AMI is a life-threatening disease caused by the abrupt interruption of the mesenteric blood circulation. Because of its hidden onset, difficulty 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 cases2, 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 fibrillation or myocardial infarction, valvular vegetation caused by rheumatic heart disease and thrombosis after prosthetic valve replacement4.On the other hand, SMA lesions such as superior mesenteric artery dissection, could also cause acute thrombosis leading to AMI7. 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 unsatisfactory5. Therefore, when acute abdominal symptoms are accompanied by atrial fibrillation, general atherosclerosis, coagulation disorder or other circulatory diseases, the diagnosis of SMAE should be considered8.
At present, CTA is the golden standard for clinical diagnosis of SMAE, which could not only confirm 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 possible9. According to research, ischemia-modifie albumin could be used as a biochemical marker for the diagnosis of SMAE, but the real value should be further evaluated10.
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 syndrome11–13.
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 complications14. Several studies have shown that PMT is a safe and effective therapy for arterial and venous thromboembolism15, 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 Scientific, 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 orifices in the distal tip of the catheter to create a localized low-pressure zone (Bernoulli effect), resulting in the dissociation and removal of thrombus18. The advantages of this procedure lie in its minimal invasiveness, clean the thrombus and restore the intestinal blood flow rapidly, reduce use of thrombolytic drugs and low complication rate19. The inadequacies include the possibility of vessel rupture and risk of bleeding, while such complications can be managed by operating carefully20. 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 Scientific, USA), of which the applicable minimum diameter is 3 mm. This makes recanalization of the distal branch difficult 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 first. 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 identification 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, inflammation 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 sufficient evidence of aggravated ischemia or intestinal necrosis, exploratory laparotomy should be performed immediately. Conversely, without definite evidence, we recommend trying PMT therapy first. 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.