Fig. 3.1
Deep and superficial palmar arches formed by radial and ulnar artery
3.2 Deep and Superficial Palmar Arch
Moving closer towards the hand, the radial artery makes its way into the palm by going through the gap between the metacarpal bones of the thumb and index finger, which then passes the little finger metacarpal bone, where the terminal parts of the radial artery meet with the ulnar artery’s deep palmar branch to form the deep palmar arch (Deep vola arch). The deep palmer arch is formed mainly by terminal parts of radial artery and gives branch of the palmar metacarpal arteries which serve the fingers but not the thumb,latter is supplied by princeps pollicis artery (Fig. 3.1). The palmar metacarpal arteries terminate at finger clefts by joining the common digital branches of the superficial palmer arch. Dorsally, the deep palmer arch also gives off three perforating arteries (proximally) in connecting the digital branches of the superficial palmar arch with dorsal metacarpal arteries.
In completion of the superficial palmer arch (superficial vola arch), the superficial palmer branch of the radial artery links with the terminal branch of ulnar artery at the palmar region. The superficial palmer arch gives branch to 4 common palmer digital arteries supplying the medial 3 1/2 fingers. The superficial palmar arch is formed predominantly by the ulnar artery, with a contribution from the superficial palmar branch of the radial artery. However in some individuals the contribution from the radial artery might be absent, and instead anastomoses with either the princeps pollicis artery, the radialis indicis artery, or the median artery, the former two of which are branches from the radial artery.
The presence of variations in the superficial palmer arch is of great surgical importance. The anatomic variation of palmer arch has been described by many previous papers with different results and percentages. However, most paper suggest that majority hand showed complete superficial palmer arch which implies that collateral circulation is present in majority of cases [1]. In addition, studies also showed that there were no cases of an incomplete superficial and deep palmar arch being present in the same hand. Such as in the case of the incomplete deep palmar arch, all these hands had complete superficial palmar arches [2]. This would result in least number of complications considering radial artery harvesting for coronary bypass or transradial cannulation, thus provides a rational for performing these procedures. However, since all specimen in these studies were free of atherosclerosis disease, the authors from those studies still recommend testing the hand (by using the modified Allen test, Doppler ultrasonography, photoplethysmography, or oximetric techniques) before performing an arterial intervention to identify the occasional case in which collateral circulation is compromised by the presence of arterial disease [2].
In conclusion : Both the radial and ulnar arteries sub branch in such a manner that blood is sufficiently provided to the entire hand, allowing dual blood supply which also gives a critical advantage to transradial intervention in rivalry to transfemoral intervention.
3.3 Allen’s Test
The aim of the Allen’s test is to inspect the superficial and deep palmar arches. Acute vascular disease is indicated by presence of abnormal arches. The superficial and deep palmar arches provide the blood supply to the fingers. The radial artery and the ulnar artery supplies the deep palmar arch and superficial palmar arch, respectively. Allen’s test had been performed prior to radial puncture interventions.
The examiner performs the test by initially palpating and applying pressure on the radial and ulnar arteries by using three fingers on each artery. This act occludes the blood supply to the entire hand. The patient is then asked to clinch then open his/her hand tightly 10 times, ending with an open hand position. The patient should not over extend the fingers and wrist as this could cause the soft tissues to appear white due to tension, leading to a false positive result. The palmar region of the hand should then appear white or pale. Then the examiner releases the pressure applied from one of the arteries. A positive result is noted when it takes >5 s for palmar blood supply to return (note colour). Repeat these same tests to assess the un-examined artery (Fig. 3.2).
Fig. 3.2
(a) Palpation of the radial and ulnar arteries. (b) Manual compression of the radial and ulnar artery upon clenching the fist (c) Palmar blanching upon opening the fist. (d) The ulnar artery pressure is released; if the colour returns to pink, it is indication of positive test; if the colour does not return to pink, it indicates a negative test [3]
Because Allen’s test is more subjective, in some labs, patients who are considered for transradial catheterization should be tested by the modified Allen’s test by means of a pulse oximeter, also known as the Barbeau test. The modified Allen’s test involves a few alterations. After the patient is asked to close the fist, the examiner massages blood out of the hand. The pressure to both arteries will then be given by using the thumb rather than three fingers. After the patient opens his/her hand paleness should be noted around the thenar. The examiner will then release the thumb off the ulnar artery and observe the thenar eminence. If the normal colour returns within 15 s, it indicates intact blood flow. The same steps should be repeated for the radial artery however, the pressure applied by the thumb should first be released off the radial artery [4] (Fig. 3.3).
Fig. 3.3
(a) Modified Allen’s test by means of a pulse oximeter, also known as the Barbeau test; (b) Type A: No damping of pulse tracing immediately after radial artery compression, Type B: Damping of pulse tracing, Type C: Loss of pulse tracing followed by recovery of pulse tracing within 2 min Type D: Loss of pulse tracing without recovery within 2 min
This is a great method to test adequate blood flow, because with the pressure applied occlusion is formed within the arteries limiting the blood to enter the hand. Clinching the hand repetitively pushes the blood out of the hand which justifies the white/pale colour. At the time when the examiner releases the pressure from one of the arteries and normal colour is visible self-explains adequate blood circulation from that particular artery.
The sensor clamp is preferably applied to the thumb. The presence of a pulse tracing during radial artery compression, as in types A and B, represents uninterrupted pulsatile arterial blood filling. Because the radial artery pulse could be present with a patent palmar arch in several cases of radial artery occlusion (RAO), that is occasionally seen in the type A pattern; in which, pulsatile blood flow to the thumb is not reduced. RAO can then be suspected when ulnar artery compression produces a type D reading, enabling pre- and post-procedural evaluation of radial artery patency.
In type C, pulsatile blood flow, and pulse oximetry, is abolished temporarily by radial artery compression, but it reappears within a pre-specified amount of time, arbitrarily chosen to be 2 min. When radial artery compression is repeated within approximately 1 min, a type C pattern is often changed into a type B pattern, suggesting collaterals recruitment induced by relative hand ischemia. In type D, pulsatile blood flow, and pulse oximetry, is abolished by radial artery compression and does not reappear within 2 min. The type D pattern was considered to be a contra-indication for the transradial approach.
Whether the Allens test is still a valid method to examine both the radial and ulnar blood flow for transradial interventions?
According to studies till date, it has been a rather controversial topic predicting whether the Allens test is sufficient to certify that ischemic complications post transradial access will not occur. According to readings from earlier studies, after 30 min of radial artery occlusion patients with a negative Allens test result proved to have an inadequate amount of blood circulation to the thumb, and an increased thumb capillary lactate, which is suggestive of ischemia. This suggested that patients with an abnormal Allens test should not undergo procedure via the transradial route. On the contrary, a more recent RADAR study suggests that the Allens test and oximetry–plethysmography are not scientifically reliable and predictive for noting rises in lactate levels, weakness in the hand, or persistent discomfort for transradial interventions. Thus, the study concluded that completely denying radial access due to a negative Allens test result is not a solid enough justification. Currently, many transradial centres have come very close to completely nullifying the Allens test for pre–procedure tests for TRA. However, emphasis on techniques such as oximetry–plethsmography for patent hemostasis along with other techniques should be strengthened to minimise potential RAO complication [5, 6].
3.4 Anatomic Anomalies at Brachial Bifurcation
The radial and ulnar arteries both run through either side of the forearm to the wrist. Proximally, they both form recurrent arteries that complete the arterial anastomosis at the elbow. In addition, the ulnar artery gives off an intraosseous branch that bifurcates to form anterior, posterior and recurrent branches. Anatomic anomalies are frequently encountered at brachial bifurcation which impede the successful cannulation (Fig. 3.4).
Fig. 3.4
An artwork illustrates anatomic course of the right radial/ulnar artery from elbow (brachial bifurcation) to wrist (palm arch)
Radial recurrent artery
The radial current or pseudo radial artery is a small artery that branches of the radial artery just below the elbow. Its incidence rate is 8.3 % [1]. It runs next to the brachial artery then joins the brachial artery close to the axillary artery. During catheterization in TRI, the wire could possibly travel up the radial recurrent artery instead of the brachial artery (Fig. 3.5a). This could be problematic as the lumen of the radial recurrent artery is small, leading to wiring challenges and possible perforation (Fig. 3.5b).
Fig. 3.5
(a) Radial recurrent artery (white arrow) (b) Hydrophilic wire entering into the radial recurrent branch
Radial loop
The radial loop is a tight bend forming a 360° loop which occurs in the radial artery, distal to the bifurcation of the brachial artery. Occurring in approximately 2 % [2] of patients, the radial loop poses a higher chance of technical failure. The radial loop has a tendency to avert the straight tipped wire up the side to the recurrent radial artery, which runs parallel to the brachial artery. Patients with a radial loop have a high tendency of having a recurrent radial artery branch or pseudo radial artery. This puts the patient at risk of avulsion and wire perforation as well as causing wiring challenges (Fig. 3.6).
