Surgical Management Of Acute Type Research Articles

C40 SYSTEMATIC TOTAL ARCH REPLACEMENT WITH THORAFLEX HYBRID GRAFT IN ACUTE TYPE A AORTIC DISSECTION: A SINGLE CENTRE EXPERIENCE

Abstract Introduction The traditional surgical management for acute Type A aortic dissection focuses on handling emergencies in the aortic root and ascending aorta. The remaining untreated distal portion of the aorta has a potential risk of rupture or causing malperfusion syndrome. Therefore, an aggressive repair approach using total aortic arch replacement combined with the frozen elephant trunk (FET) implantation has been advocated. We describe the early and midterm clinical outcomes of the Thoraflex Hybrid graft for the treatment of emergency type A aortic dissection. Methods Between December 2017 and January 2022, 69 consecutive patients were admitted with acute type A aortic dissection; of those, 66 patients (62.9 ± 10.2 years of age, 81.8% men) underwent emergency hybrid aortic arch and frozen elephant trunk repair with the multibranched Thoraflex hybrid graft and were enrolled in the study. Primary end point were 30 days– and in–hospital mortality. To better clarify the impact of age on surgical outcomes, we have divided the study population into two groups: group A for patients < 70 years of age (47 patients), group B for patients ≥ 70 years (19 patients). Results All 66 device implants were technically successful. Mean follow–up was 19.7 ±17.4 months. 30–days– and in–hospital mortality were 10.6 and 13.6%, respectively. Stroke occurred in 3 (4.5%) patients. Two (3.0%) patients experienced spinal cord ischemia. Renal failure requiring CVVH and respiratory failure requiring tracheostomy were 30.3% and 28.8%, respectively. Overall survival for the entire cohort at 3 months, 6 months, 12 months and 24 months was 85%, 80.3%, 76.5%, 74.4% respectively. We did not find any statistically significant difference among the two groups in terms of main post–operative outcomes. The multivariable Cox proportional hazard model showed left ventricular ejection fraction (HR: 0.83, 95% CI: 0.79–0.92, p <0.01), peripheral vascular disease (HR: 15.8, 95% CI: 3.9–62.9, p < 0.01), coronary malperfusion (HR: 0.10, 95% CI: 0.01–0.77, p =0.03), lower limbs malperfusion (HR: 5.1, 95% CI: 1.10–23.4, p = 0.04) and cardiopulmonary bypass time (HR: 1.02, 95% CI: 1 – 1.04, p = 0.01) as independent predictors of long term mortality. Conclusions Hybrid aortic arch and frozen elephant trunk repair with the Thoraflex Hybrid graft to treat emergency type A aortic dissection appears to be associated with good early and mid–term clinical outcomes even in the elderly.

Current Surgical Management of AcuteType A Aortic Dissection in China: A Multicenter Registry Study.

Many countries and regions have established multicenter registration studies to improve the outcomes of acute type A aortic dissection (ATAAD). The aims of this study were to report actual preoperative management, surgery type, and early outcomes of surgical treatment for ATAAD in China. This cohort study uses data from the China Registry of Type A Aortic Dissection, a national clinical registry to investigate management of patients with Stanford type A aortic dissection. The data, including surgical management and outcomes of patients with ATAAD, were analyzed from January 2018 to December2021. A total of 1,058 patients with ATAAD were enrolled in this study between January 2018 and December 2021. The mean age of all patients was 51.6 ±11.7 years. The median interval from onset to hospital was 10.65 hours (IQR: 6-24 hours), and the median interval from entering the emergency room to starting operation was 13 hours (IQR: 4.08-28.7 hours). Total arch repair was performed in 938 patients (88.7%), and frozen elephant trunk repair was performed in 800 patients (75.6%). The incidence of early mortality was 7.6%. The population of patients with ATAAD in China experienced a longer interval from onset to arrival at the hospital, received more extensive aortic arch repair, and showed a relatively lower early mortality. These findings suggest that there may be a huge survivor bias in patients with ATAAD in China, more efforts should be made to promote prehospital emergency care and preoperative management of Chinese ATAAD patients. (A multicenter registration study of aortic dissection in China; ChiCTR1800015338).

Surgical management of acute type A aortic dissection in complicated cases: experience with branch-first aortic arch replacement technique.

Surgical management of acute type A aortic dissection in complicated cases: experience with branch-first aortic arch replacement technique.

Surgical Management of Acute Type A Aortic Dissection: An Overview

Acute type A aortic dissection is a catastrophic disease that develops from a tear within the intima of the aortic wall, thereby creating a false lumen in the ascending aorta. Early suspicion, diagnosis, and prompt surgery play a key role in the survival of patients. It is a surgical emergency and requires replacement of the ascending aorta/aortic root with or without aortic arch replacement. Over the past decade the surgical outcomes have improved in specialized tertiary centers.

Medical and surgical management of acute type B aortic intramural hematoma.

Type B acute aortic dissection (AAD) and intramural hematoma (IMH) can both present as potentially catastrophic lesions of the descending aorta. IMH is distinguished from AAD by the absence of an intimal tear and flap. With short-term outcomes being similar to type B AAD, IMH is treated identically to AAD in the corresponding segment of the aorta. While all patients with any acute aortic syndrome of the descending aorta receive prompt anti-impulse therapy, thoracic endovascular aortic repair (TEVAR) is reserved for patients presenting with certain complications, namely malperfusion, rupture, or periaortic hematoma. Technical aspects of TEVAR for IMH include maximal endograft oversizing of 10% with 20 mm landing zones of the healthy aorta, revascularization of the left subclavian artery when covered, use of cerebrospinal fluid drainage with extensive coverage, and restoration of branch vessel perfusion. With respect to disease evolution, IMH may progress to classic AD, frank rupture, or aneurysmal dilation; yet, IMH may also regress and be completely resorbed. However, since the natural history of IMH is unpredictable, TEVAR is being used more aggressively to improve long-term survival, rates of secondary reintervention, and positive aortic remodeling. Much remains unknown for acute type B IMH, including the use of prophylactic TEVAR for stable uncomplicated presentations, as well as the optimal timing of intervention and certain technical aspects of TEVAR. As such, IMH remains a diagnostic and therapeutic challenge for cardiovascular surgeons.

The surgical management of acute type A aortic dissection: Current options and future trends.

Acute type A aortic dissection (ATAAD) is a catastrophic condition that can be fatal if not treated immediately. We sought to examine the literature and identify evidence behind each method of surgical intervention. A comprehensive electronic literature search was done to identify the articles that reported outcomes and discussed surgical techniques in ATAAD. No limits were placed on timing or type of the articles; all results are summarized in a narrative manner within each relevant section. Different units have different approaches for extensive ATAAD; experienced and high-volume units tend to perform aortic root and total-arch replacement, whereas others tend to perform only hemiarch replacement. The evidence shows no significant differences in long-term outcomes. Frozen elephant trunk and endovascular repair play key roles in managing the rest of the aortic dissection that involve the thoracic aorta, and the evidence evolve with their impact on false lumen patency. The management of ATAAD is tailored by individual surgeons and unit experience to save lives. Future directions for reducing mortality depend on effective early recognition and accessibility to centralized specialist centers with experience in a wide range of surgical techniques.

Classification of Dissecting Aortic Aneurysm as a Guide for Surgical Management

Mortality in acute dissecting type A aortic aneurysm remains high. The existing classifications are intended to give an accurate, and, very importantly (given the acute course of the pathology), a prompt answer to the clinician’s and the cardiac surgeon’s questions: how the patients should be treated, and which of them should undergo surgical intervention, and which procedure is to be used.
 Aim. A review and analysis of the existing classifications of dissecting aortic aneurysms and their transformation taking into account the advances in diagnostic technologies and methods of surgical management. The first classification was proposed by DeBakey; it systematized morphological variants of the disease and explained the origin of its accompanying phenomena such as heart tamponade, acute aortic valve insufficiency, and visceral and limb ischemia, but provided no guidelines on treatment techniques. A more recent Stanford classification was based on the principle of differentiation into conservative or operative approach. Owing to the use of CT and MRI angiography, new dissection subtypes were discovered and formulated in the Svensson classification. The Penn classification recommends that the choice of management can be based on the extent of aortic dissection, the site of the primary intimal tear, and the presence of malperfusion. The latest TEM classification identifies type A and type B dissection, as well as additional non-A-non-B type, in which the descending aorta and the arch, but not the ascending aorta, are involved. The most appropriate surgical procedures for the retrograde type A aortic dissection treatment are discussed as well.
 Conclusions. 1. The purpose of clinical classification of acute aortic dissection is, in addition to systematizing concepts and categories, facilitating the selection of an optimal state-of-the-art treatment method. 2. Introducing such classifications as Penn or TEM will bring to a common denominator the results of surgical management of acute type A dissection by unifying the characteristics of the patients and eliminating their deliberate or accidental pre-selection, which possibly accounts for the difference in mortality rates among different surgical groups.

Early Mortality in Patients who Received Extensive Surgical Management for Acute Type A Aortic Dissection - Analysis of 452 Consecutive Cases from a Single-center Experience.

Objective To detect the potential risk factors associated with early mortality in patients who received extensive surgical management, in the form of total arch replacement plus frozen elephant trunk and arch debranching (hybrid repair technique), for acute type A aortic dissection.Methods The clinical and surgical data of 452 surgically treated patients with acute type A aortic dissection at our center, between March 2010 and December 2016, have been retrieved. Uni and multivariate logistic regression analyses were carried out to detect the effect of various preoperative demographics and different perioperative variables on early mortality.Results Overall 30-day mortality occurred in 70 out of 452 patients (15.4%). The principal causes of death were multiple organ failure (n=38), cardiac failure (n=18), and severe pulmonary infection (n=10). Risk factors for early mortality were identified with multivariate analysis. Preoperatively, overweight (P<0.025), alcohol drinking (P<0.002), coronary artery disease (P<0.014), hemodynamic shock (P<0.006), and elevated white blood cells count (P<0.002) were associated with higher mortality rate. Postoperatively, prolonged operation time (P<0.008), stroke (P<0.0001), and acute renal dysfunction (P<0.0001) were highly associated with death.ConclusionConsidering the advantages of extensive surgical management for acute type A aortic dissection over the other less aggressive surgical approaches, it should be advised whenever indicated, provided that being carried out by experts in the field of adult aortic surgery in high-volume centers. The surgeon should be aware of the patient’s preoperative comorbidities and other risk factors for early mortality, in particular, prolonged operation time.

Acute Type A Aortic Dissection: Pre-Operative Clinical and Radiological Predictors of Outcome

AbstractBackground: Acute type A aortic dissection is a surgical emergency associated with high morbidity and mortality and is still a surgical challenge. The aim of our work is to evaluate the impact of pre-operative clinical status of different malp-erfusion symptoms (according to Penn classification) and radiological findings on surgical outcome of acute type A dissection patients.Aim of Study: Is to report our experience in surgical management of acute type A dissection patients and to deter-mine the impact of pre-operative ischaemia (by Penn class) on post-operative outcome.Patients and Methods: Between January 2012 and De-cember 2014, 30 patients (23 males, 7 females) with acute type A aortic dissection were operated upon at Kasr Al-Aini Cardiac Surgery Unit, Cairo University. All patients presented with severe chest pain and pulse deficit. Their age ranged from 30 to 70 years. 2 patients had bicuspid aortic valve and 8 patients had Marfan syndrome. 3 patients had acute lower limb ischemia, 6 had renal malperfusion and 4 had massive pericardial effusion. All patients had pre-operative multislice CT aortography with 4 patients showing extensive arch tears and 4 patients had dissected coronary arteries on multislice CT of the coronaries. 13 patients had supracoronary conduit replacement of ascending aorta, 13 had modified Bentall operation, and 4 had valve-sparing (David) operation. All patients had circulatory arrest at moderate hypothermia and cerebral protection for open repair of the dissected aortic arch.Results: The mean cross clamp time was 145±25minutes, and total circulatory arrest time was 25±10 minutes. Patients with pre-operative malperfusion had more prolonged and complicated post-operative stay. There was 5 (17%) post-operative mortality: 1 due to massive bleeding, 2 due to prolonged ventilation following stroke, 1 due to hepato-renal failure and 1 due to myocardial failure.Conclusion: Surgical treatment of acute type A aortic dissection is challenging and requires a well-planned strategy to get optimum outcome.Dissection patients with malperfusion syndromes, circum-ferential arch tears, and dissected coronaries carry higher risk of mortality.

Comparison of Direct Versus Side-Arm Graft Cannulation of the Axillary Artery in Patients With Acute Type A Aortic Dissection

Aim: In our unit, we use the axillary artery as an arterial cannulation site to reduce intraoperative malperfusion and facilitate antegrade cerebral perfusion in patients undergoing surgical management of acute type A aortic dissection (ATAAD). Two techniques used to achieve this are cannulation directly or through the use of a side-arm graft. The purpose of this study was to evaluate our unit's experience with both techniques and investigate cannulation-related morbidity and patient outcomes.

Experience With the Axillary Artery as an Arterial Cannulation Site in Patients With Acute Type A Aortic Dissection

The optimal arterial cannulation site in patients undergoing surgical management of acute type A aortic dissection (ATAAD) remains controversial. The axillary artery is rarely involved in the dissection process, provides antegrade flow in the descending aorta and minimises intraoperative malperfusion. The purpose of this study is to evaluate a single surgeon's experience of axillary artery cannulation for ATAAD repair. All consecutive patients over a 15-year period having surgical repair of ATAAD were included in this study. There were 55 patients with a mean age of 67years. The most common risk factors were hypertension (83.6%), connective tissue disease (7.3%) and a bicuspid aortic valve (7.3%). Axillary artery cannulation was performed on 50 patients (90.9%) and was contraindicated in the remaining five patients. Forty-nine patients survived to 30days with a 10.9% 30-day mortality rate. There was one confirmed stroke (1.8%) and no new malperfusion noted postoperatively. There were no major axillary artery complications or new dissection related to cannulation. We attribute these results, which are lower than those reported in the International Registry of Acute Aortic Dissection (IRAD) database, to axillary artery cannulation providing antegrade flow in the descending aorta from the outset and reducing intraoperative malperfusion. We believe this technique offers a cerebroprotective advantage and also facilitates selective antegrade cerebral perfusion (SACP) when aortic arch replacement is required. We believe the axillary artery is the ideal cannulation site of ATAAD and helps to reduce mortality and neurological complications in this high-risk group of patients.

Regional Practice Patterns and Outcomes of Surgery for Acute Type A Aortic Dissection

The surgical management of acute type A aortic dissection is evolving, and many aortic centers of excellence are reporting superior outcomes. We hypothesize that similar trends exist in a multiinstitutional regional consortium. Records for 884 consecutive patients who underwent aortic operations (2003 to 2015) for acute type A aortic dissection were extracted from a regional The Society of Thoracic Surgeons database. Patients were stratified into three equal operative eras. Differences in outcomes and risk factors for morbidity and mortality were determined. Surgical procedures for type A aortic dissection are increasing in extent and complexity. Aortic root repair was performed in 16% of early era cases compared with 67% currently (p < 0.0001). Similarly, aortic arch repair increased from 27% to 37% cases (p < 0.0001). Cerebral perfusion is currently used in 85% of circulatory arrest cases, most frequently antegrade (57%). Total circulatory arrest times increased (29 minutes vs 31 minutes vs 36 minutes; p= 0.005), but times without cerebral perfusion were stable (12 minutes vs 6 minutes; p=0.68). Although the operative mortality rate remained stable at 18.9% during the 3 operative eras, there were significant decreases in pneumonia and reoperations (p< 0.05). Predictors of operative mortality and major morbidity are age (odds ratio [OR], 1.04; p < 0.0001), previous stroke (OR, 2.09; p= 0.03), and elevated creatinine (OR, 1.31; p= 0.01). Importantly, the extent of aortic operation did not increase risk for morbidity or mortality. Operative morbidity and mortality remain significant for type A aortic dissection, but lower than historical outcomes. The extent of aortic surgery has increased, resulting in adaptive cerebral protection changes in contemporary "real-world" practice.

Uncomplicated Acute Type B Aortic Dissection: Selection Guidelines for TEVAR.

Traditionally, the surgical management of acute type B aortic dissections was reserved for patients with signs of malperfusion, rapid expansion, retrograde dissection or rupture. The adjunct of endovascular techniques has brought a paradigm shift, leaning towards preventing long term dissection complications. Multiple risk factors have been proposed to identify patients at risk for long term aortic complications. The patients, who are offered a prophylactic endovascular therapy for uncomplicated aortic dissection, should be selected carefully, and offered intervention by an experienced team in a high-volume center. (This is a review article based on the invited lecture of the 57th Annual Meeting of Japanese College of Angiology.)

Technical aspects of total aortic repair in the surgical management of acute type A aortic dissection

Technical aspects of total aortic repair in the surgical management of acute type A aortic dissection

Technical aspects of total aortic repair in the surgical management of acute type A aortic dissection

Traditional surgical techniques for the management of acute type A aortic dissection (ATAAD) focus on open distal anastomosis with or without hemiarch replacement under a period of deep hypothermic circulatory arrest. This is associated with high rates of false lumen (FL) patency, which exposes the patient to the risk of ongoing end-organ malperfusion and to the formation of complex arch and thoracoabdominal dissection aneurysms. Furthermore, persistent malperfusion is a major source of morbidity and mortality and is not easily reversed following traditional central repair. Arch replacement using the “branch first” technique allows for complete root, ascending and arch replacement (1-3). A long landing zone is created for proximal endografting with a covered stent. Extended thoracoabdominal stenting is performed in patients with: Ongoing or recurrent branch vessel ischaemia or malperfusion; Radiological true lumen (TL) collapse; Rapid dilatation of the FL; Markers of compromised TL perfusion. The following video (Video 1) illustrates a case of TAAD with clinical and radiological malperfusion and shows the benefits of “branch first” arch replacement followed by stent grafting in this situation. Video 1 Technical aspects of total aortic repair in the surgical management of acute type A aortic dissection.

Surgical management of acute type A aortic dissection: branch-first arch replacement with total aortic repair.

Acute type A dissection (ATAAD) remains a morbid condition with reported surgical mortality as high as 25%. We describe our surgical approach to ATAAD and discuss the indications for adjunct techniques such as the frozen elephant trunk or complete aortic repair with endovascular methods. Arch replacement using the "branch-first technique" allows for complete root, ascending aorta, and arch replacement. A long landing zone is created for proximal endografting with a covered stent. Balloon-assisted intimal disruption and bare metal stenting of all residual dissected aorta to the level of the aortic bifurcation is then performed to obliterate the false lumen (FL) and achieve single true lumen (TL) flow. Additional branch vessel stenting is performed as required.

Total aortic repair: the new paradigm in the treatment of acute type A aortic dissection

The surgical management of acute type A aortic dissection (ATAAD) is in a period of rapid evolution. Understanding the complex physiology and anatomy of both acute and chronic dissection has been enhanced by the ready availability of state of the art imaging techniques. Technical advances in the intraoperative monitoring of organ perfusion, together with adjuncts to limit organ injury and increasing sophistication in open and endovascular surgery have led to a major reduction in both perioperative morbidity and mortality. In many centers, there has been a transition in mindset and surgical approach away from a purely central aortic operation focusing on the ascending aorta and a 'live to fight another day' philosophy. The current more global perspective recognizes the importance of aortic valve function, malperfusion, false lumen (FL) patency and the potential for future complex aneurysm development. The time is now right to transition into the next phase of sophistication in the management of ATAAD with the aim of achieving not only a safe acute operation, but to either entirely prevent chronic complications or to greatly simplify their management by the creation of an anatomical situation that facilitates future endovascular intervention in place of complex re-do surgery. We present our view on the evolution of surgery for ATAAD leading to our current technique of Branch First Arch replacement and Total Aortic Repair, which not only provides a safe immediate operation, but also offers the hope of a simplified future management if not a total cure for the pathology.

Comparison of vascular ring connector and conventional suture technique in the surgical management of acute type A aortic dissection

Background: The aim of this study was to examine the utility of the vascular ring connector (VRC) and compare the clinical outcomes to conventional suture technique in the operation for acute type A aortic dissection (AAAD). Methods: We retrospectively enrolled 64 consecutive patients (mean age 57.4 ± 12.7 years, range 24-82 years) with AAAD who underwent emergent surgery in our institution from September 2010 to November 2014. Patients were divided into VRC group (55 patients) and conventional suture group (nine patients) based on the use of VRC during the operation. The preoperative characteristics, operative variables, and postoperative outcomes were collected and analyzed. Results: Male patients predominated in both groups. The mean times of cardiopulmonary bypass and aortic cross-clamp were 200.1 ± 99.9 and 193.6 ± 54.7 min ( P = 0.425) and 107.5 ± 56.2 and 112.3 ± 40.8 min ( P = 0.404) in the VRC group and suture group, respectively. There were more blood transfusions within 24 h (1513.3 ± 949.2 vs. 841.8 ± 801.1 ml) and more mediastinal drainage amount (1314.4 ± 650.3 ml vs. 942.1 ± 527.2 ml) in the suture group than in the VRC group. In the VRC group, 36.3% of patients did not require blood transfusion. Moreover, the pumping time and cardiac ischemic times were longer in the one-VRC group than in the two-VRC group. Operative mortality did not differ between the two groups (10.9% in VRC and 11.1% in suture group, P = 0.985). No dislodgement of VRC during or after operation and no bleeding from sutureless anastomosis site were noted. Conclusion: Use of VRC is associated with equivalent operative mortality and morbidity compared to suture group in patients with AAAD undergoing an emergent operation. This study demonstrates the clinical safety and efficacy of VRC in reducing the need of blood transfusion within 24 h and mediastinal drainage within 72 h. However, further randomized studies and long-term surveillance of the use of VRC in AAAD are still mandatory.

Dacron Graft Intussusception Technique for Treatment of Type A Aortic Dissections: Technical Notes and Preliminary Results

IntroductionOptimal surgical management for acute type A aortic dissection (AAAD) remains unclear. The in-hospital mortality rate is still high (15%), and the intraoperative bleeding is an independent risk factor for hospital mortality.ObjectiveThe aim of our study was describe a new method for aortic anastomosis in the repair of AAAD and report the hospital mortality and bleeding complications.MethodsBetween January 2008 and November 2014, 24 patients, 16 male, median age 62 years, underwent surgical treatment of AAAD. The surgical technique consisted of intussusception of a Dacron tube in the dissected aorta, which is anastomosed with a first line of 2-0 polyester everting mattress suture and a second line of 3-0 polypropylene running suture placed at the outermost side. Open distal anastomosis was performed with bilateral selective antegrade cerebral perfusion in 13 (54.1%) patients.ResultsCardiopulmonary bypass and aortic clamping time ranged from 75 to 135 min (mean=85 min) and 60 to 100 min (mean=67 min), respectively. The systemic circulatory arrest ranged from 29 to 60 min (mean=44.5 min). One (4.1%) patient required reoperation for bleeding, due to the use of preoperative clopidogrel. The postoperative bleeding was 382-1270 ml (mean=654 ml). We used an average of 4.2 units of red blood cells/patient. There were two (8.3%) hospital deaths, one due to intraoperative bleeding and another due to mesenteric ischemia. The average length of stay in the intensive care unit and hospital was 44 hours and 6.7 days, respectively.ConclusionThis new method for surgical correction of AAAD was reproducible and resulted in satisfactory clinical outcomes.

Surgical management for acute type A aortic dissection in patients over 70 years-old

BackgroundThis study aimed to retrospectively investigate our experience of surgical treatment for acute type A aortic dissection in patients older than 70 years.MethodsFrom September 2005 to January 2012, eleven patients who were older than 70 years underwent surgical treatment for type A aortic dissection at our center and were included in this study. Total arch replacement was performed in three patients, seven patients underwent subtotal arch replacement and one with single-branched stent graft implantation. One patient underwent a valve-sparing (David) procedure while another underwent a concomitant aortic valve replacement (Wheat procedure). One patient required coronary artery bypass grafting. All operations were performed under deep hypothermic circulatory arrest and selective antegrade cerebral perfusion.ResultsThere was one in-hospital death (9.1%) and no operative mortality within 30 days. Cardiopulmonary bypass time, myocardial ischemic time and antegrade cerebral perfusion time accounted for 151.4±33.5 minutes, 68.5±41.4 minutes and 30.3±12.9 minutes, respectively. Overall in-hospital duration, intensive care unit (ICU) time and mean ventilation time were 40.9±40.3 days, 16.5±22.5 days and 90.5±139.4 hours, respectively. New postoperative permanent neurological dysfunction and temporary neurological dysfunction were observed in one patient (9.1%) and in three patients (27.3%), respectively. Mean follow-up was 49.0±19.9 months and nine patients are still alive, one patient died of cancer after 24 months postoperation.ConclusionsSurgical management for acute type A dissection in patients older than 70 years is a safe alternative with acceptable risk of death and the early and late results are satisfactory.