Abstract & Commentary
The Allen’s Test Prior to Transradial Access: A Necessary Precaution or a Waste of Time?
Jeffrey Zimmet, MD, PhD
Associate Professor of Medicine, University of California, San Francisco, Director, Cardiac Catheterization Laboratory, San Francisco VA Medical Center
Source: Valgimigli M, et al. Trans-radial coronary catheterization and intervention across the whole spectrum of Allen’s test results. J Am Coll Cardiol 2014; Feb. 14. [Epub ahead of print].
The transradial approach to cardiac catheterization has been steadily gaining ground over the past several years due to advantages over the femoral approach in terms of bleeding risk, vascular injury, procedural cost, and patient comfort. In many countries around the world, the transradial technique has become the dominant method for cardiac catheterization. The forearm in most patients has a dual blood supply, with the radial and ulnar arteries anastomosing in the palmar arch of the hand. The procedural sheath is often occlusive to antegrade flow for the duration of the procedure. In addition, every published study has demonstrated some risk of occlusion of the radial artery, with frequencies over a wide range as low as 0.8% and as high as 30%. The modified Allen’s test (AT) has classically been used to evaluate the patency of the dual blood supply and palmar arch prior to transradial catheterization, despite its well-described issues with subjectivity and reproducibility (patients excluded based on the AT range from 1-25%). Multiple centers have reported that they no longer assess the blood supply to the hand prior to cardiac catheterization, proceeding with transradial access without the AT.
Valgimigli and colleagues sought to more fully characterize the safety of transradial access in patients across the full range of AT results — normal, intermediate, and abnormal. A total of 203 patients were enrolled between 2007 and 2009 at a single center, and were grouped according to the AT result: 83, 60, and 60 presented a normal, intermediate, and abnormal AT result, respectively. The primary endpoint was the thumb capillary lactate measured at six time points during and after the procedure. The Barbeau modified AT was performed on each subject, with test results reported as A, B, C, or D as per the original description (with pattern D describing no return of pulse tracing within 2 minutes of radial artery compression). Blood flow to the hand at radial sheath insertion and removal was measured semi-quantitatively by ulnar artery angiographic frame counting. Discomfort and handgrip strength were assessed, and each patient also underwent assessment of radial artery patency and plethysmography at follow-up. In the reported cohort of patients, capillary thumb lactate did not differ among the groups immediately after the procedure or at any time point. Likewise, the handgrip strength and discomfort ratings did not differ among groups. Both plethysmography and ulnar frame count readings suggested an improvement in ulnar collateral flow following transradial catheterization, specifically in those with abnormal AT at baseline. The authors concluded that the patency of collateral circulation of the hand is highly dynamic, and that collaterals may be recruited during and after transradial procedures, especially in those with baseline deficiency in said testing. They take this as evidence that the transradial approach should not be denied to appropriate patients based on the AT.
Transradial access for cardiac catheterization is increasingly common, and reported ischemic complications to the hand are rare. Of the few reported cases in the literature, several describe such difficulties in the setting of small vessel disease of the hand, such as CREST syndrome or severe Raynaud’s disease. It is unlikely that tests of ulnar collateral patency would predict these complications.
It is certainly reassuring that thumb capillary lactate, the very measurement that resulted in some early recommendations against transradial access in patients with abnormal AT, did not differ among the groups studied. Other concerns over differential hand strength and discomfort also seem to be laid to rest. The hypothesis of collateral recruitment during and after radial access in patients with baseline abnormal testing is certainly supported by their results, and appears to be a reasonable conclusion.
On the other hand, the number of cases studied here was small. The authors reported that 40% of the abnormal AT group had Barbeau type D patterns (the only pattern for which most labs would exclude the transradial approach) on plethysmography; this corresponds to only 24 patients in the study. At 1 day post-procedure, only five patients had documented radial artery occlusion, and only one of these was even from the abnormal AT group. All five had documented collateral flow by doppler ultrasound. Does this prove that all patients with abnormal AT (Barbeau type D) will remain asymptomatic if they develop radial artery occlusion? It is certainly suggestive, but I for one would like to see more evidence of follow up in the type D population before discarding this test entirely. In the meantime, we would all do well to follow established means for reducing the incidence of radial artery occlusion in our transradial patients.