Intravascular sonotherapy decreases neointimal hyperplasia after stent implantation in swine

Abstract

Background - Intimal hyperplasia and subsequent in-stent restenosis remain a major limitation after stent implantation. In vitro cell culture studies show that low-frequency, noncavitational ultrasound energy may impact smooth muscle cell proliferation. Accordingly, we assessed the efficacy of intravascular sonotherapy treatment on intimal hyperplasia in a swine stent model. Methods and Results - After balloon injury, biliary stents (Johnson & Johnson) were implanted in the femoral arteries of 14 swine. A total of 48 stented sites were randomized to sonotherapy or sham treatment using a custom-built, 8-French catheter intravascular sonotherapy system (URX, PharmaSonics Inc). After stent deployment, ultrasound energy (700 KHz) was applied to the treatment group for up to 5 minutes. Smooth muscle cell proliferation was assessed using bromodeoxyuridine histology preparation (BrdU) at 7 days in 28 stented sites. At 28 days, the neointimal thickness and the ratio of neointimal/stent area (percent stenosis) was calculated by histomorphometric quantification in 20 stented sites. At 7 days, percent of BrdU staining was significantly reduced in the sonotherapy group compared with the sham group (24.1±7.0% versus 31.2±3.0%, P<0.05). At 28 days, percent stenosis was significantly less in the sonotherapy group than in the sham group (36±24% versus 44±27%, P<0.05), and the mean neointimal thickness in the sonotherapy group was less than in the sham group (417±461 μm versus 643±869 μm, P=0.06). Conclusions - In this swine peripheral model, intravascular sonotherapy seemed to decelerate cellular proliferation and decrease in-stent hyperplasia. Therefore, intravascular sonotherapy may be an effective form of nonionizing energy to reduce in-stent restenosis.