Response to the letter regarding: Description of Doppler waveforms to detect lower extremity peripheral artery disease

The current published evidence and clinical literature on continuous-wave Doppler (CWD), as stated by Mahé et al. in their letter, includes a variety of classification terminology used nationally and internationally by various vascular clinicians and researchers. The most commonly used terms of ‘triphasic, biphasic and monophasic’ waveforms ¹ help characterise the presence and severity of peripheral arterial disease, usually when used along with other non-invasive tests, such as pulse palpation and ankle/toe pressure assessment. This CWD terminology helps characterise normal and abnormal waveforms on a disease spectrum, and these are currently the most widely used terms internationally, in both research and clinical practice settings.

This terminology has since been further redefined by some vascular clinicians and authors, using just two descriptions of CWD – multiphasic (normal) and monophasic (abnormal). These redefined terms to characterise Doppler waveforms have been accepted and used previously in peer-reviewed journals and publications^2,3 other than the study by Tehan et al. The use of such published CWD terms by Tehan et al. in their study therefore appears reasonable. The colour Doppler ultrasound (CDU) and CWD waveforms were collected by qualified ultrasonographers, and inter-tested reliability methods were also described. Their method and interpretation is described clearly, and the use of the terms is discussed in their study, including the limitations they found in relation to identification of less severe disease. While it would have been useful to see some visual representations of the types of waveform classified as multiphasic and monophasic, these have been described previously, ³ and the lack of visual examples in this study does not appear to render the study and findings invalid, as suggested by Mahé et al.

The letter by Mahé et al. ⁴ must also be viewed in the context of their recent proposed classification for CWD. The data collection and interpretation in Tehan et al.’s publication was completed in 2016–2017, before Mahé et al. ⁴ published in 2017. While Mahé et al.’s proposal for a 10-type (Saint-Bonnet) classification of CWD signals is interesting and provides a more detailed description to account for the possible spectrum of disease indicated by CWD, it may also have limitations. It has not yet been agreed or adopted internationally and may be of limited use to front line vascular clinicians due to its more complex classification types; particularly, when considering similar limitations, Mahé et al. ⁴ have highlighted concerning the existing 2–3 type CWD classification systems.

In summary, we would suggest that the study by Tehan et al. provides useful research findings, clinical observations and new insights in a relatively poorly evidenced but long established area of non-invasive diagnostic testing for peripheral arterial disease (PAD). In the context of the current wide use of CWD in clinical practice, this study provides further validation and support, as well as caution on the use of this modality to help diagnose and manage PAD, in both the non-diabetes and diabetes populations presenting to lower limb clinicians, worldwide. It adds value to the existing fairly scant body of evidence in this area. The Saint-Bonnet classification proposal ⁴ does, however, look promising. An independent comparative review of all three of the current CWD classifications would be a welcome next step in helping further consolidate terminology and determine further the value of CWD in PAD research, diagnosis and management.