A systematic review on the use of deep venous stenting for acute venous thrombosis of the lower limb

Optimizing Venous Stenting: Consensus Recommendations for Enhanced Management of Lower Extremity Deep Vein Thrombosis

INTRODUCTION

 Deep vein thrombosis (DVT) poses a complex challenge and often leads to postthrombotic syndrome (PTS), a debilitating complication. The emergence of venous stents offers a potential preventive avenue against this complication. This study aimed to provide consensus recommendations on the use of venous stent for DVT.

MATERIALS AND METHODS

 From June to July 2023, 20 internal medicine, angiology and vascular surgery, and vascular and interventional radiology experts were involved in the Delphi process. Thirty-one recommendations, categorized into three thematic areas, were rigorously evaluated: indications for stent use, stent selection and placement, and monitoring and prevention of complications. Agreement was evaluated using a Likert scale, with consensus defined as agreement by two-thirds of the participants.

RESULTS

 Consensus was reached for 23 (74.2%) of 31 recommendations. The agreement was centered on considerations, such as stent placement in specific acute DVT scenarios, emphasizing pivotal stent characteristics. However, there were divergences in the recommended stent length to prevent migration and stent characteristics based on iliocaval bifurcation morphology. Notably, there was no consensus on whether patients with DVT caused by a major transient risk factor need more than 3 months of anticoagulation therapy or whether aspirin should be added to anticoagulant treatment after venous stenting.

CONCLUSIONS

 These consensus recommendations offer practical insights into optimizing venous stent use to prevent PTS in DVT patients. Addressing the critical aspects of stent selection, placement, and postprocedural care, these recommendations contribute to clinical decision-making. The identified divergences underscore the importance of consensus and thus indicate the need for further investigation.

The role and principles of stenting in acute iliofemoral thrombosis

Catheter-directed interventions for acute iliofemoral deep venous thrombosis (DVT) have been increasingly used over the past 15 years to target severe symptomatology and prevention of post-thrombotic syndrome incidence or reduce its severity if it were to develop. Aside from successful thrombus removal, adjunctive stents are frequently required to treat an uncovered lesion or significant residual thrombus to ensure quality of life improvement besides retarding DVT recurrence and post-thrombotic syndrome. As the evidence is mounting, the need and role for stenting, as well as the principles of an optimal technique, in the acute DVT setting are now better understood. Accumulating experience appears to favor stenting in the acute setting. The diameter of the stent, the length, the extent of overlapping, and the landing zones are crucial determinants of a successful durable outcome. This article endeavors to guide the interventionalist on stenting when encountering a patient with acute symptomatic iliofemoral DVT with concerns of quality of life impairment.

The background and role of catheter-directed thrombolysis evolving procedures for acute iliofemoral deep venous thrombosis

Minimal invasive treatment such as early endovenous thrombus removal for iliofemoral deep venous thrombosis (DVT) emerged in the end of last century. The principle is catheter-directed thrombolysis (CDT) using either plasminogen activating agents alone, as ultrasound-assisted CDT, or in combination with mechanical devices as pharmaco-mechanical CDT. The interest for this treatment modality is the high rate of post-thrombotic syndrome (PTS) with anticoagulation (AC) alone, especially after iliofemoral DVT. Recently published randomized controlled trials (RCTs) comparing early thrombus removal with AC alone, as well as non-randomized studies, have demonstrated favorable rates, or at least a decrease of moderate and severe PTS, in favor of these procedures. This article will summarize the background and evolution of the procedures in the last three decades and discuss fundamental criteria for inclusion and exclusion, focusing on the procedures regarding thrombus age and location, technical issues, complications and results including different outcome measures for PTS, for which iliac DVT involvement is a massive risk factor to be prevented.

Effects of Deep Venous Thrombosis Treatments on Early and Long-term Quality of Life: Medical Therapy vs. Systemic Thrombolysis vs. Pharmacomechanical Thrombolysis

OBJECTIVES

The present study aimed to compare the effects of medical therapy (MT), systemic thrombolysis (ST), and pharmacomechanical thrombolysis (PMT) methods used in our clinic for the treatment of deep venous thrombosis (DVT) on symptom reduction, the incidence of post-thrombotic syndrome (PTS) development, and quality of life.

METHODS

Data from160 patients diagnosed with acute DVT between January 2012 and May 2021 and treated and followed up in our clinic were retrospectively analyzed. The patients were divided into three groups according to treatment method. The patients who received MT treatment were defined as Group 1, anticoagulant treatment after ST as Group 2, and anticoagulant treatment after PMT as Group 3. The patients were called to the outpatient clinic, informed consent was obtained, EuroQol-5D-3 L (EQ-5D-3 L) scoring and Villalta scoring were performed, and anamnesis was taken.

RESULTS

A total of 160 patients were included, with 71 (44.4%) patients in Group 1, 45 (28.1%) in Group 2, and 44 (27.5%) in Group 3. The mean age was 48.9 ± 14.9 years for Group 1, 42.2 ± 10.8 for Group 2, and 29.0 ± 7.2 for Group 3. When the time to return to normal life and the EQ-5D-3 L score index were compared, the differences between Groups 1 and 2 and between Groups 1 and 3 were statistically significant (P = .000 and P = .000, respectively). However, the differences between Groups 2 and 3 were statistically insignificant (P = .213 andp = .074, respectively). When Villalta scores and EQ Visual Analogue Scale (EQ-VAS) scores were compared between groups, the difference between all groups was statistically significant (P = .000).

CONCLUSIONS

The medical treatment alone was observed to be insufficient in terms of symptomatic improvement, development of PTS, quality of life, and long-term complications. When the ST and PMT groups were compared, it was determined that PMT treatment was more advantageous in terms of EQ-VAS score and PTS development, although there was no statistical difference regarding complications, such as return to normal life and long-term quality of life, the incidence of recurrent DVT development, and pulmonary thromboembolism incidence.

Antithrombotic management of patients with deep vein thrombosis and venous stents: an international registry

BACKGROUND

In patients with acute deep vein thrombosis (DVT) treated with catheter-based thrombolysis and venous stenting, poststenting anticoagulant management is uncertain.

OBJECTIVES

To determine the type and duration of antithrombotic therapy used in patients who have received venous stents for treatment of acute lower extremity DVT.

METHODS

We created an international registry of patients with leg DVT from 2005 to 2019 who received venous stents as part of their acute management. We collected data on baseline clinical characteristics and pre-venous and post-venous stent antithrombotic therapy.

RESULTS

We studied 173 patients with venous stents: 101 (58%) were aged ≤50 years, 105 (61%) were female, and 128 (74%) had risk factors for thrombotic disease. DVT was iliofemoral in 150 (87%) patients, and catheter-based treatment was given within 7 days of diagnosis in 92 (53%) patients. After venous stenting, 109 (63%) patients received anticoagulant-only therapy with a direct oral anticoagulant (29%), warfarin (22%), or low-molecular-weight heparin (10%), and 59 (34%) received anticoagulant-antiplatelet therapy. In patients taking anticoagulant-only therapy, 29% received indefinite treatment; in patients on anticoagulant-antiplatelet therapy, 19% received indefinite treatment. Factors associated with combined anticoagulant-antiplatelet therapy vs anticoagulant-only therapy were use of thrombolytic, thrombectomy, and aspiration interventions (odds ratio [OR], 5.11; 95% CI, 1.45-18.05); use of balloon angioplasty (OR, 2.62; 95% CI, 1.20-5.76); and immediate stent restenosis (OR, 7.2; 95% CI, 1.45-5.89).

CONCLUSION

Anticoagulant therapy without concomitant antiplatelet therapy appears to be the most common antithrombotic strategy in patients with DVT and venous stenting. More research is needed to determine outcomes of venous stenting in relation to antithrombotic therapy.

Long Term Follow Up, Causes for Re-intervention, and Consequences for Surveillance After Stenting for Proximal Deep Vein Obstruction

OBJECTIVE

Venous stenting is performed increasingly for acute deep vein thrombosis (DVT) and post-thrombotic syndrome (PTS) with good short term patency results, but long term data are scarce. The purpose of this study was to evaluate long term outcome of stenting for acute DVT and PTS and to study causes of re-intervention.

METHODS

All patients stented for acute DVT and PTS between May 2006 and November 2021 were included retrospectively in this single centre cohort study. Patency was studied by duplex ultrasound (DUS) or computed tomography. The primary endpoint was stent patency. Re-intervention free survival was calculated using Kaplan-Meier methods. Secondary endpoints were causes of re-intervention, using the Pouncey classification system (2022). Binary logistic regression was used to calculate odds ratios for predictors of re-intervention.

RESULTS

A total of 114 patients were included, with 129 limbs involved (acute DVT n = 53; 41%), PTS n = 76; 59%). Median follow up was 2.3 years (interquartile range [IQR] 2.3) for acute DVT and 5.2 years (IQR 7.1) for PTS. Primary patency, secondary patency, and permanent occlusion were 73.5%, 98.1%, and 1.9% for acute DVT, and 63.2%, 92.1%, and 7.9% for PTS limbs. Overall, 41 limbs underwent at least one re-intervention: 14 in the acute DVT group and 27 for PTS. Most re-interventions (82.9%) were performed within the first year after stenting. Missed inflow, insufficient flow, and thrombosis despite anticoagulation were the most common causes of re-intervention. The strongest predictor for re-intervention for PTS was inflow disease (odds ratio 3.57, 95% confidence interval 1.26 - 10.13, p= .017).

CONCLUSION

Long term patency of deep venous stenting is good. Re-interventions are typically performed in the first year and are potentially preventable by improving the procedure and patient selection. Since secondary patency rates are excellent, selected patients may be considered for discharge from long term surveillance.

Predictive Factors of Stent Patency in Iliofemoral Venous Diseases in a Multicentre Cohort Study

OBJECTIVE

This study assessed primary stent patency predictive factors in three groups of patients with history of lower limb (LL) vein thrombosis: non-thrombotic iliac vein lesion (NIVL), acute deep vein thrombosis (aDVT), and post-thrombotic syndrome (PTS).

METHODS

Consecutive patients from January 2014 to December 2020 with history of LL vein stenting from seven hospitals were included. All patients received an iliac or common femoral venous stent and had at least a six month follow up available with stent imaging. Anticoagulant and antiplatelet therapy strategies employed after venous stenting are reported and compared between groups.

RESULTS

This study included 377 patients: 134 NIVL, 55 aDVT, and 188 PTS. Primary patency was statistically significantly higher in the NIVL group (99.3%) compared with the PTS group (68.6%) (p < .001) and the aDVT group (83.6%) (p = .002). PTS patients received a statistically significantly greater number of stents (p < .001) and had more stents below the inguinal ligament (p < .001). Median follow up was 28.8 months (IQR 16, 47). Discontinuation of antiplatelet therapy at the last assessment was 83.6% for NIVL, 100% for aDVT, and 95.7% for the PTS group (p < .001). Discontinuation of anticoagulation therapy at the last assessment was 93.2% for NIVL, 25.0% for aDVT, and 70.3% for the PTS group (p < .001). The only predictor of worse primary patency in the aDVT group was long term anticoagulation before stenting.

CONCLUSION

Patients with NIVL have better primary patency after venous stenting than patients with venous thrombotic disorders. Long term anticoagulation before stenting was the only factor associated with poorer primary patency in patients with aDVT.

Effect of the timing of iliac vein stent implantation on catheter-directed thrombolysis in acute lower extremity deep venous thrombosis patients with severe iliac vein stenosis: a retrospective study

OBJECTIVE

To investigate the effect of the timing of iliac vein stent implantation on catheter-directed thrombolysis (CDT) in acute lower extremity deep venous thrombosis (DVT) patients with severe iliac vein stenosis.

METHODS

The clinical data of 66 patients with acute lower extremity DVT complicated with severe iliac vein stenosis from May 2017 to May 2020 were retrospectively analyzed. Patients were divided into two groups by timing of iliac vein stent implantation: group A (iliac vein stent implantation before CDT treatment) for 34 and group B (iliac vein stent implantation after CDT treatment) for 32. The detumescence rate of affected limb, the thrombus clearance rate, the thrombolytic efficiency, the complication rate, the hospitalization cost, the stent patency rate within 1 year, and the scores (venous clinical severity score, Villalta, and chronic venous insufficiency questionnaire (CIVIQ) score) at 1 year postoperatively were compared between the two groups.

RESULTS

The thrombolytic efficiency of group A was higher than that of group B, while the incidence of complications and hospitalization expenses in group A were lower than those in group B. There was no statistical significance in the detumescence rate of affected limb, the thrombus clearance rate, the stent patency rate within 1 year, and the scores (VCSS, Villalta, and CIVIQ score) at 1 year postoperatively between the two groups.

CONCLUSIONS

For acute lower extremity DVT patients with severe iliac vein stenosis, iliac vein stent implantation before CDT treatment can improve the thrombolytic efficiency, and reduce the incidence of complications and hospitalization costs.

Lower Limb Weakness due to Spinal Venous Congestion in Chronic Inferior Vena Cava Occlusion: A Case Report

CASE REPORT

A 31 year-old male presented with a long history of reduced sensation and motor function in his lower limbs upon waking every morning, lasting 30-50 minutes during which he was unable to ambulate. He was involved in a severe road traffic accident as a child, and was born prematurely requiring prolonged neonatal hospitalisation. Both duplex ultrasonography and magnetic resonance venography identified an occlusion of the IVC, with patent common femoral and iliac veins draining into large spinal collaterals. No other cause was identified for his symptoms. After appropriate multidisciplinary team discussion and patient counselling, the patient proceeded to have endovenous recanalization of his IVC and common iliac veins with dedicated venous stents. Post-operatively, the patient reported an immediate resolution of neurological symptoms, with an improvement in quality of life questionnaire scores and with stent patency at 9-month follow up.

CONCLUSION

IVC occlusion with symptomatic spinal venous congestion is a rare condition which may be successfully treated with endovascular iliocaval recanalization, although long-term outcomes of this treatment are still unknown.

Stent Embolization Mimicking Acute Myocardial Infarction

Venous thromboembolism is associated with significant morbidity and mortality if left untreated. Anticoagulation is the cornerstone of treatment. Venous stents are a relatively newer entity that are increasingly being used to treat venous stenosis/occlusion. It is a safe procedure, but complications include vein rupture, arterial puncture, retroperitoneal bleeding, and in-stent thrombosis. Stent migration is a rare but potentially fatal complication. We present a case of venous stent embolization to the heart that presented as a non-ST segment elevation myocardial infarction.

Percutaneous endovenous intervention without vena cava filter for acute proximal deep vein thrombosis secondary to iliac vein compression syndrome: preliminary outcomes

The aim is to report the preliminary outcomes of percutaneous endovenous intervention (PEVI) for acute proximal deep vein thrombosis (DVT) secondary to iliac vein compression syndrome (IVCS) without inferior vena cava filter (IVCF) placement. Acute DVT patients who underwent PEVI without IVCF were analyzed retrospectively. PEVI consisted of catheter-directed thrombolysis, manual aspiration thrombectomy, balloon angioplasty and stenting. CT was used to evaluate the left common iliac vein (LCIV). Sixty-two consecutive patients (17 men and 45 women, mean age, 59.4 ± 15.2 years) were enrolled. The compression percentage of the LCIV ranged from 51.7% to 95.2% (median 83.2%). Iliac DVT was present in 7 patients; iliofemoral, in 30 patients; and iliofemoropopliteal, in 25 patients. Complete technical success and clinical improvement were obtained in all subjects without the occurrence of symptomatic pulmonary embolism (PE). Five patients experienced recurrent thrombosis. The primary patency rates at 12 and 24 months were 93.8% and 91.4%, respectively, which remained stable at 36, 48 and 60 months. The secondary patency rates at 12 and 24 months were 95.7% and 93.3%, respectively, and there was no change at 60 months. Although limited, our preliminary results suggested that PEVI without IVCF placement seemed to be safe and effective for acute proximal DVT secondary to IVCS without inferior vena cava thrombosis or symptomatic PE.

Role of venous stenting for venous thromboembolism

Endovenous stenting has emerged as the method of choice to treat iliofemoral venous outflow obstruction. It is used in patients with established postthrombotic syndrome (PTS) after previous deep vein thrombosis (DVT) to reduce symptoms of chronic pain and swelling and to aid ulcer healing in severe cases. Venous stenting is used to alleviate symptoms of obstruction in patients presenting with acute DVT, with the aim of preventing development of PTS. There is a low risk of morbidity and mortality associated with the use of endovenous stenting, and although significant advances have been made, particularly improvements in stent design for use in the venous circulation, data are lacking on beneficial long-term outcomes. Unmet research needs include optimal patient selection, anticoagulant choice and duration, best practice for postoperative surveillance, and use of validated assessment tools to measure outcomes. In this article, I address the potential benefits, as well as the challenges, of endovenous stenting.

An Artificial Neural Network Approach and a Data Augmentation Algorithm to Systematize the Diagnosis of Deep-Vein Thrombosis by Using Wells’ Criteria

The use of a back-propagation artificial neural network (ANN) to systematize the reliability of a Deep Vein Thrombosis (DVT) diagnostic by using Wells’ criteria is introduced herein. In this paper, a new ANN model is proposed to improve the Accuracy when dealing with a highly unbalanced dataset. To create the training dataset, a new data augmentation algorithm based on statistical data known as the prevalence of DVT of real cases reported in literature and from the public hospital is proposed. The above is used to generate one dataset of 10,000 synthetic cases. Each synthetic case has nine risk factors according to Wells’ criteria and also the use of two additional factors, such as gender and age, is proposed. According to interviews with medical specialists, a training scheme was established. In addition, a new algorithm is presented to improve the Accuracy and Sensitivity/Recall. According to the proposed algorithm, two thresholds of decision were found, the first one is 0.484, which is to improve Accuracy. The other one is 0.138 to improve Sensitivity/Recall. The Accuracy achieved is 90.99%, which is greater than that obtained with other related machine learning methods. The proposed ANN model was validated performing the k-fold cross validation technique using a dataset with 10,000 synthetic cases. The test was performed by using 59 real cases obtained from a regional hospital, achieving an Accuracy of 98.30%.

Outcome of AngioJet mechanical thrombus aspiration in the treatment of acute lower extremities deep venous thrombosis

OBJECTIVES

The objective of this study was to evaluate the efficacy and safety in patients with acute lower extremity deep venous thrombosis who underwent pharmacomechanical thrombectomy (PMT, AngioJet mechanical thrombus aspiration).

METHODS

In this retrospective, 424 consecutive patients with acute lower extremity deep venous thrombosis from three institutions were enrolled in the study from January 2015 to December 2018. Of these, patients were divided into two groups, AngioJet group (n = 186) and catheter-directed thrombolysis (CDT) group (n = 238). Evaluation indexes including limb circumference difference, length of stay (LOS), urokinase dosage, periprocedural complications, follow-up imaging findings and villalta scores were analyzed from the medical records.

RESULTS

A total of 424 patients diagnosed with acute lower extremity deep venous thrombosis were collected in this study. These patients were categorized into AngioJet group and CDT group. Significant differences were observed between the two groups with respect to the thigh circumference difference (5.32 ± 1.85 cm vs. 4.69 ± 2.15 cm; p = 0.04), calf circumference difference (2.79 ± 1.54 cm vs. 2.35 ± 1.25 cm; p = 0.01), thigh detumescence rate (72.19 ± 19.55% vs. 65.35 ± 17.26%; p = 0.00) and calf detumescence rate (62.79 ± 18.56% vs. 55.75 ± 17.27%; p = 0.00). The mean dose of urokinase in AngioJet group was 95.16 ± 45.89 million IU significantly less than that in the CDT group 293.76 ± 42.71 million IU (p = 0.00). The overall bleeding complication rate was 9.91% (19 patients in AngioJet group and 23 patients in CDT group), which included three major (0.71%, 3/424) and 39 minor (9.2%,39/424) events. In the AngioJet group, serum creatinine (sCr) concentration and urine erythrocyte from the hemolysis caused by the mechanical process were higher than baseline data at admission (p = 0.00, p = 0.00). The postoperative red blood cell and hemoglobin in two groups were lower than baseline data (p = 0.00, p = 0.00). Compared with CDT, AngioJet thrombectomy has significantly lower estimated incidence of PTS in the follow-up.

CONCLUSION

AngioJet thrombectomy has stronger clearance ability for acute lower extremity deep venous thrombosis leading to significant reduction in the consumption of hospital resources, total dose of thrombolytic agents, and infusion time, thereby preventing adverse bleeding events, but patients with renal insufficiency should be careful. Ideal short-term and medium-term efficacy and safety are certain.

Outcomes of endovascular venous stenting in patients on direct oral anticoagulants and antiplatelet therapy at a tertiary referral center

BACKGROUND

Endovenous revascularization is the standard in the management of acute thrombotic, chronic post-thrombotic iliocaval or iliofemoral obstruction, and nonthrombotic iliac vein lesions. The purpose of this study is to describe our single-center experience of postprocedure anticoagulation and antiplatelet regimens used after endovenous revascularization for a variety of venous occlusive conditions.

METHODS

We conducted a retrospective analysis of 100 consecutive patients who underwent endovenous stenting for iliocaval or iliofemoral obstruction from January 1, 2014, to April 30, 2018. Patients treated with direct oral anticoagulants, warfarin, or low-molecular-weight heparin (LMWH) with or without antiplatelet therapy were identified. Demographic, procedural, patency, and follow-up data were collected. Stent patency was evaluated using duplex Doppler ultrasound examination or contrast venography.

RESULTS

Seventy-one of 100 patients were treated with direct oral anticoagulant therapy (DOAC). Sixteen (23%) were lost to follow-up, leaving 55 (77%) available for analysis. The mean follow-up was 14 months (range, 1-43 months) with 32 patients (58%) followed for 12 months or longer. Primary, primary-assisted, and secondary-assisted patency rates were 87%, 97%, and 98%, respectively, at 12 months. In the non-DOAC group (patients treated with warfarin or LMWH), these rates were 87%, 93%, and 95%, respectively, at 12 months. Antiplatelet therapy, including clopidogrel, aspirin, or both, was used in 53 of 55 patients in the DOAC cohort and 18 of 19 patients in the non-DOAC group.

CONCLUSIONS

Our-single center retrospective analysis demonstrates acceptable primary patency rates when using DOAC therapy compared with those treated with warfarin or LMWH.

[Antithrombotic therapy after iliac vein stenting]

Stenting for iliac vein stenosis or compression has become a common therapeutic approach in recent years. The antithrombotic therapy after the stent deployment, however, reaches no consensus. Medications strategies and patients' prognoses differ in non-thrombotic, acute thrombotic and chronic thrombotic these three circumstances. Non-thrombotic patients usually possess satisfactory stent patency whatever antithrombotic therapy is used. Anticoagulant is the basic medication for acute thrombotic patients, benefits from additional antiplatelet drug remains to be clarified. In terms of chronic thrombotic patients, their prognoses are unsatisfactory under all antithrombotic therapies. In this review, we outlined the recent progress of antithrombotic therapy after iliac vein stenting, aiming to provide feasible medication plans for each circumstance.

Contralateral deep vein thrombosis after stenting across the iliocaval confluence in chronic venous disease – A systematic review

Objective

Stenting of the iliac veins is increasingly considered in the presence of symptomatic obstructive chronic lesions in the iliac vein segment. However, it is often necessary to extend the stented zone into the inferior vena cava, increasing the risk of contralateral iliac vein thrombosis. This study aims to review the current literature concerning the incidence of contralateral deep vein thrombosis after stenting across the iliocaval confluence.

Methods

A systematic review from potentially relevant published articles reporting contralateral deep vein thrombosis after iliac venous stenting between January 2007 and February 2019 was performed.

Results

A total of 764 references were retrieved initially. Twelve studies reporting events of contralateral deep vein thrombosis were selected for review, with a total of 1864 patients. Contralateral deep vein thrombosis incidence varied between 0% and 15.6%. The post-interventional and follow-up anticoagulation regimens were heterogeneous between studies. The decision to maintain patients on anticoagulation and the duration of treatment was based on the presence of comorbidities, hypercoagulable states, post-thrombotic syndrome and history of recurrent deep vein thrombosis. Patients with non-thrombotic iliac vein lesions were either anticoagulated for three or six months after stenting or received no anticoagulation. Patients with post-thrombotic syndrome were anticoagulated for longer periods. Most studies (eight studies) used an oral vitamin K antagonist agent. The data on compliance with anticoagulation treatment is scarce and few references present data on whether contralateral deep vein thrombosis occurred during anticoagulation treatment. The use of antiplatelet agents in addition to the anticoagulant treatment in the follow-up period was also variable.

Conclusion

The incidence of contralateral deep vein thrombosis due to iliac vein jailing is not negligible and reported being as high as 15.6%. Large-scale studies on the ideal antithrombotic treatment and its impact are necessary. It is possible that patients with stent crossing the iliocaval confluence might benefit from long-term antithrombotic treatment.