The goal of testing after lower limb endovascular therapy is to provide objective hemodynamic and anatomic information on the treated arterial segments, classify stenosis severity when present, and provide reliable threshold criteria for reintervention. Duplex ultrasound testing after an open or endovascular intervention can both confirm procedural success and predict the likelihood of failure when a residual stenosis is identified (see Chapter 17).¹,⁶ Subsequent testing is based on patient symptoms and the presence of clinical risk factors associated with treatment site failure. The application of duplex surveillance to detect and then repair stenotic lesions after arterial intervention has been shown to improve patient outcomes compared with clinical assessment alone after lower limb bypass grafting, endovascular aneurysm repair, and renal/visceral artery angioplasty.¹,⁵,¹²,¹³ After lower limb endovascular intervention, the reported incidence of failure ranges from 20% to 40% within the first year, suggesting that an appropriate surveillance protocol may improve outcomes.³,¹²,¹³ Bui et al.¹⁴ conducted a prospective duplex surveillance study of 94 limbs with femoropopliteal occlusive disease treated by percutaneous transluminal angioplasty. Initial duplex testing was normal in two-thirds of limbs and remained normal in 38 (40%) limbs. New or progressive angioplasty site stenosis occurred in more than one-third of limbs and was associated with a 10% to 20% incidence of arterial thrombosis. Severe (>70%) stenosis was associated with ischemic symptoms in one-half of patients. The sensitivity and specificity of duplex testing to predict occlusion were 88% and 60%, respectively.

The presence of a duplex-detected stenosis after endovascular therapy (atherectomy, transluminal balloon angioplasty, stent angioplasty) is a known risk factor for early (<6 months) procedure failure.⁵,⁶,⁷,¹³,¹⁴ This observation has prompted some interventionalists to perform immediate (i.e., intraprocedural) or early (<30 days) duplex scanning to verify that the treated arterial segment has no residual stenosis based on spectral waveform velocity criteria. Early duplex testing indicates that the prevalence of endovascular treatment site stenosis is lowest after stent angioplasty or stent grafting (<5%) and higher after balloon angioplasty (15% to 20%) or atherectomy (25%). An angiogram-monitored angioplasty with less than 20% to 30% residual stenosis does correlate with 30-day patency
(i.e., technical success), but does not reliably predict a stenosis-free angioplasty site when evaluated by duplex ultrasound.³,¹⁵,¹⁶,¹⁷

Endovascular intervention has emerged as first-line therapy for symptomatic iliac and femoropopliteal arterial occlusive disease. In 2007, the work group for the Trans-Atlantic Inter-Society Consensus (TASC) updated consensus guidelines (TASC II) for the management of PAD and endorsed endovascular therapy for the treatment of infrainguinal PAD.¹¹ Most vascular specialists have adopted an “endovascular first” policy for the management of both claudication and CLI. Endovascular intervention for TASC II D lesions can be safely performed with excellent immediate hemodynamic improvement and limb salvage, but restenosis is common, and the success of this clinical approach mandates strict patient follow-up using vascular laboratory testing.¹²,¹³ In the treatment of superficial femoral artery (SFA) occlusive lesions, Schillinger et al.⁵ documented that duplex-detected greater than 50% stenosis developed more frequently after balloon angioplasty than after nitinol stenting at both 6 months (45% vs. 25%, P = 0.06) and 12 months (63% vs. 37%, P = 0.01). Other techniques used to treat native SFA lesions or angioplasty site stenosis, such as cutting or cryoplasty balloon angioplasty, atherectomy, and stent grafting, have a high (>95%) technical success rate, but restenosis and treatment site thrombosis are common and observed in 20% to 50% of limbs by 1 year, depending on TASC lesion severity.¹⁴,¹⁵,¹⁶,¹⁷,¹⁸ Duplex criteria for stenosis severity based on PSV correlate with procedural failure.³ Angioplasty site stenosis with a PSV ratio (Vr) greater than 2.5 was predictive (P < 0.001) of recurrent claudication with a sensitivity of 71% and specificity of 72%.¹⁰ Surveillance of stent grafts placed for lower extremity arterial occlusive disease indicated that focal sites of PSV greater than 300 cm/s, Vr greater than 3.0, and, most importantly, a uniformly low PSV less than 50 cm/s throughout the stent graft were predictive of impending thrombosis.¹⁹

The observed deterioration in primary patency after endovascular intervention is a significant clinical concern, especially in the treatment of CLI, since treatment site thrombosis can result in limb loss. The restoration of secondary patency (after occlusion of a previously treated SFA) is associated with a lower rate of technical success and a risk of distal embolization when mechanical thrombectomy techniques are utilized. It remains a subject of debate as to whether duplex surveillance coupled with reintervention for progressive stenosis is a strategy that will result in improved long-term functional capacity and limb salvage. It is clear that the application of less invasive endovascular therapies for PAD will continue, and further expansion of this technology is expected by both vascular specialists and patients. As device technology and endovascular techniques evolve, improvements in durability are likely. The challenge for the noninvasive vascular laboratory is to provide objective, reliable, anatomic, and hemodynamic information for the complete spectrum of endovascular repairs, assist clinicians in detection of treatment site failure, and provide threshold criteria for intervention when abnormalities are identified.

The essentials of vascular laboratory testing after peripheral endovascular intervention mirror those that apply to bypass graft surveillance and can be summarized as follows:

A proposed testing protocol for angioplasty surveillance is shown in Figure 18.1. The vascular technologist should query the patient for claudication symptoms and examine the limb for signs of ischemia (dependent rubor, ulceration, gangrene, cyanosis). In the patient with claudication, indirect physiologic testing is performed to verify improvement in the ABI to a normal (>0.9) or an improved (increase of >0.2) level, which is predictive that walking distance is likely to be improved. Exercise treadmill testing can be used selectively to document walking ability and ankle pressure response to exercise, as discussed in Chapter 13. In limbs treated for CLI, testing should include measurement of toe systolic pressure, since reliance on ABI alone may not accurately reflect forefoot perfusion due to concomitant plantar arch disease, or the ABI may be falsely elevated in the diabetic patient because of tibial artery calcification and vessel incompressibility. In general, a toe pressure greater than 30 mm Hg is required to relieve rest pain, while a value greater than 40 mm Hg is a reliable predictor of foot wound (ulcer, amputation) healing.