A new study has found that the dual antiplatelet therapy (DAPT) score, which is recommended by both US and European guidelines, did not adequately determine ischaemic and bleeding risk in an unselected patient population. These findings suggest that the score may not be generalisable to real-world populations.
Peter Ueda (Clinical Epidemiology Division, Department of Medicine, Solna, Karolinska Instituet, Stockholm, Sweden) and others write in the Journal of the American College of Cardiology that the DAPT score is used to determine which patients would benefit from receiving DAPT for an extended period—a further 18 months after 12 months’ DAPT without an ischaemic or bleeding event—following percutaneous coronary intervention (PCI). They add that both US and European DAPT guidelines advise physicians to consider using the score when determining duration of DAPT (in patients who have already completed 12 months of DAPT without an event).
However, the authors observe that the score has only been validated using clinical trial populations. Specifically, the score was based on the results of the DAPT study and a large proportion of patients in that study received first-generation drug-eluting stents. “The performance of the risk score in an unselected real-world patient population receiving contemporary PCI treatment is uncertain,” Ueda et al comment. Therefore, the aim of the present study was to assess the ability of the DAPT score to stratify ischaemic and bleeding risk after 12 months of DAPT and compare and ischaemic and bleeding event rates after those with observed in the DAPT study.
Using data from the SWEDEHEART registry, the authors identified 41,101 patients who had received DAPT for 12 months without experiencing an ischaemic or bleeding event. Of these, 55% had a “low” DAPT score (<2 points) and 45% had a high DAPT score (≥2 points); according to the decision rule of the score, patients with a score of two or above should receive DAPT beyond 12 months.
Ueda et al report that the DAPT score had a C-statistic of 0.58 for myocardial infarction and stent thrombosis and 0.54 for major adverse cardiac cerebrovascular events (MACCE). They note that patients with a high DAPT score had significantly higher rates of myocardial infarction, stent thrombosis and MACCE than those with a low DAPT score. However, the difference in risk of myocardial infarction and stent thrombosis was largely driven by those with scores of 3 and higher and rates of MACCE did not increase linearly with score level “Compared with scores of -1 and -2, event rates were lower at scores of 1 and 2 and significantly increased only at scores of 4 and ≥5,” the authors state. Furthermore, the score had a C statistic of 0.49 for fatal or major bleeding, and the risk of this event between low and high risk groups was similar. Ueda et al observe: “These findings, which remained similar when limiting the analyses to patients receiving new generation drug-eluting stents, indicate that the DAPT score is not useful for discriminating bleeding and ischaemic risk.”
After comparing the patient population of the DAPT study with that of the SWEDEHEART registry, Ueda et al found differences in event rates and state: “Notably, rates of fatal or major bleeding in the SWEDHEART registry were roughly one half of those for the GUSTO moderate or severe bleeding in the placebo arm of the DAPT study. Although this could partly be explained by the different bleeding outcome definition used and the potential risk of incomplete registration of events in health registries, the rates of fatal or major bleeding in our study were similar to those in other coronary patient populations from real-world databases and clinical trials.” However, the authors note that patients perceived to be at high risk of bleeding in the SWEDEHEART registry may have been prescribed DAPT for less than 12 months (patients in the DAPT study had to receive DAPT for at least 12 months) and, therefore, would not have been included in this present analysis (potentially affecting the results).
Ueda told Cardiovascular News: “Although we could not assess the effect of extended DAPT in patients stratified using the score, our data on discrimination and calibration of the risk score indicate that the ischaemic vs. bleeding risk trade-off seen among high and low score patients in the DAPT Study may not be generalisable to external populations, including the SWEDEHEART Register. Generalisability, especially with respect to calibration, is a well-known challenge in the area of risk scores.”
Ueda presented the study at the 2018 European Society of Cardiology (ESC) Congress (25-29 August, Munich, Germany).