Stent thrombosis is a recognized complication occurring in 1-2% of patients with coronary artery disease treated by percutaneous coronary intervention ( PCI ) with stent implantation. Its occurrence is expected to increase with the number of stent implantation procedures done worldwide.

Drug-eluting stents ( DES ), which are increasingly replacing bare metal stents ( BMS ) because of their higher patency rate, are expected to increase its frequency. Re-PCI is the commonly adopted treatment to re-establish coronary flow to the heart tissue by reopening a stent obstructed by thrombosis. However, little scientific data is available on the outcome of PCI for stent thrombosis in the contemporary DES era.

OPTIMIST ( The Outcome of PCI for stent-ThrombosIs MultIcentre Study) is a independent, large-scale, multi-centre study conducted by 11 hospitals located in the urban area of Rome, Italy. During a period of 2 years ( 2005-2006 ) all patients who were admitted to participating hospitals with stent thrombosis and treated by PCI were enrolled. The clinical and procedural data was recorded on a detailed questionnaire and the clinical outcome up to 6 month after intervention was assessed by ambulatory visit or phone contact. Moreover, the efficacy of the procedure to re-establish optimal coronary blood flow was assessed by performing detailed analyses in an independent core laboratory.

During the study, 110 patients were recruited, thus constituting the largest series of patients with stent thrombosis ever collected. A first original observation arising from the study was that stent thrombosis, even if it is a rare event, accounted for 3.6% of the emergency PCI performed in patients with acute myocardial infarction. This data reinforces the perception that stent thrombosis has more than a negligible impact on the contemporary health system and further investigations on its causes and management are called for.

Regarding the supposed increased DES thrombogenicity, the type of data collected in the OPTIMIST study did not allow for the clarification of whether risk of thrombosis is higher after DES or BMS implantation. However, the data supports the hypothesis that stent thrombosis may have different mechanisms of occurrence in different types of stents. Indeed DES thrombosis, compared to BMS, happened more often after 30 days of implantation or after 15 days of antiplatelet drug therapy withdrawal. On the other hand, once stent thrombosis has occurred, we observed that the clinical manifestations, the procedural and the clinical outcomes, are not influenced by the type ( DES or BMS ) of previously implanted stent.

A primary goal of the OPTIMIST study was to provide data on the clinical outcome of patients with stent thrombosis undergoing urgent PCI in the contemporary era as it was unknown. We discovered that the clinical outcome during the 6-month follow-up, despite good utilization of all the best pharmacological and technical resources, was a disappointing 17% mortality rate and 29% rate of major adverse coronary or cerebral events ( death or myocardial infarction or stroke or necessity of a new interventional procedure ). These results show that stent thrombosis is not a benign disease and emergency PCI in this setting is still associated with unsatisfactory outcome.

As the individuation of factors associated with worse case outcome may be useful in clinical practice, a series of analyses of the independent predictors of bad outcome was performed in OPTIMIST. Such analyses showed that mortality is significantly higher when stent thrombosis occurred 1 year after stent implantation; when the attempted PCI result was not optimal and when a further stent was implanted during the PCI. The first point suggests that clinical surveillance after a successful PCI should not be reduced after 1 year and that the possible value of long-term anti-thrombotic drug administration should be investigated. The other two factors may together provide some interesting suggestions to the interventional cardiologists who must perform emergency PCI procedures in patients with stent thrombosis. Indeed, it seems that they should aim to re-establish optimal coronary blood flow and not to eliminate any residual coronary vessel narrowing by further stent implantations.

The OPTIMIST study also evaluated the efficacy of novel techniques of PCI in the high risk scenario of stent thrombosis. Previous studies have suggested that thrombus removal ( thrombectomy ) by new, specifically-designed, devices may facilitate restoration of coronary blood flow in thrombotic lesions by reducing distal embolization of thrombotic debris.
In the OPTIMIST study, 1 in every 4 patients was treated using thrombectomy devices as a first strategy. Despite the fact that patients treated by thrombectomy were sicker than the others, no excess of adverse clinical events was observed, thus supporting the safety of this novel approach. While the pre-selected parameters of procedural technical efficacy were not significantly improved by thrombectomy, the clinical usefulness of such an approach should not be discarded. Patients without unstable conditions ( absence of shock ) treated by thrombectomy had a 5-fold improved rate of optimal coronary flow restoration. This suggests that the role of distal embolization and its prevention may be important only before advanced heart damage has been established.

In conclusion, PCI for stent thrombosis is not a rare type of emergency procedure in the hospitals performing coronary interventions and it is associated with high rate of adverse clinical outcome. Factors causing DES thrombosis may be different from that operating in BMS so that DES technology introduction in clinical practice should be carefully monitored. However, once thrombosis has occurred, the outcome of PCI is not affected by the type of implanted stent but may be influenced by the timing of thrombosis and by procedural factors. Finally, the usage of thrombectomy devices in PCI for stent thrombosis is feasible but should be considered for patients without cardiogenic shock.

Source: European Society of Cardiology ( ESC ) – Congress, 2007

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