considerations
Factors influencing success of the radial access route include radial artery diameter; anatomical variations; and operator proficiency and expertise with the radial approach [2,6]. Simple palpation of the radial pulse provides a reasonable feel for selection of sheath size and feasibility of TRA. Sheath: artery ratio is an important determinant of radial spasm, patient discomfort and radial artery occlusion.
There is generous vascularization to the hand by the radial, ulnar and interosseous arteries. This collateralized blood supply provides excellent protection against distal ischemia, which outside of distal embolization from the radial sheath is exceptionally rare [12]. The modified Allen’s and Barbeau tests are still used by some operators to assess the patency of the ipsilateral ulnar circulation. A number of RCTs have demonstrated that in patients undergoing TRA, an abnormal modified Allen's or Barbeau tests does not predict adverse events or increased hand ischemia (either clinical or subclinical). As such, tests of ulnar/collateral patency are not supported in current guidelines for access site selection [3,13].
Radial vs ulnar
Compared with the radial artery, the ulnar artery takes a deeper course; is in close proximity to the ulnar nerve; and is further from bone. As a result, hemostasis is more challenging with higher rates of neurovascular complications associated with trans‐ulnar access. A meta‐analysis of randomized trials comparing radial and ulnar approaches suggests similar time to access and fluoroscopy time, but over three‐fold increase in access complications (RR 3.58; 95% CI, 2.67 – 4.79, p < 0.001) [14]. We therefore prefer TRA except in patients with diminutive/hypoplastic radial artery with very large dominant ulnar artery at the wrist.
Right vs left radial
The feasibility and outcomes of right and left trans‐radial TRA are similar [15], however many operators prefer right TRA due to its compatibility with the traditional cardiac catheterization laboratory layout.
Operators should be familiar with left radial access which is commonly indicated in case of failed right TRA, occluded right radial artery, extreme right radial artery tortuosity, arteria lusoria, arteriovenous shunt in the right arm or plans for a future shunt, past or future use of the right radial artery as a free graft, post bypass grafting with the left internal mammary artery (LIMA) and patient or operator preference [16]. For patients post‐coronary artery bypass grafting (CABG) requiring angiography, left TRA early in the learning curve is associated with increased procedure time, contrast use and operator radiation exposure [17]. Importantly, a recent RCT with experienced radial operators shows left TRA as non‐inferior to a TFA strategy in CABG patients with known anatomy [18].
The left TRA is more convenient for right hand dominant patients, sparing them from temporary post‐procedural reduced use of their dominant hand. For the operator, left radial access can be cumbersome, especially in obese patients. The left arm is required to be in the volar position, however this limits flexion of the forearm to the operator. Furthermore, the operator is exposed to higher radiation doses due to their closer proximity to the radiation source and scatter from the patient’s body [16].
Proximal vs distal radial approach
Recent iterations to TRA technique have seen a large increase in distal radial artery access – as the distal radial runs in the anatomical snuffbox on the dorsum of the hand. This has potential advantages to both patient and operator. A number of studies have demonstrated distal radial access as a feasible and safe alternative to traditional radial access for both coronary angiography and PCI [16,19] with a success rate of 88–100% [20]. Ferdinand Kiemeneij was a pioneer of TRA for coronary interventions in the early 1990s and recently presented his cohort of patients undergoing coronary procedures from the left distal radial artery[16]. For most patients, it is preferable to retain their dominant right hand immediately following the procedure. Given the distal puncture site, any arterial occlusion spares antegrade flow through the superficial palmar branch thereby reducing risk of proximal RAO. Additionally, the distal artery runs in the hand compartment where hemostasis can be achieved with lighter compression immediately over the scaphoid and metacarpal bones.
Potential limitations of the distal radial approach include the slightly smaller caliber of the distal radial artery, which may pre‐dispose to spasm, as well as the close proximity to tendon sheaths and bone that can increase discomfort if punctured. Another important consideration is that distal radial access increases the distance to target vessels by 3–5 cm. As a result, in patients above 6'1", standard length catheters may not reach the coronary circulation. Table 3.1 details common diagnostic and guide catheters with radial specific and traditional catheter types.
Access technique and navigating common problems
Access technique
Data suggests that over half of failed TRAs relate to inadequate radial artery puncture (57% due to failure to cannulate)[21]. Careful vessel palpation and puncture remain key to successful transradial procedure – particularly given the inherent risk of spasm with multiple punctures. The Society for Coronary Angiography and Interventions (SCAI) consensus document highlights the role for ultrasound stating that operators should develop “proficiency with ultrasound guidance to facilitate forearm vascular access”[22]. Contemporary evidence is emerging in support of this approach. A recent Australian factorial 2x2 randomized trial of traditional puncture versus ultrasound‐guided and radial versus femoral access showed that ultrasound reduced time to vascular access (93 vs 111s; p = 0.009), number of punctures and improved first‐pass success [23]. Bleeding and vascular complications were similar between approaches. As such operators should aim to utilise ultrasound guided vascular access whenever feasible.
We use conscious sedation with intravenous benzodiazepine and opioids for enhanced patient comfort. Subcutaneous 2% lignocaine (lidocaine) is useful for anesthetic and can be mixed with a small amount of subcutaneous nitroglycerin to facilitate a bigger target for puncture in small calibre radial arteries. Larger volumes of subcutaneous lignocaine can aid needle identification by increasing subcutaneous tissue depth on ultrasound. There are two main techniques with which to perform arterial puncture: a traditional Seldinger technique (“through‐and‐through” puncture) and a modified Seldinger technique (“anterior only” puncture). In the former, a needle with overlying Teflon coated cannula sheath is used to puncture the artery at approximately 30°. A flash of blood indicates anterior arterial wall puncture, and the needle is advanced through the posterior radial artery wall. After removal of the needle, a 0.021" guidewire is placed in the hub of the Teflon cannula and the entire system is withdrawn backwards until pulsatile flow occurs into the hub of the Teflon cannula (indicating luminal cannula sheath position). The guidewire can be advanced and subsequently the hydrophilic introducer sheath inserted over the guidewire. Alternatively, the modified Seldinger technique uses a short 21‐gauge bare needle with anterior‐only puncture technique. After puncture of the anterior wall of the radial artery, a 0.021" guidewire is advanced into the artery allowing removal of the needle and sheathing over the guidewire. A randomized trial showed the traditional Seldinger technique (through‐and‐through) to be a more reliable way to obtain radial artery access with greater success rates, shorter procedure time, and shorter time to gain access. Procedure related complications such as radial hematoma or radial artery obstruction were similar between the two approaches [24]. In the event of failed access, repeat procedures or attempts can be performed more proximally if required.
Table 3.1 Common diagnostic and guide catheter shapes for TRA.
| Universal diagnostic | Diagnostic | Universal guide | Guide (left) | Guide (right) |
|---|---|---|---|---|