**4. Saphenous vein graft conduits**

Reversed saphenous vein grafts (RSVG) have been utilized for CABG since the procedure's inception [52] and remain an important graft conduit option in the present era and in numerous clinical scenarios [53, 54]. Historically, patency rates of RSVG aorto-coronary artery grafts have been observed to be approximately 50-60% at 10 years [7, 55]. However, as previously noted, recent RSVG patency data are less encouraging [8-10]. For example, the PREVENT-IV study evaluated 3,000 patients undergoing CABG with 1-year routine angiographic follow-up. At this early time point, 30% of RSVG conduits were occluded and over 45% had "failed," as defined by 75% stenosis [10]. Importantly, study patients with vein graft failure had significantly increased rates of perioperative complications including MI, death or MI, or MACE relative to the cohort without vein graft complications [10]. Similar results have been noted elsewhere [56-59]. Additionally, surprisingly poor early-tomid-term RSVG patency rates have been reported elsewhere. The Portland Endoscopic SVG Harvest Trial demonstrated 69% [8], patency by angiography at 6-months, while the PRAGUE 4 trial showed one-year RSVG patency of 52.5% [9]. The potential impact of poor vein graft performance cannot be overstated as RSVG failure is significant contributor to

PCI group, primarily related to the increased need for repeat intervention. Death and postprocedure MI were not significantly different between the two groups, but there was an increased stroke rate in the CABG group compared with PCI, which is somewhat offset by the fact that surgical patients were not managed with aggressive antiplatelet therapy as compared to the PCI group, and many of the cerebrovascular events occurred outside of the perioperative period. More recently, three-year follow up SYNTAX data were reported confirming advantages of CABG over PCI with regard to MACE. Unlike 12-month data, however, composite safety endpoints were no longer different between the two groups, including a similar stroke rate [42]. The SYNTAX authors concluded that CABG remains the preferred therapy for 3-vessel or left main CAD but recommend longer follow up, as is

Despite the favorable data for CABG emanating from carefully designed and conducted randomized trials, rates of CABG referral have decreased consistently since the introduction of PCI with stent technologies [43]. Preference for PCI appears driven by disparate interpretation of PCI-versus-CABG studies, by strong patient preference for less invasive procedures with presumed lower periprocedural risk, and by the promise for faster recovery. As a result, the percentage of patients referred for CABG with previous PCI has increased steadily [44] with higher acuity relative to patients without previous intervention [45]. Additionally, technical details of CABG in current surgical practices are considered more challenging compared with previous eras due to more diffuse CAD, subjectively smaller distal coronary targets, particularly among diabetic patients, and the high incidence of prior PCI [46]. Consequently, contemporary results for CABG following PCI are characterized by worse perioperative outcomes when compared with CABG patients without previous intervention. For example, higher rates of postoperative mortality, MACE, and other perioperative complications following CABG in both diabetic and nondiabetic patients have been observed [47-50]. More importantly, increased mid-term mortality in diabetic patients with prior PCI has been observed after CABG [50], and Rao et al demonstrated increased long-term mortality in patients with prior PCI who subsequently

Reversed saphenous vein grafts (RSVG) have been utilized for CABG since the procedure's inception [52] and remain an important graft conduit option in the present era and in numerous clinical scenarios [53, 54]. Historically, patency rates of RSVG aorto-coronary artery grafts have been observed to be approximately 50-60% at 10 years [7, 55]. However, as previously noted, recent RSVG patency data are less encouraging [8-10]. For example, the PREVENT-IV study evaluated 3,000 patients undergoing CABG with 1-year routine angiographic follow-up. At this early time point, 30% of RSVG conduits were occluded and over 45% had "failed," as defined by 75% stenosis [10]. Importantly, study patients with vein graft failure had significantly increased rates of perioperative complications including MI, death or MI, or MACE relative to the cohort without vein graft complications [10]. Similar results have been noted elsewhere [56-59]. Additionally, surprisingly poor early-tomid-term RSVG patency rates have been reported elsewhere. The Portland Endoscopic SVG Harvest Trial demonstrated 69% [8], patency by angiography at 6-months, while the PRAGUE 4 trial showed one-year RSVG patency of 52.5% [9]. The potential impact of poor vein graft performance cannot be overstated as RSVG failure is significant contributor to

planned for an additional two years [6].

underwent CABG [51].

**4. Saphenous vein graft conduits** 

redo coronary surgery [60]. In addition, early vein graft failure is associated with increased perioperative myocardial infarction [10, 61], which consequently affects survival after CABG [58, 59].

Several potential explanations exist for the recently chronicled poor performance of RSVG as aorto-coronary conduits including early technical errors, endothelial injury, and early thrombosis, which may be related to insufficient biologic reaction to aspirin or inadequate antiplatelet effect of aspirin [62-64]. One important contributor to poor RSVG conduit performance, receiving significant recent attention, may be the practice of harvesting the conduit endoscopically (EVH). This technique was introduced and popularized in the 1990s and has been widely adopted due to increased incisional comfort and patient satisfaction, and decreased wound complications compared to open vein harvesting [65, 66] such that at least 70% of CABG patients undergo EVH based on recent Society of Thoracic Surgeons Database reporting [67]. However, EVH has been associated with increased endothelial injury, which may have significant negative consequences including graft patency and possibly long-term survival [68, 69]. Desai et al recently demonstrated using optical coherence tomography that EVH operators had a steep learning curve with regard to subtle RSVG injuries and that vein grafts with four or more intimal or medial dissections showed significantly worse early patency rates than those with fewer intimal injuries (67% vs. 96%) [70].

In contrast, when RSVGs are harvested using a "no touch" technique, better patency results have been noted. The "no touch" method avoids vein stripping, taking surrounding tissue, and avoids over-distending the vein conduit as it is being prepared for coronary anastomosis [71]. This has also been shown recently to preserve the venous vasa vasorum [72]. Perhaps this helps to explain differences in contemporary SVG patency rates versus those reported historically, which were always done by an open surgical technique. Other predictors of improved vein patency include grafting to the LAD coronary artery versus other target sites, smaller venous conduit size, and larger diameter target coronary artery. In contrast, young age and low EF reduced long-term patency [60]. The type of distal anastomosis (sequential, y- or t-grafts, or other composite grafts) did not affect long-term patency [60]. Based on these data, some suggest SVG from the calf/lower leg since size and possible thickness of the vein is better [60]. Additionally, EVH is more difficult to perform on the lower leg; therefore, programs committed to EVH likely neglect this potentially advantageous conduit.

Current surgical patient cohorts have also been implicated in reduced vein graft patencies. For example, it is generally accepted that contemporary patients referred for surgery are older and more medically complex [73]. For example, many patients referred for CABG are diabetic, a condition that is notorious for more complicated and diffuse CAD [46, 74]. In addition, it has been proposed that venous grafts in elderly may be of inferior quality relative to younger patients [75].
