"Because HORIZONS-AMI is the first trial to determine the efficacy of drug-eluting stents in patients with acute MI, we expected that some adverse morphological reaction might occur," said Akiko Maehara, MD, director of intravascular imaging and physiology core laboratories at the Cardiovascular Research Foundation in New York City. "For this reason we decided to do an IVUS [intravascular ultrasound] substudy. IVUS lets us see what is actually going on inside the vessel so that we can understand not only what is happening with revascularization, but also what the mechanism behind the pathophysiology is setting."
A substudy of the HORIZONS-AMI (Harmonizing Outcomes with Revascularization and Stents in Acute Myocardial Infarction) patient, including included 402 patients with a total of 429 lesions, sought to determine vascular responses using IVUS after stenting with Boston Scientific's Taxus paclitaxel-eluting stents. HORIZONS-AMI was a dual-arm factorial randomized trial in patients with STEMI. All patients were randomized to recieve either unfractionated heparin plus routine GP IIb/IIIa inhibition or bivalirudin alone in a 1:1 randomization, as well as a Taxus stent or a Boston Scientific's Express bare-metal stent in a 3:1 randomization. The patients had IVUS at baseline, following stent placement and later at 13-month follow-up. The mean total stent length was 23.4 mm.
At baseline, Maehara reported that tissue protrusion through the stent struts into the lumen was observed in 69 percent of the lesions, most likely representing thrombus. At 13-month follow-up, the Taxus stents had a larger minimum lumen area due to less neointima.
However, Maehara noted that there was also more stent vessel wall malapposition because of positive remodeling, or increase in vessel area. The mean neointima volume in the 324 patients who received the Taxus stent was 6.5 percent and the mean neointima volume in the 105 patients who received the Express stent was 15.6 percent. The change in mean vessel area was 0.7 in the Taxus group and -0.3 in the Express group. The rate of stent-vessel wall malapposition at baseline post PCI was 31.8 percent in the Taxus group and 32.4 percent in the Express group. At 13 months, that rate was 28.3 percent for the Taxus group versus 7.9 percent for the Express group.
Maehara reported that approximately two-thirds of stents had tissue protrusion or intraluminal thrombus immediately after stent implantation, almost all of which resolved during follow-up. "New aneurysm formation and stent fracture were uncommon, although seen only in Taxus stents," she added.
"We do not know the significance of this stent malapposition," Maehara said. "Long-term clinical follow-up, which is ongoing, is required to establish the significance of this finding."