Abstract
Objective:
Cryopreserved vein grafts serve as alternative conduits for infrainguinal bypass when autogenous vein is unavailable or inadequate. Anticoagulation has been advocated to improve outcomes, but published studies demonstrate conflicting results. We assessed the association of anticoagulation on outcomes after infrainguinal bypass with cryopreserved vein in patients with chronic limb threatening ischemia (CLTI).
Methods:
The Vascular Quality Initiative was queried (2003–2022) for infrainguinal bypass performed using cryopreserved vein graft for CLTI. Baseline characteristics, procedural details, and outcomes between those discharged with or without anticoagulation were recorded. Univariable, Kaplan-Meier, and multivariable analyses were performed.
Results:
There were 2336 patients who underwent an infrainguinal bypass with cryopreserved vein conduit. The average age was 70.6 years and 63.5% were male. Bypass targets were femoral/popliteal (27.5%) and tibial (72.5%). Indication for intervention included rest pain (25.7%) and tissue loss (74.3%). Patients were discharged with aspirin (80.1%), a P2Y12 inhibitor (45.6%), and anticoagulation (47.3%). Patients discharged on postoperative anticoagulation more often were treated for rest pain (28.1% vs. 23.5%), had a tibial bypass target (78.4% vs. 67.2%), and less often underwent endarterectomy (27.8% vs. 34.2%) (all P<.05).
Kaplan-Meier analysis at one-year demonstrated that postoperative anticoagulation had similar freedom from loss of primary patency/death (28.9% vs. 34.3%), major amputation/death (62.3% vs. 63.8%), and reintervention/major amputation/death (50.6% vs. 53.8%) (all P>.05), but higher survival (85.1% vs. 81.7%, P=.03). Multivariable analysis at one-year demonstrated that postoperative anticoagulation had a similar likelihood for loss of primary patency/death (HR .95, 95% CI .83.−1.09), major amputation/death (HR .88, 95% CI .74–1.05), and reintervention/major amputation/death (HR .93, 95% CI .79–1.08) (all P>.05), but lower likelihood for death (HR .59, 95% CI .46–.74, P<.001) compared to no anticoagulation. Postoperative aspirin was associated with decreased likelihood for amputation/death (HR .74, 95% CI .61–.91, P=.003) and reintervention/major amputation/death (HR .76, 95% CI .64–.9, P=.002). Postoperative P2Y12 inhibitor was associated with decreased likelihood for amputation/death (HR .75, 95% CI .63–.9, P=.002) and reintervention/major amputation/death (HR .78, 95% CI .67–.91, P=.001). Results were similar when analyzing patients who were not on anticoagulation preoperatively.
Conclusions:
Postoperative anticoagulation following infrainguinal bypass using cryopreserved vein did not affect patency or limb salvage. Antiplatelet agents were associated with improved outcomes. Overall patency and limb salvage rates at one year were poor. When cryopreserved vein is used, surgeons should consider antiplatelet therapy for cryopreserved graft patency rather than anticoagulation.
Keywords: ischemia, cryopreserved, chronic limb threatening ischemia, anticoagulation
Table of Contents Summary
In 2336 patients undergoing infrainguinal bypass with cryopreserved vein for chronic limb threatening ischemia in the Vascular Quality Initiative, multivariable analysis at one-year demonstrated that postoperative anticoagulation had a similar likelihood for loss of primary patency/death, major amputation/death, and reintervention/major amputation/death whereas postoperative aspirin and P2Y12 inhibitor use were protective.
Introduction:
Although endovascular interventions have become more common in infrainguinal revascularization for chronic limb threatening ischemia (CLTI), lower extremity infrainguinal bypass is still commonly performed.1,2 Single segment greater saphenous vein bypass has been shown to be the most effective bypass conduit, but may not always be available.3–5 Alternative conduits, such as prosthetic grafts, alternative autogenous veins, and cryopreserved veins remain viable options, particularly when endovascular interventions have failed or are not possible.6–11
Cryopreserved vein has been widely used as an alternative conduit option for lower extremity bypass in patients with CLTI when autogenous vein is not available, in the setting of active infection or infected fields, or when there is only a pedal target for bypass.11–17 Notwithstanding, these conduits have been hampered by poor durability in prior analyses and there is broad variability in the data for supporting medication adjuncts that improve outcomes. Previous publications have shown mixed results on whether anticoagulation has improved patency.11,12 In addition, most prior analyses are limited by small sample size and are single center studies. This creates uncertainty among surgeons about how to best manage patients after a cryopreserved vein bypass.
Our goal was to assess one-year patency for cryopreserved vein infrainguinal bypass using the Vascular Quality Initiative (VQI) infrainguinal bypass registry. Furthermore, we assessed factors that were associated with improved patency such as anticoagulation and antiplatelet medications. Our hypothesis was that primary patency and associated outcomes would be improved with postoperative anticoagulation.
Methods:
A retrospective review of the VQI infrainguinal bypass registry was performed between 2003 and 2022. Patients who underwent infrainguinal bypass for rest pain or tissue loss were included. The study was approved by the VQI Research Advisory Committee and the Boston University Institutional Review Board, which deemed it as non-human subject research and consent was waived.
The primary exposure groups were patients who had a cryopreserved bypass and were treated postoperatively with anticoagulation at discharge versus those who were not treated with anticoagulation at discharge. Baseline demographic characteristics and comorbidities were compared between the two study groups such as age, sex, race, insurance type, home living, body mass index (BMI), and ambulatory status. Comorbidities included congestive heart failure (CHF), coronary artery disease (CAD), prior percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG), diabetes mellitus (DM), chronic obstructive pulmonary disease (COPD), chronic renal insufficiency, hypertension (HTN), and prior or current smoking. Preoperative anticoagulation was also assessed. Post-operative aspirin use, P2Y12 inhibitor use, and statin use were also recorded. Additionally, prior revascularization history was evaluated, which included prior inflow and leg procedures.
Procedural details analyzed were indication for bypass (rest pain or tissue loss) and vessels intervened on (classified anatomically as femoropopliteal or and infrapopliteal vessels). Other procedural characteristics recorded were concomitant bypass, peripheral vascular intervention (PVI), and endarterectomy as well as estimated blood loss (EBL) and procedure time. Postoperative outcomes included 30-day mortality, wound complications, return to operating room (RTOR), bleeding, stroke, cardiac, respiratory, and renal complications. The primary outcome was one-year freedom from loss of primary patency or death. Secondary outcomes included one-year major amputation-free survival, one-year reintervention or major amputation-free survival, and one-year survival.
Patient characteristics, procedural details, and outcomes were compared with and without anticoagulation. Cox proportional hazard regression analysis was performed to determine hazard ratios for primary patency, amputation/death and death. One-year outcomes were analyzed by Kaplan-Meier survival analysis. Statistical analysis was performed using SAS Software Version 9.4 (SAS Institute Inc., Cary, NC, USA). A P value of <.05 was considered statistically significant for all tests.
Results:
Demographics and Medical History
There were 2,336 patients who underwent an infrainguinal bypass with cryopreserved vein conduit. The average age was 70.6 years and 63.5% were male. 29.9% of patients were current smokers, 49.5% were non-ambulatory, and 93.8% lived at home. The majority had Medicare (63.4%) insurance coverage. The most common comorbidities were HTN (92.9%), DM (58.4%), CAD (39.3%), CHF (29.9%), and COPD (29.3%). 20.3% of patients had a previous inflow PVI and 9.1% had a previous inflow bypass. 42.5% of patients had a previous infrainguinal PVI and 34.5% had a previous infrainguinal leg bypass. Of all patients, 27.3% on preoperative anticoagulation. Comparison of patients who were treated with and without postoperative anticoagulation, revealed that those on postoperative anticoagulation more often were obese, had primary Medicare insurance, CHF, previous infrainguinal revascularization, and preoperative anticoagulation (all P< .05) (Table I). The type of anticoagulation used postoperatively were warfarin (49%), rivaroxaban (19.5%), dabigatran (0.9%), and other (30.6%).
Table I –
Demographics and Comorbidities
| Characteristic | Overall (N=2336) | Post-Op Anticoagulation (N=1104) | No Post-Op Anticoagulation (N=1232) | P-value |
|---|---|---|---|---|
| Demographics | ||||
| Age | 70.6+/−10.4 | 70.6+/−10.4 | 70.6+/−10.3 | .99 |
| White race | 1753 (75%) | 847 (76.7%) | 906 (73.5%) | .08 |
| Male sex | 1483 (63.5%) | 719 (65.1%) | 764 (62%) | .12 |
| Obese (BMI ≥ 30kg/m2) | 599 (25.7%) | 306 (27.8%) | 293 (23.8%) | .03 |
| Smoking - Never | 501 (21.5%) | 229 (20.8%) | 272 (22.1%) | .59 |
| Smoking - Prior | 1135 (48.6%) | 548 (49.7%) | 587 (47.7%) | |
| Smoking - Current | 698 (29.9%) | 326 (29.6%) | 372 (30.2%) | |
| Non-ambulatory | 1155 (49.5%) | 532 (48.3%) | 623 (50.6%) | .27 |
| Home living | 2192 (93.8%) | 1048 (94.9%) | 1144 (92.9%) | .05 |
| Primary Medicare | 1386 (63.4%) | 693 (66.1%) | 693 (61%) | .004 |
| Primary Medicaid | 122 (5.6%) | 55 (5.2%) | 67 (5.9%) | |
| Primary Commercial | 594 (27.2%) | 265 (25.3%) | 329 (29%) | |
| Medical History | ||||
| Hypertension | 2163 (92.9%) | 1012 (92.1%) | 1151 (93.6%) | .16 |
| Diabetes | 1365 (58.4%) | 627 (56.8%) | 738 (59.9%) | .13 |
| Chronic renal insufficiency | 678 (32.4%) | 317 (31.6%) | 361 (33.1%) | .49 |
| COPD | 684 (29.3%) | 330 (29.9%) | 354 (28.8%) | .56 |
| CAD | 918 (39.3%) | 433 (39.3%) | 485 (39.4%) | .96 |
| CHF | 698 (29.9%) | 358 (32.4%) | 340 (27.6%) | .01 |
| CABG/PCI | 1040 (47.6%) | 502 (47.8%) | 538 (47.3%) | .82 |
| Previous Inflow PVI | 473 (20.3%) | 224 (20.3%) | 249 (20.2%) | .96 |
| Previous Inflow Bypass | 213 (9.1%) | 103 (9.3%) | 110 (8.9%) | .74 |
| Previous Leg PVI | 990 (42.5%) | 506 (45.9%) | 484 (39.4%) | .002 |
| Previous Leg Bypass | 805 (34.5%) | 437 (39.6%) | 368 (29.9%) | <.001 |
| Preoperative Anticoagulant | 597 (27.3%) | 528 (50.3%) | 69 (6.1%) | <.001 |
Abbreviations: BMI – body mass index; CAD – coronary artery disease; CABG – coronary artery bypass graft; CHF – congestive heart failure; COPD – chronic obstructive pulmonary disease; PVI – peripheral vascular intervention
Operative Details and Perioperative Complications
The primary indication was tissue loss which accounted for 74.3% of cases. The bypass target was infrapopliteal in 72.5% of cases and concomitant femoral endarterectomy was performed in 31.2% of cases. In 80.1% of cases, 45.6% of cases, and 47.3% of cases, patients were discharge on aspirin, P2Y12 inhibitor, and anticoagulation, respectively. Patients discharged with postoperative anticoagulation, compared to those without more often were treated for rest pain (28.1% vs. 23.5%), had an infrapopliteal bypass target (78.4% vs. 67.2%), and less often underwent concomitant femoral endarterectomy (27.8% vs. 34.2%) (all P<.05) (Table II). Overall, thirty-day mortality was 2.2%. In 17.1% of cases, patients returned to the operating room during their index admission. In 9.1% of cases, 5.3% of cases, 3.1% of cases, and 2.9% of cases, patients had cardiac complications, worsening renal function, wound complications, and pulmonary complications, respectively. Bleeding complications requiring return to the operating room occurred in 1.5% of cases.
Table II –
Procedural Details and Perioperative Outcomes
| Characteristic | Overall (N=2336) | Post-Op Anticoagulation (N=1104) | No Post-Op Anticoagulation (N=1232) | P-value |
|---|---|---|---|---|
| Procedure | ||||
| Rest pain - indication | 600 (25.7%) | 310 (28.1%) | 290 (23.5%) | .012 |
| Tissue loss - indication | 1736 (74.3%) | 794 (71.9%) | 942 (76.5%) | |
| Infrapopliteal target | 1692 (72.5%) | 865 (78.4%) | 827 (67.2%) | <.001 |
| Concomitant bypass | 51 (2.2%) | 21 (1.9%) | 30 (2.5%) | .37 |
| Concomitant PVI | 196 (8.4%) | 95 (8.6%) | 101 (8.2%) | .73 |
| Concomitant endarterectomy | 728 (31.2%) | 307 (27.8%) | 421 (34.2%) | .001 |
| EBL (mL) | 281.3+/−340.9 | 290.0+/−367.4 | 273.6+/−315.3 | .25 |
| Operative time (minutes) | 227.1+/−103.8 | 235.1+/−108.4 | 219.9+/−99.1 | <.001 |
| Postoperative Medications | ||||
| Discharge ASA | 1870 (80.1%) | 809 (73.3%) | 1061 (86.1%) | <.001 |
| Discharge P2Y12 inhibitor | 1065 (45.6%) | 329 (29.9%) | 736 (59.7%) | <.001 |
| Discharge Statin | 1928 (82.9%) | 922 (84%) | 1006 (82%) | .21 |
| Perioperative Outcomes | ||||
| 30 day mortality | 51 (2.2%) | 6 (.5%) | 45 (3.7%) | <.001 |
| Return to OR | 400 (17.1%) | 191 (17.3%) | 209 (17%) | .81 |
| Cardiac complications | 213 (9.1%) | 88 (8%) | 125 (10.2%) | .07 |
| Stroke | 9 (.4%) | 3 (.3%) | 6 (.5%) | .4 |
| Pulmonary complications | 68 (2.9%) | 25 (2.3%) | 43 (3.5%) | .08 |
| Change in renal function | 123 (5.3%) | 52 (4.7%) | 71 (5.8%) | .25 |
| Wound complication | 73 (3.1%) | 30 (2.7%) | 43 (3.5%) | .29 |
| Bleeding complication requiring return to OR | 35 (1.5%) | 18 (1.6%) | 17 (1.4%) | .62 |
Abbreviations: EBL – estimated blood loss; mL – milliliters; PVI – peripheral vascular intervention
One-year Outcomes
One-year Outcomes: Primary Patency or Death
For patients treated with postoperative anticoagulation compared to no postoperative anticoagulation after infrainguinal bypass with cryopreserved vein, Kaplan-Meier analysis at one year demonstrated similar freedom from loss of primary patency or death at 28.9% vs. 34.3%, respectively (P=.13) (Figure 1). Multivariable analysis demonstrated that postoperative anticoagulation was not associated with improved one-year primary patency or death (HR .95, 95% CI .83 – 1.09, P=.48) (Figure 2). However, postoperative P2Y12 inhibitor use (HR .78, 95% CI .68 – .9, P=.001) and postoperative aspirin use (HR .79, 95% CI .67 – .93, P=.004) were protective.
Figure 1 –
One-Year Kaplan-Meier Analysis for Freedom from Primary Patency Loss or Death
Figure 2 –
Forest Plot of Multivariable Analysis for One-Year Outcomes
One-year outcomes: Reintervention, Major Amputation, or Death
At one year, Kaplan-Meier analysis showed similar freedom from reintervention, major amputation or death at 50.6% vs. 53.8% between patients on postoperative anticoagulation compared to no anticoagulation, respectively (P=.28) (Figure 3). Multivariable analysis revealed that postoperative anticoagulation was also not associated with improved one-year reintervention, major amputation, or death (HR .93, 95% CI .79 – 1.08, P=.33) (Figure 2). Postoperative P2Y12 inhibitor use (HR .78, 95% .67 – .91, P=.001) and postoperative aspirin use (HR .76, 95% CI .64 – .9, P=.002) were again protective.
Figure 3 –
One-Year Kaplan-Meier Analysis for Freedom from Reintervention, Major Amputation, or Death
One-year Outcomes: Major Amputation or Death
Kaplan-Meier analysis showed similar freedom from major amputation or death at one year in patients treated with postoperative anticoagulation compared to no anticoagulation at 62.3% vs. 63.8%, respectively (P=.68) (Figure 4). In multivariable analysis, postoperative anticoagulation was also not associated with improved one-year major amputation or death (HR .88, 95% CI .74 – 1.05, P=.15) (Figure 2). Similarly, postoperative P2Y12 inhibitor use (HR .75, 95% CI .63 – .9, P=.002) and postoperative aspirin use (HR .74, 95% CI .61 – .91, P=.003) were protective (Figure 2).
Figure 4 –
One-Year Kaplan-Meier Analysis for Freedom from Major Amputation, or Death
One-year outcome: Survival
Survival at one year, by Kaplan-Meier analysis, was higher for patients on postoperative anticoagulation compared to without anticoagulation at 85.1% vs. 81.7%, respectively (P=.03) (Figure 5). Multivariable analysis for one-year death demonstrated that postoperative anticoagulation (HR .59, 95% CI .46 – .74, P<.001), postoperative P2Y12 inhibitor use (HR .61, 95% CI .48 – .77, P<.001), and postoperative aspirin (HR .48, 95% CI .38 – .61, P<.001) were protective (Figure 2).
Figure 5 –
One-Year Kaplan-Meier Analysis for Survival
Other Patient Factors Associated with Outcomes
In multivariable analysis, several other covariates were associated with worse outcomes at one year (Supplemental Table I). Tissue loss was associated with higher primary patency loss or death, major amputation or death, and death. An infrapopliteal target was associated with higher primary patency loss or death, reintervention, major amputation or death, major amputation or death, and death. CHF and age were also associated with those outcomes. Concomitant endarterectomy was noted to be protective against primary patency loss or death.
In a separate multivariable analysis of patients who were not on preoperative anticoagulation, similar patterns for anticoagulation and antiplatelet use were seen for one-year freedom from loss of primary patency or death, reintervention, major amputation or death, major amputation or death, and survival (Supplemental Figure 1). Patients with chronic renal insufficiency (estimated glomerular filtration rate <60 mL/min/1.73m2) were more likely to die at 1 year (HR 1.44, 95% CI 1.06 – 1.96, P=.02).
Discussion:
Our analysis demonstrated that anticoagulation did not improve limb outcomes in patients treated with infrainguinal bypass using cryopreserved vein, but those on anticoagulation had higher survival. Antiplatelet agents, including aspirin and P2Y12 inhibitors, were associated with fewer reinterventions, improved patency, limb salvage, and survival. Although patency at one year was low across the cohort, limb salvage rates were consistent with the literature in this high-risk population, but this at-risk population remains with a high rate of return to the OR, cardiac complications, and renal complications. Based on these findings, surgeons may consider choosing antiplatelet therapy instead of anticoagulation to preserve bypass patency for patients who undergo revascularization with a cryopreserved graft.
The effect of anticoagulation and other factors on cryopreserved bypasses in the literature has been quite variable.11–16 A single center retrospective analysis of 81 cryopreserved bypasses showed one year outcomes of primary patency at 27%, amputation-free survival at 43%, and survival at 84%. Postoperative warfarin use was associated with improved limb salvage.11 Another single center analysis of 240 cryopreserved infrainguinal bypasses demonstrated a primary patency rate was 30% at 12 months. This analysis did not find any association with warfarin or antiplatelet therapy with graft patency.12 Other factors discussed, but cannot be assessed in this current study’s dataset, that can influence cryopreserved vein outcomes are warm ischemia time of the vein and donor-to-recipient ABO compatibility. In one single study, shorter warm ischemia time demonstrated improved primary patency.13 However, ABO donor compatibility was not associated with loss of primary patency. Analyses of ABO donor compatibility in other studies have had variable results.14–16
Anticoagulation and antiplatelet agents have also been examined for bypasses with other conduits for infrainguinal bypass in the VQI. An analysis of 7,612 bypass grafts looked at one-year outcomes where 28.6% of patients were discharged on postoperative anticoagulation. Patients that were anticoagulated more often had infrapopliteal bypass targets and non-single-segment vein conduits, and were more likely to have a previous ipsilateral bypass or stent. There was no significant association of anticoagulation on primary patency in the overall cohort.17 Another VQI analysis examine antiplatelet agents on outcomes after 13,020 infrainguinal lower extremity bypasses. There were 52.2% discharged on aspirin alone and 47.8% on dual antiplatelet therapy. The proportion of patients discharged on dual antiplatelet therapy increased from 10.6% to 60.6% from 2003 to 2018. These patients were younger, had more medical comorbidities, more distal targets, prior operations, and prosthetic conduit. Risk adjusted analysis did not show any difference between the dual antiplatelet therapy and aspirin for primary patency.18
Unlike other studies in the literature, our study is a multicenter, contemporary analysis of a large number of infrainguinal bypasses performed with cryopreserved vein that provides evidence that antiplatelet therapy should be performed postoperatively and not anticoagulation therapy. This counters the paradigm of anticoagulation therapy after high-risk bypass such as those with cryopreserved vein that have been based on small, single-center studies. Our study’s findings are further augmented by the results of the Vascular Outcomes Study of Acetylsalicylic Acid Along With Rivaroxaban in Endovascular or Surgical Limb Revascularization for Peripheral Artery Disease (VOYAGER) trial. In the VOYAGER’s composite primary endpoint of acute limb ischemia, major amputation, myocardial infarction, ischemic stroke, or death low-dose rivaroxaban and aspirin had a significantly lower incidence of this composite outcome compared to aspirin alone.19 However, there was no significant association with major amputation between low-dose rivaroxaban with aspirin and aspirin alone in the VOYAGER trial. This further supports our data that antiplatelet therapy alone is adequate. Furthermore, it is unknown in VOYAGER whether there is an association between low-dose rivaroxaban and aspirin and bypass conduit, and no bypass patency data is available. Thus, one area for future work is investigating the association of type and dosage anticoagulation with cryopreserved vein bypass patency, limb salvage, death, and risk of bleeding. Another area for future work includes wound healing after cryopreserved vein bypass as the current VQI dataset does not allow for direct interrogation of whether a wound was healed other than if an amputation was performed.
This study has multiple limitations. It is a retrospective review of prospectively collected data that includes selection bias. One example of this study limitation is that our results demonstrated that patients who underwent concomitant femoral endarterectomy was protective against primary patency loss or death. It is difficult to ascertain whether performing a concomitant femoral endarterectomy is related to selection bias or if common femoral artery disease is undertreated in this study population. The VQI database does not include atrial fibrillation as a comorbidity, however we attempted to control for it by performing a separate analysis that excluded patients with preoperative anticoagulation. The dosage, duration, and long-term adherence of medication is unknown as well as reasons for medication discontinuation (ie: bleeding). The specific P2Y12 inhibitor and anticoagulation dosing and duration was not analyzed as it was not available in the dataset. Follow-up for the analyzed outcomes loses accuracy after one year. Given that the rate of patency loss was high at 1 year, we believe that it is sufficient for analysis as cryopreserved vein bypasses are not expected to stay patent long-term and are often used to represent short-term solutions to heal wounds. We are unable to assess other possible contributing factors such as warm ischemia time, and ABO incompatibility or immunosuppression.
Conclusions:
Postoperative anticoagulation following infrainguinal bypass with cryopreserved vein graft did not affect patency or limb salvage. Antiplatelet agents are associated with improved outcomes. Anticoagulation was not associated with improved limb outcomes, but had higher survival. Overall patency and limb salvage rates at one year were poor. When cryopreserved vein is used, surgeons should consider antiplatelet therapy for cryopreserved graft patency and anticoagulation should not be utilized.
Supplementary Material
ARTICLE HIGHLIGHTS.
Type of Research:
Retrospective review of prospectively collected data of the Vascular Quality Initiative (VQI) database
Key Findings:
In 2336 patients undergoing infrainguinal bypass with cryopreserved vein for chronic limb threatening ischemia, multivariable analysis at one-year demonstrated that postoperative anticoagulation had a similar likelihood for loss of primary patency/death, major amputation/death, and reintervention/major amputation/death whereas postoperative aspirin and P2Y12 inhibitor use were protective.
Take home Message:
Postoperative anticoagulation following infrainguinal bypass using cryopreserved vein did not affect patency or limb salvage. Antiplatelet agents were associated with improved outcomes.
Funding:
There were no sponsors for this work.
Footnotes
Presented as a plenary oral podium presentation at the New England Society for Vascular Surgery, Portland, ME, October 27, 2024
Conflict of interest: Dr. Alik Farber – Sanifit consultant and Principal Investigator for Best-CLI trial. Dr. Jeffery Siracuse – Education grant WL Gore and BD paid to Boston University. No other competing interests for other authors.
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