Automated ankle brachial pressure index measurement devices to detect peripheral arterial disease in people with leg ulcers

Leg ulcers can be painful and ABPI assessment can be uncomfortable

3.1 A patient expert explained that leg ulcers are unpleasant and painful. There is anxiety and shame about their appearance which can lead to depression. Manual assessment for ABPI can cause pain and discomfort. People with leg ulcers often have mobility issues making it difficult to travel to appointments, particularly if they are in a specialist setting. They noted a potential benefit of the automated devices is a shorter ABPI assessment, which may reduce discomfort for the person being assessed. They also noted that automated devices may increase ease of carrying out the assessment in a home setting if they can be used more widely in primary and community care by staff less experienced in assessing peripheral arterial disease. This would improve access to the assessment for those less able to travel.

Waiting times for ABPI assessment can be long, which may delay appropriate treatment

3.2 The patient expert explained that it can take a long time between referral and ABPI assessment for peripheral arterial disease, which can cause anxiety, and that waiting times vary geographically. Clinical experts agreed that access to ABPI assessment varies across the UK, with people waiting between 2 weeks and 12 weeks for an appointment. The committee heard that the National Wound Care Strategy Programme (NWSCP) recommendations for lower limb ulcers recommends application of mild compression while waiting for the full clinical assessment (including ABPI assessment) if peripheral arterial disease is not initially suspected. However, a clinical expert noted that this often does not happen in practice and that only about 25% of people with leg ulcers have mild compression before full clinical assessment. The NWCSP preventing and improving care of chronic lower limb wounds: implementation case reports that most people with leg ulcers have venous leg ulcers (about 65%). So, delays in ABPI assessment can delay starting treatment. The committee heard that one of the claimed benefits of the automated devices is improved access to ABPI assessment. This could lead to quicker treatment and healing of the leg ulcer for people without peripheral arterial disease. Clinical experts noted that the devices may be of more benefit in areas with limited availability of healthcare professionals able to do manual Doppler assessment.

The committee concluded that if evidence shows the automated devices lead to earlier access to treatment, then this could improve healing time and would be of substantial benefit.

How the automated devices fit into the care pathway is unclear

3.3 The committee discussed how the automated devices might be used in different settings or by staff with less expertise in ABPI measurement, including in primary care and the community. Clinical experts advised that if the devices could be safely used by staff with less expertise then this could improve time to assessment and therefore treatment and healing. It was noted that care pathways are evolving and that in some parts of the country tissue viability-, dermatology- or vascular service-led leg ulcer clinics are in use or are being implemented. These may increasingly do initial ABPI assessment. Clinical experts questioned whether treatment for venous leg ulcers could still be started alongside ABPI assessment if the automated devices were used in settings or by people with less expertise in ABPI measurement. The clinical experts highlighted that some treatments such as compression stockings needed less expertise but that others such as bandaging may still require a specialist to apply. Therefore, in these cases there may be no improvement in time to treatment even if the ABPI measurement could be done earlier.

Most of the studies on use of the automated devices were done in specialist settings. Clinical experts advised that this could impact the generalisability of the results to other less specialist settings. The committee noted that 1 of the studies identified by the external assessment group (EAG), Green et al. 2020, was done in GP surgeries. The study reported that GPs thought that using the automated device improved clinical management of leg ulcers. However, it also reported that the GPs had concerns about whether they had time available and whether it was within their remit to assess wounds.

The committee concluded that it is unclear where in the care pathway it is best to use the devices. It agreed that automated devices could have substantial benefits for people with leg ulcers. This is if they could be safely used in a wider range of settings or by a greater number of healthcare professionals and if they lead to earlier access to treatment.

The diagnostic accuracy evidence available for automated ABPI devices is not generalisable to people with leg ulcers

3.4 The committee noted that only 2 observational studies from the 24 identified were in people with leg ulcers (1 excluded marked oedema) and these did not report diagnostic accuracy data (sensitivity or specificity). The EAG extracted diagnostic accuracy data from 22 studies in people without leg ulcers, 6 of which reported results for people with diabetes. Clinical experts were concerned about the generalisability of these studies to the leg ulcer population because taking measurements in people with leg ulcers may be more difficult, particularly when they have oedema or swollen limbs. People with leg ulcers are more likely to have these complications and clinical experts advised that from their experience technical failure (failure of the device to produce a result) is more likely in people with oedema. They also commented that in their experience, technical failure is more likely in people with peripheral arterial disease and this was seen in some of the studies. The committee noted that prevalence of peripheral arterial disease in the studies varied widely.

Because of this, it is likely that the accuracy data in the available studies is not applicable to people with leg ulcers. There was also limited evidence of use of the devices in people with diabetes or other conditions associated with an increased risk of leg ulcers. These conditions can cause hardening of the arteries which can make the ABPI result appear misleadingly normal. Consequently, there is considerable uncertainty about the accuracy of the test in these populations.

The committee concluded that the diagnostic accuracy data on the automated devices could not be generalised to a leg ulcer population, so there is considerable uncertainty about the diagnostic accuracy of the devices in this population.

Automated devices may increase risk of inappropriate treatment in people with peripheral arterial disease

3.5 The committee discussed the accuracy of the automated devices. It commented that data suggested automated devices generally had good specificity but only moderate sensitivity for detecting peripheral arterial disease. The EAG report suggested that the automated devices tend to overestimate ABPI which could lead to cases of peripheral arterial disease being missed. This could mean some people have inappropriate compression, causing harm. It noted, however, that some of the differences seen between the results from the automated devices and from manual Doppler may not have been clinically significant.

Clinical experts further noted that NWCSP guidance states that ABPI assessment should be done by someone with expertise to recognise symptoms of and red flags for peripheral arterial disease. There was concern that these red flags could be missed if automated devices were used in settings or by staff with less expertise in assessing peripheral arterial disease. This, combined with the suggested lower sensitivity of the automated devices, could cause cases of peripheral arterial disease to be missed, leading to inappropriate treatment and harm for people with arterial leg ulcers. Clinical experts also highlighted that ABPI results may be unreliable in people with certain comorbidities, such as diabetes. It is important that other outputs such as Doppler waveform are used to validate the ABPI result in these cases. The EAG confirmed that accuracy data reported in the studies was based on ABPI result alone and that no studies reporting on the use of other outputs of the devices or the impact of test results on clinical decision making were identified. Therefore, no conclusions could be drawn on the impact of use of the devices on clinical decision making but there was concern that cases of peripheral arterial disease would be missed because of an inaccurate result. The committee concluded that future studies should look at how the test result is used to direct treatment so that the impact of false results on clinical decisions can be fully understood.

Impact of the automated devices on health outcomes is uncertain

3.6 The committee heard that no evidence looking at the impact of inaccurate test results on clinical outcomes was found. Therefore, the impact of inaccurate test results on health outcomes is uncertain. Clinical experts discussed that inappropriate compression treatment of leg ulcers in people with peripheral arterial disease could risk harm. They also noted that misdiagnosing people with peripheral arterial disease could cause unnecessary delays to the treatment of venous leg ulcers.

The committee concluded that the impact of misdiagnosis is uncertain but that consequences could be more severe for people with peripheral arterial disease. However, people with peripheral arterial disease would represent a smaller proportion of the population with leg ulcers (see section 3.2). The committee noted that it would be helpful to have further information on how incorrect results impact health outcomes, to inform decision making in the future.

Impact of the automated devices on time to treatment is uncertain

3.7 The committee discussed whether the use of automated devices in alternative settings or by staff with less specialist expertise could improve access to ABPI assessment and therefore reduce time to treatment and improve ulcer healing for some people (see section 3.2). It heard that there were no studies looking at the effect of automated devices on time to assessment or time to treatment. One study in people with leg ulcers reported that GPs felt that using the MESI ABPI MD automated device improved clinical management (Green et al. 2020). However, other studies were done in specialist settings.

Clinical experts advised that the impact of the devices on time to treatment would depend on the setting and availability of expertise and that this varies widely across the country. They also noted it would depend on whether there was enough expertise in these settings to start treatment of leg ulcers in people without peripheral arterial disease more quickly (see section 3.3).

The committee concluded that the devices may improve access to ABPI assessment and may therefore improve time to ulcer treatment and healing. However, no evidence was identified.

The impact of automated devices on the time taken for ABPI assessment is uncertain

3.8 The committee discussed how long the ABPI assessment takes and noted that evidence suggests automated devices can reduce the duration of the assessment. Patient experts explained that this may make assessments more comfortable for people with leg ulcers and could increase access to ABPI assessment by increasing the number of people who can be assessed. The committee heard that studies reported that most people with leg ulcers found the automated devices acceptable, but some felt discomfort when the cuff was fully inflated. It also heard that time taken for assessments was not consistently reported across studies and generally assessments with automated devices were only a few minutes faster than manual assessments. Clinical experts questioned whether the amount of time saved was enough to have a meaningful impact. They also noted that technical failure of the automated devices could mean manual Doppler would then need to be done, increasing the length of the overall assessment. This could occur more often in people with peripheral arterial disease, oedema, diabetes or other conditions that cause calciphylaxis in tissues (see section 3.4).

The committee concluded that evidence suggests automated devices reduce the time taken for ABPI assessment but that the amount of time saved and the impact of this are uncertain.

Automated devices are unlikely to be cost effective unless they reduce time to treatment

3.9 The committee noted that the economic model results suggested that the automated devices were unlikely to be cost effective unless improved access to ABPI assessment and therefore treatment could be shown (see section 3.3). No evidence was identified to suggest that automated devices may speed up access to treatment (see section 3.7).

The committee concluded that there is potential for the devices to be cost effective. However, there is currently not enough evidence on whether they improve time to treatment or ulcer healing.

Economic model results are very uncertain

3.10 The committee noted that there were substantial uncertainties in the economic model because of a lack of data to inform key model inputs. The model results appeared highly sensitive to improvements in ulcer healing time for venous ulcers (because of quicker access to treatment, see section 3.9). The impact of inaccurate test results on clinical decision making and clinical outcomes was highly uncertain because no evidence was identified to inform these inputs in the model (see section 3.6). Clinical expert opinion was used to inform these inputs in the model.

The committee further noted that diagnostic accuracy estimates in the model were based on single studies for each of the devices and these studies were done in people without leg ulcers (see section 3.4). The EAG advised that it pooled data on the devices where possible but that it did not consider the results to be robust because of the differences between studies. Only 2 of the devices had enough studies to allow for pooling of data. Pooling the studies reduced the sensitivity of both devices (MESI ABPI MD and WatchBP Office ABI). It therefore opted to use single estimates in the model.

The committee concluded that evidence on the impact of the automated devices on clinical decision making or clinical outcomes would improve the robustness of the economic model results.

Consideration of the most appropriate care pathway is needed

3.11 The committee considered that a key benefit of the automated devices could be improvements in time to treatment and healing of venous ulcers (see section 3.2). However, this could depend on how and where the devices were used in the care pathway and the availability of expertise. Clinical experts questioned whether staff with less expertise would be able to start some of the treatments such as compression bandaging for people identified as having venous leg ulcers (see section 3.3). They also raised concerns about whether less-experienced healthcare professionals would be able to perform a holistic assessment of the ulcer and recognise red flags for peripheral arterial disease (see section 3.5). The committee concluded that consideration of the most appropriate place for the automated devices in the care pathway was needed and that studies should be done in these settings.

Consideration of alternative thresholds may be helpful

3.12 The committee acknowledged that the EAG's report extracted data from some studies that looked at the optimal threshold for the automated devices. These studies reported that using an ABPI threshold higher than the commonly used value of 0.9 could improve sensitivity and therefore reduce the risk of missing peripheral arterial disease. The committee noted that it is possible that an alternative threshold may help prevent inappropriate treatment and associated consequences in some cases (see section 3.5). However, clinical experts advised that higher thresholds are not currently used in practice and would therefore need validating in independent studies in people with leg ulcers.