Utilizing the ultrasonic shear for internal mammary artery harvesting in minimally invasive coronary artery bypass grafting surgery is worth considering

In contemporary coronary artery bypass grafting (CABG), the left internal mammary artery (IMA) graft to the left anterior descending (LAD) artery has become the gold standard procedure (1,2). Compared to the great saphenous vein grafts (SVGs), IMA grafts demonstrate significantly lower failure (stenosis or occlusion) rates at both 5- and 10-year follow-ups, as well as better clinical outcomes (3,4). However, early failure of IMA grafts can significantly affect clinical outcomes. Harskamp et al. conducted a study involving 1,539 patients and found that those with IMA graft failure faced a significantly higher risk of acute events—such as death, myocardial infarction, or revascularization—within 14 days [14.4% vs. 4.9%; hazard ratio (HR) 3.92; 95% confidence interval (CI): 2.30–6.68; P<0.0001]. This trend of increased adverse events associated with IMA graft failure persisted for over four years, although it was not statistically significant (HR 1.45; 95% CI: 0.85–2.48; P=0.17) (5). Among the various factors influencing IMA graft failure, the techniques used for harvesting (pedicle vs. skeletonized) and the quality of anastomosis are of paramount importance.

Currently, IMA graft harvesting techniques can be categorized into skeletonized and pedicle techniques. Early on, Boodhwani et al. conducted a randomized controlled trial (RCT) involving 48 patients, which revealed that skeletonized IMA harvesting, compared to pedicle harvesting, showed a trend towards increased IMA graft length (18.2±0.3 vs. 17.7±0.3 cm, P=0.09), reduced postoperative pain levels at three months, and significantly decreased major sensory deficits at both the four-week and three-month follow-ups (17% vs. 50%, P=0.002) (6). Subsequent studies over the decades have further demonstrated several advantages of IMA skeletonization. A meta-analysis encompassing 31 studies reported that skeletonized harvesting, in comparison to pedicle harvesting, resulted in significantly lower odds of sternal wound infection (SWI) [odds ratio (OR) 0.45; 95% CI: 0.32–0.66; P=0.0001], a longer conduit [weighted mean difference (WMD) −2.48; 95% CI: −3.75 to −1.20; P=0.0001], and a higher postoperative flow rate (WMD −13.11; 95% CI: −22.52 to −3.70; P=0.006) (7). Similar outcomes have also been reported by several other meta-analyses and systematic reviews, although some studies found no significant difference in SWI rates between pedicle and skeletonized harvesting (8,9).

However, whether skeletonized IMA harvesting can improve graft patency and provide better safety for patients remains debatable. A meta-analysis involving 5 studies and 1,764 patients showed no significant difference in postoperative graft occlusion rates between pedicle and skeletonized IMA grafts (10). Whereas Lamy et al. analyzed the CABG cohort of the COMPASS trial involving 27,395 patients and found that skeletonized IMA had a higher occlusion rate at 1-year post-CABG compared to pedicle harvesting (9.6% vs. 3.9%; graft-level adjusted OR 2.41; P=0.002). During the 23-month follow-up, patients with skeletonized IMA grafts had significantly higher major adverse cardiovascular events (MACE) rates (7.1% vs. 2.1%; adjusted HR 3.19; P=0.002) and repeat revascularization rates (5.0% vs. 1.4%; adjusted HR 2.75; P=0.03) compared to those with pedicle IMA (11). Similarly, Gaudino’s 10-year follow-up data of 2,161 patients showed a higher long-term MACE risk with skeletonized IMA grafts (HR 1.25; 95% CI: 1.06–1.47; P=0.01). It is noteworthy that this difference was not significant among surgeons with more than 51 surgeries, suggesting that the prognosis of skeletonized IMA is associated with the surgeon’s proficiency (12). In contrast to MACE, several studies have shown no significant difference in all-cause mortality rates between skeletonized and pedicle IMA over a 10-year follow-up (12,13). Therefore, the clinical outcomes of skeletonized IMA harvesting are also dependent on the surgeon’s expertise.

In current guidelines and practical applications, there is no unified recommendation or regulation regarding the method of graft harvesting. The choice of scissors, electrocautery, harmonic scalpel, or robot-assisted harvesting primarily depends on the surgeon’s personal preference and the available equipment. Although electrocautery is the most commonly used method, it poses a risk of thermal damage to the graft vessel due to local tissue temperatures reaching over 300 ℃, especially during skeletonized harvesting. In this context, the harmonic scalpel offers significant advantages. The harmonic scalpel uses mechanical vibrations for tissue dissection and coagulation, which reduces the obstruction of the visual field by smoke and keeps tissue temperatures around only 80 ℃. When harvesting at relatively close distances (1 mm or more), it minimizes the risk of IMA tissue denaturation and endothelial damage (14-16), achieving a significantly higher endothelial integrity rate compared to electrocautery (95% vs. 81%, P<0.01) (17). Additionally, studies have reported that IMA harvesting with the harmonic scalpel requires significantly fewer hemostatic clips than electrocautery (18). When skeletonizing vessels, the harmonic scalpel also demonstrates good safety and patency. Higami et al. first reported the use of the harmonic scalpel for skeletonized IMA harvesting in 2000, showing that it could obtain sufficient graft length with excellent flow and patency (19). In a subsequent study involving 200 patients, they reported a patency rate of 99.7% to 100% at 1 month postoperatively using the harmonic scalpel for skeletonized IMA harvesting (20).

With the development of minimally invasive coronary artery bypass grafting (MICABG), there has been increasing interest in the application of the harmonic scalpel for IMA harvesting in minimally invasive procedures. As early as 1997, Ohtsuka et al. reported the use of thoracoscopic harmonic scalpel IMA harvesting for MICABG, achieving satisfactory graft length, anastomotic blood flow, and postoperative outcomes (21). Kikuchi et al. reported a study on direct-vision harmonic scalpel harvesting of bilateral IMAs for off-pump MICABG, demonstrating good perioperative safety and patency with a small left chest incision (22). In a retrospective study involving 247 patients, Tachibana also reported good safety with harmonic scalpel IMA harvesting for MICABG, with only 2.8% of patients requiring reintervention for postoperative bleeding, 2.0% experiencing postoperative chest infections, and only one perioperative death (23).

The harvesting of IMA in MICABG differs significantly from that in conventional sternotomy. While sternotomy provides adequate exposure of the entire chest wall, allowing surgeons a full view of both bilateral IMAs, it is more traumatic. This extensive exposure facilitates the harvesting and skeletonization of IMAs with relatively fewer difficulties and minimizes the risk of collateral injury to the graft. In contrast, MICABG employs small incisions, such as anterolateral intercostal incisions measuring only 5–8 cm, resulting in a confined surgical field. Additionally, harvesting the IMA, particularly the right IMA, involves the use of relatively long instruments to mobilize the vessel, which can amplify unwanted minor movements. Consequently, a more delicate and precise dissection of the vessel and its surrounding tissue is essential to avoid graft injury. Achieving hemostasis of the IMA branches can also be challenging, as directly ligating the branches in such limited space during MICABG is difficult, and the use of vascular clips may lead to injury or misplacement.

In the aforementioned studies, the surgeries utilized a hook-type harmonic scalpel for IMA harvesting. In this paper, Jung et al. first reported the use of a shear-tip harmonic scalpel for skeletonized IMA harvesting in MICABG. This study included 40 patients, with an average induction-to-left IMA harvesting time of 87 minutes, and right IMA harvesting time of 24 minutes using the shear-tip harmonic scalpel, and demonstrated good patency and safety (24). The harvesting time is similar to previous reports using the hook-type harmonic scalpel for IMA skeletonization (25,26). No perioperative graft-related adverse events or complications occurred among the patients, and during the 15.2-month follow-up, only one patient experienced graft occlusion. Notably, traditional hook-type harmonic scalpels often involve some degree of tissue traction and tension during graft harvesting. In contrast, the shear-tip harmonic scalpel relies more on shear forces for tissue cutting and coagulation, allowing for more precise control of vascular branches, easier tissue cutting, and reduced surrounding tissue damage. Additionally, the shear-tip harmonic scalpel provides more stable and effective hemostasis during cutting, reducing the need for clips. Compared with the traditional hook-type harmonic scalpel, these advantages of the shear-tip harmonic scalpel make it a more favorable and safe option for IMA harvesting, especially during MICABG, addressing the difficulties mentioned previously (24).

Overall, this study suggests that the shear-tip harmonic scalpel is an efficient, safe, and suitable surgical instrument for IMA harvesting in MICABG, with clinical utility. However, this study has notable limitations and concerns. Firstly, only 40 patients were included over a span of four years, raising questions about whether the surgeon has adequately overcome the learning curve given the relatively low case volume and surgery density (24). The learning curve for harmonic skeletonization has been estimated to be approximately 20 harvests for sternotomy (25). Given the increased surgical difficulties of MICABG, a greater number of procedures may be necessary. Another concern is that in this cohort, patients were ventilated for an average of 10 hours, and the average postoperative transfusion was 2.33 packs (400 cc per pack). The authors attributed the bleeding to damage to surrounding blood vessels caused by electrocautery rather than the harmonic scalpel itself (24). However, the mean ventilation time and blood loss during MICABG have been reported as 240±193.68 minutes and 365.92±156.84 cc, respectively (27). These findings raise potential concerns about the surgical expertise and postoperative management in this study. As a single-center, retrospective study with small sample size and a maximum follow-up of only 15.2 months, its results and conclusions may not be universally applicable (24). Larger sample sizes and longer follow-up periods in multicenter, prospective RCTs are needed in the future to confirm the advantages of the shear-tip harmonic scalpel compared to traditional skeletonized harvesting methods and its impact on the long-term outcomes of CABG patients (24). Importantly, as previously noted, concerns have been raised regarding whether the skeletonization of IMA truly enhances graft patency and safety. It is anticipated that with improved precision and coagulation, the shear-tip harmonic scalpel may contribute to better prognosis and outcomes for IMA skeletonization. However, these benefits can only be confirmed through long-term follow-up and extensive comparative studies.

Acknowledgments

Funding: None.

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