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Does the radial artery provide better long-term patency than the saphenous vein
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     a Department of Cardiothoracic Surgery, Rabin Medical Center, Beilinson Campus, Petah Tiqva 49 100, Israel

    b Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel

    c Department of Cardiothoracic Surgery, James Cook University Hospital, Middlesbrough, UK

    Abstract

    A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was whether the radial artery provides better long-term patency than the saphenous vein. Altogether 379 papers were found using the reported search, of which 12 presented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. We concluded that there is evidence that radial artery grafts have a higher rate of patency than saphenous vein grafts. Surgeons can confidently use the radial artery as a second arterial bypass graft, particularly in patients with severe native-vessel stenosis.

    Key Words: Evidence-based medicine; Radial artery; Thoracic surgery; Review

    1. Introduction

    A best evidence topic was constructed according to a structured protocol. This protocol is fully described in the ICVTS [1].

    2. Clinical scenario

    You are about to perform a coronary artery bypass graft (CABG) on an obese 65-year-old man who has triple-vessel disease involving the left anterior descending (LAD) artery, the first obtuse marginal (OM) branch, and the posterior descending artery (PDA), and an akinetic inferior wall with an estimated ejection fraction of 40%. You wonder whether you should use the saphenous vein (SV) or the radial artery (RA) to graft a heavily diseased PDA or OM to achieve long-term patency.

    3. Three part question

    In patients undergoing [coronary artery bypass grafting] is the [radial artery or saphenous vein] the better conduit to achieve [long-term patency].

    4. Search strategy

    Medline 1966–Feb 2005 using OVID interface. [exp Cardiac Surgical Procedures/OR exp Coronary Artery Bypass/OR exp Myocardial Revascularization/OR exp Cardiovascular Surgical Procedures/OR exp Cardiopulmonary Bypass/OR Coronary art$ bypass.mp OR CABG.mp OR Cardiac surg$.mp] AND (exp radial artery/OR radial arter$.mp] AND [exp veins/OR vein.mp]

    5. Search outcome

    Three hundred and seventy-seven papers were found of which 9 were deemed relevant. Cross-checking of the reference lists revealed another three papers [2–13]. The 12 papers are presented in Table 1.

    6. Comments

    Several angiographic observational studies have shown that the RA has excellent short-, mid-, and long-term patency when used as a conduit for revascularization [2–10,12,13] (Table 1). However, Khot et al. [11] reported a high rate of both occlusion and severe flow-limiting disease with the use of RA grafts in patients presenting predominantly with recurrent signs or symptoms of myocardial ischemia after CABG. The RA graft results were dramatically inferior to those for internal mammary artery (IMA) bypass grafts and SV grafts. Although angiographic outcomes with the RA graft were poorer in both sexes, women had particularly high rates of occlusion. It should be noted, though, that this study had a number of limitations. The results were confounded by a selection bias, because the sample was limited to patients with symptoms or signs of recurrent ischemia. Thus, the low RA graft patency rate may have been attributable to the high-risk status of the population rather than an intrinsic tendency of the graft itself. Furthermore, previous studies restricted RA graft placement to patients with high-grade stenosis and good distal runoff, whereas in this study, the decision to use a RA graft was made at the discretion of the individual surgeon, thereby mimicking ‘real-life’ use. As such, the results may have reflected the less stringent criteria for RA bypass.

    Recently, Zacharias et al. [13] evaluated the 6-year outcome of propensity-matched patients undergoing left IMA (LIMA)-to-LAD grafting with one or more additional RA grafts or vein-only grafts (n=925 each). Perioperative outcomes, including death rate, were similar in the two groups, although cumulative survival was better in the patients with the RA graft(s). Angiographic data in restudied symptomatic patients showed a trend for greater RA graft patency. In patients who received both types of grafts, the extent of failure was significantly worse in the vein graft than the RA graft. These findings favor the use of the RA as a second arterial conduit in LIMA-LAD CABG.

    Possati et al. [9], in a series of 90 consecutive patients with CABG, reported an 88% long-term (mean 105±9 months) angiographic patency of RA grafts anastomosed to an OM or PDA. This rate was lower than for LIMA grafts (96.3%) but significantly higher than for SV grafts (53.4%), supporting the use of the RA as a complementary conduit for myocardial revascularization. Although these results are encouraging, there are few additional long-term randomized, controlled studies on RA graft patency in symptom-free patients.

    To bridge this gap, the prospective single-center Radial Artery Patency and Clinical Outcome (RAPCO) Study [8] is conducting a 10-year comparison of angiographic patency and cardiac outcome between RA grafts and either free right IMA (RIMA) grafts (n=25, age <70 years) or SV grafts (n=153, age 75 years) branched to the largest available coronary artery other than the LAD. Interim analysis at 5 years showed no differences in angiographic failure rates or major clinical outcomes (namely, survival and cardiac event-free survival) between the groups. However, these findings were based on only a small proportion of the expected angiographic results. Furthermore, the SV graft patency rates were much higher than rates in both previous reports and in the non-study SVs, perhaps because in SV grafts, atherosclerosis and dysfunction begin to increase only 5 to 10 years postoperatively. The final results at 10 years should help to clarify whether RA grafts are superior to RIMA and SV grafts in this setting.

    The interim results of a second prospective multicenter trial, the Radial Artery Patency Study (RAPS) [11], were published in 2004. The investigators compared the 8- to 12-month protocol-directed angiographic patency of RA and SV grafts to the right or circumflex coronary arteries in 561 patients. Each patient served as his/her own control. Significantly higher patency rates were noted in the RA graft group (91.8% vs. 86.4%; P=0.01; graft occlusion odds ratio=0.53; 95% confidence interval 0.31–0.85); rates of perfect graft patency (i.e., TIMI 3 flow) were similar (87.7% vs. 85.7%, P=0.37). In the RA group, graft patency was similar in the inferior (right coronary) and lateral (circumflex) territories, and perfect patency was highly dependent on the severity of the proximal native coronary artery stenosis (70–89% coronary stenosis: 81.7% patency, 90% stenosis: 91.5% patency). The long-term (5 to 10 years) findings will be assessed in follow-up studies.

    In summary, RA patency rates exceeded those of SV grafts at all time points, except in one study [5]. The tabulated studies show a 10-year patency of 50–90% for RA grafts and of 30–50% for SV grafts.

    7. Clinical bottom line

    The RA graft has a significantly better long-term patency than the SV graft. Although these findings are encouraging, the final results of the RAPCO and RAPS trials after 10 years of follow-up in symptom-free patients should help to clarify the long-term patency rates of RA grafts and to determine whether RA grafts yield better results than SV grafts.

    Appendix A. ICVTS on-line discussion

    Authors: Brian F. Buxton and Siven Seevanayagam (Austin Hospital, Melbourne, Australia)

    eComment: The structured protocol defines patient groups, study type and outcomes. A variety of different anatomic classifications of graft failure and statistical methods are used in current practice, which potentially has an impact on the reported outcomes.

    Different classifications of graft patency commonly used include: Fitzgibbon ABO class, where graft failure was defined as >50% (B) or total occlusion (O) [A1]. The endpoint of total occlusion was used by Desai et al. for comparing the radial and saphenous veins in the Multicenter Radial Artery Patency Study (RAPS) [A2]. Another classification defines patency as <70%, severe disease as 70 to 99% stenosis, and total occlusion [A3]. In some publications the string sign (a functional occlusion) was included as a graft failure, patent or analysed separately. Tatoulis et al. analysed the results as a binary outcome, patent or failure; failure was defined as stenosis greater than or equal to 80%, a total occlusion, or a string sign [A4].

    The type of statistical analysis employed also has an impact on patency results. Common actuarial techniques such as Kaplan-Meier estimates, when assessing non-fatal complications such as graft failure, overestimate the number of events. The cumulative incidence of graft failure is more likely to give representative results [A5]. Unadjusted graft patency can be obtained by categoric patency rates at different time intervals. However, a problem with all the above estimates of graft patency is that the time of graft failure is unknown. Graft failure occurs somewhere in the interval between surgery and the time of angiography. In an attempt to overcome this problem, interval censoring techniques have been used to adjust the time of graft failure.

    Recently, a comparison of reangiographic assessment of graft patency in trial patients based on a predetermined protocol, has shown to have approximately half the failure rate of those reangiograms based on symptoms or signs of ischemia [A6].

    Another potential difficulty in comparing radial artery and saphenous vein graft patencies has been the apparent improvement in saphenous vein patency. More recently, and particularly in trial patients, careful preparation of conduits has focused on harvesting techniques, vasodilatation and preservation prior to implantation. Post surgery, the use of calcium channel blockers, ACE inhibitors, lipid-lowering and anti-platelet therapy, may have contributed to improvement in saphenous vein graft patency, thus narrowing the gap between radial artery and saphenous vein graft outcomes, at least in the short term. Longer follow-up studies will be necessary to detect true biologic differences between conduits.

    The study type of Zacharias has been designated as a prospective randomized study [A7]. While the data may have been collected prospectively, it is a retrospective, propensity matched trial of 925 patients in each group [A7]. The evidence provided by this study is therefore Level 2. Although the radial artery patency rates were greater than the saphenous vein in the same patients, target artery bias cannot be excluded.

    This systematic review of the literature with weighted comparisons provides us with an excellent overview of current practice. Standard reporting techniques might help minimize some of the unexplained differences in outcomes. The late outcome from randomized controlled trial will provide the best chance of excluding bias and assessing comparisons between conduits.

    References

    A1 Fitzgibbon GM, Leach AJ, Kafka HP, Keon WJ. Corronary bypass graft fate: long-term angiographic study. J Am Coll Cardiol 1991;17:1075–1080.

    A2 25Desai ND, Cohen EA, Naylor CD, Fremes SE. A randomized comparison of radial-artery and saphenous-vein coronory bypass grafts. N Engl J Med 2004;351:2262–2264.

    A3 Khot UN, Friedman DT, Pettersson G, Smedira NG, Li J, Ellis SG. Radial artery bypass grafts have an increased occurrence of angiographically severe stenosis and occlusion compared with left internal mammary arteries and saphenous vein grafts. Circulation 2004;209:2086–2091.

    A4 Tatoulis J, Buxton BF, Fuller JA. The radial artery in reoperative coronary bypass surgery. J Card Surg 2004;19:296–302.

    A5 Grunkemeir GL, Wu Y. Actual versus actuarial event-free percentages. Ann Thorac Surg 2001;72:677–678.

    A6 Buxton BF, Gordon I, Hare DL, Moten S, Durairaj M, Seevanayagam S. Do the angiographic results from symptom-directed studies reflect the true graft patency Ann Thor Surg (in press).

    A7 Zacharias A, Habib RH, Schwan TA, Riordan CJ, Durham SJ, Shah A. Improved survival with radial artery versus vein conduits in coronary bypass surgery with left internal thoracic artery to left anterior descending artery grafting. Circulation 2004;109:1489–1496.

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