Aortic aneurysm or coarctation often extensively involves the ascending aorta, aortic arch, and descending aorta, making surgical resection and revascularization quite complex. The classic elephant trunk (ET) procedure, in which an artificial vessel is inserted into the descending aorta along with a replacement of the aortic arch to reduce the difficulty of reoperating distally, was first introduced by Borst et al. in 1983, thus opening the way for the application of the elephant trunk technique to simplify staged surgery [1]. I. Soft elephant trunk surgery The earliest was the direct insertion of a segment of the artificial vessel into the descending aorta, which was improved by Svensson et al. in 1990 and is generally accomplished in a two-stage procedure [2]. In the first stage of surgery, the aortic ascending arch is reconstructed by opening the chest medially and placing the artificial vessel itself with the folded edge facing upward into the descending aortic lumen, and the folded edge of the artificial vessel is double-lined in the lumen and anastomosed with the proximal end of the descending aorta, and then pulling out the vessel overlaid in the inner layer to reconstruct the arch, while the outer vessel is placed free and open in the descending aortic lumen to form the so-called “elephant trunk”. The outer vessel is placed free and open in the lumen of the descending aorta to form the so-called “elephant trunk”, because it is in the same direction as the aortic blood flow and the distal end of the vessel generally does not fold. Stage II thoracic and or abdominal aortic replacement surgery is performed through the left posterior lateral fourth or fifth intercostal space into the thoracic cavity, and the end of the elephant trunk vessel is anastomosed to the distal aorta or artificial vessel. Complications of the elephant trunk technique: (1) Brain and spinal cord injury. svensson et al. suggested that the length of the vessel placed into the descending aorta should not exceed 15 cm to avoid affecting the blood supply to important spinal cord segments. flores et al. found that the distal end of the elephant trunk beyond the T7 level was associated with spinal cord injury [3]. (2) Bleeding and related complications. the chance of rupture of the diseased aorta during the interval between stage I and II surgery is 1.4 to 2.1 %. (3) Embolism. Dislodgement of the thrombus formed around the free vessel, resulting in embolization of the limb or organ artery. (4) Blood flow disorders. Distortion and deflation of the elephant trunk vessel and hemodynamic obstruction can result in distal obstruction of blood flow. Taniguchi et al. used a long elephant trunk technique in which the distal anastomosis is brought proximal to the opening of the innominate artery and the distal end is placed into the long elephant trunk to approximately T6-T8 level, but this method has some difficulty in positioning the end of the trunk [5]. The thrombus formation in the blind pocket between the elephant trunk vessel and the aneurysmal wall can increase the incidence of embolic events, and the long elephant trunk often causes obstruction of the critical intercostal artery leading to hemiparesis. Okada et al. reported a double-stacked three-layer elephant trunk technique in which the artificial vessel is folded twice to make a three-layer elephant trunk, with the main aim of preventing thromboembolic events [6]. The first fold was 7 cm from the end and the second fold was 5 cm back over the proximal end. the distance between the proximal end and the second fold was 2 cm and sutures were used to fix the proximal and distal edges of the trunk to prevent blood flow into the blind pocket of the folded trunk. The original length of the elephant trunk was 17 cm, and after folding it was about 7 cm long. surgical method: in stage I surgery, the prefabricated elephant trunk was inserted into the distal aneurysm, and in stage II surgery, the proximal end was blocked at the 2 cm long single layer of the elephant trunk vessel, the aneurysm was opened, the fixation line was removed, the elephant trunk was pulled out, and the three layers of the double-folded vessel were stretched into a single layer to anastomose with the other prosthesis. The distal end of the conventional elephant trunk floats in the blood stream and has the potential to twist or crease, thereby creating a pressure differential within the elephant trunk vessel and may be able to cause re-injury to the lining. The ideal elephant trunk vessel should be stiff and long enough, and this double stacked triple elephant trunk technique is well suited to meet this requirement. When the distal aortic dilatation is not obvious and the anatomical location is deep, anastomosis and insertion of the soft elephant trunk are difficult, and anastomotic bleeding, prolonged extracorporeal circulation or ischemia can lead to high complications and increased mortality. sleeve graft” technique to facilitate the management of the distal anastomosis [7]. By turning the artificial vessel outward and leaving the end in the lumen, the tube can be curled along the longitudinal axis to facilitate insertion into the distal aorta. The reflexed edge is distal with the blind pocket facing the operator, the proximal outer vessel is anastomosed to the aortic wall, and the inner vessel is then pulled out of the aortic lumen to anastomose with the reconstructed vessel in the arch. The advantages of this approach include: the distal aortic perfusion can be performed by blocking the pulled out elephant trunk vessel immediately after the distal anastomosis is completed, which reduces the ischemic time of the organ; there is a good view of the distal suture margin for blood leakage and hemostasis is easier; and the anastomosis can be 8 cm away from the opening of the subclavian artery, which also facilitates the adjustment of the curvature and direction of the arch graft. This method was later used in cases where the thoracic descending aorta needed to be repaired first but the arch might need to be reoperated in the distant future [8]. Bidirectional ET technique: The bidirectional ET technique is an extension of the reverse ET technique in which the proximal and distal sides of the thoracic descending aorta are used for a broader range of aortic lesions [9]. Fourth, the stented elephant trunk technique Traditional elephant trunks floating in the lumen of the descending aorta can interfere with the formation of thrombus between the vessel and the aneurysmal wall, and thrombosis is a prerequisite for reducing the tension in the aneurysmal wall, preventing the aortic diameter from continuing to expand.The concept of stented elephant trunks was first introduced by Kato et al. who attempted to anchor the distal end of the elephant trunk to the aortic wall by fixing an annular stent within an artificial vessel [10,11]. The annular tension created by this stent vessel allowed the vessel to adhere tightly to the aortic wall, and complete thrombosis of the aneurysmal or intercalated pseudolumen was achieved within 1 year after the initial application in 10 patients.Kark et al. 2002 used a similar approach by releasing a stent vessel (Dacron vascular prosthesis with its distal end covered with a stainless steel stent) through a sheath placed in the descending aorta under direct visualization in stage I surgery. The proximal end of the artificial vessel is anastomosed to the aortic wall or to a vessel in the replacement arch. The first stent vessels used were between 20-28 cm in length, with the distal stents being 22 mm long, each 5 mm adjacent to the other to provide proper elasticity. The distal stent portion was dilated with a balloon catheter after release. This approach combines the elephant trunk principle with the concept of an interventional stent vessel and can be accomplished simultaneously through a median sternotomy. The advantage is that it anchors at a specific level in the descending aortic aneurysm wall and promotes thrombosis between the elephant trunk vessel and the aneurysm wall, thus avoiding the possibility of a stage II procedure due to advanced aneurysm or rupture of the descending aorta. Borst, the inventor of the elephant trunk technique, named it the “Frozen” elephant trunk technique [12]. V. The whole-support elephant trunk technique The true lumen of aortic coarctation is often narrow, making the placement of artificial vessels difficult, and the soft elephant trunk often interferes with the blood supply to the branch arteries. In the replacement of aortic arch, the use of supported artificial vessel as the trunk in the thoracic descending aorta has the following advantages: (1) The supported artificial vessel is compressed before release and needs to be supported by a sheath, which is easy to be placed; after release, it is not easy to twist and deflate with the support of a metal stent. (2) The expansion of the metal stent gives circumferential tension to the aortic wall, which can promote the closure of the pseudolumen or isolate the aneurysmal lumen, avoiding the distal embolism caused by the dislodgement of thrombus in the aneurysmal lumen or pseudolumen; the position is more fixed and not easy to be displaced. In 2003, Sun Lizhong et al. began to use the technique of using a full-supported elephant trunk combined with four-branch artificial vessels to reconstruct the arch (Sun’s procedure) for the treatment of aortic aneurysm or coarctation. The stent vessel (approximately 10 cm in length and 26-30 mm in diameter) was inserted into the true lumen of the descending aorta, and the stent vessel was released by holding the shaft stem and slowly withdrawing the fixation wire, and then the proximal trim was trimmed with the residual descending aortic margin as the outer lining and the four-branch vessel trunk together with continuous sutures. After completion of the anastomosis, perfusion of the lower body is restored and rewarming is initiated with one branch, followed by sequential reconstruction of the cephalic vessels and anastomosis to the proximal ascending aorta. Both ends of the stented vessel were designed to leave about 1 cm of bare stent-free area for suturing [13]. Sun Lizhong et al. 2011 reported the results of 107 cases of acute type A aortic coarctation and 89 cases of chronic type A aortic coarctation treated by Sun’s procedure, showing a significant reduction in the perioperative risk of aortic coarctation treated with the braced elephant trunk technique. In the follow-up observation, the rate of peri-stent pseudolumen closure was 94.2% in chronic aortic coarctation and 95% in acute aortic coarctation with self-closing pseudolumen [14]. Indications for the stented elephant trunk technique: (1) primary ruptured endothelial opening of aortic coarctation in the aortic arch or its distal end, with retrograde dissection of the coarctation to near the arch; (2) aneurysm formation in the arch or distal end; (3) aortic coarctation with dissection of the cephalic brachial artery; and (4) Marfan syndrome involving the arch. There are also stented elephant trunk vessels with branch stents currently in clinical trials on this basis. VI. Short elephant trunk technique When the rupture of aortic entrapment in type A entrapment is located in the ascending aorta and there is no intimal rupture far from the arch, the cephalic brachial artery is not involved and the arch is not dilated in simple cases, the traditional surgical approach is aortic root replacement or ascending aortic replacement. Sometimes, some of the entrapment lesions still remain far from the distal anastomosis of these clips, and a short stent vessel can be used to anastomose the distal end in order to improve the closure rate of the distal pseudolumen and to strengthen the strength of the distal anastomosis. The method is to transect the ascending aorta at a distance of 3 cm from the innominate artery and place a 2 cm long stent vessel at the distal end to ensure that the distal end of the stent should be more than 1 cm from the opening of the innominate artery, and the stent vessel is used as a liner to make a “sandwich” anastomosis with the proximal graft vessel and the distal ascending aortic wall. This avoids the need for arch manipulation and deep hypothermic stopping of circulation, and makes hemostasis easy, and is most suitable for patients with clamping who cannot tolerate extensive surgery in the acute phase. Another type of short elephant trunk is used for left-sided open-heart partial thoracic aortic replacement, in which the proximal end of the descending aorta is blocked and then anastomosed with an artificial vessel, and a 5-cm-long supporting artificial vessel is placed in the distal end of the descending aorta, which is then anastomosed with the descending aorta and the artificial vessel, but it is only suitable for type B coarctation in which the descending aorta is not dilated or only proximally dilated, and the middle and distal diameters are close to normal [15]. VII. hybrid elephant trunk technique The hybrid elephant trunk technique refers to the placement of a stent vessel in the descending aorta through an interventional approach, with the arch and proximal end of the procedure completed openly; or the placement of an overlapping stent vessel in the descending aorta under phase II intervention of elephant trunk surgery to cover the distal end of the elephant trunk vessel placed during phase I surgery [16]. Since the phase II procedure is minimally invasive, the time between procedures can be greatly reduced or even completed at the same time, thus reducing the risk of death due to aneurysm rupture or clamping progression during the interoperative interval, etc. Greenberg et al. and Matsuda et al. reported successful experiences with the application of the hybrid elephant trunk technique for aortic disease, respectively [17, 18]. The main perioperative complications are stent migration, endoleaks and branch artery ischemia. Shimamura et al. developed a branching support vessel with a polyester artificial vessel lined distally with a Gianturco stent (William Cook Eruope A/S, Bjaeverskov, Denmark) and proximally with one to three branches lined with a Palmatz stent (Cordis, Denmark). Palmatz stent (Cordis Endovascular System, Miami Lakes, Fla). The diameter of each segment of the artificial vessel, the diameter of the anchorage zone of the descending aorta and the cephalic artery, and the distance between the cephalic branches were determined by preoperative CT imaging. Vessels 10-15% larger than the normal diameter were generally selected for aneurysms, and vessels 5-10% larger than the true lumen were selected for aortic coarctation. The specific method is to cannulate and perfuse the right axillary artery and femoral artery, and puncture and place guide wires into the left subclavian artery and left femoral artery respectively; make a median sternotomy, dissociate the aortic arch between the unnamed artery and the left common carotid artery, pull out the left subclavian artery and left femoral artery puncture guide wires to penetrate the stent vessel trunk and branches, extend the stent vessel into the descending aorta and the corresponding cephalic brachial artery, first release the left common carotid and left subclavian artery The branches of the left common carotid and left subclavian arteries are released first, followed by release of the stent vessel trunk in the descending aorta, and adequate release can be confirmed with a balloon. Finally, an incisional suture is performed between the proximal trunk and the distal aortic arch. If total aortic arch replacement is required, the proximal replacement is completed with an additional Dacron vessel with two branches, one for perfusion and the other for anastomosis to the innominate artery [19]. The use of the elephant trunk technique in aortic surgery has been on the rise as medical care has improved and the number of clinical visits for aortic aneurysms and coarctations has gradually increased. So far, the supported elephant trunk technique for aortic coarctation has achieved good near- to mid-term results and has begun to gradually replace the traditional elephant trunk surgical approach in major centers at home and abroad. The hybrid elephant trunk technique combined with minimally invasive techniques reduces the risk of surgery and has a promising future. At the same time, the continuous improvement of technical details can better promote the application and development of the elephant trunk technique.