Femoral Angiography

Akkawat Janchai,MD

In recent years, duplex ultrasonography, magnetic resonance angiography and CT angiography have gained a measure of acceptance in evaluation of lower extremity vascular disease. However, conventional femoral angiogram is still the gold standard.

Angiographic Techniques

Access route ( 1) In general, Seldinger catheterization of common femoral artery is the common access site. site. When one femoral pulse is completely absent, the contralateral femoral should be accessed. Although most operators avoid entering on the side of a stenosis or occlusion, others do so preferentially. The benefits and risks of each approach depend upon the site and nature of the known or suspected disease. Entering on the side of known or suspected iliac disease has the advantages of preserving the relatively normal contralateral iliac anatomy, facilitating the measurement of pressure gradients, and allowing easy conversion of a diag-nostic procedure to a percutaneous intervention. The disadvantages include possible access failure, subintimal incursion, occlusion of a very stenotic lumen by the diagnostic catheter, and displacement of fresh thrombus. In addition, one is not able to visualize the diseased system in an undisturbed state. With infrainguinal disease, the benefit of ipsilateral entry is preservation of the relatively normal side.Contralateral access, by comparison, gives one the ability to cross over the aortic bifurcation and advance a catheter into distal branches of the diseasedsystem for more detailed angiography. This capability is of particular importance when there

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is concern for thrombus extending below the inguinal ligament: contralateral access greatly facilitates catheter-directed thrombolysis. While ipsilateral antegrade access would theoretically offer the same benefit, this approach is technically challenging, has a higher risk of complications, and is rarely employed unless one is planning percutaneous intervention of a known lesion. If the patient has bypass graft, single-wall technique of graft access is recommended. A final consideration is vascular access after previous placement of an iliac stent. Ipsilateral access is appropriate if stent dysfunction is suspected, as it facilitates pressure measurement and angioplasty or the placement of additional stents. Accessthrough the opposite groin is preferred in most other circumstances, however, because it can be extremely difficult to advance a guide wire through a stent. If the stent struts are not completely apposed to the vessel wall, the guide wire and/or catheter can be unknowingly passed through interstices in the side of the stent. When followed by a catheter, sheath, or balloon, this can lead to deformation of the stent, entrapment of angiographic equipment, or severe vascular injury. Initial access through a stent should thus be accomplished using a soft J-tip guide wire. If the wire does not pass easily, it should not be forced: in all likelihood, the wire will be anterior or posterior to the stent. Oblique views will demonstrate this and often facilitate guide-wire passage. Once the stent has been traversed, access through the lumen should be continually maintained by a wire, catheter, or sheath.

Imaging technique (1) Image acquisition varies from institution to institution. Although film/screen (also known as cut-film) studies provide better image quality and greater spatial resolution than digital studies, they are time-consuming, heavily dependent upon timing and technique, and require a greater volume and density of intravascular contrast. As a result, digital acquisition is rapidly becoming the modality of

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choice; in fact, film/screen units are unavailable for most angiographic systems currently being produced. Studies can be acquired in a stepwise or bolus-chase manner. The former uses repeated contrast injections with filming over a series of stationary points (or a dedicated long-cassette film changer, of which few are still in use). The latter uses a single contrast bolus but requires horizontal movement of the table or the radiographic imaging apparatus to maintain the moving bolus within the imaging field. The advantages of stepwise acquisition are its speed and flexibility: positioning is simplified and images can be viewed real-time and acquired for exactly the period required to fully visualize the vasculature at each station. This technique is articularly useful when the flow rates are asymmetric. The advantages of bolus-chase include a reduced contrast load and the assurance of anatomic overlap at each station.

Hemodynamic assessment Once a vascular stenosis has been identified angiographically, there may be a question as to its physiologic impact. The most objective mechanism for evaluating emodynamic significance is to measure blood pressure above and below the lesion. A gradient is then obtained by subtracting the distal pressure from the proximal. Simultaneous measurements obtained though a coaxial cathetersheath combination are the most accurate, assuming adequate clearance between the sheath and catheter (at least #0.5 Fr is required) . This technique also assumes that the catheter itself doesnot cause a significant impediment to flow within the stenosis. When a coaxial system is impractical, “pullback” measurement can be performed with a single catheter. With either technique, the measuring catheter should have side holes, as a single endhole may be partially blocked as the catheter rests against the vessel wall. The side holes should be near the catheter tip, so that the measurement represents a specific site rather

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than the average over a long region. Ideally, pullback measurement is performed over a guide wire, so that access across the lesion is maintained. There is some debate over what constitutes a significant stenosis. ( 2,3) Most authors agree that a systolic gradient of 15 mmHg is significant, while others use 10 mmHg. Still others refer to the gradient of mean blood pressure, applying yet another set of criteria. While no universally accepted criterion for a significant gradient exists, a systolic gradient of 10 mmHg can generally be considered borderline; a gradient of 15 mmHg can be considered abnormal. If the issue remains in doubt, a physiologic challenge may be useful. Tolazoline is a peripheral vasodilator that can be used to simulate exercise pharmacologically. Tolazoline is usually injected in 25-mg aliquots, diluted to 10 mL and injected into the artery in question over 1 to 2 minutes. Subsequent elevation of the gradient suggests a hemodynamically significant lesion, while little or no change in the gradient suggests that the lesion is not significant.

Special situations and techniques (1) Simultaneous bilateral lower extremity studies can be difficult or impossible when blood flow in the legs is markedly asymmetric, particularly when the bolus-chase technique is employed. In such cases, iatrogenically induced hyperemia can be useful by accelerating flow on the delayed side. Pharmacologic and physiologic techniques have been used with equal success. Pharmacologic hyperemia is induced with 25 mg of tolazoline. The drug is diluted in 10 mL of normal saline and injected into the common femoral artery over 2 to 4 minutes, followed promptly by arteriography. Physiologic postocclusive hyperemia is induced with a blood pres-sure cuff placed on the thigh and inflated to a pressure 10 to 20 mmHg higher than systolic pressure. After 8 to 10 minutes of ischemia, the tourniquet is released and angiography is performed immediately. Neither technique is

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effective if the limb in question is ischemic and thus maximally vasodilated at rest. When the blood supply to one leg is supplied by pelvic collaterals while the contralateral iliac vasculature is relatively intact, preferential flow to the “normal” limb makes imaging of the distal vasculature in the affected limb difficult or impossible. A modification of the above technique is useful in such situations. A blood pressure cuff is applied to the normal thigh and inflated to a pressure 10 to 20 mmHg above systolic. Angiography of the abnormal limb is conducted with the cuff inflated, and flow is thus diverted through the collateral bed. This technique precludes simultaneous bilateral angiography. Although the catheters and guide wires used for angiography cause minimal trauma, vascular spasm can develop during catheter and wire manipulation. This is particularly true during subselective catheterization of small vessels. Spasm, when it occurs, can be angiographically indistinguishable from intrinsic vascular disease. When spasm is suspected, the intra-arterial injection of vasodilators can be a useful diagnostic and therapeutic tool. The most commonly used agent is nitroglycerin, which is given through the angiographic catheter inaliquots of 100 to 200 g.

References:1. Robert T. Andrews, Seminars In

Interventional Radiology, Vol. 17, number 1, 2000, page 71-111.

2. Kinney TB, Rose SC, Intraarterial pressure measurements during angiographic evaluation of peripheral vascular disease: Techniques, interpretation, applications, and limitations. AJR 1996;166(2):277-284

3. Kamphuis AG, van Engelen AD, Tetteroo E, et al. Impact of different hemodynamic criteria for stent placement after suboptimal iliac angioplasty. Dutch Iliac Stent Trial Study Group. JVIR 1999;10(6):741-746

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