Propensity Score–Matched Analysis of Early Clinical Outcomes From the CLOUT and ATTRACT Studies Presented

November 2, 2022—A propensity score–matched analysis found that patients in the CLOUT registry of mechanical thrombectomy with the ClotTriever (Inari Medical, Inc.) showed better thrombus extraction and improvement in 30-day Villalta scores than patients in the ATTRACT trial of interventional treatment for deep vein thrombosis (DVT).

The results were presented by Steven Abramowitz, MD, in a Late-Breaking Clinical Trials session at The VEINS conference, hosted by the VIVA Foundation and held October 30-31, 2022, in Las Vegas, Nevada.

The background of the analysis is that since the completion of the ATTRACT trial, which showed no added benefit compared to anticoagulation, new interventions have emerged and their comparative effectiveness is unknown.

In December 2017, 2-year data from the ATTRACT (Acute Venous Thrombosis: Thrombus Removal With Adjunctive Catheter-Directed Thrombolysis) trial, which was sponsored by the National Institutes of Health, were published by Suresh Vedantham, MD, et al in The New England Journal of Medicine (2017;377:2240-2252).

In September 2018, Inari announced the enrollment of the first patient in the real-world, prospective, multicenter, single-arm CLOUT registry with an expected total enrollment of 500 patients.

As summarized in the VIVA Foundation press release, propensity score matching (1:1) on 11 baseline covariates was performed between the remaining CLOUT and ATTRACT patients, resulting in 166 matched pairs. The baseline covariates were age, sex, body mass index, sidedness, previous venous thromboembolism, race, symptom duration, DVT location, presence of provoked DVT, Villalta score, and Marder score.

The investigators adjusted for differences in study design by excluding patients with bilateral DVT, symptom duration > 4 weeks, or incomplete case data. No significant differences in baseline characteristics remained after matching.

Dr. Abramowitz reported that between CLOUT and ATTRACT rates of stenting and venoplasty were similar between the groups and, as expected based on differences in the mechanism of action, rates of thrombolytic use (0% vs 100%; P < .0001), single-session treatment (98.2% vs 25.3%; P < .0001), and postprocedural hospital overnights (mean, 1.7 vs 3.4; P < .0001) were significantly different, respectively.

Thrombus extraction as measured by core laboratory–assessed Marder scores was 22.3% better in CLOUT patients (P < .0001). Also, 22.2% more CLOUT patients achieved ≥ 75% thrombus clearance (P < .0001). Similarly, 12.7% fewer CLOUT patients had Villalta scores ≥ 5 at 30 days (P < .05). Logistic regression on ATTRACT showed that 30-day Villalta scores significantly predicted post-thrombotic syndrome at 6 months, 1 year, and 2 years (odds ratios: 1.37, 1.32, and 1.43; P < .0001), highlighting the potential long-term effect of these differences.

Dr. Abramowitz concluded that in this propensity score–matched analysis, CLOUT patients showed better thrombus extraction and improvement in 30-day Villalta scores than ATTRACT patients. Thirty-day Villalta scores in ATTRACT predicted post-thrombotic syndrome through 2 years, suggesting potentially long-term implications for these findings. Future randomized controlled trials, such as DEFIANCE, will further clarify the role of the ClotTriever system in treating DVT, reported the VIVA Foundation press release.