A fully biodegradable coronary artery stent appeared to be safe at 10 years, according to a single-center study published April 16 in Circulation. The authors said their findings will facilitate entry of biodegradable coronary stents in interventional cardiology.
Igaki-Tamai bioabsorbable stents made of poly-L-lactic acid (PLLA) received CE Mark in 2007 to treat peripheral artery disease but have not been approved in any country as a coronary artery stent. In the era of bare-metal stents (BMS), fully biodegradable coronary artery stents were hailed as a possible alternative to BMS, which carry the potential risk of stent thrombosis.
The introduction of drug-eluting stents, which reduced in-stent restenosis and target lesion revascularization (TLR) rates compared with BMS, overshadowed biodegradable stents. More recently, reports of DES-related very late stent thrombosis (VLST) problems have emerged, making biodegradable stents once again an attractive option.
Soji Nishio, MD, of the cardiology department at Shiga Medical Center for Adults in Moriyama City, Japan, and colleagues suggested that further research needed to be done to evaluate the long-term safety of biodegradable coronary stents. “Before putting the biodegradable drug-eluting PLLA stent into routine clinical practice, we need to confirm that PLLA does not cause any critical adverse events during the whole process of biodegradation,” they wrote.
To assess long-term safety of these stents in coronary arteries, Nishio and colleagues designed an observational prospective study that enrolled 50 patients (44 men, six women) from a single center in Japan between September 1998 and April 2000. To participate, patients needed to have stable ischemic heart disease that could be treated electively by the Igaki-Tamai bioabsorbable stent. Patients with acute coronary syndrome, lesions located in the left main trunk or chronic total occlusion were excluded.
The 50 patients had 63 lesions that were treated with 84 biodegradable stents. The patients were followed for 10 years to assess long-term major cardiac adverse events (MACE); definite and probable scaffold thrombosis; cardiac death; and non-cardiac death. MACE included all-cause death; nonfatal myocardial infarction (MI); and TLR and target vessel revascularization (TVR).
The overall clinical follow-up period was 121 months. During that time, two patients were lost to follow-up, one died from unknown causes and was categorized as a cardiac death; four died from non-cardiac causes and four had MIs. Nishio et al reported survival rates at 10 years free of all-cause death, cardiac death and MACE of 87 percent, 98 percent and 50 percent, respectively. Cumulative rates of TLR were 16 percent at one year, 18 percent at five years and 28 percent at 10 years; for TVR, rates were 16 percent for one year, 22 percent at five years and 38 percent at 10 years.
They recorded two cases of definite stent thrombosis, one subacute and one very late. “Currently, DES are the treatment of choice for coronary artery stenosis; however, VLST has become an important safety issue,” the authors wrote. “Several mechanisms of VLST have been proposed including delayed endothelialization, chronic inflammation of arteries, hypersensitivity reactions (eosinophilic infiltration) and incomplete stent apposition with vessel remodeling. All these problems with metallic stents can be solved by using fully biodegradable stents, because there are no foreign materials after PLLA degradation.”
They noted that biodegradable coronary stents had a high survival rate at 10 years, demonstrating the long-term safety of the stents. Based on analyses using intravascular ultrasound data, they calculated that PLLA stents degrade within three years.
Nishio and colleagues attributed the decrease in MACE survival rates to the increase in TLR and TVR rates. “During the process of biodegradation (one to three years), TLR and TVR reached a near plateau, suggesting that the process of PLLA biodegradation does not correlate with increased risk of clinical events,” they suggested. “There is the possibility that if the Igaki-Tamai stent becomes drug-eluting, the TLR rates could be improved.”
Their study enrolled a small number of patients and was observational, single-center and non-randomized. Despite those limitations, they argued the findings pave the way for the clinical use of bioabsorbable PLLA stents in interventional cardiology.