STOP-DAPT 2 ACS: 1 Month of DAPT Proves Inadequate for Patients With Recent ACS

Mitchel L. Zoler, PhD

September 03, 2021

One month of dual antiplatelet therapy (DAPT) followed by 11 months of clopidogrel monotherapy failed to prove noninferiority to 12 unbroken months of DAPT for net clinical benefit in a multicenter Japanese trial that randomized more than 4000 patients who underwent percutaneous coronary intervention (PCI) after a recent acute coronary syndrome episode.

The outcomes showed that while truncating DAPT duration could, as expected, cut major bleeding episodes roughly in half, it also led to a significant near doubling of myocardial infarction (MI) and showed a strong trend toward also increasing a composite tally of several types of ischemic events. These data were reported this week by Hirotoshi Watanabe, MD, PhD, at the virtual annual congress of the European Society of Cardiology. All study patients had undergone PCI with cobalt-chromium everolimus-eluting (CCEE) coronary stents (Xience™).

These findings from the STOPDAPT-2 ACS trial highlighted the limits of minimizing DAPT after PCI in patients at high ischemic risk, such as after an acute coronary syndrome (ACS) event.

It also was a counterpoint to a somewhat similar study also reported at the congress, MASTER DAPT, which showed that 1 month of DAPT was noninferior to 3 or more months of DAPT for net clinical benefit in a distinctly different population of patients undergoing PCI (and using a different type of coronary stent) — those at high bleeding risk and with only about half the patients having had a recent ACS.

The results of STOPDAPT-2 ACS "do not support use of 1 month of DAPT followed by P2Y12 inhibitor monotherapy with clopidogrel compared with standard DAPT," commented Robert A. Byrne, MBBCh, PhD, designated discussant for the report and professor at the RCSI University of Medicine and Health Sciences in Dublin, Ireland.

"Although major bleeding was significantly reduced with this approach, there appeared to be a significant increase in adverse ischemic events, and there was a clear signal in relation to overall mortality, the ultimate arbiter of net clinical benefit," added Byrne, who is also director of cardiology at Mater Private Hospital in Dublin.

He suggested that a mechanistic explanation for the signal of harm seem in STOPDAPT-2 ACS was the relatively low potency of clopidogrel (Plavix) as an antiplatelet agent, compared with other P2Y12 inhibitors such as prasugrel (Effient) and ticagrelor (Brilinta), as well as the genetically driven variability in response to clopidogrel that's also absent with alternative agents.

These between-agent differences are of "particular clinical relevance in the early aftermath of an ACS event," Byrne said.

12-Month DAPT Remains Standard for PCI Patients With Recent ACS

The totality of clinical evidence "continues to support a standard 12-month duration of DAPT — using aspirin and either prasugrel or ticagrelor — as the preferred default approach," Byrne concluded.

He acknowledged that an abbreviated duration of DAPT followed by P2Y12 inhibitor monotherapy "might be considered as an alternative." In patients following an ACS event who do not have high risk for bleeding, he said, the minimum duration of DAPT should be at least 3 months and with preferential use of a more potent P2Y12 inhibitor.

Twelve months of DAPT treatment with aspirin and a P2Y12 inhibitor for patients following PCI "remains the standard of care in guidelines," noted Marco Roffi, MD, a second discussant at the congress. But several questions remain, he added, such as which P2Y12 inhibitors work best and whether DAPT can be less than 12 months.

"The investigators [for STOPDAPT-2 ACS] pushed these questions to the limit with 1 month of DAPT and clopidogrel monotherapy," said Roffi, professor and director of interventional cardiology at University Hospital, Geneva, Switzerland.

"This was a risky bet, and the investigators lost by not proving noninferiority and with excess ischemic events," he commented.

First Came STOPDAPT-2

Watanabe and colleagues designed STOPDAPT-2 ACS as a follow-up to their prior STOPDAPT-2 trial, which randomly assigned slightly more than 3000 patients at 90 Japanese centers to the identical two treatment options: 1 month of DAPT followed by 11 months of clopidogrel monotherapy or 12 months of DAPT, except the trial enrolled all types of patients undergoing PCI. This meant that a minority, 38%, had a recent ACS event, while the remaining patients had chronic coronary artery disease. As in STOPDAPT-2 ACS, all patients in STOPDAPT-2 had received a CCEE stent.

STOPDAPT-2 also used the same primary endpoint to tally net clinical benefit as STOPDAPT-2 ACS: cardiovascular death, MI, stroke of any type, definite stent thrombosis, or TIMI major or minor bleeding classification.

In STOPDAPT-2, using the mixed population with both recent ACS and chronic coronary disease, the regimen of 1 month of DAPT followed by 11 months of clopidogrel monotherapy was both noninferior to and superior to 12 months of DAPT, reducing the net adverse-event tally by 36% relative to 12-month DAPT and by an absolute reduction of 1.34%, as reported in 2019.

Despite this superiority, the results from STOPDAPT-2 had little impact on global practice, commented Kurt Huber, MD, professor and director of the cardiology ICU at the Medical University of Vienna, Austria.

"STOP-DAPT-2 did not give us a clear message with respect to reducing antiplatelet treatment after 1 month. I thought that for ACS patients 1 month might be too short," Huber said during a press briefing.

Focusing on Post-ACS

To directly address this issue, the investigators launched STOPDAPT-2 ACS, which used the same design as the preceding study but only enrolled patients soon after an ACS event. The trial included for its main analysis 3008 newly enrolled patients with recent ACS, and 1161 patients who had a recent ACS event and had been randomly assigned in STOPDAPT-2, creating a total study cohort for the new analysis of 4136 patients treated and followed for the study's full 12 months.

The patients averaged 67 years old, 79% were men, and 30% had diabetes. About 56% had a recent ST elevation MI, about 20% a recent non-ST elevation MI, and the remaining 24% had unstable angina. For their unspecified P2Y12 inhibition, roughly half the patients received clopidogrel and the rest received prasugrel. Adherence to the two assigned treatment regimens was very good, with a very small number of patients not adhering to their assigned protocol.

The composite adverse event incidence over 12 months was 3.2% among those who received 1-month DAPT and 2.83% in those on DAPT for 12 months, a difference that failed to achieve the prespecified definition of noninferiority for 1-month DAPT, reported Watanabe, an interventional cardiologist at Kyoto University.

The ischemic event composite was 50% lower among those on 12-month DAPT compared with 1 month of DAPT, a difference that just missed significance. The rate of MI was 91% higher with 1-month DAPT compared with 12 months, a significant difference.

One-month DAPT also significantly reduced the primary measure of bleeding events — the combination of TIMI major and minor bleeds — by a significant 54% compared with 12-month DAPT. A second metric of clinically meaningful bleeds, those that meet either the type 3 or 5 definition of the Bleeding Academic Research Consortium (BARC), were reduced by a significant 59% by 1-month DAPT compared with 12 months of DAPT.

The new findings from STOPDAPT-2 ACS contrasted with those from MASTER DAPT, but in an explicable way that related to different patient types, different P2Y12 inhibitors, different treatment durations, and different stents.

"We've seen in MASTER DAPT that if you use the right stent and use ticagrelor for monotherapy there may be some ability to shorten DAPT, but we still do not know what would happen in patients with very high ischemic risk," concluded Huber.

"A reduction in DAPT duration might work in patients without high bleeding risk, but I would exclude patients with very high ischemic risk," he added. "I also can't tell you whether 1 month or 3 months is the right approach, and I think clopidogrel is not the right drug to use for monotherapy after ACS."

STOPDAPT-2 and STOPDAPT-2 ACS were both sponsored by Abbott Vascular, which markets the cobalt-chromium everolimus-eluting (Xience) stents used in both studies. Watanabe has received lecture fees from Abbott and from Daiichi-Sankyo. Byrne has received research funding from Abbott Vascular as well as from Biosensors, Biotronik, and Boston Scientific. Roffi has received research funding from Biotronik, Boston Scientific, GE Healthcare, Medtronic, and Terumo. Huber has received lecture fees from AstraZeneca, Bayer, Boehringer Ingelheim, Bristol Myers Squibb, Daiichi-Sankyo, Eli Lilly, Pfizer, sanofi-aventis, and The Medicines Company.

European Society of Cardiology (ESC) Congress 2021. Presented August 30, 2021.

Mitchel L. Zoler is a reporter with Medscape and MDedge based in the Philadelphia region. @mitchelzoler

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