Transradial access (TRA) has become increasingly utilized in neurointerventions because it reduces access site complications. However, radial artery anomalies can be difficult to navigate, often necessitating conversion to femoral access. We describe the case of a female patient in her early 70s who underwent preoperative embolization of a carotid body tumor via right TRA. Her radial angiogram demonstrated the presence of a radial artery loop which was successfully navigated with a triaxial system but would not spontaneously reduce, even after the guide catheter was advanced into the subclavian artery. However, manual manipulation of the catheters in the antecubital fossa under direct fluoroscopic visualization reduced the loop, allowing the procedure to continue transradially. Although most radial loops can be traversed and reduced using standard techniques, this case demonstrates that manual reduction can be successful when other measures fail. We recommend attempting this method prior to converting the access site.
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As neuroendovascular treatment options continue to increase, mitigating undue procedural risk has become paramount. As such, transradial access (TRA) has increasingly gained popularity as an alternative to transfemoral access, given the consistently lower rates of access site complications.1–5 However, radial artery anomalies, such as a loop, remain one of the most frequently cited factors resulting in TRA failures.6 Although algorithms have been created to help interventionalists navigate these loops, they primarily focus on techniques used to advance the guide catheter past the loop into the brachial artery.7 Few strategies exist describing how to reduce a radial loop that cannot straighten spontaneously after the guide catheter has traversed it.8–10 We discuss a case in which a radial loop would not reduce even after a triaxial system was advanced into the subclavian artery. Ultimately, the catheter system was manually manipulated under fluoroscopy in the antecubital fossa to reduce the loop, allowing the procedure to continue transradially.
A woman in her early 70s with a left carotid body tumor presented for preoperative balloon test occlusion and tumor embolization. At our institution, if two arterial access sites are needed, an effort is made to avoid puncturing bilateral femoral arteries so that an alternative access site is available in the event that it is needed. Thus after administration of general anesthesia, a 7 F 23 cm radial sheath was introduced into the right radial artery and a 5 F femoral sheath was introduced into the right femoral artery. Nitroglycerine 200 µg and verapamil 2.5 mg were administered through the radial sheath to prevent radial artery spasm. Right radial and femoral artery angiograms were obtained to confirm successful access. At this point, a right radial loop with a small (1–2 mm) recurrent radial artery was identified (figure 1). As a result, the radial sheath was only advanced 10 cm into the distal radial artery to prevent inadvertent selection of the recurrent radial. A triaxial system was then introduced into the radial sheath using a soft 0.014 in microwire within a 0.027 microcatheter, a 5 F Sim 2 diagnostic catheter, and a 6 F guide catheter. The microwire was successfully navigated through the loop and the microcatheter was advanced over it (figure 2). The microwire was then exchanged for a stiffer 0.018 in microwire to provide more support. The microsystem was advanced into the subclavian artery allowing the diagnostic and guide catheters to traverse the loop.
Although this was successful, the loop did not spontaneously reduce. The microsystem was removed and a 0.035 inch guidewire was then advanced through the diagnostic catheter into the right subclavian artery. The diagnostic and guide catheters were then brought into the subclavian artery over the guidewire. Nevertheless, the radial loop did not reduce (figure 3). Manual manipulation of the catheter system in the antecubital fossa was performed under direct fluoroscopy to reduce the loop (figure 4). The guide catheter was then advanced further into the subclavian artery to further reduce the loop. The 23 cm sheath was then advanced over the guide catheter into the brachial artery. The procedure was completed transradially without complications. Prior to removal of the guide catheter, a brachial artery angiogram was performed to confirm that the loop was still straight and without vessel injury (figure 5). The catheter was then removed, and a final angiogram was obtained through the sheath as it was retracted through the loop ensuring it regained its original shape (figure 6).
A radial artery loop is an uncommon anatomical variant of the radial artery that can create significant challenges during transradial neurointerventions. They occur in approximately 1–2% of patients and result in TRA failure rates as high as 80%, even in the most experienced hands.7 Their etiology is believed to be a result of incomplete involution of the recurrent radial artery during development, which ultimately tethers the true radial artery as the arm grows. This leads to the formation of a 360° turn in the proximal radial artery just distal to the brachial bifurcation. The recurrent radial artery is typically located at the distal apex of the loop, resulting in an acute turn in the true radial artery. This makes traversing the loop difficult as wires often preferentially go into the recurrent radial. Furthermore, it often prevents the loop from initially reducing, even when navigated successfully. As a result, experienced transradialists suggest using a microwire to select the loop to prevent multiple attempts with a larger guidewire which can lead to radial artery spasm and even vessel perforation. We have also found that routinely obtaining a radial artery angiogram prior to catheter advancement also helps obviate the risk of inadvertent injury to the recurrent radial.11
Most operators run into issues while attempting to traverse the loop, and therefore most available algorithms focus on this aspect of radial loop navigation and employ variations of the same principle: using a shapeable 0.014 inch microwire and a microcatheter to preferentially select the radial loop and avoid the recurrent radial artery.7 12 13 Some have also suggested using a second microwire for additional support if the microcatheter will not track through the loop. A partially inflated balloon at the end of the guide catheter can also be employed so that it tracks into the larger lumen of the loop and avoids the recurrent radial artery as it is advanced.7 12 13 However, minimal discussion exists on the management of loops that have not reduced after being traversed successfully.
A stepwise escalation of stiffer catheter systems and wires, similar to the techniques described in this case, is often employed once the loop has been navigated successfully but has not reduced spontaneously. The introduction of a stiffer braided diagnostic catheter with a VERT style tip into the brachial artery will frequently reduce the loop as they provide more support than the standard Simmons catheters used in TRA. Using increasingly stiffer wires within such a catheter can also aid in the reduction of the loop. In those instances where a radial loop does not reduce after these techniques, manual manipulation of the catheter system at the level of the antecubital fossa should be attempted prior to converting to a different access site. Although there is some theoretical risk of arterial avulsion during these reduction techniques, in most large series where radial angiography was performed prior to navigating a radial artery loop, there does not appear to be any increased risk of forearm hematoma in those patients where the loop was navigated and reduced successfully.7 14–16 As such, we suggest using the technique outlined above as it may reduce the loop when other measures have failed.
A radial artery loop is a rare and potentially challenging anatomical variant to navigate transradially.
A triaxial system with a 0.014 inch microwire and microcatheter should be used to navigate a radial artery loop if a 0.035 inch guidewire does not easily traverse the loop.
Once successfully traversed with a microsystem, the diagnostic and guide catheters should be advanced through the loop cautiously. If more support is needed, the microwire can be exchanged for a stiffer 0.018 inch microwire.
If the diagnostic and guide catheters can be advanced into the subclavian artery but the loop has not reduced, exchanging the microsystem for a stiff 0.35 inch guidewire may help to reduce it.
If the loop still will not reduce, manual manipulation of the catheter in the antecubital fossa should be performed in an attempt to straighten the system before access site conversion is considered.
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Contributors All authors contributed significantly to the development of this manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial, or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.