The distal radial artery is formed by the dorsal carpal branch of the proximal radial artery, which forms the deep palmar arch with the branches of the ulnar artery. Operators can palpate the distal radial artery in the "snuffbox" area, offering a new approach for the interventional treatment of coronary heart disease [14]. The average diameter of the distal radial artery was 2.04 ± 0.43 mm in males and 1.96 ± 0.44 mm in females, meeting the basic requirements of the interventional approach [15]. As a new interventional approach, the distal radial artery can achieve a lower radial artery occlusion rate, which has been confirmed in some studies [6,7,8, 16]. However, the operation and lesion characteristics of coronary angiography and interventional therapy through the distal radial artery are generally unknown (Fig. 3).
In our study, 53 (35.1%) patients underwent CAG, and 98 (64.9%) patients underwent PCI in the dTRI group. These values were was similar to those reported in a study by Yu et al. [17]. The TRI group had higher rates of triple vessel lesions, calcification lesions, CTO lesions, and coronary atherectomy/ELCA techniques compared with the dTRI group. The possible reasons are as follows. For complex lesions, a slender 7Fr sheath combined with 7Fr guidance can provide a higher supporting force to successfully meet the needs of complex operations, such as coronary rotational atherectomy, and to completely address a series of complex lesions, such as CTO and calcification. The RAD of the distal radial artery is relatively small, and the use of a large-diameter sheath may aggravate damage to the radial artery intima and media. On the other hand, some interventional devices (such as guiding, laser catheter, etc.) may not possess sufficient length to treat some patients with long arm and tall stature given that the distal radial artery approach is closer to the distal end of the heart. The LCX stent diameter in the TRI group was greater than that in the dTRI group. The conventional radial artery approach has more advantages in the treatment of lesions with larger reference vessel diameters. During the intervention process, the guiding catheter does not need to be passed through the dorsal wrist to the proximal radial artery, which facilitates the delivery of a larger stent and balloon.
The procedure success rate of 97.4% in the dTRI group was consistent with other studies [17, 18]. Therefore, the distal radial artery approach can complete coronary angiography and most PCI processes with a high procedure success rate and good immediate angiography results. The operation time, contrast volume and total radiation dose in the dTRI group were lower than those in the TRI group but were greater than those in Kim Y and Valsecchi O’s study [19, 20]. Various possible reasons can explain the differences. For example, the surgical complexity of all patients in this study was greater than that of the above two studies, and the number of CTOs, triple vessel lesions and other complex lesions and techniques used in the TRI group was greater than that in the dTRI group.
Preoperative radial artery examination of the puncture site is helpful and necessary to determine the vascular condition (whether there is tortuosity or occlusion) in the radial artery and improve the success rate of the puncture process. The average RAD of the TRI group was greater than that of the dTRI group, which is similar to Meo D’s conclusion and consistent with the anatomical structure [21]. The overall cannulation success rate in the dTRI group was lower than that in the TRI group, and the dTRI group had more puncture attempts and lower one-time successful cannulation rates, which were consistent with the results of Coomes EA’s study [22]. The learning curve of the new puncture technique, the difficulty in palpating the distal radial artery, and the relatively small diameter of the distal radial artery may explain the result.
Six (4.0%) cannulation failures were puncture failures, 8 (5.3%) were wire failures, and 1 (0.7%) was attributed to sheath failure in the dTRI group. The relative tortuosity of the distal radial artery compared with the conventional radial artery may explain the wire failure, whereas the small RAD of the distal radial artery may explain puncture failure. The compression time (273.417 ± 42.098 min) of the TRI group in this study was similar to that of a Japanese study (378 ± 253 min) [23], reporting that the compression time was short in Europe and the United States and long in Asia. This finding may be related to the slower metabolism of heparin in Asians [24]. The hemostasis time of the dTRI group (173.272 ± 41.817 min) was less than that of the TRI group, which was similar to the findings of Vefalı V’s study given the superficial location and the relatively small RAD of the distal radial artery [25]. Therefore, it was easier to compress and finish the hemostasis procedure. This may also explain the finding that although the VAS pain score in the dTRI group was greater than that in the TRI group, the satisfaction score of the two groups was not significantly different, which was similar to that reported in Lee JW’s study [12]. In contrast to those patients in the TRI group, patients under hemostasis in the dTRI group could still move the wrist in an unconstrained fashion; thus, these patients’ quality of life was not affected.
The RAO rates of the dTRI group were lower than those of the TRI group, which was consistent with the conclusion of Cai et al. [26]. This finding may be attributed to the double blood supply of the distal radial artery formed by the superficial palmar arch and deep palmar arch. The smaller RAD of the dTRI group may explain the increased incidence of RAS in the dTRI group. No significant differences in serious complications, including severe hematoma and arteriovenous fistula, were observed between the groups, which was similar to the research results of Lee JW et al. [12].
RAD at the puncture site and other indicators, including BMI, diabetes and acute coronary syndrome (ACS) as described by our clinical experience and a previous study [27], were included in multivariate analysis of the overall cannulation rate success rate in the dTRI group. We found that RAD with an AUC of 0.747 (95% CI 0.663–0.860) was a predictor for the overall cannulation success rate, which may be explained by the notion that a larger diameter can enhance palpation of the distal radial artery. BMI was identified as a risk factor for cannulation failure in a previous study [27]. This inconsistency may be due to the different sample sizes.
Some limitations in this study should be noted. The effect of coronary intervention via the dTRI approach on the treatment of complex and high-risk lesions and the effect on complex coronary intervention techniques via the dTRI approach were not determined. In the future, the exact indications, safety, and feasibility of distal radial artery interventional therapy should be confirmed by further large-scale, multicenter clinical trials. In addition, the distal transradial approach refers to two distinct entry sites, including the anatomical snuffbox and dorsum of the hand. The dorsum of the hand approach was not studied, and we will consider assessing the use of this approach in future studies [28].