Advice

Evidence review

Evidence review

Clinical and technical evidence

Regulatory bodies

A search of the Medicines and Healthcare Products Regulatory Agency (MHRA) website revealed no manufacturer Field Safety Notices or Medical Device Alerts for this equipment.No reports of adverse events were identified from searches of the US Food and Drug Administration (FDA) database: Manufacturer and User Device Facility Experience (MAUDE).

Clinical evidence

Forty‑eight studies of potential relevance to the Spiral Flow PV graft were identified, of which 41 were excluded from further assessment because they did not meet the inclusion criteria. A further 2 studies were excluded because they covered the same patients as a more recent publication. The remaining 5 studies are summarised in this briefing. The 5 remaining studies, 2 fully published (Stonebridge et al. 2012; Bechara 2014) and 3 available only as abstracts (Shaper 2014; Marusiak et al. 2014; Çetingök 2011) are summarised in this briefing (tables 1–5).

Study outcome definitions and results

Several of the studies describe outcomes in terms of patency. Patency describes whether a graft remains open and functional over time. Primary patency refers to grafts or vessels that remain patent over time, or that have limited restenosis that has not needed further intervention. Primary assisted patency refers to grafts or vessels that remain patent over time, but which have needed some further intervention to maintain patency. Secondary patency describes grafts or vessels that are currently patent, including those which have previously occluded and have had an intervention to restore patency.

The study by Bechara (2014) compared the primary and secondary patency rates of the Spiral Flow PV graft, to those of a non‑spiral flow inducing Propaten graft (WL Gore) that has a thromboresistant surface. This retrospective study compared the primary and secondary patency rates in 20 Spiral Flow PV grafts and 39 Propaten grafts. The full results are presented in table 1. The authors concluded that the concept of mimicking natural flow was interesting but did not translate into a clinical benefit for the Spiral Flow PV graft because primary and secondary patency rates were either similar or worse in the Spiral Flow PV graft. No statistical analysis was included in this study.

The study by Stonebridge et al. (2012) was a prospective, multicentre, non‑consecutive, non‑comparative study to assess the safety and medium‑term patency performance of the Spiral Flow PV graft. The results showed primary patency rates of 81% (above the knee) and 57% (below the knee) and secondary patency rates of 81% and 64% (above and below the knee respectively) at both 24 months and 30 months follow‑up, and also showed that the Spiral Flow PV grafts can remain patent for 30 months (table 2). There were no amputations in the 30‑month study period.

The case series reported by Cetingok (2011) was only available as an abstract and is presented in table 3. In total, 73 Spiral Flow PV grafts were implanted in 47 people from June 2009 to August 2011. The primary and secondary patency rates at 14‑month follow‑up were 93% and 98% respectively. This study did not have a comparator group. The authors reported 1 death that was unrelated to the graft, and that 5 grafts became thrombosed. These were successfully thrombolysed to restore graft patency. There is no information on the cause of occlusions in this study.

The case series presented by Marusiak et al. (2014) was also only available as an abstract and did not have a comparator group. In this study, 75 devices were implanted in 72 people with an observed primary patency rate of 85% and a secondary patency rate of 96% (table 4). The authors attributed the deaths of 2 of the study participants to critical limb ischaemia in people presenting with serious comorbidities. The authors also reported some adverse events, namely occlusion of 11 grafts. Patency was successfully restored in 8 out of 11 of the occluded grafts through thrombolysis, transluminal angioplasty or open surgical intervention. The cause of the occlusions was not given.

Shaper (2014) carried out a single‑centre prospective study with a retrospective control group, and this study was also only available as an abstract. The authors carried out a comparison of 54 Spiral Flow PV grafts and 124 conventional polytetrafluoroethylene (PTFE) grafts at 1‑year follow‑up. The manufacturer of the PTFE graft was not stated by the authors. The overall primary and secondary patency rates for the conventional graft were 48% and 55% respectively, and the primary and secondary patency rates were 76% and 87% for the Spiral Flow PV graft. No statistical analysis has been reported. Adverse events were reported for the conventional PTFE graft and the Spiral Flow PV graft. The amputation rate for the conventional PTFE graft was 10%, and it was 2% for the Spiral Flow PV graft. Full results are presented in table 5.

Table 1 Summary of the Bechara (2014) retrospective comparative study

Study component

Description

Objectives/hypotheses

The primary and secondary patency rates of the Spiral Flow peripheral vascular graft were compared with the Propaten graft.

Study design

Retrospective, single centre, comparative study.

Intervention

Spiral Flow graft (SFG) manufactured by Vascular Flow Technologies.

Comparator: Propaten graft (PG) manufactured by WL Gore.

Setting

A hospital in the USA. Patients treated between January 2010 and January 2012.

Inclusion/exclusion criteria

Not stated.

Primary outcomes

Primary and secondary patency rates.

Methods

Data were retrospectively reviewed for patients having below‑the‑groin (infrainguinal) bypass using prosthetic grafts. Kaplan–Meier analyses were done to estimate primary and secondary patency rates. Short‑term and mid‑term data between these 2 grafts was examined.

Participants

59 adults.

20 people were treated with the SFG and 39 using a PG. The number of grafts used is not reported.

14/20 Spiral Flow grafts (70%) were femoral to popliteal artery bypass (above and below the knee), and 6/20 cases (30%) were femoral to tibial artery bypass. Similar percentages were seen in the Propaten graft group.

Results

The author states that statistically, the 6-, 12-, 18-, and 24‑month primary and secondary patency rates for both grafts were the same, regardless of the distal target artery. However there is no statistical analysis to support this and results for the PGs were better in most groups. For the popliteal artery (above and below knee) target group the primary patency rates were as follows:

  • at 6 months: PG=94%; SFG=79%

  • at 12 months: PG=61%; SFG=50%

  • at 18 months: PG=61%; SFG=50%

  • at 24 months: PG=54%; SFG=50%.

For the popliteal artery (above and below knee) target group the secondary patency rates were:

  • at 6 months: PG=94%; SFG=86%

  • at 12 months: PG=66%; SFG=57%

  • at 18 months: PG=66%; SFG=57%

  • at 24 months: PG=66%; SFG= 57%.

For the tibial artery bypass groups the primary patency rates were:

  • at 6 months: PG=51%; SFG=50%

  • at 12 months: PG=36%; SFG=33%

  • at 18 months: PG=37%; SFG=17%.

For the tibial artery bypass groups the secondary patency rates were:

  • at 6 months: PG=54%; SFG=60%

  • at 12 months: PG=34%; SFG=40%

  • at 18 months: PG=34%; SFG=20%.

Adverse events

None reported.

Conclusions

The authors concluded that the design of the Spiral Flow PV graft to mimic physiologic flow at the distal anastomosis is an interesting concept but has not translated into clinical benefit compared with another ePTFE graft. There should be different graft configurations for tibial targets and popliteal artery targets.

Abbreviations: ePTFE, expanded polytetrafluoroethylene; PG, Propaten graft; SFG, Spiral Flow graft.

Table 2 Summary of the Stonebridge et al. (2012) case series

Study component

Description

Objectives/hypotheses

To assess safety and medium‑term patency performance of the Spiral Flow peripheral vascular (PV) graft.

Study design

Prospective, multicentre, non‑consecutive, non‑comparative study.

Intervention

Spiral Flow PV graft.

Setting

10 hospitals in the Netherlands and Belgium. Enrolment took place between February 2006 and November 2007.

Inclusion/exclusion criteria

Inclusion criteria:

  • Aged 40–75 years.

  • Must need above‑the‑knee or below‑the‑knee outflow unilateral infrainguinal bypass graft for PAD of superficial femoral artery.

  • Use of a perioperative/postoperative antiplatelet agent.

  • Must provide written, informed consent.

Exclusion criteria:

  • Known hypersensitivity to graft constituents.

  • Sensitivity, allergy, or contraindication to antithrombotics and antiplatelet medication.

  • Severe comorbid condition.

  • Significantly disordered hepatic function.

  • A recognised form of thrombophilia, a history of deep vein thrombosis, or early pregnancy loss.

  • Presence of a significant medical condition.

  • Vascular operative reconstruction in the same leg.

  • Poorly controlled diabetes mellitus (haemoglobin A1C >7.5%).

Primary outcomes

Primary and secondary patency rates.

Methods

Procedures were done in accordance with local preference, with no special requirement, except securing the distal anastomosis first. No adjuvant surgical technique was used. A completion angiography was done in all cases.

Patients were followed up at 6 weeks and at 3, 6, 9, 12, 18, 24 and 30 months. Follow‑up assessment included clinical assessment and colour Doppler assessment.

10 patients had additional examination at 3 and 6 months to assess whether the graft actually produced and maintained spiral laminar flow.

Kaplan–Meier analyses were used to calculate primary and secondary patency rates.

Participants

39 people with PAD leading to pain at rest or lifestyle‑inhibiting or severe claudication needing an above‑the‑knee or a below‑the‑knee bypass graft. The study was limited to a patient group needing only a unilateral bypass graft to optimise patient survival and add a degree of group homogeneity. The number of grafts used is not reported.

Treated patient demographics:

  • mean age 70.3 (range 38–83) years

  • sex (male:female) 3:1

  • side (right/left) 23/16

  • recorded diabetes (yes/no) 8/31

  • previous vascular surgery 19

  • above‑the‑knee 23/below‑the‑knee 16.

Results

The 12, 18, 24 and 30‑month assessment respective primary patency rates were:

  • 86%, 81%, 81% and 81% for above‑the‑knee bypasses

  • 73%, 73%, 57% and 57% for below‑the‑knee bypasses.

In the case of secondary patency rates, respective numbers at 12, 18, 24 and 30 months were:

  • 86%, 81%, 81% and 81% for above‑the‑knee bypasses

  • 86%, 79%, 64% and 64% for below‑the‑knee bypasses.

Adverse events

2 withdrawals (a graft dehiscence after trauma at 14 days, and a graft infection at 45 days); both cases needed graft excision.

1 death due to cancer.

3 early occlusions in the above‑the‑knee group; all from the same centre (at 49, 51 and 72 days). None of these had either thrombolysis or re‑exploration, so no information is available as to the underlying cause.

2 people in the below‑the‑knee group had thrombolysis on occlusion (247 days and 276 days); the former occluded due to an iliac stenosis and the latter due to a distal outflow artery stenosis, not identified by preoperative angiography.

There were no amputations in the study group.

Conclusions

The graft's performance was equal to, or better than, some of the recently published results for other enhanced grafts.

No amputations were done on people in this study and this suggests a different mode of prosthetic graft failure that may not be predominantly distal anastomotic neointimal hyperplasia.

A bigger spiral flow‑inducing advantage may be possible where blood flow rates are higher. The flow inducer may need to be tailored differently for low flow or more distal environments.

This study shows potential for the idea of spiral flow‑enhanced prosthetic grafts.

Abbreviations: DVT, deep vein thrombosis; PAD, peripheral arterial disease.

Table 3 Summary of Cetingok (2011) case series

Study component

Description

Objectives/hypotheses

Not stated.

Study design

Not stated.

Intervention

Spiral Flow peripheral vascular graft.

Setting

People treated from June 2009 to August 2011, country unknown.

Inclusion/exclusion criteria

Not stated.

Primary outcomes

Not stated.

Methods

47 patients with a mean follow‑up period of 14 months. A total of 73 implantations were carried out (a number of patients had more than one graft):

  • 45% above‑the‑knee bypass

  • 55% below‑the‑knee bypass.

Participants

94% male

6% female

Mean age at operation was 67 (41–89).

77% were stage IIb Fontaine Classification

23% were stage III Fontaine Classification.

Results

At 14 months mean follow‑up:

  • primary patency=93%

  • secondary patency=98%.

Adverse events

5 grafts (7%) thrombosed and were successfully thrombolysed to fully restore patency.

There was 1 patient death unrelated to the graft.

Conclusions

Not stated.

Table 4 Summary of Marusiak et al. (2014) case series

Study component

Description

Objectives/hypotheses

Not stated.

Study design

Retrospective multicentre study carried out between February 2010 and February 2013.

Intervention

Spiral Flow PV graft.

Setting

Not stated.

Inclusion/exclusion criteria

Inclusion – severe claudication, critical limb ischaemia, ulcer or rest pain.

Exclusion – none specified.

Primary outcomes

Not stated.

Methods

72 patients suitable for surgical revascularisation were enrolled:

  • 68% above‑the‑knee femoral to popliteal bypass

  • 32% below‑the‑knee femoral to popliteal bypass.

Median follow‑up was 11 months (2–36 months).

Low molecular weight heparin was given postoperatively for 12 weeks.

Risk factors involved and scored included smoking, diabetes, hypertension and being overweight.

Risk factors for vascular disease and indications for surgery were similarly distributed in above‑knee and below‑knee bypasses.

Patients had duplex sonography at 3 months to verify spiral flow.

Participants

75 devices implanted.

Demographics:

  • 61 male and 11 female

  • Mean age not stated.

Results

Technical success was achieved in 100% of cases.

Primary patency rate: 85%

Secondary patency rate: 96%

Adverse events

11 grafts became occluded; 8 were successfully reopened through thrombolysis, percutaneous transluminal angioplasty or open surgical intervention. There were 3 permanent occlusions.

2 deaths were reported; these were linked to serious comorbidities.

There was no bleeding or infections.

Conclusions

This new concept of vascular graft focuses on the preservation of a spiral outflow from the graft. The existence of spiral flow is well documented in healthy arteries and it may prevent atherosclerotic disease.

Abbreviations: PV, peripheral vascular.

Table 5 Summary of Shaper (2014) case series

Study component

Description

Objectives/hypotheses

Not stated.

Study design

Single‑centre prospective study with retrospective control group.

Intervention

Spiral Flow peripheral vascular (PV) graft.

Comparator: Conventional PTFE grafts.

Setting

Single centre, country unknown.

Inclusion/exclusion criteria

Not stated.

Primary outcomes

Primary and secondary patency rates at 1 year.

Methods

Data available for 68 Spiral Flow PV grafts from February 2011 to October 2014. 136 conventional PTFE grafts from same unit from Jan 2003 to Dec 2008. Retrospective analysis.

Comparison based on 1 year data available on 124 conventional and 54 Spiral Flow PV grafts.

Participants

Number of patients not stated.

Standard grafts: Age 70.3 (45–93) years, 48% male, 55% critical limb ischemia, AK 13%, BK 87% BK/TV/C.

Spiral Flow PV grafts: Age 69.6 (47–92) years, 78% male, 53% critical limb ischemia, AK 48%, BK/TV/C 52%.

Results

Standard grafts:

Overall primary patency was 48%: 50% AK, 48% BK/TV/C

Overall secondary patency was 55%: 71% AK, 53% BK/TV/C.

Spiral Flow PV grafts:

Overall primary patency was 76%: AK 77%, BK/TV/C 61%

Overall secondary patency was 87%: AK 88%, BK/TV/C 79%.

Adverse events

Standard graft amputation rate=10%.

Spiral flow PV graft amputation rate=2%.

Conclusions

The authors' conclusions were that:

  • Benchmarked against conventional grafts, the Spiral Flow PV grafts achieved 30% actuarial improvement in primary and secondary patency.

  • Results up to 3 years, particularly of more complex grafts, would appear to indicate a sustained patency advantage over conventional grafts.

  • Initial results were sufficiently encouraging to warrant continued usage and further long‑term data acquisition.

Abbreviations: AK, above knee; BK, below knee; C, complex; PTFE, polytetrafluoroethylene; TV, tibial vein.

Recent and ongoing studies

The manufacturer has stated that there is an ongoing open enrolment, post market observational registry for the use of the Spiral Flow PV graft in peripheral vascular disease and peripheral bypass. This registry involves more than 20 sites in the UK, Europe and the USA. It aims to enrol 50 patients and to record follow‑up data at up to 12 months. The data from this registry are intended to be published at the end of 2016.

Costs and resource consequences

No published evidence on resource consequences was identified.

The Spiral Flow PV graft can be used as an alternative to standard expanded polytetrafluoroethylene grafts and no additional resources would be used before or during the bypass procedure. The manufacturer states that the Spiral Flow PV graft is currently used in approximately 22 hospital trusts in the UK.

The techniques for using the device are the same as for current methods, and no additional training would be needed.

Strengths and limitations of the evidence

The currently available evidence for the clinical effectiveness of the Spiral Flow PV graft was limited in both quantity and quality, and comprised 1 fully‑published comparative study, 1 fully‑published non‑comparative study and 3 case series available as abstracts for conference presentations. It is unclear whether any of the studies were carried out in the UK, therefore results may not be generalisable to current NHS practice.

All of the included studies involved small numbers of patients, with a maximum of 72 people being treated with the Spiral Flow PV graft in each study. It is unclear whether patients in these studies were enrolled consecutively and this raises concerns about selection and attrition bias. Additionally, the Stonebridge et al. (2012) multicentre study treated 39 patients in 10 sites; this indicates that the number of patients treated at each centre was very low with a risk of significant selection bias. The paper does not report how many patients were lost to follow‑up.

Only 1 paper (Stonebridge et al. 2012) clearly reports the inclusion and exclusion criteria. However, the inclusion age of this study was stated as 40–75 years but the reported age range of people enrolled was 38–83 years. Primary outcomes were not reported by Cetingok (2011) or Marusiak et al. (2014), while Bechara (2014) did not report any adverse events.

Two studies (Bechara 2014; Shaper 2014) reported comparative data. The Bechara study collected all data retrospectively and the study by Shaper (2014) collected prospective data on Spiral Flow PV grafts, but gathered control group data retrospectively. There is a possibility of changes in clinical practice confounding the results because the test and control group were collected at different time points. Additionally there was an imbalance in patient enrolment in the Shaper (2014) study, and the prospective group treated with Spiral Flow PV grafts was small compared with the retrospective control group (54 compared to 124 respectively at 1 year). This, together with the retrospective data collection in both the Shaper and Bechara studies raises the possibility of selection bias.

The Bechara (2014) study, reporting on 20 patients, did not make any distinction between above- and below‑knee popliteal grafts, which have very different results (Vermassen 2010). This makes it difficult to draw meaningful conclusions from the data.

Three of the included studies (Cetinkgok 2011, Marusiak et al. 2014, and Shaper 2014) were not reported in full, and are available only as abstracts that have not been peer reviewed. The lack of available detail on these studies means that these results should be treated with caution.

Dr Shaper is a consultant to Vascular Flow Technologies, the manufacturer of the Spiral Flow PV graft and this could be a source of potential bias. Similarly, 3 of the authors of the Stonebridge et al. (2012) study are founder members of TFT, a company developed to commercialise spiral flow applications in vascular devices.