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ORLANDO -- Identifying patients who benefit from extended dual antiplatelet therapy following stenting and other percutaneous coronary interventions is a matter of balancing ischemic risk against bleeding risk, which may be easier with a new risk calculator.

Using the calculator, which was developed using data from the 11,648 patient DAPT trial, it is possible to accurately assess net risk at 1 year, said , of Beth Israel Deaconess Medical Center and Harvard Medical School in Boston.

Unlike other risk scores, which assess just ischemic risk or just bleeding risk, the DAPT risk score simultaneously assesses both, assigning a numerical score.

"With a low DAPT score -- less than 2 -- extended DAPT is almost three times more likely to cause bleeding than it is to prevent a heart attack," Yeh said in an interview. "With a high DAPT score -- 2 or more -- extended DAPT is eight to nine times more likely to help prevent a heart attack than to cause a bleeding event."

The number needed to treat to prevent a heart attack for patients with a DAPT score of 2 or higher is 34 and the number needed to harm (to cause bleeding) is 272, Yeh said. When the score is less than 2, the number needed to treat to prevent ischemia is 153 and the number needed to harm is 64.

Bleeding predictors in the DAPT population were age, with age 75 or older having the greatest risk. Ischemia risks include a history of myocardial infarction and prior PCI, MI at presentation, stent diameter less than 3 mm, diabetes, and a saphenous vein PCI.

Three factors -- hypertension, renal insufficiency, and peripheral arterial disease -- are risk factors for both ischemia and bleeding, "so we did not include those in the calculator," Yeh said.

In the original DAPT trial, patients who completed 12 months of dual-antiplatelet therapy were randomized to continue thienopyridine plus aspirin versus aspirin alone.

After 30 months, dual therapy cut stent thrombosis rates by a relative 71% compared with aspirin alone after 12 months (rate 0.4% versus 1.4% from months 12 to 30, P<0.001). But moderate or severe bleeding was elevated with continued thienopyridine treatment (2.5% versus 1.6%, P=0.001).

Although the DAPT results were generally considered positive, the increased bleeding led many, including , of UT Southwestern Medical Center at Dallas, to say the results were null.

"The adjusted hazard ratio for post-discharge bleeding with DES [drug-eluting stents] is more than twice the risk of an ischemic event -- 5.0 versus 1.9," said de Lemos, who was discussant for the DAPT risk score paper.

The risk score, "changes my interpretation of the findings from DAPT, which I considered essentially null because of the trade-off with bleeding," de Lemos said.

Yeh presented the findings at a late-breaking clinical trials session at the .

"This is exactly what we need," said , a professor of medicine at the University of North Carolina in Chapel Hill and a member of the ACC/AHA writing group that is preparing an updated recommendation for DAPT therapy.

"This is a wonderful and needed tool," said of Mount Sinai Medical Center in New York, but she pointed out that Yeh and colleagues developed the risk score using data from DAPT, which she said was "a very clean population: there were no events for 12 months."

Mehran said that validating the score in other populations is necessary. Moreover, "what we really need is a tool that we can use at the time of PCI or even before when we are counseling our patients about the procedure, about the long term risks."

Asked about the utility of the DAPT risk score for estimating risk at zero to 12 months, Yeh it was likely "there are the same factors present in the first 12 months ... we are now working on that population (0-12 months) within the DAPT data."

Yeh said the risk calculator is can be accessed and will eventually be available in an app.

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