Introduction
The radial artery (RA) has been used in coronary artery bypass grafting since it was first introduced into clinical practice in the 1970s by Carpentier . It is a versatile, surgeon- and patient-friendly arterial conduit and is associated with improved long-term outcomes . It is easily harvested either endoscopically or via a traditional open approach. Importantly, RA harvesting can be done concurrently with harvesting of the other conduits including internal thoracic arteries or saphenous veins and thus its use does not extend the duration of surgery. It can reach, with few exceptions, all coronary targets. It is easily anastomosed to the aorta using standard instruments. In contradistinction to the use of bilateral thoracic arteries as coronary grafts to facilitate multiarterial coronary reconstruction, its use is not associated with any increased risk of sternal wound complications. Given its size, there is minimal size discrepancy between the RA and coronary targets, an element thought important in graft durability. The RA is easy to handle and requires no additional technical training for the cardiac surgeon who has mastered grafting the coronary circulation using internal thoracic artery grafts. Surgeons, with interest and expertise in the use of RA, utilize this graft routinely in approximately 60%–75% of all coronary artery bypass grafting patients with excellent results . The use of the RA does require some additional planning, including assessment of collateral circulation of the hand via the ulnar artery, appropriate arterial line management, and the need for an additional team member skilled in harvesting of the RA. To insure the recently reported excellent RA patency rate of 89% , a dedicated harvester with both open and endoscopic harvesting expertise and experience is needed. Given the cosmetic advantages , most patients prefer endoscopic RA harvesting.
Assessing ulnar collateral circulation
It is essential to assure adequate ulnar collateral circulation of the hand in any patient who is thought to be a candidate for RA coronary artery grafting. This can be accomplished in a variety of ways although there is no one agreed upon standard. The simplest and most frequently used technique, is the traditional Allen’s Test assessing for adequate hand reperfusion via the ulnar artery by visual inspection of the hand following opening of the wrist after releasing of digital compression of the ulnar artery while maintaining continued compression of the RA. This maneuver functionally eliminates RA perfusion of the hand and allows for the assessment of hand perfusion based strictly on ulnar flow which will be the only blood supply to the hand following RA harvesting. Reappearance of perfusion of the palm within 5 seconds of releasing ulnar artery compression indicates the presence of adequate collateral perfusion. Reappearance of palmar perfusion within 5–10 seconds is considered borderline collateral perfusion, while the lack of reappearance of perfusion longer than 10 seconds after ulnar release is considered to be indicative of inadequate collateral perfusion. False negative results may be obtained with inadequate RA compression. False positives may be seen if the test is performed in a cool environment resulting in vasoconstriction of both the radial and ulnar arteries. This assessment can easily be done at the patient’s bedside and does not require any additional equipment. It is reliable and inexpensive and it is a good initial screening test that maybe followed by more objective tests . A more quantitative variant of the Allen’s Test, which is used by our group, relies on an oxymetric assessment of adequacy of ulnar collateral flow. This is performed by using a portable pulse oximeter to determine adequate ulnar collateral flow by reappearance of baseline oxygen saturation levels and plethysmographic tracing following the release of digital pressure on the ulnar artery while the RA remains compressed. When the wave form and saturation numbers return almost instantaneously to baseline after the release of the RA, harvesting of the conduit is safe. We believe that this modality adds objectivity to the standard Allen’s Test. In our practice, this preoperative assessment is further confirmed intraoperatively by monitoring the pulse oximetry readings from the index finger once the patient has been heparinized; all the RA branches have been transected and the RA is clamped with an atraumatic clamp prior to its proximal and distal transection. Using this approach, we have not experienced any instances of hand ischemia following harvesting of the RA. Other modalities available for the assessment of adequate ulnar collateral flow that have been used in clinical practice include Duplex ultrasonography and formal segmental plethysmographic measurement. Ultrasonography may provide additional useful information on the size of the RA, possible calcifications, and anatomic variations although we have not found these to be clinically essential. To date, there are no head-to-head comparative outcome studies between these various techniques assessing ulnar collateral circulation, but regardless of which technique is utilized, the incidence of ischemic hand complication following harvesting of the RA is exceedingly rare.
Anatomy of the forearm
Understanding the anatomy of the forearm is essential for safe and efficient RA harvesting ( Fig. 3.1 ). The RA originates from the brachial artery at the elbow. Its first large named branch is the recurrent RA. This vessel should not be mistaken for the much larger ulnar artery and can be transected with impunity maximizing the length of the available conduit. The RA courses in the forearm between the brachioradialis and flexor carpi radialis muscles and lies beneath the fascia connecting these muscles. Proximally, the RA courses deep to the bicipital aponeurosis with its origin from the brachial artery just distal to the insertion of the biceps tendon onto the radius. The collateral circulation between the RA and the ulnar artery is facilitated by the deep and superficial palmar arterial arches. The RA is not in proximity to any motor nerves and thus motor deficits have not been reported following RA harvesting. There are two sensory nerves ( Fig. 3.2 ) that need to be considered during RA harvesting, and these provide sensation to the forearm, the thumb, and the dorsum of the hand. The lateral antebrachial cutaneous nerve, a branch of the musculocutaneous branch of the lateral cord of the brachial plexus, lies in proximity, but not immediately adjacent, to the RA in its proximal third. It provides sensory innervation of the radial aspect of the forearm. The superficial radial nerve which provides sensation to the thenar eminence and the dorsum of the radial aspect of the hand including the index and middle fingers, courses beneath the brachioradialis muscle, and is close to the RA in the distal third of the forearm. Given their anatomical proximity to the RA, these nerves are at most risk for injury in the harvesting process. Sensory deficits following RA harvesting are not uncommon even up to a year postoperatively . Gabapentin has been used successfully to mitigate this complaint if it becomes a source of concern for the patient. The median nerve courses close to the ulnar artery ( Fig. 3.2 ) and must be avoided and preserved especially in its proximal extent at the elbow where the ulnar and radial arteries are in relatively close proximity.
A number of anatomic variations from the normal anatomy have been described including duplication of the RA and a RA course superficial to the fascia . Although rare, such anatomic variability must be kept in mind during the RA harvesting process.
Radial artery harvesting technique
Patient positioning
The patient is positioned in the supine position with the upper extremity from which the RA is to be harvested extended at the patient’s side on an arm board. Usually the nondominant arm is chosen to harvest the RA, but the final decision is based on the adequacy of ulnar collateral flow as well as whether the patient had previous instrumentation of the RA during cardiac catheterization. RA recently used for cardiac catheterization should be avoided if possible under most circumstances. Care should be taken not to hyper extend the extremity past 90 degrees with respect to the operative table to prevent brachial plexus traction injury. The arm is prepped and draped circumferentially. Adequate padding to minimize neurologic complications in the form of nerve palsy is essential. A sterile pulse oximetry probe is applied to the index finger for continuous monitoring of the plethysmography and oxygen saturation levels during the harvesting process and in preparation for an intraoperative Allen’s Test as the final determinant of the adequacy of ulnar collateral circulation just prior to ligation and transection of the RA. A sterile towel is wrapped around the hand and a Steri-Drape is used to secure the arm on the arm board with the wrist extended over a rolled towel at the wrist.
Open harvesting technique
The RA is harvested through an incision extending approximately from 1 cm distal to the elbow crease to 1 cm proximal to the wrist crease ( Fig. 3.3A ). Palpating the brachial artery pulse at the elbow and the RA pulse at the wrist are helpful in locating the proximal and distal aspects of the harvest incision. Hemostasis is achieved with low power (20 W) electrocautery. The dissection is carried through the subcutaneous tissues with subsequent opening of the fascia between the brachioradialis and flexor carpi radialis muscles. This exposes the RA quite clearly as it courses in the areolar connective tissue below the fascia. A Weitlaner retractor gently retracting the two muscles is helpful in exposing the RA. The recurrent superficial RA is identified and maybe divided between fine clips or 4-0 silk ties to maximize graft length. Hemostasis is essential in the harvesting process and prevents misidentification of vessels and nerves. The patient receives 5000 units of heparin intravenously prior to harvesting any of the RA branches. Proximally, the ulnar artery must be unambiguously identified and preserved prior to RA transection. Distally, the superficial palmar arch should be preserved to optimize collateral flow to the hand via the ulnar artery. Preservation of RA endothelial integrity is an important aspect of the harvesting process and impacts long-term durability of the graft. Thus minimal manipulation, and preferably relying on the “no touch technique” of the RA during its harvesting should be the guiding principle and requires an experienced harvester. Typically, the RA is harvested in a pedicled fashion with its venea comitantes and a variable amount of surrounding connective tissue included in the harvested pedicle. We prefer to transect the RA branches between fine clips using scissors. Alternatively, similar to the harvesting technique of internal thoracic arteries, the RA side of its tributaries can be clipped and the distal aspects controlled with electrocautery with excellent outcomes . Once all the branches have been ligated, an atraumatic clamp is placed on the RA and the signal from the pulse oximeter on the ipsilateral hand is checked for any changes as the final check of the adequacy of ulnar collateral circulation ( Fig. 3.3B ). If no changes are noted, the RA is ligated proximally and distally with a heavy nonabsorbable tie and transected. Its proximal end is cannulated with a fine olive tipped cannula and gently flushed with an appropriate vasodilator solution. Gentle distension of the RA with the vasodilator solution allows for application of any additional clips to the RA branches to insure meticulous hemostasis when the RA is placed into the coronary circulation. The RA maybe marked with an indelible marker to minimize twisting of the graft when placed into the coronary system. Following this preparation, the RA is stored in an appropriate warmed bath on the back table ( Table 3.1 ).
