In the hands of experienced operators and high-volume transradial catheterization centers, transradial coronary angiography and intervention offer improved patient comfort, decreased access-site complications, and decreased costs without compromising procedural success or long-term outcomes. Patients presenting with ST-elevation myocardial infarction (STEMI), in particular, benefit from a transradial approach to coronary intervention.
Attaining proficiency in transradial catheterization and intervention, especially for a seasoned practitioner experienced in transfemoral procedures, requires time, effort, and humility. Despite this, the United States has seen a dramatic increase in recent years in cardiologists willing to “make the leap” to transradial cardiac catheterization. Transradial access has become the default mode of catheterization for a growing number of cardiologists and will undoubtedly continue to be increasingly performed.
Percutaneous coronary intervention (PCI) today is not what it was two decades ago. The field of interventional cardiology has seen a dramatic increase in procedural success and declines in ischemic and bleeding complications, largely because of advances in antithrombotic therapies, evidence-based pharmacological strategies, and device technology.  With these successes, recent attention has turned to reducing complications associated with vascular access.  The search for a procedural approach to bleeding reduction, coupled with the goal of improving patient comfort, has led to a renewed interest in radial artery access, as opposed to the traditional femoral artery access, for coronary catheterization and intervention.
Approaching the heart from the upper extremity is not a new concept. Indeed, the first human cardiac catheterization was performed via the brachial vein by Werner Forssman in 1929,  and the first transradial aortic cannulation was described in 1948.  Initial angioplasties in the 1970s involved large guide catheters, however, which required larger arterial access, so femoral cannulation became the primary mode of arterial access for coronary catheterization and intervention.
Although the first transradial angiography was reported by Campeau et al in 1989,  followed shortly thereafter by the first transradial coronary stenting by Kiemeneij and Laarman in 1993,  transradial coronary catheterization was relegated to “backup” access for patients without alternate arterial access.
The transfemoral approach has remained the primary route of arterial access for cardiac catheterization in the United States. As recently as 2008, only 1.3% of coronary interventions in the United States were performed via the transradial approach.  Transradial catheterization is currently much more frequently performed in Europe and Asia. [8, 9] However, transradial cardiac catheterization in the United States has seen growing use and enthusiasm over recent years, driven by improved patient comfort, decreased length of stay and hospital costs, and accumulating data showing clinical benefit, primarily in terms of decreased access-site complications. In the United States, the proportion of transradial PCI procedures increased from 1.2% in the first quarter of 2007 to 16.1% in the third quarter of 2012 and accounted for 6.3% of total procedures from 2007 to 2012 (n=178,643). 
Advantages of transradial cardiac catheterization and intervention
The primary advantage of transradial cardiac catheterization and intervention is reduced access-site complications. [7, 11, 12] Because the radial artery is small and superficial, it is easily compressible, and bleeding complications associated with radial arterial access are extremely rare.
Femoral arterial cannulation, contrarily, carries a significant risk of access-site bleeding complications. Hematomas and pseudoaneurysms at the site of arterial access are frequent and often painful complications of cardiac catheterization that are much less common with transradial access.  Retroperitoneal hemorrhage is a potentially life-threatening complication of femoral arterial catheterization. Certain patient populations, such as elderly and obese patients, are at an increased risk of bleeding complications from femoral arterial catheterization.
Patient groups who derive an increased benefit from transradial cardiac catheterization include elderly persons,  those with acute coronary syndrome,  and those receiving IIb/IIIa inhibitors. 
Improved patient comfort is also a significant advantage to transradial cardiac catheterization. Even with vascular closure devices, transfemoral cardiac catheterization requires that the patient maintain a supine position for an extended period postprocedure in order to achieve hemostasis. This can be especially uncomfortable in patients with chronic back problems. Transradial catheterization obviates the need for postprocedural flat time, and most patients are able to ambulate immediately following the procedure. Patient preference is clearly in favor of transradial catheterization.
In the RIVAL trial, 90% of patients randomized to undergo the transradial approach reported preference for the same approach if a repeat procedure was needed, as opposed to 49% in the transfemoral arm.  Other studies have reported improved quality-of-life measures with transradial versus transfemoral cardiac catheterization. 
Transradial catheterization also has the potential to reduce procedural costs. [22, 23] Fewer complications equate to shorter hospital stays.  Additionally, less staffing is needed to care for patients following transradial catheterization. Furthermore, same-day discharge is feasible after coronary intervention, which shortens stays and significantly reduces costs. [24, 25] One study showed PCI with transradial access was associated with a cost savings exceeding $800 per patient relative to transfemoral access. 
Disadvantages of transradial cardiac catheterization and intervention
Transradial cardiac catheterization and intervention has a steep learning curve. [27, 28] Negotiating the radial artery and aortic arch with guidewires and catheters from the transradial approach is more technically challenging than from the femoral approach. The radial and subclavian arteries are frequently tortuous and require operator proficiency at navigating such vessels.
Catheter manipulation and engagement of coronary arteries from the transradial approach is also technically different than that from the femoral artery and requires a different skillset. Studies have shown a significant decrease in procedural failure, access-site crossover, procedural time, and fluoroscopic time with increasing operator volume and experience. [20, 29] Jolly et al found that, among experienced transradial operators, the procedural success rate of the transradial approach compared with transfemoral approach did not differ, but, among inexperienced operators, the procedural failure rate was high.  A substudy of the RIVAL trial further evaluated the role of center and operator volume on clinical outcomes. The authors found a strong interaction between overall and transradial center volumes, and clinical outcomes, but not transfemoral center volumes. 
One study found that independent predictors of transradial failure among low-to-intermediate volume transradial operators included patient age older than 75 years, prior coronary artery bypass grafting (CABG), and short stature. 
Increased procedural time and increased radiation exposure are both a concern with transradial cardiac catheterization. Several studies have shown longer procedural time and fluoroscopy time for transradial coronary angiography compared with transfemoral catheterization. [32, 33] The gap, however, significantly decreases with operator volume and experience. For experienced operators, there is little difference in fluoroscopy time; indeed, procedural times are actually shorter with transradial catheterization.  Cumulative radiation exposure to the operator with either left or right radial artery approach is well under the annual dose-equivalent limit. 
Radial artery occlusion is a potential complication with transradial catheterization, though rarely a clinically significant event if adequate ulnar supply to the palmar arch is confirmed preprocedurally. Radial artery occlusion can potentially limit future radial access and limit the use of the radial artery for dialysis fistulas or as grafts for coronary artery bypass, so attempts should be made to avoid occlusion. Procedural techniques have been shown to significantly reduce radial artery occlusion. [35, 36, 37]
Hand ischemia following transradial angiography is extremely rare. Of the estimated 650,000 transradial procedures performed annually around the world,  only one incident of hand ischemia has been reported, which was successfully revascularized percutaneously. 
Coronary interventions in specific patient/coronary lesion subsets
Most complex coronary interventions can be safely performed using a transradial approach. Bifurcation procedures, thrombus aspiration, chronic total occlusion procedures, ostial lesions, rotational atherectomy (with up to 1.5-mm diameter burr size), and embolic protection can all be successfully and routinely performed through 6F sheaths, meaning that the vast majority of patients are suitable to undergo these procedures via the transradial approach.
In a single-center study, transradial percutaneous coronary revascularization for unprotected left main coronary disease was associated with similar procedural success, abbreviated hospitalization, reduced bleeding, and comparable late-term clinical safety and efficacy compared with transfemoral catheterization.  Revascularization of coronary chronic total occlusions via a transradial approach has also been shown to be safe and effective. 
Patients presenting with STEMI have been a subject of much investigation with regard to suitability for transradial primary PCI. In this population known to be at an increased risk of bleeding, transradial catheterization would seem well suited to reduce access site and bleeding complications. Initial concerns regarding a perceived increase in procedural time and decreased door-to-balloon time have been allayed by multiple studies showing transradial catheterization safe and feasible for STEMI patients without compromise in door-to-balloon time. [41, 42, 43, 44, 45, 46, 47]
The RIVAL trial, a large multicenter randomized trial with a prespecified subset analysis of nearly 2000 STEMI patients, showed a significant benefit in a combined outcome of death, myocardial infarction, stroke, or non–CABG-related major bleeding at 30 days among patients undergoing transradial versus transfemoral catheterization.  Patients in cardiogenic shock have mostly been excluded from these studies.
Two additional randomized trials have compared transradial versus transfemoral arterial access for primary or rescue PCI in patients presenting with STEMI. The RIFLE STE-ACS trial was a multicenter randomized controlled trial enrolling 1000 patients with STEMI undergoing primary or rescue PCI and included patients in cardiogenic shock. The primary endpoint of 30-day combined events occurred in 68 patients (13.6%) in the transradial group and 105 patients (21%) in the transfemoral group (P = .003). Transradial access was associated with significantly lower rates of cardiac mortality (5.2% vs 9.2%, P = .020), bleeding (7.8% vs 12.2%, P = .026), and shorter hospital stay (5 d vs 6 d; P = .03). 
The STEMI-RADIAL Trial also randomized patients presenting with STEMI to transradial or transfemoral access and enrolled over 700 patients. The primary endpoint, the cumulative incidence of major bleeding and access-site complications, at 30 days, occurred in 1.4% of radial access (n=348) and 7.2% of femoral access (n=359) (P = .001). Combined adverse events occurred in 4.6% of radial access and 11% of femoral access (P = .028), although mortality rates were similar (2.3% vs 3.6%, respectively, P = .31). The authors concluded that “in patients with STEMI undergoing primary PCI by operators experienced in both access sites, the radial approach was associated with significantly lower incidence of major bleeding and access site complications and superior net clinical benefit. These findings support the use of the radial approach in primary PCI as first choice after proper training.” 
One study specifically examined the question of safety and efficacy of transradial PCI in women. The SAFE-PCI trial enrolled nearly 1800 women undergoing elective PCI who were randomized to transradial or transfemoral approach. There was no difference in death, vascular complications, or unplanned revascularization at 30 days: 5.2% vs 3.4% (P = .26). 
Alternate arterial access should be considered in patients with abnormal Allen test findings, poor hand perfusion, or physical examination results suggesting that the radial artery is too small for sheath insertion.
Patients with a known arterial occlusion or anatomy that has previously been demonstrated to be prohibitive to transradial access should undergo catheterization via an alternate arterial access site.
Ipsilateral radial access in patients with hemodialysis fistulae or shunts is generally avoided.
Challenges of transradial cardiac catheterization and intervention
Guide catheter size via transradial catheterization is limited in comparison with the transfemoral approach. Ultrasonographic evaluation of normal radial arteries has shown a mean diameter of 2.69 ±0.40 mm in men and 2.43 ±0.38 mm in women.  Generally, a 6F sheath (2 mm in diameter) is the largest size that can be used in a radial artery, although 5F may be the largest sheath size suitable for smaller patients. Although most coronary interventions can be easily performed with a 6F sheath, a larger guide catheter is helpful in some situations, for example when added guide support is needed or if two stents are needed simultaneously.
Thin-walled sheathless guide catheters have been developed that allow a larger inner-diameter catheter without increasing the outer diameter of the catheter in the artery or the size of the arteriotomy. [52, 53]
Radial artery spasm frequently presents a challenge to performing transradial catheterization. Because the size of the catheter and sheath approach the size of the radial artery, even subtle spasm of the radial artery can lead to patient discomfort and complicate manipulation of the catheter. This condition is generally preventable with the administration of intra-arterial vasodilators. Ample sedation also decreases radial artery spasm. The use of smaller catheters also prevents radial artery spasm. See the videos below.
Several anatomical variations present difficulty in performing transradial coronary catheterization. The radial artery is often tortuous or has “loops,” which are obstacles to the advancement of wires and catheters. An experienced operator can overcome most of these radial anomalies (see the videos below).
Likewise, the subclavian artery is often tortuous, especially in elderly and hypertensive patients. This presents not only an obstacle to advancing a catheter but also makes manipulation of the catheter in the aorta challenging. The course of the patient’s aorta can also serve as a technical impediment during transradial catheterization. Patients with a high arch often have a very acute angle at the right subclavian takeoff, making coronary engagement and guide support for interventions a challenge, even for the most experienced operator. See the videos below.
Because the hand receives dual blood supply from the radial and ulnar arteries, a patent palmar arch is confirmed with the intent of reducing the likelihood of hand ischemia in the event of radial artery occlusion. Preprocedural assessment of the upper-extremity circulation includes evaluation of the radial pulse and patency of the palmar arch with Allen testing. Plethysmography is also often used to confirm patency of the palmar arch. 
A careful physical examination, including a thorough assessment of upper- and lower-extremity pulses, is essential in choosing the most appropriate arterial access site for cardiac catheterization. Allen testing and plethysmography are performed to assess hand perfusion. The risks and benefits of all potential arterial access sites should be considered on a case-by-case basis.
Intra-arterial vasodilators are administered to prevent radial artery spasm. Heparin is given to reduce radial artery occlusion. Patent hemostasis, in which gentle postprocedural pressure is applied to the wrist without obstructing blood flow, has been demonstrated to reduce radial artery occlusion.
The RIVAL trial
The largest randomized trial to date comparing transradial and transfemoral approaches for coronary angiography and intervention was published in April 2011.  The RIVAL trial randomized over 7,000 patients with acute coronary syndrome from 158 hospitals in 32 countries to transradial versus transfemoral cardiac catheterization and/or coronary intervention. This contemporary trial, enrolling participants over a 4-year period ending November 2010, utilized modern pharmacological therapies and interventional technologies that well-reflect current practices in interventional cardiology.
In the RIVAL trial, there was little difference between the catheterization groups in terms of primary outcome of death, myocardial infarction, stroke, or non–CABG-related major bleeding at 30 days (3.7% of patients in the radial access group and 4% in the femoral access group [P = 0.50]). Procedural success rates were high in both groups: 95.4% in the transradial arm, 95.2% in the transfemoral arm (P = 0.83).
The rate of access-site crossover was higher for the transradial arm (7.6%) than the transfemoral arm (2%, P < 0.0001). Reasons for crossover in the radial group (when available) included radial spasm (5%), radial artery loop (1.3%), and subclavian tortuosity (1.9%). The reasons for crossover in the femoral group included femoral iliac tortuosity (0.6%) and peripheral vascular disease (0.6%).
There was no significant difference in major bleeding events between the groups. Major vascular complication rates were higher in the transfemoral arm (3.7% vs. 1.4%, P < 0.0001). Ultrasound-confirmed symptomatic radial occlusion requiring medical attention occurred in 6 patients (0.2%) in the radial group. No cases of major access-site bleeding at the radial access site were reported.
The median fluoroscopy time was higher in the radial group than in the femoral group (7.8 min vs. 6.5 min, P < 0.0001).
Analysis of prespecified subgroups in the RIVAL trial found no difference between the transradial and transfemoral approach among patients older than 75 years or patients with high body-mass index. There was a nonsignificant trend favoring the radial approach among women.
There was a nonsignificant trend favoring a transradial approach among higher-volume operators. The transradial approach was significantly favorable among centers with the highest tertile volume of radial procedures (primary outcome of 1.6% vs 3.2%; P = 0.015), whereas neither approach was favored among the lowest-volume tertile. Although patients with cardiogenic shock were excluded from the RIVAL trial, 1958 of the patients enrolled had STEMI, among whom a transradial approach was significantly favorable compared with a transfemoral approach (primary outcome 3.1% vs 5.2%; P = 0.026).
Limitations of the RIVAL trial include what some have deemed a low rate of vascular closure devices (25.6%) in the femoral arm and an unexpectedly low bleeding event rate. The latter suggests expertise in the trial above that of the average practitioner (the RIVAL operators’ median PCI volume was >300 procedures per year, far greater than the average US operator). In addition, bivalirudin, a direct thrombin inhibitor with demonstrated reduction in bleeding risk over the combination of heparin and IIb/IIIa antagonists in primary PCI for acute myocardial infarction, [55, 56] was used at a very low rate (2.2% of patients in the radial group and 3.1% of those in the femoral group received bivalirudin).
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