Pulse Wave Velocity Imaging in the Assessment of PAD

Peripheral artery disease (PAD) is the narrowing of arteries in the extremities, resulting in insufficient blood supply to tissue in the extremities. In its mildest form, PAD may be asymptomatic, or may show mild symptoms such as intermittent claudication (IC), a pain one may experience while walking. [Hirsch et al, 2006; Criqui et al, 1992; Beckman, 2002] At its extreme, PAD may lead to critical limb ischaemia (CLI), necrosis, gangrene, amputation, or even death. [Hirsch et al, 2006; Hirsch et al, 2001; Criqui et al, 1992] PAD affects over 20% of all patients aged 70 and above, or aged 50 to 69 with a history of smoking or diabetes. [Hirsch et al, 2001; Beckman et al, 2006] In primary care, the ankle-brachial index (ABI) has been used as a screening tool for PAD. [Aboyans et al., 2012] The ABI consists of the ratio of systolic blood pressures measured at the ankle to that of the brachial artery. An ABI of 0.9 - 1.1 is considered normal, and ABI ≤ 0.9 is considered abnormal. [Aboyans et al., 2012; Hirsch et al., 2001] By way of the ABI, a primary care practitioner may be able to diagnose PAD with a high degree of specificity (up to 99%), but sensitivity can vary greatly (15-79%). [Xu et al, 2010] More recently, the use of the brachial-ankle pulse wave velocity (baPWV) has been used as another diagnostic tool with regards to coronary artery disease (CAD). [Katakami et al., 2014; Chae et al., 2013; Yamashina et al., 2002] Sugawara et al. have shown that the variability in the baPWV is due 58% to aortic pulse wave velocity (PWV), and 23% to leg PWV. [Sugawara et al., 2005] Although aortic stiffness is a larger component of the baPWV, numerous studies have shown that there is a correlation between baPWV and PAD. [Yokoyama et al., 2003; Amoh-Tonto et al., 2009; Xu et al., 2008] Additionally, it has been shown that baPWV can increase after percutaneous transluminal angioplasty in the lower extremities. [Yokoyama et al., 2003] In context with CLI, although methods of diagnosis have improved over the past decades, amputation rates have seen an increase. [Beckman, 2007] Revascularization surgery has been shown to increase ambulatory function and quality of life in those affected by CLI as compared to those who had undergone amputation. [Brosi et al., 2007; Deneuville \& Perrouillet, 2006; Oresanya et al, 2015] This, and the cut-off ABI value <0.95 set by Motobe et al. in 2005 for the accuracy of baPWV measurements, requires further investigation into leg PWV for a better understanding of PAD and CLI and the effects revascularization surgery has. [Wohlfart et al., 2013] The investigators believe that the ability to determine the success of revascularization surgery at the time of surgery would guide vascular surgeons in the intra-operative treatment and monitoring of these patients. The current standard of care is Doppler of the dorsalis pedis or posterior tibial artery post-operatively and at the bedside. This is not always an accurate determinate of the success of a revascularized limb and subsequently patients require either Duplex ultrasound, computed tomography angiography (CTA) or angiography. The results from these more sophisticated investigations provide accurate information about blood flow and its characteristics. Our group has designed a device called Pulse Wave Velocity imaging (PWVI). This device has the capacity to determine pulse wave velocity, pulse transit time and a waveform analysis at the bedside and can be designed as a small handheld tool. This is essentially a culmination of the information obtained from Duplex ultrasound and photoplethysmography but can be acquired within 30 seconds in any environment (eg. Operating room, bedside, patient's home).