De-implementing the Allen`s Test

The arm, from an evolutionary prospective, is a vital structure that has evolved with redundant blood supplies in order to enhance functional survivability. This robust blood supply has allowed the radial artery, and at times the ulnar artery, to be used by interventional cardiologists and other vascular specialists to access the heart and the arterial system. Concerns over the risk of hand ischemia with radial artery occlusion (RAO) have limited the uptake of transradial procedures, but a lingering question since the development of transradial catheterization is whether this concern is founded in evidence or is simply a theoretical risk. Despite the demonstration of safety in modern transradial catheterization that has existed since 1989, the ritual of collateral testing persists as a triage tool for determining suitability for transradial approach. In this issue of the Journal of Invasive Cardiology, Shah et al¹ review multiple lines of scientific evidence to conclude that the robustness of the forearm circulation explains the lack of association between routine tests for hand collaterals and risk for ischemic complications after catheterization. While they conclude that the test is flawed, they also suggest that only a randomized trial would truly answer the question. While strictly true, such a trial would ostensibly require thousands of patients for an outcome – radial artery occlusion – that has little clinical consequence. Therefore, given that a clinical trial will likely never be performed, clinicians must rely on the available evidence to determine the role of testing for collaterals in assessing a patient’s suitability for transradial procedures.

Let us first review commonly cited reasons for using the Allen’s test. One reason is to reduce hand or digital ischemia – a rationale that is clearly refuted by the data presented by Shah and colleagues. Another concern, particularly in the United States, is a medicolegal one. Medical malpractice requires a break in the standard of care, and according to the Federal Rules of Evidence, the basis of what testimony can be heard in federal courts and often used as a guide for state and local courts, requires testimony to be “the product of reliable principles and methods.”² In other words, such testimony by medical experts must be based on sound scientific data. Again, the work of Shah and colleagues demonstrates the weak evidence base for collateral testing to predict postprocedure hand complications. Thus, as the literature has evolved to elucidate the extent and function of the upper limb arterial vasculature, the “standard of care” should evolve as well.

While there may be no role for Allen’s testing to determine the suitability of a patient for transradial procedures, there may be a role for these tests in determining whether the radial artery is patent. Patients with highly efficient hand collaterals may have a radial occlusion from previous catheterization, yet still have a prominent pulse in the distal radial stump. The so-called “reverse Barbeau” test, where both the radial and ulnar arteries are compressed and the radial pressure is released, can demonstrate whether there is antegrade radial artery flow. Likewise, understanding the pattern of collateral flow before the procedure may be helpful in managing patent hemostasis after the procedure. Some hemostasis protocols use distal evidence of antegrade blood flow in the hand to determine pressure required for hemostasis. The signal measured may be different as a function of how efficient collateral flow is, and understanding the crude results from collateral testing can help manage hemostasis.

Early pioneers of transradial procedures used collateral testing out of an abundance of caution to eliminate or reduce potential risks as they explored a new approach to catheterization. It is now clear that collateral testing for triage decisions regarding access site is not helpful and likely will prevent patients who can benefit from radial access from undergoing a safer procedure. While there is still a role for collateral testing in some circumstances for periprocedural management, the use of collateral testing to primarily exclude the use of radial access can be “de-implemented” as it has no scientific support and is not predictive of hand or digital ischemia.

References

1. Shah AH, Pancholy S, Shah S, Buch AN, Patel TM. Allen’s test: does it have any significance in current practice? J Invasive Cardiol. 2015;27:E70-E73.
2. Federal Rules of Evidence, Rule 702 Testimony by Expert Witnesses. Pub. L. 93–595, §1, Jan. 2, 1975, 88 Stat. 1937; Apr. 17, 2000, eff. Dec. 1, 2000; Apr. 26, 2011, eff. Dec. 1, 2011.

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From Penn State Hershey Medical Center, Hershey, Pennsylvania; and Duke University Medical Center, Durham, North Carolina.

Address for correspondence: Sunil V. Rao, MD, 508 Fulton Street (111A), Durham, NC 27705. Email: sunil.rao@duke.edu