The forest plots given in Figure 3 display the results, individually and in aggregate, for all studies that reported on each relevant clinical outcome. When there was statistical heterogeneity, the difference between randomized and nonrandomized results was scrutinized to determine whether study design (and, presumably, selection bias in the nonrandomized trials could explain the heterogeneity). Sensitivity analysis for redo surgeries, diabetic patients, elderly patients, and publication status age was not possible due to inadequate data.
Heterogeneity was detected for the outcomes of wound complications, edema, hematoma, harvest vein repairs, pain scores in hospital, patient dissatisfaction, harvest time, operative time, closure time, time to ambulation, and hospital length of stay. When only the randomized data are analyzed for these heterogeneous data, the heterogeneity is generally reduced (or eliminated), suggesting that the nonrandomized data accounts for the heterogeneity. Therefore, for these clinical outcomes, the results of the randomized data should be given higher priority in clinical decision-making than the results of the nonrandomized data, due to the risk of bias in the latter.
The risk of wound complication was significantly reduced by 69% with EVH compared with OVH (OR 0.31, 95% CI 0.23–0.41; P < 0.0001) with an estimated NNT of 11 (95% CI, 10 to 13). Similarly, the risk of wound infections were significantly reduced by 67% with EVH compared with OVH (OR 0.23, 95% CI 0.20–0.53; P < 0.0001), with an estimated NNT of 19 (95% CI, 15 to 25). The need for surgical intervention for wound infection was also significantly reduced (OR 0.16, 95% CI 0.08–0.29; P < 0.0001), with a NNT of 45 (35 to 60). The risk for most of the individual subcomponents of the definition of wound complications, including edema, seroma/lymphocele, necrosis, wound drainage, dehiscence, and need for antibiotics was significantly reduced (odds reductions ranging from 56% to 94%), with corresponding NNT estimates ranging from 4 to 45 (Table 4). However, hematomas and abscess formation were not significantly different between EVH and OVH groups.
Quality of Harvested Conduit
Although the mean number of venous repair stitches per person was increased by a mean of 1.11 stitches per patient with EVH compared with OVH (WMD 1.11, 95% CI 0.52–1.69, P = 0.0002), the odds of requiring harvest vein repair during the harvest procedure was not significantly different (OR 2.39, 95% CI 0.95–6.05, P = 0.07). Endothelial damage scores were not significantly different (SMD –0.09, 95% CI –0.27, 0.09, P = 0.3), and medial continuity score was not significantly different (WMD 0.00, 95% CI –0.22, 0.22, P = 1.0). Biochemical markers (IL-1, IL-2, IL-10, and ICAM) were reported in one nonrandomized trial only and were not significantly different between EVH and OVH (Table 4).
Major coronary adverse events (MACE) such as postoperative myocardial infarction, stroke, rethoracotomy for bleeding, reintervention for ischemia or angina recurrence, and all-cause mortality were not significantly different for EVH versus OVH at 30 days (Table 4) or up to 5 years.13 Clinical outcomes at 30 days were as follows: all-cause mortality (OR 0.71, 95% CI 0.34–1.48, P = 0.4), postoperative myocardial infarction (OR 1.02, 95% CI 0.58–1.78, P = 0.9), angina recurrence or reintervention for ischemia (OR 1.06, 95% CI 0.38–2.96, P = 0.9), and rethoracotomy for bleeding (OR 0.91, 95% CI 0.09–8.89, P = 0.9). One randomized trial reported survival free of MACE (death, myocardial infarction, heart failure, or angina recurrence) at up to 5 years, and found no significant difference (75% vs. 74%, P = 0.85).13
Angiographic outcomes were reported in only a few trials, generally at up to 3 to 6 months of follow-up, and were not significantly different (Fig. 3). Similarly, no difference was found for graft occlusion at 3 to 6 months (OR 1.30, 95% CI 0.79–2.15, P = 0.3) and stenosis greater than 50% after 3 months (OR 0.79, 95% CI 0.44–1.45, P = 0.5).
Pain and Mobility
The incidence of moderate to severe pain was reduced with EVH compared with OVH in the postoperative period by 74% (OR 0.26, 95% CI 0.12–0.55, P < 0.0001) and by 83% at up to 6 months of follow-up (OR 0.17, 95% CI 0.05–0.60, P = 0.006). The incidence of mobility disturbance at postoperative day 2 to 4 was reduced by 69% (OR 0.31, 95% CI 0.15–0.65, P = 0.002). Similarly, the incidence of neuralgia was reduced by 75% at 4 to 6 weeks, and by 78% at 3 to 6 months of follow-up (Table 4). A significant difference in neuralgia was no longer found at 12 months (1 trial). Visual analog score (VAS) for pain on postoperative day 0 or 1 was significantly reduced by more than 2 points with EVH versus OVH (WMD –2.18, 95% CI –3.56 to –0.79 points), and by less than 1 point at 4 to 6 weeks of follow-up (WMD –0.35, 95% CI –0.58, –0.12 points). In-hospital morphine equivalents use was significantly reduced by 0.14 mg/kg (WMD –0.14, 95% CI –0.20, –0.08 mg/kg). Duration of analgesia use was significantly reduced by a weighted mean of nearly 14 days (WMD –13.8 days, 95% CI, –21.22 to –6.38 days). The number of patients with restricted mobility on postoperative day 2 to 4 was significantly reduced (OR 0.31, 95% CI 0.15–0.65), and at day 30 (OR 0.06, 95% CI 0.008–0.49). Mean time to ambulation was not significantly different (Table 4).
Measures of patient satisfaction were infrequently reported, and therefore the resulting estimates are based on very few trials. Patient scores for subjective assessment of mobility were significantly improved for EVH compared with OVH at discharge (WMD 2.40 points, 95% CI 2.05 to 2.75). Patients’ satisfaction with pain experience during hospitalization was significantly improved (WMD 1.88 points, 95% CI 1.49–2.28), but was no longer significant at 6 weeks postdischarge (WMD 0.24 points, 95% CI –0.09 to 0.57). Patient satisfaction scores for cosmetic result was significantly higher with EVH compared with OVH at discharge (WMD 2.33 points, 95% CI 1.9–2.75) and at 6 weeks (WMD 0.93 points, 95% CI 0.58–1.27). The incidence of patient dissatisfaction with EVH overall surgical results compared with OVH was not significantly reduced (OR 0.005, 95% CI 0.00–14.6), but incidence of cosmetic dissatisfaction was significantly reduced with EVH compared with OVH (OR 0.24, 95% CI 0.08–0.71, P = 0.009).
Quality of Graft Harvested
Mean number of vein repairs was significantly increased in EVH compared with OVH (WMD 1.11, 95% CI 0.52–1.69, P = 0.0002). Clinical outcomes that may ultimately be an expression of the quality of graft include myocardial infarction, rethoracotomy for bleeding, angina recurrence or reintervention for ischemia, and death. Aggregate analysis and subanalysis of randomized and nonrandomized data showed no difference between EVH and OVH for myocardial infarction, rethoracotomy, angina recurrence or reintervention, and death over the short term (ie, at 4–6 weeks) (Table 4, Fig. 3). One trial reported clinical outcomes at 5 years, and showed no difference in 5-year event-free survival (freedom from myocardial infarction, angina recurrence, congestive heart failure, or death).13
When vein segments were analyzed from small subsets of patients were observed by microscopy, they showed preservation of vascular integrity when defined by no difference in immunoperoxidase stains (vimentin, Factor VIII, and CD31) and no evidence of trauma of the saphenous vein wall shown on hematoxylin and eosin stains.33 Similarly, no difference in evidence of mechanical or thermal damage was found under stained light microscopy examination.32 Measurement of IL-1, IL-2, and IL-10 did not differ significantly in samples taken during EVH and OVH technique. Although ICAM levels were reduced, the clinical significance remains undefined.27–30 Aggregate analysis of studies that reported a 5-point endothelial damage score showed no significant difference between estimates of endothelial damage between EVH and OVH groups (SMD –0.09, –0.27 to 0.09).
The mean time required to harvest the graft was increased (WMD 11.23 minutes, 95% CI 7.12–15.34, P < 0.0001), mean closure time was significantly reduced (WMD –23.12 minutes; 95% CI –30.57, –15.66; P < 0.0001), and total operative time was significantly increased (WMD 15.26 minutes, 95% CI 0.01–30.51, P < 0.05) for EVH compared to OVH. The rate of vascular harvest was not significantly different with EVH and OVH (WMD –0.10 cm/min; 95% CI –0.34, 0.14; P = 0.4). Total blood loss was not reduced with EVH (–9.57 mL; 95% CI –56.55, 37.41; P = 0.7), and incidence of blood product transfusion was not reported.
Time to ambulation was not significantly different with EVH and OVH (–0.38 days; 95% CI –1.17, 0.41; P = 0.4). Total hospital length of stay was reduced significantly (WMD –0.85 days; 95% CI –1.55, –0.15; P = 0.02), but ICU length of stay was not reduced (WMD 0.07; 95% CI –0.20, 0.34; P = 0.6) with EVH.
Aggregate analysis of physician visits and emergency room visits showed significant reduction (OR 0.26, 95% CI 0.12–0.57, P = 0.001), and need for nursing or home care services was also significantly reduced (OR 0.17, 95% CI 0.08–0.38, P < 0.0001) with EVH compared with OVH. In addition, hospital readmissions for wound complications were significantly reduced (OR 0.53, 95% CI 0.29–0.98, P = 0.04) with EVH.
Although two studies that reported costs from the payer perspective in the United States suggested cost savings ranging from US $68 to $1,500 savings per patient undergoing EVH instead of OVH (Table 5), these cost estimates should be interpreted with caution due to variations in definitions of applicable costs (direct and indirect, in hospital and follow-up costs). A formal assessment of the incremental cost-effectiveness ratio would be necessary before conclusions about the relative cost-effectiveness of the two techniques could be made.
Study Quality and Heterogeneity
Subanalysis of randomized trials showed similar results as for the combined randomized and nonrandomized data (see Fig. 3). However, significant heterogeneity between trials was detected for some of the categories of wound complications. In most cases, for outcomes showing statistically significant heterogeneity, the excess heterogeneity was attributable to the nonrandomized cohort of studies. This emphasizes the need to rely first on highest levels of evidence to inform decision making.
This meta-analysis suggests that EVH results in improved clinical outcomes and may have favorable implications for resource utilization.
Endoscopic harvest of saphenous vein results in reduced risk of wound complications compared with OVH. Specific subtypes of wound complications that were reduced included wound infections, antibiotics given, edema, seroma/lymphocele, necrosis, wound drainage, dehiscence, and surgical wound interventions. For each of these endpoints, the reduction in risk was not only statistically significant, but also likely to be considered clinically significant. Assuming that these results are applicable to patients outside of the clinical setting, these results predict that for every 1,000 patients (of similar characteristics to those included in this meta-analysis) who undergo EVH instead of OVH, there would be on average 91 fewer patients with at least 1 wound complication, 250 fewer experiencing edema, 71 fewer with wound drainage, 62 fewer with dehiscence, 53 fewer with wound infections, 48 fewer with necrosis, 40 fewer requiring antibiotics, and 31 fewer with seroma/lymphocele. In addition, average pain scores over the short and long term would decrease, incidence of neuralgia would decrease, and patient satisfaction would be improved if EVH were used rather than OVH.
The results of this meta-analysis also suggest the potential for favorable impact on resource utilization, such that for every 1,000 patients treated with EVH instead of OVH, there would be approximately 850 fewer hospital days of stay, 100 fewer patients requiring physician or ER visits, 33 fewer patients requiring nurse or homecare visits, 22 fewer patients requiring surgical intervention for wound complications, and 7 fewer hospital admissions, and over 13,000 fewer days of analgesic use (mostly outpatient use). However, the mean harvest time and total operative time would be increased by over 10 minutes per patient, and overall operation time by about 15 minutes per patient.
Judgments about whether the costs of EVH are reasonable and feasible depend on the definition of cost-effectiveness and on the perspective taken (ie, the different perspectives of patients, physicians, hospitals, health care systems, society would result in differing definitions of relevant costs and outcomes). Because formal economic analyses have not been conducted for studies of EVH and OVH, there are limited data to base recommendations on the resource implications of the two techniques.
Strength and Limitations
The results of this meta-analysis should be interpreted in light of its strengths and limitations. Although this meta-analysis represents a comprehensive analysis of currently available randomized and nonrandomized evidence, it is possible that new evidence will emerge to better inform the longer-term outcomes, and this newer evidence will need to be incorporated over time. In addition, it is also important to note that the results of this analysis are technique- and skill-dependent, and the results described herein are no guarantee for outcomes produced by individual surgeons or physician assistants who may have less technical competence or experience than those represented within the trials. It is clear, from examination of Tables 1 and 2 that the included trials give mixed representation of surgeons (single or multiple) and physician's assistants who conducted the vein harvest, some of whom were very early in their experience, and others of whom had significant experience before conducting the trial. Because a number of the trials described their experience as early in their learning curve, it is likely safe to suggest that the results of this meta-analysis provide a conservative estimate of the potential benefit that would have been possible had only experienced operators been included in the trials.
A significant limitation of the results of this meta-analysis is that some of the prognostically significant characteristics of the patients differed significantly at baseline. These baseline differences were often attributable to the nonrandomized trials. This is of particular concern since it suggests that younger, male, obese patients were preferentially selected to undergo EVH rather than OVH, which could potentially result in bias. Fortunately, we have subanalyzed the randomized trials separately from the nonrandomized trials so that the results of the methodologically rigorous trials can be considered in isolation of the selection biases of the nonrandomized trials. When the randomized trials are considered separately from the nonrandomized trials, the conclusions remain unchanged for the majority of outcomes (Fig. 3).
Although endothelial damage scores and markers or endothelial injury were considered to inform the question of quality of conduit harvested, no guidelines and no agreement exists in the literature regarding the validity of these indices of quality of conduit harvested. In particular, there are no guidelines for appropriate preparation and valid measurement of markers of injury in vein segments, no consensus is available regarding which biochemical markers represent a valid marker of injury, and no empirical information is available to inform whether these markers (and at what threshold) represent clinically meaningful associations with clinical outcomes such as graft patency and MACE. Similar limitations exist for other indicators of endothelial injury, such as visual inspection of endothelial intimal integrity through electron microscopy. Therefore, these preliminary indicators of graft quality should be interpreted with caution. Rather, greater emphasis should be placed on the more clinically relevant outcomes of myocardial infarction, need for reintervention, heart failure, and survival over the longer term.
None of the clinically relevant cardiovascular outcomes or overall survival differed significantly for EVH compared with OVH; however, the confidence intervals remain wide since the power to rule out significant differences was relatively low, even with aggregate analysis of all trials through meta-analysis. Inadequate power also hindered the precision of outcome estimates for graft patency, since few studies reported angiographic outcomes, and of those that did, a significant proportion of patients did not undergo angiography during longer-term follow-up. Therefore, the angiographic results should be interpreted conservatively at this time, until further studies with adequate follow-up become available. Because measures of patient satisfaction were infrequently reported, the resulting should be interpreted with caution, and further research should be encouraged in this area.
A Consensus Conference and Statement on EVH Versus OVH
A consensus conference was facilitated by the International Society for Minimally Invasive Cardiac Surgery (ISMICS) to clarify, for clinical practitioners and health care planners or administrators, the suggested role of endoscopic vascular harvest relative to open vascular harvest in adults undergoing CABG surgery. The primary objective of the consensus conference was to provide the best available evidence on the question: “Does endoscopic vascular graft harvesting (EVH) compared to conventional open vascular harvesting (OVH) in adults undergoing coronary artery bypass surgery improve clinical and resource outcomes?”52 Furthermore, economic analysis from the perspective of the institution and the health care system were examined to determine whether the clinical benefits of EVH would be worthy of the required resource shifts. The ISMICS Consensus Conference suggested that “EVH is recommended to reduce wound related complications, improve patient satisfaction, and decrease postoperative pain, hospital LOS, and outpatient wound management resources when compared to OVH (Class I; Level A).” Based on quality of conduit harvested, either endoscopic or open vein harvest technique may be used (Class IIa; Level B). Based on major adverse cardiac events and angiographic patency at 6 months, either endoscopic or open vein harvest technique may be used (Class IIa; Level A). It also recommended that given these statements, EVH should be considered standard of care for patients who require saphenous vein grafts for coronary revascularization (Class I; Level B).
However, it should be cautioned that the very important issue of operator technical competency must be further explored and adequate training standards and technical competence should be considered before widespread implementation of EVH as a standard of care. In addition, future research should address long-term angiographic patency, MACE, and cost-effectiveness in patients undergoing saphenous vein harvest and in patients undergoing endoarterial harvest.
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Keywords:© 2005 Lippincott Williams & Wilkins, Inc.
meta-analysis; endoscopic vascular harvest; coronary artery bypass surgery