Keep an Open Mind About Distal Radial Access

Ferdinand Kiemeneij1, MD, PhD, Darren Klass2, MD, PhD, and Sandeep Nathan3, MD, MSc

Ferdinand Kiemeneij1, MD, PhD, Darren Klass2, MD, PhD, and Sandeep Nathan3, MD, MSc

One of the interesting aspects of practicing as an interventional radiologist or cardiologist is that our fields are extremely dynamic. Over the course of our careers, we have witnessed the introduction of numerous techniques that have promised to make procedures safer and more convenient for patients, more efficient for operators, and/or more cost-effective for the institution. Some of these techniques have fallen by the historical wayside, while others, such as transradial access (TRA) for coronary angiography and interventions, have more than stood the test of time since the first reports were published.1-4 In the case of the latter, transitioning to radial access is supported by data showing lower rates of: complications in stable patients, including mortality, major adverse cardiac events, and access site complications5-7; acute coronary syndromes8; and acute myocardial infarctions.9-10 TRA is also associated with quicker time to ambulation, decreased length of stay, and greater patient comfort, which explains why patients frequently request TRA when it is presented as an option.7 In 2016, the European Society recommended transradial access for coronary interventions as a Class I, level A guideline.11

The benefits of TRA are even easier to appreciate in the context of the evolving nature of the instrumentation used during procedures. Over time, advancements in the engineering of catheters, sheaths, and other equipment have helped drive evolutions in technique, and arguably, vice versa. At a practical level, the positive feedback loop created by the interplay of improved techniques and instruments has yielded the development of a better way to gain access during percutaneous procedures. Radial access has become the default option for each of us in diagnostic and procedural vascular interventions. Perhaps equally as important, though, is that the evolving nature of TRA challenges each of us to continually assess and reassess how we perform our procedures with the aim of making incremental improvements in outcomes.

It is in this spirit of dynamism that all of us are now approaching the concept of distal radial access, which is itself an evolution of the forearm radial technique. From an anatomic perspective, the distal aspect of the radial artery presents more superficially and runs along hard bone, which makes it is easier to compress, suggesting the potential for faster and easier hemostasis. Furthermore, puncturing distal to the superficial palmar branch theoretically maintains antegrade flow through the radial artery even if occlusion occurs, thereby likely preventing thrombosis over a long segment. Thus, accessing the radial artery distal to the wrist in the anatomic snuffbox is a reasonable option for primary access, as well as a suitable bailout option.


Avtandil Babunashvili, MD, PhD, an interventional cardiologist based in Moscow, and Alexandr Kaledin, MD, PhD, of St. Petersburg, Russia, should be credited with introducing the concept of distal radial access. Dr. Babunashvili initially used distal access for retrograde angioplasty of occluded radial arteries12, and was subsequently an author of a paper describing the anatomic basis and physiologic rationale for considering the distal radial artery as the primary access site.13 Dr. Kaledin presented data in 2014 at the EuroPCR meeting on a large group of patients who had undergone distal radial access.14

Both operators influenced Farshad Roghani-Dehkordi, MD, from the Isfahan Cardiovascular Research Institute. Dr. Roghani presented a series of patients undergoing distal radial access at the Third Isfahan Transradial Course in Iran in 2016, where Dr. Kiemeneij was also lecturing.15 The technique seemed radical at first, but it was later revealed to be a rather ingenious solution to a unique problem: Dr. Roghani got the idea to attempt distal access because many of his female patients wear bracelets that cover the forearm. While he found it feasible to perform radial access in the forearm, achieving hemostasis was often difficult (personal communication [FK]).

Ultimately, though, what piqued Dr. Kiemeneij’s interest in this technique was the suggestion of improved safety, as noted above, and the ergonomic advantages that left distal radial access seems to provide.16 For example, the patient’s wrist can be placed in an even more comfortable working position relative to forearm TRA, and there is rarely a need to reach over the patient to perform the procedure via the left radial artery. It is also not necessary to change the room orientation specifically for left distal access. Although hemostasis can be rapidly achieved, there still is need for close monitoring by nurses and staff. In most cases, left distal access is utilized, particularly if the patient is right-hand dominant, and the time to regain full function is minimal.

Suggested Benefits Associated With Radial Access

More and more positive data on (left) distal radial access are being published.17-28 In fairness, the more publications appear, the more local complications will be described as well.29 Simultaneously, many of the benefits associated with distal access are becoming less and less theoretical at this point of time. While our collective experience is that hemostasis time is shortened with distal access compared to forearm TRA, longer-term follow-up and accumulation of data on outcomes from more patients is necessary to definitively determine if that is the case. Likewise, while our consensus is that distal access is preferable to forearm TRA for most cases, there is not as yet solid justification for abandoning other access techniques — but because the jury is still out on distal access, neither is there rationale to ignore it altogether. The ergonomic benefits and aspects of room setup might be enough to continue exploring distal access as an option, particularly in peripheral TRA, where left-sided access is preferable due to the shorter distance to vessels below the diaphragm. The suggestion that distal access might be more advantageous for safety reasons demands we keep an open mind. A prospective prevalence study on the effect on hand function after distal radial access is ongoing to shine light on this important question.

Certainly, using distal access does not exclude utilizing other forms of percutaneous access when necessary: we are all “radial first”, not “radial only” operators. Ultimately, the patient’s presenting anatomy and fitness for radial access are important determining factors, as are patient and operator preference. Nevertheless, we feel that operators should become comfortable with gaining access using different sites, inclusive of good practices for maintaining hemostasis, and so distal radial access is an important addition to one’s skill set. Thus, especially in academic centers, where there is need to train surgeons in various techniques, adopting distal access as the primary technique may be practical and desirable, as proximal radial access is very easy to master after being properly trained in distal access.

Another aspect of distal radial access is that setting up the room for left-side distal radial access is done in a similar manner as preparing for a femoral case, but with the patient’s arm positioned across the body, thus allowing the operator to work from the more comfortable right-hand side. If a different access site is required, the patient can simply be repositioned. As a result, there may be practical reasons to default to distal access in appropriately selected patients.

Considerations for the Learning Curve

As with any technique, learning distal radial access is associated with a learning curve. At the same time, employing distal access is well within the scope of any interested interventional cardiologist or radiologist. While the capital outlay is minimal from the institutional standpoint, an investment of time by the operator and staff are required to successfully and safely implement distal access. For those transitioning from femoral to radial access, including distal, learning the new technique might require a number of cases before becoming comfortable with the maneuvers and instruments. However, having familiarity with forearm TRA should help flatten the learning curve. According to Kaledin’s data, and according to personal experience of the authors, the learning curve takes about 50 patients.14

As more practitioners adopt this technique, new nuances, indications, and technical aspects will assuredly continue to emerge. In addition, courses on distal access are starting to be offered at major conferences and meetings, and industry-sponsored courses, like the ThinkRadial Program offered by Merit Medical Systems, provide ample opportunities to learn the necessary techniques and instruments.

An important aspect of finding success with distal access is patient selection, as there are cases for which this particular approach is less than ideal. For example, peripheral vascular access, especially in taller patients, may be difficult to achieve. According to Dr. Klass, pelvic procedures in trauma patients and distal gastrointestinal bleeding are examples of cases performed by interventional radiologists in which distal access might compromise reach or the ability to apply the necessary torque forces to the catheter. More generally, it may be wise to avoid complicated situations during early cases, such as individuals with prominent osteoarthritis in the thumb or wrist, in which case overgrowth of bone can lead to tortuous arterial anatomy.

On the other hand, according to Dr. Kiemeneij, radial artery spasm at the forearm might be an indication for distal access, because a good pulse can be found in the anatomical snuffbox due to collaterals from the palmar and dorsal arches, making it possible to find the lumen and cross the spastic segment retrogradely. In addition, in extremely overweight patients, the radial artery is easier to find and to compress at the location of the snuffbox than at the forearm or groin, making the procedure easier and safer.

During distal access, use of ultrasound is highly recommended for a number of reasons. Importantly, it helps with identification of the exact access site within the borders of the snuffbox and avoiding too-distal access. It is worth mentioning that attempting to gain access distal to the anatomic snuffbox invites risk of accessing a branch artery, such as princeps pollicis, and increases the potential for hematoma due to the lack of bony structures below the vessel. Ultrasound also helps visualize anatomic features to avoid during needle puncture (such as the tendons that form the border of the anatomic snuffbox). As well, ultrasound can be used to gain a sense of how the wire will track over the course of the vessel in the forearm, where the anatomy can be unpredictable. In current practice, many interventional cardiologists do not routinely use ultrasound, and so the additional requirement of adopting it into use may contribute to the learning curve.

Operators also need to gain an understanding of the instrumentation used during distal access. An open metal needle for a clean anterior puncture is recommended in order to avoid painful puncture of the underlying periosteum of the scaphoid and trapezium bones, and to avoid bleeding from the backwall puncture hole that can lead to development of a hand hematoma. In our view, use of a sufficiently stiff stainless steel guidewire with a spring coiled tip helps not only with access, but also for tracking the sheath through the artery. Because of the angulation between the distal and the forearm radial artery, the sheath should be smooth and slippery, well tapered, and should have a minimal outer diameter in relation to the inner diameter, while still being kink resistant. Fortunately, industry has already responded to this emerging technique, with some companies offering kits with different needle, guidewire, and sheath options, and thus the need to assemble the necessary equipment by opening multiple packs is all but eliminated. We are also starting to see products being developed specifically for distal access procedures, such as the Prelude Sync Distal (Merit Medical) radial compression device. That company also offers a variety of guidewires, some of which are suitable for use in distal access.

Overall, the learning curve with distal radial access is navigable, but there are nuances to the technique that should be appreciated in the interest of patients’ safety.


Our consensus opinion is that, in the majority of cases, distal radial access is easier to perform and may confer better safety than forearm TRA, which has in turn proven to be safer and more convenient than transfemoral. Although we encourage operators to learn the various techniques and decide for themselves which access route is best, because a broad repertoire of skills is necessary to perform procedures in different anatomy and in different patients, we expect that distal access will become the default technique in the near future.

There may be some valuable lessons we can learn from the emergence of radial access relative to transfemoral. First, radial access was introduced over 25 years ago, and so if a transition toward distal radial is to occur, it is likely that it will be a number of years before it emerges as a preferred technique. This is actually a very good thing, as there is need for longer-term follow-up and more safety data. At the same time, for operators who have already embraced radial, distal access is just one more way to accomplish a procedure that is better for patients than the status quo.

More to the point, one of the key reasons each of us began exploring distal access is that our experiences with radial taught us to keep an open mind about procedural adjustments that might improve safety, efficiency, and patient and operator convenience, in addition to being more cost effective. The spirit of innovation eventually led to an improved way of gaining percutaneous access, and we may be on the precipice of another similar discovery with distal radial access.

It is worth repeating that over the course of the past 25 years, radial technique and instruments have evolved, and it is reasonable to assume that the distal access technique will undergo a similar maturation. The technique will almost assuredly continue to become more and more refined, perhaps miniaturized even further. At the current time, whether distal is better than forearm radial access is an open question, but in our view, that is a question well worth exploring. 


1Department of Cardiology, MC Zuiderzee Hospital, Lelystad, the Netherlands; 2Vancouver General and UBC Hospitals, Vancouver, Canada; 3University of Chicago Medical Center, Chicago, Illinois

Disclosure: Dr. Sandeep Nathan, Dr. Darren Klass, and Dr. Ferdinand Kiemeneij are paid consultants of Merit Medical.

The authors can be contacted via Dr. Ferdinand Kiemeneij at

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