To the Editor: The main cause for failed complex coronary lesions especially chronic total occlusion (CTO) revascularization is the inability of device delivery due to the lack of adequate guide support or the failure of guidewire manipulation, such as unsuccessful externalization of the retrograde guidewire and incapable reentry into the true lumen. Some devices and techniques have been used to deal with these problems, and the guide catheter extension system (GCES) is one of the effective solutions. Currently, five GCES devices are commercially available, the Proxis, Heartrail II (Terumo, Tokyo, Japan), GuideLiner (GL; Vascular Solutions, Charlotte, NC, USA), Guidezilla (GZ; Boston Scientific, Marlborough, MA, USA), and the Expressman extension system (EES; APT Medical Inc., Hunan, China). GL and GZ have been reported to enable procedural success not only by providing extra backup support but also by accommodating multiple devices and facilitating device delivery.[1] Besides, they also ensure little trauma to the ostium of CTO vessels.[2,3] However, the rate of GZ- or GL-related events, including inaccessibility to the target lesions, device damage, or coronary artery dissection, became major obstacles in using GCES in CTO percutaneous coronary intervention (PCI).[4,5] Moreover, the size of the radial artery guiding catheter limits the application of GCES in a guiding catheter that is no larger than 7 F, and it should be applied with more caution when delivering stents with a 4 mm diameter. The EES was newly developed to provide a strong backup support and an efficient approach through deep intubation. It has a 35 cm exchange tube, which is long enough to cross the aortic arch (femoral approach)/subclavian artery (radial approach) to the coronary artery; this design could avoid the circuity and fracture of the oblique mouth of the catheter caused by the bending part of the aortic arch/subclavian artery and also reduces resistance when devices are entering the catheter [Figure 1A,B]. Additionally, the side hole in the tip allows adequate antegrade blood flow and reduces the risk of blood pressure incarceration after deep insertion into the target vessel. It has two radiopaque markers at the proximal end, which show the accurate position in the coronary arteries. The tip is soft and contains an indicator ring, which decreases the incidence of vessel damage and helps to ascertain the precise placement. The hydrophilic coating provides a smooth advancing property [Figure 1A]. Moreover, the design of variable diameter at distal 10 cm allows deeper insertion and reduces the incidence of vessel dissection [Figure 1C]. It also has various specifications (3.2 F, 5.0 F, 5.5 F, 6.0 F, 6.5 F, 7.0 F, 7.5 F) to fit for different interventional conditions. This study aimed to evaluate the efficacy and safety of the EES in a series of EES-facilitated PCI.Figure 1: Design of the EES and angiographic images. (A) Special design of the EES. (a) Exchange tube; (b) hydrophilic coating; (c) side hole; (d) radiopaque markers; (e) the tip with indicator ring. (B) The 35 cm exchange tube of EES. (left) The exchange tube is long enough to cross the subclavian artery (radial approach), (right) or the aortic arch (femoral approach). (C) The design of variable diameter at distal 10 cm. (D) The EES was advanced through the stents (the stent diameter was 2.5 mm and 3.0 mm, respectively) to the distal of RCA. (E) The EES was introduced via the antegrade approach to the site of the microcatheter advanced via the retrograde approach. (F) The retrograde guidewire was advanced to the antegrade guiding catheter through the EES. Black arrow: EES; White arrow: microcatheter. EES: Expressman extension system.This retrospective study was approved by the Ethics Committee at our hospital (No. 20200119) and was conducted according to the ethical principles of the Declaration of Helsinki. Written informed consent was obtained from all patients. Analyses were performed using SPSS 21.0 (IBM Corp., Armonk, NY, USA). Continuous data were expressed as mean ± standard deviation for normal distribution and median for non-normally distributed continuous variables, while categorical variables were expressed as n (%). Between March 2020 and July 2020, 25 patients with complex coronary artery lesions using EES to enhance support for device delivery and manipulation were included. The average age was 67.52 ± 10.74 years, and men accounted for 64.0%. The mean left ventricular ejection fraction was 59.36 ± 5.72%. A total of 21 (84.0%) patients had hypertension, 10 (40.0%) patients had hypercholesterolemia, and 12 (48.0%) patients had diabetes mellitus. A total of four (16.0%) patients had a current smoking status, eight (32.0%) patients had undergone a previous PCI, five (20.0%) patients had a previous myocardial infarction, and two (8.0%) patients had chronic renal impairment. The majority of CTO target vessel was the right coronary artery (60.0%), which was followed by the left descending artery (32.0%) and the left circumflex artery (8.0%). The target lesions all belonged to type C, and the CTO accounted for 92.0%. The median J-CTO score was 3, and the mean syntax score was 30.45 ± 10.10. About 20.0% of the procedure were performed via the femoral route, while 80.0% were performed via the bilateral route. About 8.0% (n = 2) of patients were treated with EES using the 6 F mother guiding catheters, and 92% (n = 23) of patients were using the 7F mother guiding catheters. The most commonly used EES (96.0%) was with 5F specification, and in one patient (4.0%), the 3.2 F specification was applied via the microcatheter. The median depth of intubation was 4.0 cm. Besides, the forward blood flow was nearly unaffected, and no blunted blood pressure was observed during the procedure, even if the EES was introduced to the distal site of the target vessel [Figure 1D]. No EES-related complications have been observed, and no in-hospital target vessel revascularization, deaths, or acute in-stent thrombosis occurred before patient discharge. One procedure suffered hypotension because of femoral artery hematoma caused by a femoral puncture. For EES efficacy analysis, four (16.0%) patients used the EES to facilitate the externalization of the retrograde guidewire [Figure 1E,F], and all have succeeded (100%). About 20 (80.0%) patients used the EES to aid the guidewires, balloons, or stents to cross the target lesion and had a success rate of 85%. In one (4.0%) patient, EES was applied to assist the performance of the antegrade dissection reentry technique. The total technique success was achieved in 22 procedures (88.0%). One procedure failed because of the inability to cross the collateral circulation during the retrograde approach, one procedure failed due to the severe calcification of the lesion even after rotational atherectomy, and one procedure failed due to the inability to advance the guidewire to the distal vessel via the EES. As the EES is developed to provide a strong backup support and an efficient approach through deep intubation, this study highlights the safety and efficacy of the EES used for antegrade or retrograde approach. During the PCI procedure, a strong backup support is critical for the delivery of balloons and stents.[6] The EES has a stepped-diameter design of 10 cm from the distal part, such as 6 F to 5 F and 5 F to 4 F, and this unique design allows the EES to intubate deeper, which could provide extra support and is able to increase the successful rate of PCI. In this study, the deep insertion of EES provided better support for effective delivery of devices thro ugh the target lesion. A total of 80% of the enrolled cases used this effect to deliver the devices, yielding an 85% success rate among these cases. Additionally, EES was also used to provide better backup support for manipulating the guidewire reentry to the true lumen, which suggests that guidewire manipulation became more precise with EES. Externalization of the retrograde guidewire is vital for a successful retrograde approach,[7] the application of the EES shortened the distance between the antegrade guiding catheter and the reentry site, and it could even reach up to the reentry site, making the retrograde guidewire easier to enter the antegrade catheter. In this study, 16% of the enrolled cases used EES to pick up the retrograde guidewire with a 100% success rate. An EES with 5F specification was used more often due to the technical improvement of CTO PCI, as the usage of 6 F guiding catheter has increased and 5 F EES can be used under 7 F and 6 F guiding catheter. Besides, 5F EES can be delivered with the assistance of a smaller balloon. It also had a good ability of deep incubation, good trafficability, and less damage to vessels. The EES demonstrated a safety profile with no device-related complication and no in-hospital MACE as well. Moreover, the EES could be advanced inside the stent without causing stent dislodgement. It had little effect on the antegrade blood flow during the deep intubation procedure, this was credited to the design of the side hole at the tip of the EES, which allows adequate antegrade blood flow and reduces the risk of blood pressure incarceration after deep insertion into the target vessel. However, deep insertion is not recommended in some situations, such as lesions at the ostium, stents at the ostial and proximal parts of the artery, severe calcification, and vulnerable plaques; otherwise, evacuate as soon as possible after the delivery equipment is in place. Notably, it is safer and more efficient with the assistance of a small balloon (diameter 1.5–2.5 mm) when deeply inserting the EES, because direct deep insertion of the EES along the guidewire can easily cause coronary dissection or hematoma. In summary, the EES is a device designed to provide better backup support for device delivery and manipulation, and it is especially useful to serve as a connector to a shorter distance between the antegrade guiding catheter and the site of the retrograde guidewire with deeper insertion into the target vessel. Acknowledgments None Funding This study was supported by a grant from the Key Project of Medical Science Research in Hebei Province (No. 20130001). Conflicts of interest None.