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(Circulation. 2001;103:1912.)
© 2001 American Heart Association, Inc.

Basic Science Reports

Late Arterial Responses (6 and 12 Months) After ³²P ß-Emitting Stent Placement

Sustained Intimal Suppression With Incomplete Healing

Andrew Farb, MD; Sweta Shroff, MS; Michael John, BA; William Sweet, MD; Renu Virmani, MD

From the Department of Cardiovascular Pathology, Armed Forces Institute of Pathology (A.F., S.S., M.J., R.V.), Washington, DC, and the Isostent Corporation (W.S.), Belmont, Calif.

Correspondence to Renu Virmani, MD, Department of Cardiovascular Pathology, Armed Forces Institute of Pathology, Washington, DC 20306-6000.

pick;5248p1-foo;0;;clb/clb>Background—Three-month studies of stent-delivered brachytherapy in the rabbit model show reduced neointimal growth. However, intimal healing is delayed, raising the possibility that intimal inhibition is merely delayed rather than prevented. The purpose of this study was to explore the long-term histological changes after placement of ß-emitting radioactive stents in normal rabbit iliac arteries.

Methods and Results—Three-millimeter ß-emitting ³²P stents (6, 24, and 48 µCi) were placed in normal rabbit iliac arteries with nonradioactive stents as controls. Animals were euthanatized at 6 and 12 months, and histological assessment, morphometry, and analysis of endothelialization were performed. Morphometric measurements demonstrated a >50% reduction in intimal growth and percent lumen stenosis within 24- and 48-µCi stents versus control nonradioactive stents at both 6 and 12 months. However, the 24- and 48-µCi stents also showed delayed healing of the intimal surface, characterized by persistent fibrin thrombus with nonconfluent areas of matrix, incomplete endothelialization, and increased intimal cellular proliferation. Stent edge stenosis was present at 12 months in the 24- and 48-µCi stent groups, characterized by both intimal thickening and negative arterial remodeling.

Conclusions—Inhibition of intimal growth is maintained 6 and 12 months after ³²P ß-emitting stent placement. However, delayed arterial healing, incomplete endothelialization, and edge effects are present.

Key Words: angioplasty • atherosclerosis • pathology • stents