Two datasets presented during the late-breaking clinical trials session at The VEINS (Venous Endovascular Interventional Strategies) 2022 (30–31 October, Las Vegas, USA)—the latest results from CLOUT and a propensity score-matched analysis of CLOUT versus ATTRACT—bolster the evidence base for mechanical thrombectomy in the field of deep vein thrombosis (DVT) management. However, discussion at the meeting pointed to the need for further, high-quality data to solidify the role of this treatment modality.
The latest analysis from the now fully-enrolled CLOUT registry demonstrates the “excellent safety profile and effective thrombus removal” of mechanical thrombectomy with the ClotTriever system (Inari Medical) in a “real-world” DVT population of 500 patients. This is according to David Dexter (Sentara Vascular Specialists, Norfolk, USA), who presented in-hospital and 30-day outcomes from this multicentre, prospective registry at The VEINS 2022. Steven Abramowitz (MedStar Washington Hospital Center, Washington DC, USA) also presented data on the ClotTriever system, sharing results of a propensity score-matched analysis of early clinical outcomes from the CLOUT and ATTRACT studies.
The CLOUT (ClotTriever outcomes) registry is an all-comer, multicentre study evaluating patient outcomes following treatment of proximal, lower extremity DVT with the ClotTriever system, and, according to Dexter, represents the largest mechanical thrombectomy study in the field of DVT. All-comer patients were enrolled, irrespective of symptom duration, thrombus age, prior failed treatment of the current DVT, or bilateral disease. The primary endpoint was complete or near-complete (≥75%) thrombus removal, assessed by an independent core laboratory.
Dexter reported that the primary endpoint was achieved in 91.2% of limbs, and the 30-day device-related severe adverse event rate was 0.2%. Nearly all procedures were single session (99.4%), median estimated blood loss was low (40mL), and only 2.2% of patients received overnight post-thrombectomy intensive care unit monitoring, he added. Furthermore, patient symptoms (e.g. pain and oedema) were significantly reduced at discharge and showed sustained improvement through 30 days.
The presenter also revealed recovery of vessel flow and compressibility as measured by duplex ultrasound, improvements in revised Venous Clinical Severity Score and EuroQoL five dimensions quality-of-life score, median 5.5-point reduction in Villalta score, and <10% of patients with a moderate or severe Villalta score (≥10).
A question from the panel probed what is next for the field of mechanical thrombectomy in light of these results. Dexter pointed to the need for more studies, and also stressed what the focus of future research should be: “We need to show a real, long-term result on post-thrombotic syndrome”.
CLOUT versus ATTRACT
In Abramowitz’s presentation of the propensity score-matched analysis, the presenter summarised that CLOUT patients showed better thrombus extraction and improvement in 30-day Villalta scores than ATTRACT patients. Specifically, the presenter revealed that nearly two times more CLOUT patients had complete thrombus removal, and that 13% fewer CLOUT patients had Villalta scores ≥5 at 30 days.
Abramowitz explained that ATTRACT is a reference trial evaluating interventional treatment for DVT that showed no added benefit compared to anticoagulation. “New interventions have emerged since the completion of ATTRACT, and their comparative effectiveness is unknown,” he said. Using propensity score-matched data, the investigators compared outcomes from the CLOUT registry with those from the treatment arm of the ATTRACT trial.
To adjust for differences in study design, patients with bilateral DVT, symptom duration >4 weeks, or incomplete case data were excluded. Propensity score matching (1:1) on 11 baseline covariates (age, sex, body mass index, sidedness, prior venous thromboembolism, race, symptom duration, DVT location, presence of provoked DVT, Villalta score, and Marder score) was performed between the remaining CLOUT and ATTRACT patients, resulting in 166 matched pairs.
No significant differences in baseline characteristics remained after matching, the presenter noted. Rates of stenting and venoplasty were similar between the groups and, as expected based on differences in mechanism of action, rates of thrombolytic use (0% vs. 100%, p<0.0001), single-session treatment (98.2% vs. 25.3%, p<0.0001), and postprocedural hospital overnights (mean, 1.7 vs. 3.4, p<0.0001) were significantly different.
Abramowitz reported that thrombus extraction as measured by core laboratory-assessed Marder scores was 22.3% better in CLOUT patients (p<0.0001), and 22.2% more CLOUT patients achieved ≥75% thrombus clearance (p<0.0001). Similarly, 12.7% fewer CLOUT patients had Villalta scores ≥5 at 30 days (p<0.05). Logistic regression on ATTRACT showed that 30-day Villalta scores significantly predicted post-thrombotic syndrome at six months, one year, and two years (odds ratios, 1.37, 1.32, and 1.43; p<0.0001), which the presenter said highlights the potential long-term effect of these differences.
Closing his presentation, Abramowitz echoed Dexter’s call for more data, noting that randomised controlled trials such as the recently announced DEFIANCE trial “will further clarify the role of the ClotTriever system in treating DVT”.