The care of vascular patients is a lifelong focus for the healthcare provider due to the chronic nature of peripheral arterial disease (PAD). Optimizing outcomes of these patients requires periodic assessment of their clinical status, reducing risk factors, and managing medical therapies, as well as implementing monitored exercise therapies whenever possible. For the subset of PAD patients that suffer debilitating claudication, rest pain, or tissue loss, revascularization is often indicated. The follow-up of patients receiving open surgical bypass with venous conduit has been well studied, with routine duplex ultrasound and periodic clinical evaluation now widely considered standard of care.^1-5 However, for those patients that, increasingly, undergo interventional therapies such as angioplasty, atherectomy, and/or stenting procedures, there is a less robust evidence base to draw from to guide immediate and longitudinal hemodynamic evaluation.

According to the recent ACC/AHA Guidelines, duplex ultrasound is "reasonable for routine surveillance after endovascular procedures."⁶ The sources referenced in the document refer to duplex ultrasound criteria used in the surveillance of patients following endovascular therapies, specifically for iliac angioplasty and stenting, superficial femoral artery (SFA) self-expanding stenting and stent grafting. The utility of hemodynamic surveillance here is predicated on the ability to optimize long term patency rates in vessels treated via an endovascular approach, identification of impending occlusions, minimization of the frequency and extent of repeat procedures, and potentially reduction of costs of care, all in an attempt to approach the results of traditional bypass surgery.

Back et al.⁷ evaluated a surveillance algorithm for iliac artery angioplasty and primary stenting using duplex scanning within one month; PSV > 300 cm/s and PSVR > 2.0 and/or symptomatic or hemodynamic deterioration were considered failing and an indication for angiography (Figure 1). Baril et al.⁸ developed criteria that are specific and predictive for both 50% and 80% in-stent stenoses within the SFA. For asymptomatic patients who are found to have 50 to 80% stenoses either in the immediate post procedure time or at some point during their follow up, recommended surveillance is transitioned to 3 month intervals. If these patients progress to >80% stenosis or become symptomatic, they should be offered re-intervention. Those patients with stable 50 to 80% lesions after one year are then transitioned to 6 month follow up intervals (Figure 2). Troutman et al.⁹ point to duplex findings for stent grafts, noting focal PSV >300 cm/s, PSVR > 3.0 and uniform PSV < 50 cm/s throughout the stent graft that were statistically reliable markers for predicting stent graft thrombosis, indicating the need for intervention.

Figure 1

Figure 2

While the above criteria may be useful for the majority of symptomatic PAD patients, i.e., debilitated claudicants, controversy exists regarding the most appropriate endpoints for the critical limb ischemia (CLI) patient (rest pain, non-healing ulceration, or gangrene). Anatomically, these patients frequently exhibit multilevel stenoses or occlusions, so when treated endovascularly, the assessment of patency across all segments may be difficult and the hemodynamic measurements may not necessarily correlate with specific outcomes of interest, such as limb preservation. Conte et al.¹⁰ recommend a minimum schedule of vascular hemodynamic assessments as a guideline for CLI trial design, but which can also be reasonably applied to clinical practice for CLI patients:

• Baseline (pre-intervention) - ABI or toe pressure.
• Post-procedure (immediately or up to one week after) - ankle-brachial index (ABI) or toe pressure.
• One, three, six, 12 months - ABI or toe pressure for all endovascular interventions. DUS arterial examination suggested for assessment of specific endovascular-treated segments.
• Angiography (catheter-based, magnetic resonance, or computed tomography techniques) should be performed as clinically indicated by the presence of recurrent symptoms or if results of noninvasive studies suggest hemodynamic failure.

The authors suggested a definition of hemodynamic failure as: major amputation (transtibial or above), reintervention to maintain vascular patency in the index limb, failure to increase ABI by at least 0.15 post-procedure as compared with the baseline value, and (for patients with non-compressible vessels) a toe-brachial index (TBI) increase by at least 0.10. Other indicators included: a decrease in ABI by 0.15 (or TBI drop of 0.10) or greater as compared with post procedure values, a duplex ultrasound demonstrating occlusion of the graft or treated native vessel, a duplex ultrasound demonstrating critical graft stenosis (PSV >300 cm/s or PSVR >3.0), an angiogram demonstrating occlusion of the graft or any treated vessel, or a greater than 50% stenosis in the presence of recurrent clinical symptoms.

In addition to the traditional physiologic standards of ABI and TBI, there are a number of modalities that attempt to provide information on perfusion in the CLI patient following intervention. Transcutaneous oxygen monitoring has been used extensively to assess the lower extremity, with a normal value defined as 60 mmHg; while values >40 mmHg generally indicate adequate perfusion, the definitive value may not be obtained until up to several weeks after the intervention.^11-13 Furthermore, the accepted level of TcPO2 that indicates tissue healing potential remains controversial. Indocyanine green angiography uses a contrast agent that fluoresces at a wavelength between 750 and 880 nm, imaged with a laser light source and camera system, where the rate of perfusion in the affected tissue is reflected by the intensity of fluorescence. This allows for quantitative evaluation of perfusion after a revascularization procedure, but further research must be done to establish uniform standards for this modality.^14-16 Emerging experience with new technologies, such as fractional flow reserve (FFR), may elucidate efficacy and clinical applications for the hemodynamic evaluation and direction of treatment of peripheral lesions.¹⁷ Other modalities, such as SPECT nuclear imaging, laser Doppler, and implantable micro-oxygen sensors are also available, but additional study is needed to develop protocols and ensure efficacy.

While there is increasing support for surveillance following peripheral intervention, further studies are needed to determine how the indication and endpoint of endovascular therapy can be directed hemodynamically. When compared to coronary artery disease, where post-stenting FFR has been validated to be an independent predictor of target lesion revascularization, there is no analogous accepted modality for peripheral interventions.^18-21 The technologies available for endovascular therapy and the protocols that guide the hemodynamic assessment of these therapies are in need of improvement. As interventional therapies continue to evolve, our ability to assess the hemodynamic results of these procedures needs to become more refined, to provide data that allow the vascular specialist to more objectively determine the indication for an intervention and the efficacy of the procedure, ultimately to reduce the need for secondary intervention, and potentially, to reduce cost.

References

1. Jongsma H, Bekken JA, van Buchem F, Bekkers WJ, Azizi F, Fiolle B. Secondary interventions in patients with autologous infrainguinal bypass grafts strongly improve patency rates. J Vasc Surg 2016;63:385-90.
2. Ihlberg L, Luther M, Alback A, Kantonen I, Lepantalo M. Does a completely accomplished duplex-based surveillance prevent vein-graft failure? Eur J Vasc Endovasc Surg 1999;18:395-400.
3. Lundell A, Lindblad B, Bergqvist D, Hansen F. Femoropopliteal-crural graft potency is improved by an intensive surveillance program: a prospective randomized study. J Vasc Surg 1995;21:26-33.
4. Westerband A, Mills JL, Kistler S, Berman SS, Hunter GC, Marek JM. Prospective validation of threshold criteria for intervention in infrainguinal vein grafts undergoing duplex surveillance. Ann Vasc Surg 1997;11:44-8.
5. Bandyk DF, Cato RF, Towne JB. A low flow velocity predicts failure of femoropopliteal and femorotibial bypass grafts. Surgery 1985;98:799-809.
6. Gerhard-Herman MD, Gornik HL, Barrett C, et al. 2016 AHA/ACC guideline on the management of patients with lower extremity peripheral artery disease: executive summary: a report of the American College of Cardiology/American Heart Association Task Force on Clinical Practice Guidelines. J Am Coll Cardiol 2017;69:1465-1508.
7. Back MR, Novotney M, Roth SM, et al. Utility of duplex surveillance following iliac artery angioplasty and primary stenting. J Endovasc Ther 2001;8:629-37.
8. Baril DT, Marone LK. Duplex evaluation following femoropopliteal angioplasty and stenting: criteria and utility of surveillance. Vasc Endovascular Surg 2012;46:353-7.
9. Troutman DA, Madden NJ, Dougherty MJ, Calligaro KD. Duplex ultrasound diagnosis of failing stent grafts placed for occlusive disease. J Vasc Surg 2014;60:1580-4.
10. Conte MS, Geraghty PJ, Bradbury AW, et al. Suggested objective performance goals and clinical trial design for evaluating catheter-based treatment of critical limb ischemia. J Vasc Surg 2009;50:1462-73.
11. Caselli A, Latini V, Lapenna A, et al. Transcutaneous oxygen tension monitoring after successful revascularization in diabetic patients with ischaemic foot ulcers. Diabet Med 2005;22:460-5.
12. McPhail IR, Cooper LT, Hodge DO, Cabanel ME, Rooke TW. Transcutaneous partial pressure of oxygen after surgical wounds. Vasc Med 2004;9:125-7.
13. Pardo M, Alcaraz M, Ramon Breijo F, Bernal FL, Felices JM, Canteras M. Increased transcutaneous oxygen pressure is an indicator of revascularization after peripheral transluminal angioplasty. Acta Radiol 2010;51:990-3.
14. Braun JD, Trinidad-Hernandez M, Perry D, Armstrong DG, Mills JL. Early quantitative evaluation of indocyanine green angiography in patients with critical limb ischemia. J Vasc Surg 2013;57:1213-8.
15. Perry D, Bharara M, Armstrong DG, Mills J. Intraoperative fluorescence vascular angiography: during tibial bypass. J Diabetes Sci Technol 2012;6:204-8.
16. Terasaki H, Inhoue Y, Sugano N, et al. A quantitative method for evaluating local perfusion using indocyanine green fluorescence imaging. Ann Vasc Surg 2013;27:1154-61.
17. Kobayashi N, Harano K, Nakano M, et al. Measuring procedure and maximal hyperemia in the assessment of fractional flow reserve for superficial femoral artery disease. J Atheroscler Thromb 2016;23:56-66.
18. Pijls NH, van Son JA, Kirkeeide RL, De Bruyne B, Gould KL. Experimental basis of determining maximum coronary, myocardial, and collateral blood flow by pressure measurements for assessing functional stenosis severity before and after percutaneous transluminal coronary angioplasty. Circulation 1993;87:1354-67.
19. De Bruyne B, Pijls NH, Paulus WJ, Vantrimpont PJ, Sys SU, Heyndrickx GR. Transstenotic coronary pressure gradient measurement in humans: in vitro and in vivo evaluation of a new pressure monitoring angioplasty guide wire. J Am Coll Cardiol 1993;22:119-26.
20. Pijls NH, De Bruyne B, Peels K, et al. Measurement of fractional flow reserve to assess the functional severity of coronary-artery stenosis. N Engl J Med 1996;334:1703-8.
21. Pijls NH. Fractional flow reserve to guide coronary revascularization. Circ J 2013;77:561-9.

Keywords: Amputation, Angiography, Angioplasty, Ankle Brachial Index, Atherectomy, Constriction, Pathologic, Contrast Media, Coronary Artery Disease, Exercise Therapy, Femoral Artery, Gangrene, Hemodynamics, Iliac Artery, Indocyanine Green, Lower Extremity, Magnetic Resonance Spectroscopy, Peripheral Arterial Disease, Risk Factors, Stents, Thrombosis, Tomography, Tomography, Emission-Computed, Single-Photon, Ultrasonography, Doppler, Duplex, Vascular Patency

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