Long-term coronary vascular response to P-32 beta-particle-emitting stentsin a canine model

Background-The arterial placement of P-32 beta-particle-emiting stents in v arious experimental animal models results in discordant effects on neointim al formation. We studied the vascular effects of beta-particle-emitting ste nts in normal canine coronary arteries because compared with pigs and rabbi ts, the canine model may more closely mimic the vascular response of humans . Methods and Results-Thirty stents (control nonradioactive, n = 10; low-acti vity P-32, 3.5 to 6.0 mu Ci. n = 11; high-activity P-32, 6.5 to 14.4 mu Ci, n = 8) were implanted in normal canine coronary arteries through the use o f a single balloon inflation at nominal pressure. Histological analysis aft er 15 weeks included the measurement of neointimal and adventitial area and thickness. Neointimal fibrin area was measured with the use of computer-as sisted color segmentation on Movat pentachrome sections. Luminal stenosis w as significantly increased in P-32 stents compared with control stents (44. 6 +/- 16.8% versus 32.7 +/- 10.8%; P = 0.05) and was highest in the high-ac tivity group (45.5 +/- 24.3%). No evidence of an "edge effect" was seen in adjacent, nonstented coronary segments. All P-32 stents showed incomplete v ascular healing as indicated by a dose-dependent increase in fibrin area wi th increasing stent activity. Arterial radiation resulted in a decrease in adventitial size, which was maximal for high-activity P-32 stents, indicati ng an inhibitory effect on the adventitial response to injury. Conclusions-P-32 beta-particle-emitting stents have adverse vascular effect s at 15 weeks in the canine normal coronary artery model. Vascular brachyth erapy with this device causes increased neointimal formation and prominent, dose-dependent lack of healing.