PO-02-058 USING A NOVEL IN VITRO HUMAN BLOOD LOOP MODEL TO EXPLAIN SCAR TISSUE FORMATION A PHYSICIAN MAY ENCOUNTER IN EXTRACTING CORONARY SINUS LEADS

Abstract

The Medtronic Attain Stability Model 4798 (ASQ) coronary sinus (CS) lead was designed with an active fixation helix for precise placement and extractability. We sought to understand extractability of ASQ as compared to a lead with 1. favorable extractability such as Medtronic Attain Performa Model 4598, and 2. the Medtronic Star Fix® in which considerable fibrotic tissue growth involves the expanded fixation lobes, making the extraction process very challenging. Typically, animal models are used to understand lead fibrotic tissue growth, however, such studies are of limited value. In this study, we used a novel in vitro human blood loop model to evaluate flow profiles and coagulation response which has shown to be a surrogate to fibrotic tissue growth and scar formation. This model allows for improved control and accelerated test conditions in comparison to animal models. To assess thrombus formation as an early indicator of long-term scar development in three Medtronic CS leads and the impact of CS vein fixation design. In this blood donor study, leads were placed inside a closed loop system representing the average CS diameter. Loops were primed with freshly drawn heparinized human blood, donated via an IRB approved Medtronic blood donor program. Heparin concentration was chosen from prior titration studies to prevent clotting in the loop alone. Experiments were run for five hours at 37°C under continuous flow conditions comparable with known CS flow rates. Change in flow rate over time was measured. Post blood exposure, leads were subjected to histological evaluation. On histologic evaluation the Star Fix® (n=6) showed mean thrombus coverage of 70.8±28% compared to minimal thrombus coverage of 3±1.5% on ASQ (n=6) and 3±1.7% on Performa (n=3) (p < 0.05) (Image 1). At a constant pump speed, the 95th percentile of flow rate drop was 165mL/min with Star Fix® implants compared to only 13mL/min drop with ASQ and 9mL/min with Performa. This novel model demonstrates how lead design can impact flow profiles and subsequent thrombus formation as a surrogate to vascular scar formation. The ASQ has minimal thrombus formation and is comparable to Attain Performa. In contrast, Star Fix® with expanded fixation lobes has considerable flow disruption and thrombus formation consistent with the clinical findings of significant scar formation that can result in a challenging extraction procedure.