Acute Superior Mesenteric Artery Embolism treated with Percutaneous Mechanical Thrombectomy: Preliminary application and Experience

Acute superior mesenteric artery embolism is a life-threatening disease and the prognosis is very poor. Few reports have described the application of Percutaneous Mechanical Thrombectomy in Acute superior mesenteric artery embolism. In the article, we show a series of cases treated with Percutaneous Mechanical Thrombectomy and share our experience.


Background
Acute mesenteric ischemia (AMI) is a life-threatening disease caused by the abrupt interruption of the mesenteric blood circulation. Because of its hidden onset, di culty in early diagnosis and rapid progression, the prognosis of AMI is extremely poor, with an overall mortality rate as high as 60-80% 1 . Acute superior mesenteric artery embolism (SMAE) is the most common pathogenesis of AMI and accounts for approximately 40-50% of the cases 2, 3 . The most emboli originate from the heart, such as recurrent arrhythmia, especially from mural thrombus caused by atrial brillation 4 . Due to the atypical symptoms and signs of SMAE, it is easy to be misdiagnosed in the initial stage. Once extensive intestinal ischemia and necrosis, toxic shock, or even multiple organ dysfunction syndrome occur, the prognosis is very unsatisfactory 5 . Therefore, early diagnosis and treatment are crucial means for a successful outcome.
Generally, clinical treatment of SMAE includes surgical laparotomy with thrombectomy, medical conservative treatment and endovascular interventional therapy. With the continuous improvement of endovascular techniques and the development of operating instruments, endovascular therapies such as catheter directed thrombolysis, percutaneous mechanical thrombectomy (PMT), with or without angioplasty and stenting have been gradually adopted6. However, few relevant reports of PMT for SMAE have been reported at present. In the series, we summarize several cases of SMAE treated by PMT and share our experience in our institution.

preoperative cases present
All patients were admitted to our emergency department with acutely worsening abdominal pain, with or without nausea, emesis and bloody diarrhea. Six patients had known history of atrial brillation and one patient had infective endocarditis. Except for signi cantly increased white blood cells count (exceed 20.0*109/L) in two patients, no signi cant abnormalities were presented. No rebound tenderness or signs of peritonitis were found in all patients. All patients underwent emergency computed tomography angiography (CTA) and segmental occlusion of SMA stem were revealed ( Fig. 1,2). Based on the symptoms, the signs, previous medical history and auxiliary examination, the diagnosis of acute superior mesenteric artery embolism was made. Considering that no signs of intestinal necrosis were found, we performed PMT treatment to clear the thrombus load as soon as possible for all patients. surgical methods After local anesthesia, punctures were performed via the femoral artery or the brachial artery approach in all the patients according to the exiting angle between SMA and abdominal aorta. A 0.035-inch 150-cm long guidewire (TERUMO, Japan) combined with catheter inserted into SMA stem. Then, the guidewire was replaced with a 0.035-inch, stiff, straight, 260-cm long guidewire (TERUMO, Japan) and a 6F fty-ve cm Fustar adjustable sheath (Lifetech, China) was used to catheterize SMA ostium. All the patients received 5,000 IE of heparin during the procedure. Subsequently, the selective mesenteric angiography con rmed the CTA ndings. The guidewire was through the thrombus and reached the distal end of SMA stem. Then, thrombus aspiration was performed two passes with the AngioJet thrombectomy catheter (Solent Omni, Boston Scienti c, USA) in all the patients (Fig. 3). Subsequent angiography showed that the thrombus was cleared and the mesenteric ow was established immediately (Fig. 4). However, the patient who was diagnosed with infective endocarditis before surgery still showed small lling defect in the mesenteric trunk and distal branch. Considering that the patency of SMA trunk and patient's pain was alleviated signi cantly than before, no additional thrombolysis, balloon dilatation or stent implantation were performed. Finally, the femoral puncture point was sutured by Proglide (Abbott Vascular, USA) and the puncture point of brachial artery was compressed with an elastic bandage.

Results
PMT were achieved successfully in all the patients without surgical complication occurred. After the operation, all patients received a regimen of abrosia, anticoagulant therapy, antibiotic, acid-inhibitory drug, vasodilator therapy and su cient parenteral nutrition. During hospitalization, ve patients' symptoms relieved signi cantly, however, the other two patients still complained of abdominal pain and the abdominal signs aggravated gradually. Eventually, one patient underwent surgical laparotomy and intestinal resection Page 4/14 while the other patient abandoned surgical treatment. All patients received antiplatelet therapy with oral aspirin for at least six months after discharge and lifelong warfarin therapy were planned for the patients with atrial brillation (Table I).
During the rst six months of follow-up, six patients were free of any clinical symptoms or signs and one patient who refused laparotomy died two days later with septic shock.

Discussion
AMI is a life-threatening disease caused by the abrupt interruption of the mesenteric blood circulation.
Because of its hidden onset, di culty in early diagnosis, rapid progression as well as complex surgical treatment, the prognosis of AMI is extremely poor, with an overall mortality rate as high as 60-80% 1 . SMAE is the most common pathogenesis of AMI and accounts for approximately 40-50% of the cases 2, 3 . Embolism of SMA generally includes two parts: exogenous emboli and acute thrombosis caused by SMA lesions. The most exogenous emboli originate from the heart, such as mural thrombus caused by atrial brillation or myocardial infarction, valvular vegetation caused by rheumatic heart disease and thrombosis after prosthetic valve replacement 4 .On the other hand, SMA lesions such as superior mesenteric artery dissection, could also cause acute thrombosis leading to AMI 7 . Due to the atypical symptoms and signs of SMAE, many patients are easily be misdiagnosed as acute gastroenteritis, acute ileus or acute appendicitis at the initial diagnosis.
To SMAE, the time-frame for therapy is short. Once extensive intestinal ischemia and necrosis, toxic shock, or even multiple organ dysfunction syndrome occur, the prognosis is very unsatisfactory 5 . Therefore, when acute abdominal symptoms are accompanied by atrial brillation, general atherosclerosis, coagulation disorder or other circulatory diseases, the diagnosis of SMAE should be considered 8 .
At present, CTA is the golden standard for clinical diagnosis of SMAE, which could not only con rm the patency of SMA, but also understand whether bowel necrosis has occurred. Once SMAE is suspected, CTA should be performed immediately in order to proceed with therapy as soon as possible 9 . According to research, ischemia-modi e albumin could be used as a biochemical marker for the diagnosis of SMAE, but the real value should be further evaluated 10 .
Early diagnosis and treatment are crucial means for a successful outcome. Generally, current clinical treatment of SMAE includes conservative medication, surgical treatment and endovascular therapy.
Anticoagulation, thrombolysis and vasodilator therapy are the main regimen for conservative treatment. If the disease progresses, surgery or interventional treatment should be performed in time. Surgical procedures mainly involve laparotomy, thrombectomy of SMA and necrotic bowel resection. As the surgical treatment can remove thrombus and recover the blood-supply immediately, so it is feasible and effective. However, the concomitant problems associated with high surgical risk and postoperative complications make these surgeries inappropriate for patients with poor underlying conditions. Compared with traditional surgery, endovascular therapy is a minimal invasive method with lower mortality rate, at the same time, it can also protect the intestinal function and avoid the short-bowel syndrome [11][12][13] .
Clinically, endovascular therapy of SMAE common includes catheter aspiration, CDT, angioplasty and stenting. CDT is an easy and effective method, whereas it takes time to dissolve the thrombus, prolong the duration of treatment, miss the golden time to improve bowel ischemia and easy to cause bleeding complications 14 . Several studies have shown that PMT is a safe and effective therapy for arterial and venous thromboembolism 15,16 . However, as far as we know, there are only few reports of using percutaneous mechanical thrombectomy in SMAE. Zhang et al. 17 reported that PMT by the Rotarex system is a minimally invasive, safe, and effective treatment in SMAE. There are many different devices in PMT for thrombectomy.
In our institution, we performed PMT treatment for nine patients by using Angiojet Ultra (Boston Scienti c, USA) successfully. Angiojet Ultra thrombectomy system, as a representation of PMT, is a new interventional technique. Such device generates high pressure and velocity saline jets, which are introduced through ori ces in the distal tip of the catheter to create a localized low-pressure zone (Bernoulli effect), resulting in the dissociation and removal of thrombus 18 . The advantages of this procedure lie in its minimal invasiveness, clean the thrombus and restore the intestinal blood ow rapidly, reduce use of thrombolytic drugs and low complication rate 19 .
The inadequacies include the possibility of vessel rupture and risk of bleeding, while such complications can be managed by operating carefully 20 . The most technical challenge is how to clean the distal arterial embolism. Our center is equipped with the Angiojet Ultra device using Solent Omni catheter (Boston Scienti c, USA), of which the applicable minimum diameter is 3 mm. This makes recanalization of the distal branch di cult and may lead to rupture of the vessel.
In our experience, it is important to avoid using PMT repeatedly, as this may damage the SMA. If there is thrombus remains after PMT, the patency of SMA trunk and patient's symptom need to be evaluated rst. Just as the case we mentioned, even though a small amount of thrombus remains, no additional treatment was performed. However, if the situation does not improve obviously, catheter aspiration and CDT are often used as supplementary therapy for residual thrombus after PMT. Of course, whether the invisible branch vessel on angiography is caused by arterial embolism or vasospasm requires careful identi cation during the operation. In one of our cases, multiple distal branches were invisible after PMT treatment. We considered vasospasm and injected vasodilator drugs slowly through the catheter, after that, the patient's condition improved. When using CDT to treat SMAE, pay attention to the potential bleeding risk. On the other hand, the long sheath should not enter the SMA trunk completely, which may affect the perfusion of SMA. It is worth noting that the embolism caused by infective endocarditis, due to the rubbery consistency and complex composition of the embolus, the effect of using PMT or CDT may unsatisfactory.
There is no doubt that early diagnosis and treatment are the key to success. It is of outmost importance that identify whether the patient had irreversible intestinal ischemia or intestinal necrosis before surgery. When CT imaging indicates edema or thickening of the intestinal wall, this is not the indication for open surgery, nor the contraindication for endovascular treatment. Doctor is required to give a comprehensive assessment by evaluating abdominal pain, physical examination, temperature, in ammation indices and CT imaging. Zhang et al. 8 reported that a patient had increased white blood cell amount before surgery, while inevitable intestinal necrosis still occurred even after successful PMT therapy. In our institution, we encountered a similar situation. The white blood cell amount remarkably increased (exceed 20.0*109/L) in two patients and no clear evidence of intestinal necrosis was found. Even though we revascularized the SMA successfully, eventually, intestinal ischemia progressed and exploratory laparotomy was inevitable. Therefore, when patients have relatively high white blood cell amount before surgery, doctor must be alert to whether irreversible intestinal necrosis has occurred. Once there is su cient evidence of aggravated ischemia or intestinal necrosis, exploratory laparotomy should be performed immediately. Conversely, without de nite evidence, we recommend trying PMT therapy rst. Not only is a safe, effective and minimally invasive method, but also could protect the intestinal function and avoid the complications associated with laparotomy. Of course, closely monitor after surgery is also indispensable.

Conclusions
Early diagnosis and therapy are the key to success. To our knowledge, few reports have described the application of PMT in SMAE. In the article, we show PMT by Angiojet Ultra thrombectomy system is a safe, effective and minimally invasive method in the initial stage of SMAE, and share our experience and failure.
We believe PMT could be a promising alternative in selected cases. Furthermore, large sample data and long term follow-up are needed to verify its effect.Declarations

Declarations:
Declarations Ethics approval and consent to participate: The protocol was approved by the ethical committee of Hwa Mei Hospital, University of Chinese Academy of Sciences. Informed consent was waived due to the retrospective analysis of this study.

Consent for publication:
Not applicable.

Availability of data and materials
The datasets supporting the conclusions of this article appear in the manuscript, gures and