Anatomical Considerations in Transradial Intervention
Anish Chandarana Hemang Baxi
The Heart Care Clinic, Ahmedabad,Gujarat

BACKGROUND
In many parts of world, transradial approach has been gaining progressively more acceptance due to reduction of access site related complications, earlier patient mobilization, probably better clinical outcome and reduced hospital cost compared to transfemoral route. One of the important reasons why many centers are reluctant to accept this route is more frequent anatomical variations encountered in this approach leading to complications and need of crossover to other route1-4. So, all those who have adopted or wish to adopt this route for intervention, must know before and be able to recognize these variants promptly during procedure to increase the overall success rate.
NORMAL ANATOMY OF RADIAL ARTERY
The radial artery originates at the bifurcation of the brachial artery about 1 cm below the antecubital fossa. From this point, it passes on the lateral margin of the forearm until it reaches the level of the wrist. At this level it lies atop of the scaphoid bone, the trapezium and the external lateral ligament. Distal to this it dives deep (to reticulum) and laterally. In the hand it forms the deep and superficial palmer arches by joining with the branches of ulnar artery.
Just 2-3 cm above the crease of wrist, radial artery runs superficially being easily accessible for puncture and effectively compressed for achieving hemostasis. It disposes the minimum diameter needed for a 6F sheath to be easily introduced. Due to dual perfusion of hand through palmar arches, in event of radial artery thrombosis severe hand ischemia is almost rare4, 5.

FAILURE OF TRANSRADIAL APPROACH AND ROLE OF ANATOMIC VARIANTS
Even in learned hands, failure rate of 1-5% has been reported for transradial procedures6, 7. Many reasons like failure to puncture the artery, radial artery spasm, and anatomic variations of radial-brachial-axillary-subclavian artery axis or arch of aorta have been responsible for this failure.
In expert hands, anatomic variations are mostly the underlying cause of failure. Anatomic variations of the radial artery are quite common and their incidence has been reported up to 22%, though in many of these, performing transradial procedure is not much difficult For example, variation in course of radial-brachial-axillary artery usually does not pose any hindrance, but anomalous origin of radial artery does because of its frequent association with severe tortuosity and complex anatomoses with the brachial-axillary axis6-9.

Tortuosity

Radial artery tortuosity is reported between 2 to 6.1% in different angiographic and ultrasonic studies9-12. Different definitions of tortuosity (presence of a bend or angulation of more than 45˚ to 90˚) have been used in different studies4. But, more the angulation and less the diameter, procedure becomes increasingly difficult due to more chance of spasm. Brachial artery tortuosity is less common and easier to negotiate due to its larger diameter.

Correspondence: Dr Anish Chandarana The Heart Care Clinic, Balleshwar Avenue, Opp Rajpath Club, Sarkhej - Gandhinagar Road,Bodakdev, Ahmedabad – 380015 Gujarat India
Email:anish.chandarana@heartcareclinic.org

people, and patients with hypertension. Severe tortuosity results in decreased transmission of forward force and increased friction while attempting to advance catheter towards arch of aorta. Atheroemboli and dissection are likely complications while negotiating through this.
2.Anomalous origin of radial artery
Anomalous, high origin of radial artery (Figure 1a) is the most common of all anomalies with frequency reported to be between 3.2 to 9.75% in angiographic studies and as high as 14.2% in dissection materials4,9,12. When radial artery originates above the proximal boundary of ante cubital fossa, it is said to have higher origin .In many such instances either the whole vessel or part of it has a smaller caliber and tortuous course, making it prone to have severe spasm and difficult catheter passage.
3.Loops
Radial artery loop represents redundancy in the vessel which may be present since birth or develops due to aging changes (Figure 1b). It is defined as a full 360˚ loop of the artery. It may be located in the proximal part of radial artery below brachial bifurcation or in radioulnar anastomoses. Reported frequency of radial artery loop is quite low, around 0.8 to 2.3%, but when present it produces the greatest challenge to operator as it is reported to be associated with a very high transradial failure rate of 17% to 37%9,12,13. Larger the diameter of the loop and smaller the caliber of artery, it is more difficult to negotiate. Not only that, in many patients, a recurrent radial artery of a small caliber going straight up arises from the top of the loop, which allows the passage of wire or catheter upto mid arm. Unless check dye injection is performed, a lot of time is wasted and rupture of small vessels occurs if too much force is excerted.
Brachial artery loop is very rare14-17.
4.Atherosclerosis and stenosis
Presence of significant atherosclerosis and stenosis is more often seen in subclavian-brachiocephalic arterial system as compared to radial-brachial-arterial system. Usually, it is not severe enough to preclude transradial procedure, but early recognition does help to prevent complications. When present in radial artery, sheath insertion and catheter manipulation may be a major problem16-18.
5.Aortic arch and brachiocephalic trunk issues
A variety of anatomic variations may exist with aortic arch. Also ageing, high blood pressure, atherosclerosis, certain connective tissue diseases and infective-inflammatory diseases affect aortic arch posing a problem at this level during catheterization occassionally.
Retroesophageal right subclavian artery (arteria lusoria), the most common congenital anomaly of arch, is seen in 0.4-2%12,13,19 of patients. Right subclavian artery arises from posterior and distal part of arch of aorta where it joins with descending aorta. Due to high degree of angulation, it is difficult to push catheter to ascending aorta, leading to failure rate as high as 40%12.

Unfolding of aortic arch with elongation and acute angulation at take off of brachiocephalic trunk also poses almost similar technical challenge16-19.
6. Spasm
Radial artery is an extremely vasoreactive vessel. Hence, spasm (Figure 1c) is a major limitation of transradial approach. Besides causing significant discomfort to the patient, it can also lead to procedural failure too. It can occur during puncture attempt, during passage of catheters or at the end of procedure. It can lead to non ability to insert sheath or manipulate catheter or even removal of sheath8. Uncommonly it can lead to major trauma like artery evulsion.
Chances of spasm increases when artery is of smaller caliber or has tortuosity or other anatomic variations. Female gender, inexperienced operator, long and complex procedure with multiple catheter exchange etc. are other variables associated with increased risk of spasm20-21.

Figure1: Anatomic variations of the radial artery: a) High takeoff of Radial artery at almost 90˚΄s origin from brachial artery, b) Radial loop, c) Radial Artery Spasm

7.Differences between left and right radial arteries:
Though most of the anatomical considerations remain same for left and right radial arteries, a few basic differences do exist, which influences certain decisions
a)On right side, subclavian artery is a branch of innominate artery, which itself is a main branch of arch of aorta. While on left side, subclavian artery is a direct branch of aorta, eliminating a small vessel segment equivalent to innominate artery. Atheromatous disease in this segment, which has two consecutive bifurcations, would make it more rigid and increase the difficulty in maneuvering the catheter.
b)A retro-esophageal subclavian artery, rarely seen on the right side, is never seen on the left side.
c)In a post CABG patient, it is much easier to hook the LIMA and SVG through left radial route.
d)Renal arteries, other abdominal organ arteries or lower limb arteries are better accessed through left radial route because it bypasses the distances of aortic arch22.

CONCLUSION
Proper patient selection and pre-procedure preparation; gentle and patient approach; liberal use of dye injection(check shoots) when in doubt; asking patient to breathe deeply when needed and thoughtful  problem solving approach are the key factors to achieve high transradial success rate.

REFERENCES:
1.Agostoni P, Biondi-Zoccai GG, de Benedictis ML, Rigattieri S, Turri M, Anselmi M, et al. Radial versus femoral approach for percutaneous coronary diagnostic and interventional procedures; Systematic overview and meta-analysis of randomized trials. J Am Coll Cardiol. 2004;44:349-356.
2.Cooper CJ,El-Shiekh RA,Cohen DJ,Blaesing L,Burket MW,Basu A,et.al.Effect of transradial access on quality of life and cost of cardiac catheterization: A randomized comparison.Am Heart J 1999;138(3 Pt 1):430-6.
3.Roussanow O,Wilson SJ,Henley K,Estacio G, Hill J,Dogan B, et al.Cost-effectiveness of the radial verses femoral artery approach to diagnostic cardiac catheterization.J Invasive Cardiol 2007;19(8):349-53.
4.Lo TS, Nolan J, Fountzopoulos E, Behan M, Butler R, Hetherington SL, et al. Radial artery anomaly and its influence on transradial coronary procedural outcome. Heart. 2009; 95(5):410-415.
5.Layton KF, Kallmes DF, Cloft HJ. The Radial Artery Access Site for Interventional Neuroradiology Procedures. American Journal of Neuroradiology 2006; 27:1151-1154.
6.Kiemeneij F, Laarman GJ, Odekerken D, Slagboom T, van der Wieken R. A randomized comparison of percutaneous transluminal coronary angioplasty by the radial, brachial and femoral approaches: the access study. J Am Coll Cardiol. 1997; 29(6):1269-1275.
7.Ludman PF, Stephens NG, Harcombe A, Lowe MD, Shapiro LM, Schofield PM, et al. Radial versus femoral approach for diagnostic coronary angiography in stable angina pectoris. Am J Cardiol. 1997; 79(9):1239-1241.
8.Louvard Y, Pezzano M, Scheers L, Koukoui F, Marien C, Benaim R, et al. Coronary angiography by a radial artery approach: feasibility, learning curve. One operator's experience. Arch Mal Coeur Vaiss. 1998;91:209-215.
9.Yoo BS, Yoon J, Ko JY, Kim JY, Lee SH, Hwang SO, et al. Anatomical consideration of the radial artery for transradial coronary procedures: arterial diameter, branching anomaly and vessel tortuosity. Int J Cardiol. 2005; 101(3):421-427.
10.Rodríguez-Niedenführ M, Vázquez T, Nearn L, Ferreira B, Parkin I, Sañudo JR. Variations of the arterial pattern in the upper limb revisited: a morphological and statistical study, with a review of the literature. J Anat. 2001; 199(Pt 5):547-566.

11.Yokoyama N, Takeshita S, Ochiai M, Koyama Y, Hoshino S, Isshiki T, et al. Anatomic variations of the radial artery in patients undergoing transradial coronary intervention. Catheter Cardiovasc Interv. 2000; 49(4):357-362.
12.Valsecchi O, Vassileva A, Musumeci G, Rossini R, Tespili M, Guagliumi G, et al. Failure of transradial approach during coronary interventions: anatomic considerations. Catheter Cardiovasc Interv. 2006;67:870-878.
13.Hamon M, Mc Fadden E. Transradial approach for cardiovascular interventions. ESM Edition 2003. Chapter 16.
14.Louvard Y, Lefèvre T. Loops and transradial approach in coronary diagnosis and intervention. Catheter Cardiovasc Interv. 2000; 51(2):250-252.
15.Lo TS, Fountzopoulos E, Butler R, Hetherington SL, Zaman A, Perera D, et al. Incidence of radial artery anatomical variations in patients undergoing transradial coronary angiography and intervention: influence on procedural outcome. Heart 2007;93(6)(Supp 1):A27.
16.Valsecchi O, Vassileva A, Musumeci G, Rossini R,, Tespili M,Guagliumi G,et al. Failure of transradial approach during coronary interventions: anatomic considerations, Catheter Cardiovasc Interv 2006; 67(6):870-8
17.Louvard Y, Dumas P, Loubeyre C, Lefevre T, Morice MC. Predictive factors of failure in transradial coronary angiography and angioplasty.Arch Mal Coeur 2002; 95(suppl 3):514.
18.Hildick-Smith DJr, Walsh JT, Lowe MD, Stone DL, Schofield PM,Shapiro LM, et al. Coronary angiography in the presence of peripheral vascular disease: femoral or brachial/radial approach?Cathet Cardiovasc Intervent 2000; 49:32-7.
19.Abhaichand RK, Louvard Y, Gobeil JF, Loubeyre C, Lefèvre T, Morice MC. The problem of arteria lusoria in right transradial coronary angiography and angioplasty. Catheter Cardiovasc Interv 2001; 54:196-201.
20.Kiemeneij F,Vajifdar BU, Eccleshall SC, Laarman G, Siagboom T, van der Wieken R.Evaluation of a spasmolytic cocktail to prevent radial artery spasm during coronary procedures.Catheter Cardiovasc Interv 2003; 58(3):281-4.
21.Ruiz-Salmerón RJ, Mora R, Vélez-Gimón M, Ortiz J, Fernández C, Vidal B et al. Radial artery spasm in transradial cardiac catheterization. Assessment of factors related to its occurrence, and of its consequences during follow-up. Rev Esp Cardiol. 2005;58:504-511.
22.Spaulding C, Lefevere T, Funck F, Thebault B, Chauveau M, Ben Hamda K, et al.Left radial approach for coronary angiography: results of a prospective study. Cathet Caardiovasc Diagn 1996; 39(4):365-70.