The term peripheral artery disease refers to atherosclerotic disease of extracranial carotid and vertebral, abdominal mesenteric and renal, and lower extremity arteries (1).
In case of symptomatic peripheral artery disease, percutaneous interventions are nowadays the first choice in most clinical conditions. Most percutaneous peripheral interventions are carried out using the transfemoral access. However, this access is associated with a non-negligible rate of local vascular and bleeding complications (2). Moreover, the transfemoral access is sometimes precluded by severe local atherosclerosis; while in these conditions the transbrachial access has been used as the alternative route, this access is also associated with a considerable risk of local complications (3). In fact, the brachial artery is a terminal conduit and damage to it may cause forearm and hand ischemia. In addition, manual compression of the brachial artery can be difficult, and no closure device has been licensed for this access so far.
The transradial access (TRA) is an increasingly used approach for percutaneous coronary angiography and interventions (4). Advantages of this arterial access include a lower rate of local hemorrhagic and vascular complications with respect to the transfemoral and the transbrachial approaches (3), as well as enhanced comfort for the patient. Therefore, the TRA may become the natural alternative when the transfemoral access is precluded for peripheral interventions as well. However, the TRA may also be used as first choice access by experienced operators and in selected peripheral clinical conditions.
The aim of this paper is to explore the opportunity that the TRA can offer in the whole spectrum of peripheral interventions.
The transradial access when used for percutaneous peripheral interventions
The radial artery is punctured for peripheral interventions in the same way as for coronary procedures. However, it is wise first to obtain access with a small radial sheath (e.g., 5 French [0.33 mm]). Then, a long, supportive wire is advanced (often with the aid of a curved-tip diagnostic catheter) near the arterial segment to be treated (e.g., descending aorta, common carotid artery). Lastly, a long sheath or a guiding catheter is advanced over the wire in front of the lesion.
For peripheral interventions on vessels of the descending aorta (i.e., mesenteric, renal and lower extremity arteries), the left radial artery is to be preferred, if palpable. In fact, with the left access, the distance between the access site and the target lesion can be reduced with greater maneuverability of the equipment. Moreover, the left TRA minimizes the risk of brain embolization because manipulation and passage of various equipment occur only across the origin of the left vertebral artery, while with the right approach embolization to all supra-aortic vessels may occur. On the contrary, the right TRA is usually more comfortable for the operator, although, with the patient positioned upside-down on the table, with the arm open wide on a stand (5), the left access is also easy for the operator. Conversely, for supra-aortic vessel interventions, the side for the TRA should be chosen according to the anatomical characteristics of the disease (see below).
At the end of the procedure, the introducer system should be removed immediately, and hemostasis can be achieved with the aid of a dedicated radial compression device. In TRA peripheral interventions the sheath is usually larger than in coronary interventions. Therefore, it is mandatory to use the Doppler-assisted, patent hemostasis technique, to minimize the risk of radial artery occlusion.
Radial artery patency should be checked in all patients after 1 month, manually or with a Doppler probe, if the artery is not palpable. The occlusion rate of radial arteries after a TRA peripheral procedure can be as high as 16% (6). However, symptoms of discomfort or discomfort itself have been reported by patients in all the different series published so far.
The presence of an arteriovenous fistula for hemodialysis is the only contraindication for a TRA, also in the arm without the fistula, because the closure of the artery can prevent the preparation of a second fistula, should it be needed in the future.
Transradial access for percutaneous interventions of supra-aortic arteries
Carotid artery stenting
Carotid artery stenting (CAS) has been demonstrated to be an effective and safe alternative to surgical carotid endarterectomy in selected patients and when performed by experienced operators (7). This procedure is usually carried out using the transfemoral access with long sheaths or guiding catheters. Cerebral protection, either proximal or distal, is used by the majority of operators. In patients with a precluded transfemoral access, the cervical or the transbrachial approach has been used as an alternative. However, the cervical access requires direct carotid puncture and is performed only in few surgical centers. CAS has been successfully performed by the transbrachial access. However, as already mentioned, this access retains a high risk of local complications. Therefore, the TRA may become the preferred alternative to a precluded transfemoral one.
CAS by the TRA may be performed using the contralateral or the ipsilateral radial artery. The left common carotid artery is best engaged using the right TRA while the brachiocephalic trunk and the right common carotid artery are more easily cannulated using the left TRA. However, in patients with type III aortic arch (i.e., when all three supra-aortic vessels arise before and below the top of the aortic arch) the right common carotid artery is best cannulated by the right TRA. Similarly, in patients with a bovine aortic arch (i.e., when the left common carotid artery arises from the brachiocephalic trunk) undergoing a CAS by the TRA, the right arm is also to be preferred.
CAS is commonly carried out using guiding catheters or long sheaths. When using the TRA, 6 French long sheaths are preferred to 8 French guiding catheters because the smaller outer diameter is associated with a lower rate of vessel spasm and arm ischemia. An alternative approach for small caliber radial arteries is to use a 6.5 French sheathless guiding catheter (which can be advanced without a sized radial sheath) that has an outer diameter smaller than a 5 French sheath but an inner lumen as large as a 6 French sheath. The sheath or the sheathless guiding catheter is advanced in the common carotid artery over a curved diagnostic catheter and a supportive guidewire previously inserted in the external carotid artery (mother-and-child technique).
Currently available filters can also be used by the TRA for distal protection during CAS. Similarly, the 8 French MO.MA device (Medtronic Vascular, Santa Rosa, CA, USA) can progress within most radial arteries for proximal protection during CAS (8), when needed.
Most carotid stents are compatible with 6 French sheaths or 6.5 French sheathless guiding catheters and therefore they can also be deployed easily by the TRA.
The largest series of CAS by the TRA (9) was carried out, per protocol, by the right side and reported an overall success rate of 83%. However, the success rate was 97% in patients with right internal carotid artery stenosis, 80% in patients with left internal carotid artery stenosis and a bovine arch, but only 37% in patients with left internal carotid artery stenosis and normal anatomy aortic arch.
In conclusion, the TRA approach for CAS has to be considered more challenging than the transfemoral approach for most patients. This implies more catheter manipulations and, as a consequence, a higher risk of cerebral embolization. Therefore, this access should be limited to patients with a prohibited transfemoral access and who are at high risk for surgery. However, the right TRA may be preferred to the transfemoral approach in patients with right internal carotid artery stenosis and a type III aortic arch and in patients with left internal carotid artery stenosis and a bovine aortic arch. Conversely, in the presence of normal arch anatomy, the treatment of left internal carotid artery disease using the TRA, either left or right, should be discouraged.
Percutaneous interventions of other supra-aortic arteries
Up to 20% of patients with posterior circulation cerebral ischemia may have a critical stenosis of the vertebral artery. In these patients, percutaneous vertebral artery revascularization can be evaluated as a therapeutic option. Vertebral artery stenting is usually performed using the transfemoral access. However, the TRA has been used safely and effectively in case of poor femoral access or excessive kinking of the supra-aortic trunks (10) or as a first choice access (11).
Stenosis of the proximal subclavian artery may cause arm claudication or vertebrobasilar symptoms secondary to the subclavian steal phenomenon. Symptoms of myocardial ischemia are also possible in patients with a subclavian stenosis and previous internal mammary coronary artery bypass grafting. Subclavian stenosis may be treated percutaneously using the transfemoral access while the ipsilateral TRA may represent an alternative in case of poor femoral access. The better visualization of the origin of the vertebral and the internal mammary arteries can be an advantage of the TRA, thus reducing the risk of compromising the origin of these vessels through an inaccurate stent placement at the level of the subclavian artery.
The transradial access for percutaneous interventions of renal and mesenteric arteries
Renal artery stenting
Renal artery stenting (RAS) has been associated with conflicting results in randomized trials (12,13). Nevertheless, the procedure may be effective in selected patients with renal artery stenosis and uncontrolled hypertension and/or renal failure. While RAS is usually performed using the transfemoral access, the TRA may offer several advantages. For example, in patients with a downsloping take-off of renal arteries, the TRA allows an easier and more stable vessel engagement by the guiding catheter, thereby reducing the need for catheter manipulations in the aorta and the associated risk of distal embolization. In addition, this more favorable support allows the use of less aggressive guidewires, with a reduced risk of perforation of distal renal branches. Finally, direct stenting may be more frequently attempted from this approach with a reduced risk of distal renal embolization.
As for other percutaneous interventions, the TRA may minimize access-site complications (14). This observation may be of particular value in this setting because the negative results for RAS versus medical therapy in recent trials were mainly driven by access-site complications (13).
RAS by the TRA can be carried out with 6 French guiding catheters and with the same devices used for the transfemoral approach. In fact, most renal stents fit into 6 French guiding catheters.
In the largest series published so far of patients who had RAS by the TRA (14), the technical success rate was 100% without access-site complications.
In conclusion, in patients undergoing RAS and with poor femoral access, the TRA may represent the preferred alternative. However, independently of the ease of the transfemoral access, the TRA may be considered as first choice access in patients with a downsloping take-off of renal arteries.
Percutaneous interventions of other visceral arteries
Chronic mesenteric ischemia associated with stenosis of mesenteric arteries may be a cause of malabsorption and postprandial abdominal pain. In these patients, endovascular treatment is frequently preferred over surgery. The same anatomical arguments favoring the TRA for RAS also apply to the angioplasty of mesenteric arteries. In fact, mesenteric vessels also often have a downsloping take-off from the aorta and may be better cannulated from the arm than from the leg. Favorable results have been reported for the angioplasty of mesenteric arteries by the TRA (15).
Renal denervation is an endovascular procedure used to treat resistant hypertension. The devices used so far have been advanced into the renal arteries via the transfemoral access. However, some companies are developing longer denervating catheters that can be used via the TRA. This choice is made to reduce the risk of groin complications which can be encountered with the transfemoral access and which can hamper the results of the procedure.
The transradial access for percutaneous interventions of lower extremity arteries
Angioplasty of lower extremity arteries is usually performed using the transfemoral access. Iliac lesions can be treated either by retrograde ipsilateral femoral access or by contralateral femoral access with the crossover technique. Infrainguinal lesions are commonly treated by the crossover technique if located in the femoropopliteal segment and by antegrade, ipsilateral femoral access if located below the knee. However, sometimes the crossover technique may not be carried out due to occlusion, severe tortuosity or calcification of the iliac arteries or because of a very acute angle of the aortoiliac bifurcation. In addition, the crossover may be impossible in cases of previously placed kissing stents at the level of the origin of the common iliac arteries. Finally, in case of iliac occlusions, it may not be possible to cannulate a hypoperfused ipsilateral common femoral artery for a retrograde recanalization. Under these circumstances, an approach from the arm is needed and the transbrachial access has often been chosen for that purpose. However, as mentioned, the complication rate associated with this access is not negligible and the TRA may represent a valid alternative. Unfortunately, the length of available equipment does not permit below-the-knee interventions by this route.
Percutaneous interventions of above-the-knee arteries by the TRA need longer than usual introducer systems and devices. In order to have a sufficient support, the common iliac arteries should be selectively engaged with long systems. The diameters of devices also matter, as they have to be as small as possible in order to progress within radial arteries but with an inner diameter large enough to accommodate all equipment. Accordingly, with small radial arteries, a 120 cm long, 5 French sheath is to be preferred because the smaller outer diameter permits a safe progression of the sheath towards the lesion; on the other hand, in the presence of a large radial artery, a 120 cm long, 8.5 French sheathless catheter is the best choice because its larger lumen permits the use of all-size balloons and stents.
Nowadays, devices of adequate length are available on the market for lower extremity artery angioplasty by the TRA. In fact, guidewires up to 400 cm long do exist. Likewise, balloons and stents with a 180 cm long shaft can be found.
Nonetheless, some technical limitations of the TRA for lower extremity artery interventions have to be mentioned. First, the long distance from the entry site to the target lesion implies less support for the use of all devices: this point can become relevant when crossing occlusions or tight stenoses. Second, long sheaths or guiding catheters may not be tolerated in patients with arm vessels of a small diameter. Third, should distal embolization occur, it cannot be treated using the same access. Fourth, the choice of balloons and stents with a long shaft is limited. Lastly, we do not have a debulking device with a shaft long enough to be used by the TRA.
The TRA has been used in lower extremity artery angioplasty of diseased native (16,17) and stented (18) arteries, with balloons only (18) or withballoons and stents (16,17,19), with all the reports characterized by the absence of local complications. In a segment-by-segment analysis, good results are found with the TRA in occlusive and non-occlusive lesions of iliac arteries while poor results are obtained in long occlusions of the superficial femoral artery (16). The opportunity of treating bilateral lesions in the same session has been considered to be a further practical indication for a TRA (16,19).
In conclusion, the TRA may be used for lower extremity artery angioplasty in patients with poor femoral access, as an alternative. However, the TRA may be used only for above-the-knee interventions because the current length of devices does not permit below-the-knee interventions. Moreover, the use of the TRA should be discouraged for the treatment of long occlusions of the superficial femoral artery.
On the other hand, the TRA may be used as first choice for selected cases of lower extremity artery angioplasty. In fact, favorable results have been obtained with the TRA in the treatment of iliac lesions by operators who use this access routinely for coronary interventions (20) (Figure 1). The TRA may also be particularly useful for the treatment of bilateral lesions, especially if located in the suprainguinal segments.
Figure 1: The patient was an 86-year-old male with severe (Rutherford 3) left thigh claudication. At angiography he had a critical stenosis at the distal left common iliac artery (left). The lesion was successfully treated with balloon and stent via the left TRA (right). The patient was discharged the day after the procedure. At one-month follow-up visit the patient was asymptomatic.
The TRA is associated with fewer access-site complications compared to the transbrachial access and can therefore become the preferred alternative to a precluded transfemoral access for peripheral interventions.
In addition, in centers with a large experience with the TRA for percutaneous coronary interventions, this access may become the first choice approach for the treatment of lesions in selected anatomical subsets such as left internal carotid artery stenosis in a bovine aortic arch or right internal carotid artery stenosis in a type III aortic arch, renal or mesenteric artery stenosis in the presence of a downsloping take-off of these vessels, and in iliac artery lesions, especially if bilateral (Table 1).
Table 1: Clinical conditions in different segments of the arterial vasculature in which the TRA can be evaluated as first choice access.
Segment of arterial vasculature
Left carotid artery stenosis in bovine aortic arch
Right carotid artery stenosis in type III aortic arch
Subclavian artery stenosis
Vertebral artery stenosis
Stenosis in a renal artery with a downsloping take-off
Stenosis in a mesenteric artery with a downsloping take-off
Lower extremity arteries
Stenosis or occlusions in a suprainguinal artery
Bilateral lesions in suprainguinal arteries