Introduction

Transradial access for coronary angiography and percutaneous coronary intervention (PCI) has rapidly emerged as the predominant access route favored by several operators worldwide. The paradigm shift witnessed this past decade has emanated from lower access site complications, increased patient comfort, and earlier ambulation as compared to traditional transfemoral intervention.^[1] However, in some cases, tracking and navigating hardware through radial artery vasculature prove challenging due to smaller radial artery diameter, or complex, variable, or anomalous anatomy.^[2] Radial loop is one of the more challenging coronary anomalies encountered and is synonymous with procedural failure. Its prevalence ranges from 0.8% to 2.3%.^[3] We describe one such challenging case of a radial loop encountered through transradial PCI.

Case Report

A male patient presented with unstable angina. Coronary angiography revealed 95% occlusion in left anterior descending (LAD) coronary artery, 70% occlusion in the obtuse marginal branch, and a mild diffuse lesion in right coronary artery [Figure 1]a and [Figure 1]b. However, while pushing the guiding catheter through the radial artery, a radial loop was encountered [Figure 2]a and [Figure 2]b and attempts were made to straighten the catheter [Figure 1]c. A 1.5-mm GLIDEWIRE Baby-J Hydrophilic Coated Guidewire (Terumo Interventional Systems) successfully crossed the radial loop. A drug-eluting stent (DES) was implanted in LAD. However, we noticed left main coronary artery (LMCA) dissection. Attempts to straighten the loop might have pushed the catheter into the LMCA causing dissection of the artery. A second DES was deployed from the LMCA to LAD by overlapping with the first DES to treat the dissection. The DES was postdilated. However, the dissection was still visible, so postdilation was performed again [Figure 1]d and [Figure 2]e. Thrombolysis in myocardial infarction III was achieved, and the patient was discharged 2 days later [Figure 1]f.

Discussion

Radial loop is the most encountered anatomical variation responsible for procedural failure even for experienced radial interventionalists. However, with the growing numbers of transradial interventions, interventional cardiologists are bound to face obstacles at various anatomical levels beginning from the radial artery to the coronary artery level, as demonstrated in the present case and [Figure 2]. We present a case from our institution along with a literature review [Table 1].^{[1],[2],[3],[4],[5],[6],[7],[8],[9]} We also outline tips and techniques to successfully traverse the loop.

After obtaining an arteriogram, the first strategy is to traverse the radial loop with specialized wires. If a 0.035”J-wire is unsuccessful, an atraumatic 0.035” wire such as a Wholey guidewire (Medtronic) or Magic Torque guidewire (Boston Scientific Corporation) followed by a 0.014” angioplasty wire or a 0.025–0.035” hydrophilic wire may be attempted. The 0.035” 1.5-mm GLIDEWIRE Baby-J Hydrophilic Coated Guidewire (Terumo Interventional Systems) is a more advanced specialized wire that can also be employed in such cases. This wire provides lubricity of a hydrophilic wire while maintaining safety of a small trackable J-tip. If greater support is necessitated to straighten out the loop, a 4-F multipurpose diagnostic catheter or a hydrophilic catheter, such as a Glidecath Hydrophilic Coated Catheter (Terumo Interventional Systems), can be employed to track over the wire. Furthermore, rotating a low-profile catheter while pullback may straighten the loop.^[10]

Mother–daughter technique can be employed if the loop has been crossed with a wire but difficulty straightening out the loop for safe delivery of the diagnostic catheter persists. An earlier method details a pigtail-assisted tracking method. In this method, a 5-F pigtail catheter is loaded in a 6-F guide catheter. The distal pigtail is extended outside the guide and tracked over the wire through the loop. This method circumvents the razor-blade effect of the guide catheter as it passes through the tortuous segment of the radial loop. This avoids dissection in cases where the catheter is aggressively passed through the loop. The protruding pigtail lessens contact between the sharp edge of the guide catheter tip and the vessel wall.^[11]

The balloon-assisted tracking (BAT) is a technique that may be adopted. This is a technique wherein an inflated percutaneous transluminal coronary angioplasty balloon is partially protruded through the distal end of a guide catheter and deployed at 3 or 6 atm. Low-pressure inflation aids the catheter to negotiate extreme curves and loops. A 1.5-mm balloon is recommended for a 5-F diagnostic or guide catheter, whereas a 2.0-mm balloon is recommended for 6-F guide catheter. Balloons of 15 or 20 mm are sufficient. Once the balloon is partially protruded from the distal end of the catheter and deployed, the entire assembly is advanced over a soft-tipped 0.014” guidewire facilitating smooth and nontraumatic progression through difficult vasculature. The key benefit of BAT is prevention of the “razor effect” of the catheter tip to the radial artery endothelium.^[1],[2]

Conclusion

Radial loop is a rare, yet challenging anomaly associated with transradial intervention. However, technical difficulties can be overcome with adequate training, specialized wires, and techniques such as pigtail-assisted tracking and BAT. After crossing the loop with a wire, slight pull on the catheter or wire can straighten the loop. However, caution should be taken as straightening the loop may push the guide catheter a little deep into the artery.

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Conflicts of interest
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