It has been well-established that transradial access (TRA) has significant benefit compared to transfemoral arterial access (TFA) for patients at high risk for arterial access bleeding. This advantage is most notable for patients presenting with acute coronary syndromes – especially ST-elevation myocardial infarction [ 123 ]. Other benefits of TRA include early ambulation, shorter hospital stay, lower costs, and a strong patient preference for this method of arterial access [ 4567 ]. This has led to significant uptake in TRA globally and more recently in the United States [ 8 ]. As the TRA experience has matured, extensive study has led to a better understanding of the challenges presented and optimization of technique. This issue ofCardiovascular Revascularization Medicine (CRM) contains three manuscripts that pertain to this continued refinement.

Despite the advantages of TRA, enthusiasm has been dampened to some degree by the technical expertise often required to accomplish TRA compared to TFA procedures. This is illustrated by the learning curve required for TRA proficiency. While previous reports suggested a threshold of 50 cases is necessary to achieve a learning curve plateau, recently, Huded et al. reported that improved TRA results are achieved with an accrued operator experience of up to 300 cases [ 9 , 10 ]. Technical challenges associated with this learning curve are related mainly to anatomical issues such as small vessels, radial tortuosity, subclavian tortuosity, and congenital variations such as high take off radial arteries and “loops.” These anatomical challenges occur in 12.6-13.8% of cases [ 11 , 12 ]. Spasm occurs with an incidence rate of 10.3-14% despite the administration of spasmolytic cocktails and can also pose a significant challenge [ 13 , 14 ]. In order to overcome these challenges and achieve a high degree of success with TRA, it is necessary to become well-acquainted with several maneuvers and certain types of equipment. These maneuvers are often called “Tips and Tricks” and are regularly discussed at TRA meetings.

Balloon-assisted tracking (BAT) is one very valuable technique that has been used for crossing through small, tortuous, calcified, or dissected portions of arteries. Initially described by Patel et al., BAT utilizes the smooth and tapered distal portion of an angioplasty balloon to greatly reduce the friction generated by the advancement of the firm non-tapered distal edge of a sheath or guide as it is advanced through the artery [ 15 ]. BAT has been previously described but essentially involves five steps:

• 1) 

  Advancing a sheath or guide catheter proximal and adjacent to the area of concern;

• 2) 

  Crossing the area of concern with a wire;

• 3) 

  Advancing an appropriately sized angioplasty balloon (sized to the artery) over the wire, positioning it at the end of the sheath or guide such that the distal ½ extends beyond the tip;

• 4) 

  Inflating the balloon at low pressure; and

• 5) 

  Advancing the balloon/guiding catheter/sheath as a unit through the area of concern.

Since the initial report by Patel et al., there have been similar case reports from several centers indicating widespread adoption of the technique [ 161718 ]. In this issue of CRM , Felekos et al. retrospectively reviewed 1100 consecutive TRA cases performed in the United Kingdom and found that BAT was utilized in 2.72% of cases overall (n=30). The reasons for using BAT were spasm (66.6%), dissection/perforation (16.6%), tortuousity and loops (6%), and small or diseased arteries (10%). The BAT technique allowed for successful completion of the TRA procedure without crossover in all 30 cases, the majority (86.7%) of which were PCI [ 19 ]. This is consistent with prior reports of BAT from high-volume radial centers. Patel et al. examined their registry (n=8254) and reported the use of BAT in 63 patients (0.76%) with difficult radial and subclavian anatomy. They achieved a procedure success rate without crossover of 94.2% [ 20 ]. Another registry report by Obaid et al. analyzed 6 French TRA cases (n=716) and revealed a 5.4% (n=39) incidence of severe spasm refractory to spasmolytic medications. Using BAT, they reported a 91 % procedure success rate [ 21 ]. . The mean increase in procedure time for BAT compared to other cases was 3.2 minutes, and fluoroscopy time increased by only 24 seconds. The benefit of BAT may also be useful in challenging TFA cases, as recently reported by Merella et al., where it was used to navigate a diagnostic catheter through calcified and tortuous iliac anatomy [ 22 ]. Recently, we employed a 5 mm diameter peripheral balloon over a 0.035” wire to facilitate passage of a 16 Fr sheath through complex iliac anatomy in order to successfully perform a transcatheter aortic valve replacement procedure [ 23 ]. The difficult cases described above could not have been successfully performed without the benefit of BAT, which should be considered an essential addition to a radial operator’s collection of “tips and tricks.”

Initial widespread experience with cardiac catheterization as described by Sones et al. utilized upper extremity access through direct visualization of the brachial artery through a cut down procedure [ 24 ]. Due to technical challenges and a high complication rate, this approach was subsequently supplanted by the femoral arterial approach and pre-shaped (Judkins) catheters. As functional equipment with reduced catheter profiles was introduced, continued evolution of arterial access interestingly led back to upper extremity access, this time distal to the brachial artery. Currently, six possible upper extremity arterial access locations are favored for procedures utilizing ≤6 French equipment. These include the radial artery, the less frequently utilized ulnar artery and the more recently described distal radial artery or “snuffbox” approach [ 25 ]. With multiple access site options, continued improvement in equipment, and numerous studies demonstrating several advantages for TRA compared to TFA, the argument has been made for a total upper extremity arterial access approach for coronary and many peripheral vascular procedures.

In this issue of CRM , Kedev et al. present a large (n=30,848), single-center analysis of the primary success rate of right TRA. Although comprising mainly coronary procedures, 959 cases involved carotid, subclavian, or iliac/femoral procedures. These very experienced operators report a primary success rate of 94%. Crossover was mainly related to right radial access failure (4.1%), but it is important to understand that some of these crossovers occurred prior to attempted arterial access due to a poor-quality radial pulse. Kedev et al. employ a strategy of routine radial angiography following TRA that resulted in 104 further crossovers (0.35%) due to anatomic complexity. Interestingly, the primary alternative access site was the ipsilateral ulnar artery, which was used more than twice as often as contralateral radial access. TFA was used in only 0.6% of crossover cases [ 26 ]. Initially thought to be untenable, ipsilateral transulnar access in the case of TRA failure has recently been reported by this same group to be a reasonable option due to the presence of large interosseous collaterals [ 27 ]. While TFA may still be required for large-bore (>6 Fr) access and certain lower extremity (infra-inguinal) procedures, this study by Kedev et al. reinforces the notion that upper extremity access may be applied to the vast majority of patients undergoing catheter-based coronary and many peripheral vascular procedures. In those few cases where the right radial artery is inadequate or unusable, crossover to an alternative upper extremity location can be employed with a high rate of success.

TRA has been demonstrated to result in “ubiquitous” radial artery injury, which results in thrombosis and chronic radial artery occlusion (RAO) in between 1% and 10% of cases [ 282930 ]. Although rarely associated with symptoms, RAO is deleterious, as it precludes future ipsilateral TRA. It is therefore good practice to take appropriate measures to prevent RAO. Several strategies have been demonstrated to reduce the incidence of RAO and include: anti-spasm medications, smaller hydrophilic sheaths, and patent hemostasis technique for sheath removal (especially with concurrent transulnar compression) [ 31 , 32 ]. Another important intervention demonstrated to reduce the incidence of RAO is the use of systemic anticoagulation. Early in the TRA experience, Spaulding et al. reported an RAO of 71% without the use of anticoagulation. This fell to 24% and then 4.3% with the administration of 2000-3000u of heparin and 5000u of heparin respectively [ 33 ]. Subsequently, there have been consistent reports linking heparin use, particularly at higher doses, with post-TRA arterial patency [ 29 , 34, 35 ].

In this issue of CRM, Dahal et al. perform a meta-analysis of six randomized TRA studies (n=2239) that compare standard-dose (5000u) to lower-dose heparin (2500 u in five studies and 50 u/kg in one study) to prevent RAO. The endpoints examined were the dose effect on near-term RAO and bleeding complications. Both 5- and 6-Fr diameter sheaths were used in these studies. A pneumatic compression device was used for sheath removal in four studies, but details regarding the use of patent hemostasis are not available. Ultrasound evaluation was employed for the evaluation radial artery patency in five studies, and the reverse Barbeau test was used in one study. As expected, standard higher-dose heparin was associated with a trend toward a lower incidence of RAO (4.2% vs. 10.7%; RR 0.40, 95% CI: 0.16-1.0; p=0.05). The tradeoff, however, was a trend toward a higher risk for hematoma (2.2% vs. 1.1%; 1.83 (0.91-3.66); p=0.09). Details regarding the hematomas are not available for all studies, but three studies only reported hematomas >15 cm. Radial artery compression times were longer in the higher-dose heparin group by a mean of 9.64 minutes (p=0.0008) [ 36 ].

While this study supports previous evidence that anticoagulation at higher levels prevents RAO, it also points out that there is a downside with more hematomas (many of them severe) and longer compression times. This begs the question, “Is there a strategy that could yield optimal outcomes?” There is evidence to suggest that with meticulous attention to patent hemostasis technique, RAO rates may not be significantly impacted by heparin dose. In the PHARAOH study, Pancholy et al. demonstrated essentially equivalent early (7.5% vs. 7.0%; p=NS) and late (4.5% vs. 5.0%; p=NS) RAO rates for patients treated with a priori heparin (50u/kg) compared to heparin administered only provisionally for loss of flow during patent hemostasis [ 37 ]. Critically, patent hemostasis was meticulously performed per study protocol. From a practical standpoint however, properly performed patent hemostasis requires careful attention and a high level of provider intensity. Unfortunately, despite good intentions, many busy catheterization laboratories are unable to allocate sufficient resources to achieve truly consistent high quality patent hemostasis. This likely explains the benefits related to higher-dose heparin in regard to radial artery patency found in most studies and the current recommendations for higher-dose heparin [ 31 ]. Therefore, unless consistent high-quality patent hemostasis can be reliably demonstrated, higher-dose heparin (5000u or 50u/kg) should be administered as the standard of care.

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