Duplex Arterial Mapping

Duplex arterial mapping of the aortoiliac segment and CFAs can adequately assess the location of hemodynamically significant lesions (Fig. 112-2). It is particularly helpful to assess the burden of disease in the CFA, which may potentially alter a planned percutaneous approach through the CFA to an open CFA endarterectomy and concomitant iliac stent/stent graft placement. This modality is especially useful in patients with renal insufficiency who are at risk for contrast-induced renal dysfunction.¹⁷ Drawbacks of duplex arterial mapping are that it provides only a semiquantitative assessment of the degree of iliac calcification, it may not adequately image the iliac system in certain patients owing to overlying bowel gas or body habitus, and it requires a significant time commitment and a highly trained vascular technologist.^18,19 These constraints have prevented duplex arterial mapping from becoming a more widely adopted imaging modality.

Magnetic Resonance Angiography

Contrast-induced nephropathy (CIN) is defined as an increase in serum creatinine greater than 25%, or >0.5 mg/dL (44.2 µmol/L) within 3 days of intravascular contrast administration in the absence of an alternative cause. Serum creatinine usually returns to baseline within 14 days, however some patients may progress to acute kidney failure requiring dialysis.^19a Contrast induced nephropathy is the third most common cause of new-onset acute renal failure in hospitalized patients.²⁰ The incidence may be as high as 25% in patients with preexisting renal impairment or certain risk factors such as diabetes, congestive heart failure, advanced age, and concurrent administration of nephrotoxic drugs.²¹ For those patients that require dialysis, the median 2-year survival is 19%.^21a The single most important risk factor for contrast-induced nephropathy is chronic kidney disease which increases the risk by more than 20 times.^21b It is generally accepted that risk of CIN in patient with estimated glomerular filtration rate (eGFR) ≥60 mL/min is extremely low. Studies have suggested that a threshold for CIN exists for patients with eGFR 40-45 mL/min and significant concern should be raised in patients with severe renal dysfunction with eGFR <30 mL/min.^21c Patients with both renal impairment and diabetes have up to a 50% risk of developing CIN.^21d The majority of studies regarding CIN have been for patients having intra-arterial contrast administration, in particular cardiac interventions. It has been assumed that intravenous (IV) contrast administration has the same risk as intra-arterial injection; however, this assumption is being challenged in recent studies.^21c,21e-g Several trials in patients receiving IV contrast have shown a low risk of CIN in patients with eGFR >40 mL/min. Among patients that did develop CIN, none progressed to dialysis and none had fatal outcomes.^21h,21i It has thus been proposed that for patients with eGFR <60 mL/min who are receiving intra-arterial contrast, full preventive measures should be initiated. On the other hand, for patients receiving IV contrast, preventive measures are recommended for eGFR <45 mL/min. Pre­procedural volume loading and the use of low-osmolar or iso-osmolar contrast agents can decrease the risk of contrast-induced nephropathy.^22–24 However, the risk is not eliminated in some patients, even when an iso-osmolar contrast agent is used.^25,26 The risk of CIN strongly correlates with contrast volume. Contrast volume in excess of 5 mL/kg strongly predicts CIN requiring dialysis.^26a A second contrast dose within 48 hours also significantly increases the risk of CIN.^26b-d Because free radicals are postulated to mediate contrast-induced nephropathy,²⁷ alkalinizing renal tubular fluid with sodium bicarbonate²⁸ has been shown to reduce injury. Merten et al reported a single-center randomized controlled trial comparing the infusion of sodium chloride versus sodium bicarbonate as the hydration fluid to prevent renal failure in patients with stable renal insufficiency undergoing diagnostic or interventional procedures requiring radiographic contrast agent.¹⁴ The absolute risk reduction of contrast-induced nephropathy (defined as 25% change in serum creatinine) using sodium bicarbonate compared with sodium chloride was 11.9%, resulting in a number-needed-to-treat of 8.4 patients to prevent 1 case of renal failure. A recent meta-analysis and systemic review of the literature confirmed that sodium bicarbonate hydration decreased the risk of CIN, without a significant risk of renal replacement therapy, in hospital mortality or congestive heart failure compared to controls.^28a Similar results were seen for risk of CIN when sodium bicarbonate was compared to normal saline alone (OR, 0.39; 95% CI, 0.20 to 0.77). However, when sodium bicarbonate/N-acetylcysteine combination was compared with N-acetylcysteine/normal saline combination, no improvement in outcome was determined (OR, 0.68; 95% CI, 0.34 to 1.37). Results have been conflicting for the use of N-acetylcysteine (NAC) in more than 40 trials and 13 meta-analyses; the most meticulous meta-analysis does not support the use of NAC to reduce the risk of CIN.^28b,28c On the other hand, the use of NAC is not associated with any major adverse effects (except with high-dose intravenous use which carries a risk of anaphylactoid reactions^28d); thus its use is generally not contraindicated. It is, however, not considered a substitute for hydration.

Patients with eGFR <60 mL/min receiving intra-arterial contrast should therefore receive IV hydration with sodium bicarbonate. The initial intravenous bolus is 3 mL/kg bolus (MAX 300 mL) 1 hour prior to procedure AND 1 mL/kg/hour (MAX 100/mL/hr) during and for 6 hours post-procedure.¹⁴ The use of oral NAC at a dose of 1200 mg twice daily on the day before and the day of contrast administration (total of 2 days) could be optional but not considered additive.¹³ Use of the lowest concentration of contrast (<5 mL/kg) to achieve satisfactory image quality is encouraged. Dilute contrast can often be used without affecting image quality. Reasonable attempts should be made to avoid repeat contrast injections within 72 hours. Diuretics should be routinely withheld on the day of contrast injection. Metformin is not a risk factor for CIN and the injection of contrast is not contraindicated in patients taking this medication. However, serious complications (lactic acidosis) may rarely occur in patients taking metformin who subsequently develop acute kidney insufficiency. For this reason, it is recommended that metformin be stopped 48 hours before any contrast injection.

Contralateral Approach

When attempting to recanalize an occluded common iliac artery in a retrograde fashion, the guide wire frequently follows a subintimal path. Once this has occurred, it may be difficult to redirect the guide wire into the lumen. An antegrade approach from the contralateral CFA is frequently successful, especially if there is a CIA stump and the CIA is not flush occluded. A hooked catheter is used to probe the occlusion. The lesion can then be crossed with the use of hydrophilic guide wire and a supporting catheter. As soon as the guide wire has crossed the obstructive lesion and lies within the ipsilateral EIA lumen, a catheter can be advanced over the wire and intraarterial placement can be confirmed. Depending on the proximity of the occlusion to the aortic bifurcation, a crossover sheath can be placed over a stiff guide wire or the wire can be snared from the ipsilateral CFA and a sheath can be placed in a retrograde fashion.

Brachial Approach

In the presence of a flush CIA occlusion, a contralateral femoral approach to cross the lesion is frequently unsuccessful; transbrachial or ipsilateral retrograde femoral approaches are more likely to achieve success. A brachial approach reduces the risk of creating or extending an aortic dissection and provides better “pushability.” The presence of significant subclavian artery occlusive disease obviously limits this approach.

Reentry Wires and Catheters

The development of reentry wires and catheters has greatly increased the technical success of crossing complete arterial occlusions. Crossing wires and catheters designed to cross chronic total occlusions (CTO) typically involves a wire that, based on a mechanical drive system, potentiates passage of the wire through the true lumen of the CTO either by a vibrating or rotating action. The majority of these devices have been tested in the femoral-popliteal vascular bed, and their utility in the iliac vessels is uncertain.

The reentry catheters facilitate crossing CTO by a subintimal approach. No data have suggested any advantage to crossing an iliac CTO either through the native lumen or subintimally. The Outback reentry catheter (LuMend Inc., Redwood City, Calif) is a single-lumen catheter designed to facilitate access and positioning of a guide wire within the peripheral vasculature from a remote vascular entry site using a retractable needle to pierce the intima and gain access to the true lumen (Fig. 112-5). The Pioneer catheter (Medtronic, Minneapolis, Minn) works by a similar mechanism but contains an intravascular ultrasound probe in the distal portion that assists in orienting the reentry needle toward the flow lumen. To use this catheter, a 300-cm–long, 0.014-inch guide wire is passed subintimally beyond the CTO. Typically, a .035-inch wire is used to make the initial subintimal plane and then exchanged for the .014-inch wire. The reentry catheter is then advanced beyond the CTO under continuous fluoroscopy. An angiogram is performed via the contralateral access to confirm traversal of the occlusion and positioning of the lateral exit port of the catheter at the aortic bifurcation proximal to the occlusion. In the case of the Pioneer catheter, this is done with IVUS. The precise location and orientation of the lateral exit port are confirmed by aligning the fluoroscopic guide. The nitinol cannula is then advanced forward through the lateral exit port under continuous fluoroscopy. Applying firm but guarded forward pressure while deploying the cannula may contribute to a successful puncture. Free passage of the 0.014-inch wire indicates true lumen access. This is confirmed by contrast injection through a catheter placed over the wire. The catheter can be exchanged for a 3-mm–diameter angioplasty balloon that is used to dilatate the subintimal tract and puncture site. This step enables a catheter to pass and allows exchange for a standard 0.035-inch guide wire to facilitate stenting. Stenting can then be performed in a conventional manner (Fig. 112-6).