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The study by Greenwood et al. (1) carefully assessed the relative contribution of collateral palmar circulation during 30 min of radial artery occlusion. Their conclusion, however, that “transradial cardiac catheterization should not be performed in patients with an abnormal Allen’s test” is not a valid interpretation of their data.
What they have elegantly demonstrated is that among patients with an abnormal Allen’s test, occlusion of the radial artery results in an immediate reduction in blood flow to the principal artery of the thumb by 90%, improving to a 75% reduction after 30 min of arterial occlusion. At the same time, pulse oximetry gives a strong signal in 0% of patients immediately following radial artery occlusion, rising to 64% at 30 min.
The investigators infer that this reduction in blood supply has physiological significance, and that the vascular reserve inherent in hand circulation is inadequate to compensate over time for occlusion of the radial artery, despite acknowledging that either the superficial or deep palmar arch is always complete in cadaver dissections (2). They assume that further clinically relevant collateral recruitment will not be achieved, despite having shown that blood flow in the principal artery of the thumb can improve by over 100% in the first 30 min after radial artery occlusion.
The radial artery approach has now been widespread for 15 years, and is used at hundreds of cardiac centers. Therefore, many thousands of patients have undergone transradial procedures either with a false positive Allen’s test (due to incomplete digital occlusion of the radial artery) or with no assessment of palmar arch circulation at all (3,4). If one accepts that 5% of these patients will develop radial artery occlusion, then if a true positive Allen’s test is an important prerequisite for a safe transradial procedure, there should be many examples of ischemic hands following transradial catheterization. Greenwood et al. acknowledge, however, that there are none.
Finally, there is no evidence that a normal Allen’s test is required for the safe undertaking of a transradial procedure. It is important not to deny this access site to patients with an abnormal test, particularly those in whom a femoral procedure carries increased risks (5).
- American College of Cardiology Foundation
- Greenwood M.J.,
- Della-Siega A.J.,
- Fretz E.B.,
- et al.
- Ghuran A.,
- Dixon G.,
- de Belder A.,
- Holmberg S.,
- Hildick-Smith D.