Histopathologic Characterization of Chronic Total Occlusions by Directional Atherectomy: The HIPACT Study

Background. Chronic total occlusions (CTOs) and long lesions have been associated with higher reocclusion rates in femoropopliteal arteries and increased need for revascularization. While several studies have analyzed atherectomy samples, no study to date has correlated the tissue characteristics of CTOs with clinical outcomes. This pilot study assessed lesions in order to predict clinical outcomes based on lesion characteristics. Methods. Patients presenting with femoropopliteal (FP) CTO lesions, including in-stent restenosis and de novo lesions, were enrolled in a prospective, observational study. With patient consent, CTOs were crossed using a crossing catheter guided by optical coherence tomography (OCT) imaging. Atherectomy was performed with a directional atherectomy device and tissue samples were collected and subjected to histopathological analysis for the presence of adventitial tissue and thrombus, and the amounts of hypercellular cells, fibrocellular material, fibrous tissue, and lipid-rich tissue in the excised tissue were measured. The compiled data were correlated with clinical outcomes, as recorded at each patient’s clinical follow-up visit. Results. All CTO lesions (n = 19) were successfully crossed, with no dissections or perforations. Adventitial tissue was found in excised tissue from all 19 lesions (up to 57% of total lesion area), and thrombus was found in 15 lesions (up to 34% of total lesion area). The amount of hypercellular cells, fibrocellular material, fibrous tissue, and lipid-rich tissue present in the excised tissue did not correlate with the incidence of target-lesion revascularization (TLR). At 6-month follow-up exam, 79% of the treated lesions had TLR. Risk of TLR was assessed based on weighted risk of each variable; the results determined that occurrence of TLR was associated with elevated levels of adventitia and thrombus in the lesions and with lesions >15 cm in length. There was a significant correlation (P<.05) between TLR and the lesion characterization as set forth in the present study. Conclusions. Pairing the histological analysis, including content of adventitia and thrombus, with lesion length and binary clinical outcomes enabled the predictive incidence of TLR in this pilot study. Further work needs to be conducted to validate these findings in larger studies.