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Whilst various anomalies in radial, brachial, and axillary arterial circulation are common, knowledge of just three key anatomical variations is important as they determine most radial procedural failures outside of failure to puncture [25]. In the event of resistance to the 0.035" guidewire, early arm angiography should be performed. This allows identification of the radial artery origin and the nature of any cubital crossover for “high takeoff” radial bifurcation above the antecubital fossa (Figure 3.1a and b). Anatomical variations should be expected and frequently coexist (e.g. radial loop with accessory radial artery from apex of loop). Angiography helps mapping of connections within the antecubital fossa (to avoid tiny accessory radial branches and visualization of radial loops). We prefer using a hydrophilic 0.035" J tipped guidewire (“Baby J” ‐ Terumo) or occasionally a coronary wire (0.014") for safe and gentle wire manipulation through tortuous and potentially fragile upper limb arteries. With experience these hurdles can often be negotiated but when this is not possible, the asymmetrical nature of forearm vasculature leaves ipsilateral ulnar, contralateral distal or proximal radial access and the femoral approach as alternate options [26].

Figure 3.1 Anatomic variations present challenges to successful transradial access but can usually be overcome. (a) High bifurcation with minimal tortuosity but early evidence of spasm, (b) High bifurcation of radial artery originating in the axillary artery with marked tortuosity, (c) Normal origin of radial artery but radial loop with associated tiny accessory radial (remnant radial) from the apex of the loop. This association is very common and often the operator is unaware of this anatomy until upsizing from a small calibre diagnostic catheter to a larger bore guide catheter which induces spasm of this tiny vessel. (d) Spasm of a tiny accessory radial artery (with subtotal occlusion of the vessel). (e) Subclavian tortuosity in patient with previous bypass grafting. This necessitated angiographic mapping and use of a coronary wire to navigate and exchange for a stiff 0.035" wire inside the catheter to help with torque and manipulation for selective engagement. (f) RORSA: Retroesophageal right subclavian artery (also known as “arteria lusoria”) incidence of 0.5 –2.5% can make entry into the ascending aorta challenging.