To investigate the clinical application value of thrombolysis via small saphenous vein (SSV) catheter placement for the treatment of lower extremity deep vein thrombosis (DVT). Methods Forty-seven patients with lower extremity DVT admitted from May 2009 to March 2014 were retrospectively analyzed, and a thrombolytic catheter was placed via the saphenous vein-N vein under the protection of a filter, and thrombolytic drugs were continuously pumped via the thrombolytic catheter for 7-12 d, along with anticoagulation therapy. Intraoperative as well as venography was performed to evaluate the degree of venous patency. Results All patients were successfully placed with 100% success rate of catheterization and 100% effective rate of treatment, and the clinical manifestations improved to different degrees. Four of the patients underwent iliac vein balloon dilatation and vascular stenting. Conclusion: Thrombolysis for DVT via the saphenous vein-N vein route is a simple, economical, safe and effective treatment method. Deep venous thrombosis (DVT) is a common clinical disease. If this disease is not treated in time and appropriately, a series of lesions such as deep venous valve insufficiency can occur in the late stage, causing swelling, ulceration and gangrene of the affected limbs, and even pulmonary embolism (PE) resulting in death. The National Institutes of Health suggests that thrombolysis for DVT is significantly better than anticoagulation alone [1]. The small saphenous vein (SSV) is one of the major superficial venous systems of the lower extremities, which joins the N vein at the N fossa or lower. In May 2009, our hospital began to use thrombolytic therapy for DVT via the small saphenous vein-N vein route under the protection of vena cava filter (VCF), which reduced the complication rate of thrombolytic therapy and had good results, which are reported as follows. 1, data and methods 1.1 General information Among the 47 cases in this group, there were 19 males and 28 females, aged 34-71 years old, with an average age of 48.6 years old, and the duration of the disease ranged from 6h to 26d, with an average of 4.9d, among which there were 24 cases of the disease duration, 18 cases of 10~14d, and 5 cases of 14~30d. There were 36 cases of left lower extremity venous thrombosis and 11 cases of right lower extremity venous thrombosis. There were 3 cases of central type DVT and 44 cases of mixed type DVT. There were 15 cases with a history of prolonged bed rest or sedentary behavior, 6 cases after cesarean section, 17 cases after orthopedic surgery, and 9 cases with no obvious pathogenic factors. DVT was confirmed by color ultrasound of the lower extremity veins before surgery, and one case was clearly combined with partial embolism of the left lower pulmonary artery by chest CTA examination. 1.2 Treatment 1.2.1 Inferior vena cava filter placement Inferior vena cava filter placement is recommended before catheterization and thrombolysis, and recyclable filters are preferred for young patients. In this group of patients, 14 permanent filters and 33 retrievable filters are placed. Forty-six filters were placed through the healthy femoral vein, and one was placed through the jugular vein. 47 filters were placed 1 cm below the opening of the right renal vein, among which the retrievable filters were taken out at the permitted time after the end of the cannula thrombolytic therapy and after the absence of large thrombus at the filters was confirmed by angiographic ultrasonography or re-imaging. The time for removing the retrievable filter is generally not more than 16 d. 1.2.2 Methods of catheterization After the VCF is successfully inserted and the venous puncture point is fixed with a compression bandage, the patient is oriented to the healthy lateral position or prone position, and under local anesthesia of 1% lidocaine, a 1-cm longitudinal incision is made in the midpoint of the line connecting the outer ankle and the Achilles tendon to expose the starting section of the SSV, and the SSV is directly punctured with a puncture needle (Seldinger technique), and the 4F catheter sheath is inserted to ensure that no large clots are present at the filter. A 4F catheter sheath was placed, and the 4F vertebral artery catheter entered the N vein under the guidance of a 0.035 ultra-smooth guidewire, and the scope of the lower extremity deep vein thrombus and the vena cava were clarified by angiography. The vertebral artery catheter was continued to travel upward to the proximal end of the thrombus, and was exchanged for a 5F thrombolytic catheter (with a lateral hole for effective thrombolysis at a distance of 20 cm), which was placed into the proximal end of the thrombus. Suture the small incision, fix the puncture sheath tube and thrombolytic catheter, and prevent the thrombolytic catheter from being dislodged in the course of treatment. 1.2.3 Medication ① Thrombolytic medication: connect the thrombolytic catheter with infusion pump, continuously pump urokinase, 5-10 wu each time, pumped within 8 hours, 3 times a day, and push urokinase through the puncture sheath tube, 5 wu each time, q12h. ② Anticoagulant medication: subcutaneous injection of low molecular heparin sodium 40mg/0.4 ml, q12h; oral Bay Aspirin 100mg bid; ③ To activate blood circulation and remove blood stasis: intravenous infusion of Shuxuetong 6ml qd; ④ antibiotic anti-infection treatment; ⑤ oral drugs to improve venous tone: Mai Zhi Ling 300mg bid. adjust the dosage of urokinase according to coagulation indexes, according to the routine blood platelet indexes to monitor the occurrence of thrombocytopenia. Every 36-48h through the thrombolytic catheter deep vein bypass angiography to observe the thrombus changes. After the thrombus at the thrombolytic catheter was dissolved and the vein was recanalized, the thrombolytic catheter was set back 25cm, and the thrombolytic catheter was still placed into the proximal end of the thrombus, and the treatment plan remained unchanged. Until the thrombus is completely dissolved or the effective segment of the thrombolytic catheter is withdrawn from the body, the thrombolytic catheter is withdrawn; after continuing anticoagulation for 72 hours, according to the results of angiography combined with venous ultrasound, it is confirmed that the thrombus of the deep veins of the lower extremities has been completely dissolved and there is no large thrombus at the filter, then the recyclable filter is taken out; if the thrombus is not dissolved satisfactorily or there is a large thrombus at the filter, then give up to take out the recyclable filter. After the catheter was removed, the patients in this group were treated with long-term sequential compression stockings for at least 6 months, and anticoagulation therapy was continued. 1.3 Judgment of efficacy According to clinical manifestations, angiographic results and combined with Sun Jianmin thrombus recanalization typing [2]. Cure: swelling and pain of the lower limbs disappear completely, and angiography suggests that the deep veins of the lower limbs are recanalized, and there are some attached thrombi. Apparent effect: pain in the lower limbs disappeared, swelling obviously subsided, angiographic results suggest that venous return is smooth, there is thrombus remaining in the vein, and the lumen is recanalized > occluded. Effective: pain in the lower limbs disappeared, swelling subsided significantly, angiographic results suggest that there is thrombus remaining in the deep veins, lumen recanalization < occlusion. Ineffective: swelling and pain of lower limbs were not reduced, and angiographic results suggested that venous return was not smooth. Results: 47 patients in this group were successfully catheterized through the small saphenous vein-N vein, and the thrombolytic catheter was inserted through the iliac vein, with a 100% success rate of catheterization. In this group, 23 cases were cured, 15 cases had obvious effect, 9 cases had effective effect, with the apparent efficiency of 80.9%, and the total effective rate of 100%. The time of thrombolytic catheter placement was 7~12d, with an average of 9.5d; the hospitalization time was 14~20d, with an average of 16.8d. After thrombolytic treatment, all of them were subjected to lower extremity deep vein by-passing angiography, among which, 15 cases had the entire deep vein of the affected extremity smooth, with smooth wall, normal valves, and no obvious reflux. Two cases of N vein stenosis of about 50%, length <3cm< span="">. 18 cases of left iliac vein segment stenosis is obvious, 50%-100%, of which the stenosis of >75% of the 10 cases, completely inaccessible venography see the left lower limb venous blood flow through the prepubic vein and other side branch vein diversion reflux back to the inferior vena cava, 4 cases of which in the iliac vein under the supervision of DSA balloon dilatation and molding and vascular stent placement. Four of them underwent iliac vein balloon dilatation molding and vascular stenting under DSA surveillance. Nineteen retrievable filters were removed after the operation, all of which were removed after angiography combined with venous ultrasound examination confirmed that the thrombus in the deep veins of the lower limbs had been completely dissolved and there was no large thrombus at the filters; the rate of retrievable filter removal was 57.6%, and the time of removal ranged from 13 to 21 d, with an average of 16.5 d. All of the 47 cases had been followed up for the longest time of 26 months, and the shortest time of 6 months, of which 39 cases did not have any sequelae. Among them, 39 cases had no sequelae and resumed normal life and work, 8 cases had lower limb soreness, fatigue and even mild swelling of calf after activity, and they worked and lived as usual after wearing the sequential decompression compression stockings. 3.Discussion 3.1 Placement of inferior vena cava filter The treatment objectives of DVT mainly include prevention of PE and prevention of post-thrombotic syndrome of lower extremity DVT.PE is the main risk of death from DVT, and it can lead to the occurrence of chronic pulmonary arterial hypertension. Embolization of the pulmonary artery by dislodged DVT emboli may occur during movement of the affected limb, compression, physical opening of the catheter guidewire in the lumen, and pharmacologic thrombolysis. A retrospective analysis of a large number of foreign cases showed that placement of VCF could reduce the incidence of PE to less than 6%, and the incidence of fatal PE was only 0.17%-4.10% [3]. We believe that there are two high-risk factors for venous thrombus dislodgement during catheterization and thrombolytic drug intervention, physical opening of catheter guidewire and thrombolytic drug intervention, and VCF placement is recommended before catheterization and thrombolysis. Because the long-term follow-up of permanent filters is not clear, it is recommended that young people prefer recyclable filters. After the end of thrombolytic treatment, the retrievable filter can be taken out after the angiography combined with venous ultrasound examination confirms that the lower extremity DVT has been completely dissolved and there is no large thrombus at the filter. 3.2 Feasibility of catheter thrombolysis Catheter thrombolysis is also known as pharmaco-mechanical thrombectomy, and in recent years, this technique has been gradually applied to the clinic, and a large number of cases have been accumulated so far. The guidelines for catheter thrombolysis specified by the American Society for Interventional Radiology recommend that it should be applied mainly to acute iliofemoral vein thrombosis, acute or subacute inferior vena cava thrombosis (VCF placement followed by catheter thrombolysis is recommended), and femoral bruxism [4]. Fibrinogen activator injected into the thrombus via catheter can more effectively activate fibrinolytic enzymes combined with fibrin to play the role of thrombolysis; proximal thrombus thrombolysis in the catheter can protect urokinase (UK) from the neutralization of inhibitors of fibrinogen activator in the circulating blood, and at the same time, can avoid the activation of fibrinolytic enzymes neutralized by the anti-fibrinolytic enzymes in the blood, which obviously increases the amount and concentration of the local drug and improves the effect of thrombolysis, and significantly reduces the risk of thrombolysis, as well as the effect of thrombolysis. This significantly increases the local drug dosage and concentration and improves the thrombolytic effect, and at the same time significantly reduces the systemic drug dosage and the risk of bleeding and other complications, so as to achieve the optimal thrombolytic effect. If the timing of thrombolytic intervention is properly selected, the rate of complete dissolution of thrombus is high, which can maximally protect the structure and function of venous walls, valves and calf muscle pumps, and greatly reduce the possibility of the occurrence of the sequelae of thrombosis. The deep veins of the affected limbs of 15 patients in this group were smooth throughout the whole process, with smooth vein walls, normal venous valve morphology and no obvious regurgitation, which reached an ideal state in terms of function as well as morphology. It was analyzed that the timing of intervention of cannula thrombolysis, DVT typing, and the choice of cannula access were greatly related. Regarding the indications for cannula thrombolysis, we believe that it is particularly effective in patients with centralized and mixed DVT in the acute and subacute stages, especially in patients with DVT in the acute stage. All the cases in our group who achieved cure were patients in the acute stage within 10d of onset. Moreover, the follow-up results were satisfactory and no serious complication appeared after thrombolysis, which indicated that thrombolysis was safe and effective. Complications of thrombolysis mainly include bleeding, hematoma, pulmonary embolism and intracranial hemorrhage [5], of which the incidence of bleeding or hematoma is the highest, therefore, we believe that its contraindications should include: ① contraindication or allergy to anticoagulants, contrast agents and thrombolytic drugs; ② recent history of cranial, cerebral and gastrointestinal bleeding; ③ accompanied by severe trauma and infection; ④ difficult to control intractable hypertension; ⑤ pregnant or perinatal patients, etc. 3.3 Tube thrombolysis 3.3 Problems of choosing the access route for tube placement and thrombolysis In recent years, the exploration of the access route for tube placement has been one of the directions of research. Most of the routes reported in the literature at home and abroad include: retrograde deep vein cannulation via the right internal jugular vein, retrograde deep vein cannulation via the healthy femoral vein by “tipping over the mountain”, and paracentesis via the ipsilateral femoral vein, the N vein, or the saphenous vein [6-8]. There are venous valves in the deep veins of the lower limbs, and the failure rate of reverse cannulation is high and prone to damage the venous valves; ipsilateral femoral vein or saphenous vein downstream cannulation is easier, but the effect of thrombolysis is poor for the DVT far away from the femoral vein; ipsilateral N vein puncture cannulation is technically demanding, and it is easy to damage the tibial nerve during the operation to cause nerve irritation and damage to the N artery to lead to arteriovenous fistula, and it is also easy to damage the arterial fistula of the patient during the thrombolytic treatment. During thrombolytic therapy, the mandatory prone position and limb braking requirements are difficult to bear for elderly and weak patients with limited mobility, and this method of catheterization makes it difficult to effectively dissolve the thrombus in the N vein or calf segment. The small saphenous vein originates from the lateral aspect of the dorsalis pedis venous network, travels upward from the posterior aspect of the ankle, gradually turns to the midline of the dorsal aspect of the calf and penetrates into the deep fascia, and most often converges into the N vein at the midpoint of the N fossa or off to the inferior aspect of the N fossa [9]. The small saphenous vein is characterized by its superficiality, fixed position, straight alignment, trunk diameter of about 2-5 mm, and thick wall, which makes it easy to puncture and cannulate into the N vein and then into the deep venous system of the lower limbs. Anatomically, it is feasible to insert a thrombolytic catheter via the saphenous vein-N vein route, and it has been confirmed in clinical practice that the success rate of catheterization via this route is up to 100%, and there is no special position requirement for the patient during the period of catheter thrombolysis and no need for limb braking, which makes it extremely comfortable. All the cases in this group were treated with thrombolysis via SSV, the advantages of which are: ① simple method, small damage to the lower extremity deep vein valves by downstream cannulation; ② high efficiency of thrombolysis for deep vein thrombus perfusion, reducing the risk of thrombolysis complications; ③ high success rate of puncture of the small saphenous vein under direct vision, no side damage, avoiding damage to the wall of the N vein via N venous puncture, minimizing bleeding, hematoma, nerve damage caused by N venous puncture. It can minimize the incidence of bleeding, hematoma, nerve injury and other complications caused by N vein puncture; ④ Increase the effective working distance of thrombolytic catheter, so that its effective thrombolytic catheter segment can be maximally lowered to the distal segment of the thrombus to improve the therapeutic effect of thrombolysis; ⑤ The small saphenous vein is relatively superficial, and only a simple compression bandage is needed to stop the bleeding after catheter extraction, which is helpful for the venous return of the distal limb; ⑥ During the period of thrombolytic therapy through the catheter, the patient’s activity is not affected, so that it improves the compliance and comfort level of the patient. (6) During transcatheter thrombolytic therapy, it does not affect the patients’ moderate activity, which improves the patients’ compliance and comfort. The preliminary clinical application shows that the treatment of lower extremity deep vein thrombosis by catheterization via the small saphenous vein-N vein path is an effective and safe minimally invasive treatment method, which is worth promoting in clinical application.