The Utility of Duplex Ultrasonography Surveillance in Identifying Failing Aortobifemoral Grafts

Introduction

The recent Society for Vascular Surgery (SVS) guidelines for surveillance of vascular interventions noted there is no data by which recommendations can be made for following aortobifemoral (AoBiF) grafts long term. ¹ These grafts have been shown to have excellent long-term patency rates of 88-93% at 3-5 years.^2,3 These results would suggest there might be little benefit performing surveillance studies. Conversely, in the 7-12% of patients whose grafts fail during long-term follow-up, subsequent intervention can pose significant challenges with potential adverse outcomes. We have previously shown the benefit of duplex ultrasound (DU) surveillance of femoro-tibial prosthetic arterial bypasses and questioned whether DU might also prove useful for AoBiF grafts. ⁴ Therefore, we analyzed if long-term surveillance of AoBiF grafts using DU served to mitigate the incidence of limb occlusion and other graft-related complications.

Methods

We retrospectively identified patients in our prospectively maintained database who underwent AoBF bypasses between 1995-2018 at Pennsylvania Hospital in Philadelphia, PA. The study was exempt from Institutional Review Board (IRB) review, in accordance with University of Pennsylvania IRB rules for exemption, as data was obtained from retrospective, deidentified, chart review. Our surveillance regimen included DU performed in our Intersocietal Accreditation Commission-accredited non-invasive vascular laboratory (NIVL) obtained 1 week post-discharge, at 6-month intervals for the first year, and then annually if no abnormalities were detected. The duplex exam was targeted at the aorta, proximal to the proximal anastomosis, velocities along the length of the graft and both limbs, the distal anastomoses and the outflow vessels. In addition to obtaining a duplex at the follow up visit, a full history of clinical exam was obtained, in addition to bilateral lower extremity ABI/PVR. If a patient had an abnormal DU with elevated velocities that was inconsistent with previous trends, history and clinical exam, it was either repeated at a shorter interval, or the patient underwent catheter-based arteriography or CT-angiography (CT-A) followed by endovascular or surgical intervention at the discretion of the vascular surgeon. DU was considered “abnormal” if 1) peri-graft fluid or a 2) pseudoaneurysm (PSA) was identified in a patient without clinical findings or 3) focal peak systolic velocities (PSVs) greater than 350 cm/sec or adjacent PSV ratio > 3.5 at any site from the proximal aortic to the distal femoral anastomosis were identified which suggested a failing graft. These velocity and ratio thresholds for identifying threatened grafts were based off previously described velocity and ratio criteria for failing stent grafts. ⁵

Results

Sixty patients underwent AoBiF grafts and fulfilled our post-operative surveillance protocol during a mean follow-up of 4.0 years (0.5-24 years). “Normal” DU surveillance studies were documented throughout follow-up in successive examinations in 112 (93.3%) of the 120 limbs. Of these, 2 (1.7%) limbs developed acute limb occlusion. One patient developed graft kinking 2 years after the initial surgery that was likely undetected by DU due to morbid obesity. Patency was restored by open thrombectomy through the ipsilateral scarred groin and stent graft placement to ameliorate the kinked graft. The second patient experienced limb thrombosis likely due to poor outflow into a diminutive deep femoral artery. The patient was initially treated with thrombolysis, but when the limb re-occluded soon after, open thrombectomy and a common femoral artery (CFA)-to-below-knee popliteal artery bypass was performed to improve outflow.

Eight (6.7%) other limbs in 7 patients had “abnormal” DU findings, which occurred at a median of 36.5 months (range, 7-56 months) after surgery. Five had failing grafts detected with elevated velocities and/or ratios suggesting > 75% diameter stenosis at the distal anastomosis. An AoBiF graft (2 limbs) had peri-graft fluid leading to the diagnosis of graft infection before there were clinical manifestations; CTA was obtained to confirm this finding prior to operative intervention. One graft was found to have a distal anastomotic PSA that was not palpable on physical examination due to morbid obesity and dense scar tissue. Catheter-based arteriography or CT-A confirmed these findings in all 7 patients. Graft revision was performed in 7 of the 8 limbs either immediately or after 2 successive “abnormal” DU studies performed 6 weeks apart. Five of the 7 patients underwent balloon angioplasty and/or stenting of failing limbs and open surgery was avoided. In all 5 cases, stenosis identified on DU was confirmed during the procedure with diagnostic arteriography. Two patients had open surgical revision: One for infected AoBiF graft and one for an enlarging sterile PSA. One patient refused intervention.

Discussion

These results suggest that routine duplex DU of AoBiF grafts is worthwhile to maintain graft patency and mitigate complications related to PSAs and graft infections. In this series, 6.7% (8/120) of limbs had abnormalities detected during a mean follow-up of 4 years. See Table 1 for details. Seven limb abnormalities, in 6 patients, were addressed prior to requiring emergent intervention; one patient refused intervention and passed away of other causes shortly after her last visit. Intervening on these 6 patients potentially prevented acute lower extremity ischemia and sepsis or rupture of infected or pseudo-aneurysmal limbs.

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Table 1.

Aortibifemoral Grafts Requiring Intervention.

	Patient/limb	Diagnosis	Time interval from initial surgery	Intervention
Failing grafts	A/1	PSA	12 months	Open repair of PSA
	B/2, 3	Infected AoBiF graft	37 months	Excision of infected AoBiF graft and reconstruction with cryo graft
	C/4	Stenosis of distal anastomosis	39 months	Atherectomy and angioplasty of distal anastomosis
	D/5	Stenosis of distal anastomosis	36 months	Cutting balloon angioplasty of distal anastomosis
	E/6	Stenosis of distal anastomosis	7 months	Atherectomy and angioplasty of distal anastomosis
	F/7	Stenosis of distal anastomosis	28 months	Atherectomy and angioplasty of distal anastomosis
	G/8	Stenosis of distal anastomosis	56 months	Patient refused intervention
Acute occlusion	H/9	Acute limb occlusion	17 months	Open thrombectomy, repair of AoBiF limb
	I/10	Acute limb occlusion	36 months	Open thrombectomy, endarterectomy, fem-pop bypass

Abbreviations: PSA, pseudoaneurysm; AoBiF, aortobifemoral graft.

Two patients suffered acute limb occlusion (1.7%; 2/120) with prior normal DU studies, which is similar to other series in which duplex was not performed. ⁶ One patient was morbidly obese, rendering DU challenging and less accurate. The other patient had poor outflow and a likely hypercoagulable state. Morbid obesity, poor arterial outflow, and hypercoagulable state are 3 examples of the limitations of DU to identify failing limbs in AoBiF grafts.

Our recommended regimen for AoBiF graft surveillance is to obtain DU postoperatively and then every 6 months for the first year and annually thereafter. The initial scan is to detect any technical errors from the surgery and obtain baseline velocities. Scans are performed more frequently in the first year to determine whether patients develop significant intimal hyperplasia requiring intervention or closer follow-up. After the first year the likelihood of detecting an abnormality is less likely but patients may develop infections, pseudoaneurysms or stenosis several years later. In our series, all 8 abnormal DU findings occurred after the immediate postoperative study between 6-56 months after surgery. If a follow-up DU is “abnormal” compared to previous scans, at the surgeon’s discretion the scan is repeated shortly thereafter to verify an abnormality or arteriography or CT-A is urgently performed.

The strategy of implementing a DU surveillance strategy provides an opportunity to maintain graft patency, often with endovascular intervention and avoiding difficult re-do surgery. Performing aortobifemoral graft thrombectomy and revision with open surgery, often required in an emergent setting, is associated with considerable morbidity due to acute limb ischemia, operating in a re-do scarred groin, and increased chances of inadvertent nerve injury and bleeding due to technical misadventure . ⁷

Weaknesses of our study include the retrospective nature of the analysis and the arbitrary choice of a focal PSV > 350 cm/sec and adjacent PSV ratio > 3.5 as being surrogates for failing grafts. Other authors have suggested similar and differing PSVs and ratios to suggest failing peripheral vein and prosthetic bypasses.^1,4,5 These parameters were chosen retrospectively as the optimal values to both suggest a failing graft with > 75% focal stenosis (as confirmed by CT-A or arteriogram in all cases) but also as criteria predicting graft patency when PSVs were less than these values. Lastly, although to our knowledge this is the largest series to date reporting use of DU as a surveillance tool for AoBF grafts, the number of limbs that required intervention was small. This being said, our findings and failing graft rate of 7.5% (6.8% for limbs detected as “failing,” on duplex and 1.7% that acutely occluded) is consistent with other lager studies citing failure rates of 7-12%, therefore we believe that this is an accurate representation of a larger population.^2,3

Conclusion

We recommend that vascular surgeons adopt DU as a useful non-invasive surveillance tool to identify AoBiF bypasses that are failing or have other problems not identified clinically. Our suggested “abnormal” DU findings, either initially or after 2 successive studies depending on clinical judgment, should prompt elective operative or endovascular intervention.