Background
Mechanical thrombectomy for pulmonary embolism can result in significant blood loss necessitating early stoppage. The Hēlo Blood Return System (BRS) enables autologous transfusion via filtered blood reinfusion with continuous aspiration mechanical thrombectomy, a technical achievement previously considered unfeasible. ENGULF previously reported 105 patients at VIVA 2025; this presents the first 130-patient comparative analysis of the completed BRS cohort versus standard continuous aspiration without blood return.
Methods
ENGULF, a prospective single-arm IDE trial of Hēlo continuous aspiration thrombectomy system, enrolled 130 subjects: 40 BRS (with blood return) and 90 non-BRS. The primary safety endpoint was device-related Major Adverse Events (MAE: death, bleeding, serious adverse events) at 48 hours and the primary efficacy endpoint was RV/LV ratio reduction baseline to 48-hours via core lab adjudicated CT.
Results
Among 40 BRS vs 90 non-BRS patients (age 59.6/63.5 years, 50%/59% male), BRS significantly reduced median blood loss (10cc vs 340cc, p<0.001). All BRS procedures completed without adjunctive therapy vs 5 non-BRS interventions for blood loss. Ability to complete the procedure with only a single pass across the heart was significantly higher with BRS (88% vs 72%, p=0.02). The MAE rate was 0% (0/40) in BRS versus 1.1% (1/90) in non-BRS. Blood quality parameters showed no differences (all p>0.05), confirming no platelet activation or hemolysis. Hemodynamic efficacy (RV/LV reduction) was higher with BRS at 28% versus 25% in non-BRS (p=0.5). Modified Miller reduction was significantly higher with BRS at 22% versus 15% in non-BRS (p<0.001). No corking, device malfunctions, or unanticipated adverse events occurred in either cohort.
Conclusions
This first comparative analysis demonstrates blood return during continuous aspiration thrombectomy achieved excellent safety (0 MAEs, 97% less blood loss, no adjunctive therapy) while maintaining hemodynamic efficacy and improving procedural efficiency. These findings prove feasibility and benefit of autologous blood return in PE thrombectomy, supporting incorporation as a safety advancement.