SCAI Proposes New 'Clinically Meaningful' MI Definition

Shelley Wood

October 14, 2013

WASHINGTON, DC (updated) — A "clinically meaningful" definition of MI following PCI or CABG is urgently needed to replace the arbitrarily chosen "universal definition" proposed in recent years that has no relevance to patients and may be muddying clinical-trial results. Those are the conclusions of a new expert consensus document released Monday by the Society of Cardiovascular Angiography and Interventions (SCAI) and published in the October 22, 2013 issue of the Journal of the American College of Cardiology[1].

The notion of a "universal definition of MI" was first proposed in 2000 and updated in 2007 and 2012. The 2012 document defines a PCI-related MI as an increase in cardiac troponin (cTn) of more than five times the upper limit of normal (ULN) during the first 48 hours postprocedure plus specific clinical or ECG features. Post-CABG, the definition is a cTn increase of >10 times the ULN, plus different clinical or ECG features.

The problem, lead author Dr Issam Moussa (Mayo Clinic, Jacksonville, FL) told heartwire , is that these cutoffs were arbitrarily chosen and not based on any hard evidence that these biomarker levels spelled a poor prognosis. Moreover, "overnight, the rate of MI went from 5% following these procedures to 20% to 30%!" he said.

The SCAI committee, in its new document, focuses on post-PCI procedures and highlights the importance of acquiring baseline cardiac biomarkers and differentiating between patients with elevated baseline CK-MB (or cTn) in whom biomarker levels are stable or falling, as well as those in whom it hasn't been established whether biomarkers are changing.

SCAI's Proposed Clinically Meaningful MI Definitions

Group Definition
Normal baseline CK-MB

CK-MB rise of >10x ULN or >5x ULN with new pathologic Q-waves in at least 2 contiguous leads or new persistent left bundle branch block
OR
In the absence of baseline CK-MB, a cTn rise of >70x ULN or a rise of >35 ULN plus new pathologic Q-waves in at least 2 contiguous leads or new persistent left bundle branch block

Elevated baseline biomarkers that are stable or falling A CK-MB or cTn rise that is equal (by an absolute increment) to the definitions described for patients with normal CK-MB at baseline.
Elevated baseline biomarkers that have not been shown to be stable or falling

A CK-MB or cTn rise that is equal (by an absolute increment) to the definitions described for patients with normal CK-MB at baseline
Plus
New ST-segment elevation or depression
Plus
New-onset or worsening heart failure or sustained hypotension or other signs of a clinically relevant MI.

Moussa is quick to emphasize that these new clinically meaningful definitions have limited evidence to support them—and most of what exists supports CK-MB definitions, not cTn—but that the new document is based on the best scientific evidence available.

"We don't want to come out with a definitive statement" saying this is the final word on MI definitions," he stressed. "There is more science that needs to be done and there remains more uncertainty. We framed this to be inclusive and also to open the field for discussion."

His hope is that this will lead to important changes in how patients are managed and money is spent. Currently, patients with clinically meaningless biomarker elevations may become unnecessarily panicked over news that they've had a "heart attack," while hospital stays may be extended and further tests ordered on the basis of these results.

Moussa et al's proposal also has important implications for clinical trials, he continued. Currently, for studies that include periprocedural MIs as an individual end point or as part of a composite end point, the very high number of biomarker-defined "MIs" collected in the trial could potentially overwhelm the true impact of any given therapy. "You are really using an end point that is truly not relevant to patients. . . . This could really affect the whole hypothesis."

In an accompanying editorial[2], Dr Harvey White (Auckland City Hospital, New Zealand) points to a number of flaws in the proposed new definition, including its emphasis on CK-MB rather than the "more sensitive and specific troponins" used in the universal definition.

White reviews the similarities and differences between the two definitions and concludes with a key point: "It is an unresolved question whether postprocedural myonecrosis is a risk marker of atherosclerotic burden and PCI complexity or a risk factor. New definitions of periprocedural MI will of necessity be arbitrary." He continues: "The rationale for the SCAI definition has been well articulated by its authors and may be appropriate in an individual trial, but it should not supplant the universal definition of MI. The metrics for both should be available if the SCAI definition is used."

Moussa told heartwire that he is expecting some push-back from cardiologists and academics, particularly those who championed the need for the universal definition in the first place, but believes most people will welcome a clinically meaningful definition.

"I think many in the medical community will accept this because they have not really been using the universal definition in their day-to-day practice anyhow." What's more, the National Cardiovascular Data Registry (NCDR) does not include the reporting of MI postangiography, in part because of concerns that the universal definition of MI overestimates the true incidence of this problem. "I think many in the community will look at this definition as more reflective of the true incidence of MI after angioplasty, and if it's accepted, they are more likely to report it to databases like NCDR and use it to reflect quality-of-care processes."

Moussa disclosed having no conflicts of interest. Disclosures for the coauthors are listed in the paper. White is cochair for the task force for the universal definition of myocardial infarction; has received research grants from Sanofi, Eli Lilly, the Medicines Company, the National Institutes of Health, Pfizer, Roche, Johnson & Johnson, Schering-Plough, Merck Sharpe & Dohme, AstraZeneca, GlaxoSmithKline, Daiichi Sankyo Pharma Development, and Bristol-Myers Squibb; he has served on advisory boards for AstraZeneca; Merck Sharpe & Dohme; Roche; and Regado Biosciences.

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