher in the saphenous vein group, and this may have introduced bias. However, results of the sensitivity analyses performed to account for the loss to follow-up were consistent with those of the main analysis. Sixth, the number of patients included is relatively limited and, even at 10 years follow-up, the analysis may be underpowered for some comparisons.
Conclusions
In this individual participant data meta-analysis with a median follow-up of 10 years, among patients undergoing CABG, the use of the radial artery compared with saphenous vein graft was associated with a lower risk of a composite of cardiovascular outcomes.
List of the RADIAL (Radial Artery Database International ALliance) investigators.
Search Strategy
Figure e1. PRISMA-Individual Patient Data (IPD) flow diagram.
Figure e2. The Cochrane Collaboration’s tool for assessing risk of bias for the included randomized trials.
Figure e3. Details on patients lost to follow-up.
Figure e4. Goodness-of-fit and Schoenfeld residuals for the primary outcome, secondary outcome, and their individual components.
Figure e5. Post-hoc outcomes: death, myocardial infarction and repeat revascularization.
Figure e6. Time segmented analysis for the composite of death, myocardial infarction or revascularization (left panel: events in the first five years of follow-up; right panel: events after the fifth year of follow-up).
Figure e7. Time segmented analysis for the composite of death or myocardial infarction (left panel: events in the first five years of follow-up; right panel: events after the fifth year of follow-up).
Figure e8. Time segmented analysis for death (left panel: events in the first five years of follow-up; right panel: events after the fifth year of follow-up).
Figure e9. Time segmented analysis for revascularization (left panel: events in the first five years of follow-up; right panel: events after the fifth year of follow-up).
Figure e10. Analysis according to the conduit received for the primary (left panel) and secondary (right panel) endpoint.
Figure e11. Leave-one-out analysis for the two-stage meta-analytic estimate for the composite primary end point of death, myocardial infarction or revascularization.
Figure e12. Sensitivity analysis: all patients lost to follow-up were treated as non-events in both groups and assigned 10 years follow-up.
Figure e13. Tipping point analysis.
Figure e14. Extreme scenario analysis: all patients lost to follow-up in the saphenous vein (SVG) group were considered as non-event and assigned 10 years follow-up; all patients lost to follow-up in the radial artery (RA) group were considered dead at 10 years follow-up.
Figure e15. Overall event rates in the included trials.
Table e1. Baseline characteristics of patients with and without 10 years follow-up.
Table e2. Results of the sensitivity analyses for the primary outcome.
Table e3. Event rates by trials for the primary composite endpoint of death, myocardial infarction or revascularization stratified by conduit received.
Table e4. Event rates by trials for the secondary composite endpoint of death or myocardial infarction stratified by conduit received.
Table e5. Event rates by trials for death stratified by conduit received.
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Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Supplementary Materials
List of the RADIAL (Radial Artery Database International ALliance) investigators.
Search Strategy
Figure e1. PRISMA-Individual Patient Data (IPD) flow diagram.
Figure e2. The Cochrane Collaboration’s tool for assessing risk of bias for the included randomized trials.
Figure e3. Details on patients lost to follow-up.
Figure e4. Goodness-of-fit and Schoenfeld residuals for the primary outcome, secondary outcome, and their individual components.
Figure e5. Post-hoc outcomes: death, myocardial infarction and repeat revascularization.
Figure e6. Time segmented analysis for the composite of death, myocardial infarction or revascularization (left panel: events in the first five years of follow-up; right panel: events after the fifth year of follow-up).
Figure e7. Time segmented analysis for the composite of death or myocardial infarction (left panel: events in the first five years of follow-up; right panel: events after the fifth year of follow-up).
Figure e8. Time segmented analysis for death (left panel: events in the first five years of follow-up; right panel: events after the fifth year of follow-up).
Figure e9. Time segmented analysis for revascularization (left panel: events in the first five years of follow-up; right panel: events after the fifth year of follow-up).
Figure e10. Analysis according to the conduit received for the primary (left panel) and secondary (right panel) endpoint.
Figure e11. Leave-one-out analysis for the two-stage meta-analytic estimate for the composite primary end point of death, myocardial infarction or revascularization.
Figure e12. Sensitivity analysis: all patients lost to follow-up were treated as non-events in both groups and assigned 10 years follow-up.
Figure e13. Tipping point analysis.
Figure e14. Extreme scenario analysis: all patients lost to follow-up in the saphenous vein (SVG) group were considered as non-event and assigned 10 years follow-up; all patients lost to follow-up in the radial artery (RA) group were considered dead at 10 years follow-up.
Figure e15. Overall event rates in the included trials.
Table e1. Baseline characteristics of patients with and without 10 years follow-up.
Table e2. Results of the sensitivity analyses for the primary outcome.
Table e3. Event rates by trials for the primary composite endpoint of death, myocardial infarction or revascularization stratified by conduit received.
Table e4. Event rates by trials for the secondary composite endpoint of death or myocardial infarction stratified by conduit received.
Table e5. Event rates by trials for death stratified by conduit received.