2.3.1 Arteriography
Arteriography or angiography is still considered the "gold standard" for diagnostic evaluation of PAD.Nowadays, to establish the diagnosis of PAD and to plan the most adapted intervention, most vascular specialists use three-dimensional reconstructed angiography (CTA or MRA) or bidimensional images obtained with Duplex-ultrasound modalities. However, diagnostic standard angiography may still remain necessary, in selected cases, in whom anatomic details are not correctly visualized by the non-invasive imaging modalities and a specific intervention is being considered. This may be the case in patients presenting with critical limb ischemia secondary to an isolated below the knee or below the ankle disease, in whom a very detailed vascular anatomy mapping (e.g., collaterals) may be
necessary in order to correctly plan the revascularization procedure.
With contrast angiography images are easily displayed and interpreted by the vast majority of physicians caring for patients with vascular disease. Technical improvements in X-ray imaging equipment enhance image quality and allow for detection of abnormalities. Progressive improvements in image resolution have enabled better definition of affected vascular territories with contrast and have resulted in a better safety profile of the entire procedure.
Despite the fact that the standard cine-angiography acquisition images are usually of sufficient quality to allow the visualization of the vascular anatomy as well as the presence or absence of any significant disease, the substraction acquisition modality (i.e., DSA) should be preferred, because it gives better images’ resolution while using less contrast medium. Accordingly, the DSA technique provides superior definition of the vascular tree compared with unsubtracted imaging, because it eliminates much of the artifact due to bony structures and dense body tissues. Finally, selection of the appropriate amount of contrast and application of proper image-acquisition techniques, including masking and digital enhancement, are required to optimize the accuracy of the images obtained, finally resulting in reducing the contrast medium delivery as well as the time of the procedure.
The simultaneous miniaturization of catheters available for angiography and the development of more selective shapes have further enhanced the safety profile of this standard technique. In addition, non-invasive imaging with duplex, MRA, and/or CTA methods may allow for better preparation before initiation of an invasive procedure. Identification of a culprit lesion, preparation of the appropriate
37
equipment, and selection of the best access sites are all facilitated by information obtained by these non-invasive imaging modalities. Thus, there is now a wide variety of practice patterns with respect to the use of non-invasive imaging modalities for therapeutic planning.
Knowledge of inflow and outflow patterns, as well as characterization of the lesion, may affect decisions regarding therapy. From a technical standpoint, the closer the catheter is to the target vessel to be imaged, the better the image definition is and the less is the volume of contrast that is required.
Accordingly, selective and superselective catheter placement is useful in optimizing image quality.
This is particularly recommended in the setting of renal insufficiency or when occlusive distal vessels may not be visualized by a more proximal bolus injection of contrast. However, one should also take into consideration that, most of the time with selective or superselective angiography acquisitions, collaterals are not correctly visualized. Accordingly, and especially in case of vascular total occlusions, the distal reperfusion zone may be visualized only by much more proximal injection (e.g., in the distal abdominal aorta or the common femoral artery), which allows an adequate collaterals opacification (e.g., through lumbar or the profunda femoral arteries), thereby a sufficient filling of the reperfusion zone.
The acquisition of views from orthogonal angles, which has been the rule in coronary
angiography, is less prevalent in peripheral imaging, largely because of the extensive territory to be covered in a complete diagnostic peripheral runoff angiogram (as opposed to a coronary angiogram).
Nonetheless, for areas where there is doubt or uncertainty regarding the presence or absence of a significant lesion, angulated views can be useful to better delineate and define the severity of the lesion and clarify its potential contribution to the clinical syndrome. This does, however, require injection of additional contrast material and prolongs the angiographic procedure.
Adjunctive hemodynamic parameters, such as pressure gradient and duplex velocity measurements, as well as use of supportive imaging modalities, such as intravascular ultrasound, angioscopy, and optical coherence tomography, can be useful and occasionally have been used in lieu of digital subtraction angiography to guide procedures.
Angiography has several liabilities. First, it carries with it the risks associated with any invasive procedure. Such risks include those related to vascular access (e.g., bleeding, infection, and vessel disruption). In addition, there is a small but important risk of contrast reaction; the risk of a severe reaction is approximately 0.1% (105).
38
Contrast agents are also associated with a small but important incidence of nephrotoxicity.
Patients who are at increased risk of contrast nephropathy include those with severe baseline renal dysfunction, diabetes, low cardiac output state, or dehydration. Any combination of these is more problematic than an individual risk factor. Recent studies have suggested that use of low-osmolar contrast agents (e.g.,iodixanol) or pretreatment with n-acetylcysteine may reduce the incidence of renal compromise (106, 107).
In patients who are high risk for nephrotoxicity, data suggest that vigorous hydration before administration of contrast may serve as the most important strategy to prevent postprocedural deterioration in renal function. Because the occurrence of nephrotoxicity appears to be dose-dependent, it is also important to minimize contrast usage. This dose minimization can be accomplished by using digital subtraction techniques and placing catheters close to the site to be imaged (selective angiography).
Finally, complications typically associated with invasive techniques and catheter manipulation, such as atheroembolization, dissection, and inadvertent vessel-wall disruption or perforation, are all adverse events that can occur with invasive angiography. Vigilant observation and careful
manipulation of guidewire and catheter location are imperative.