An expert panel led by the Society for Cardiovascular Angiography and Intervention (SCAI) has proposed a new definition of "clinically relevant" myocardial infarction (MI) after percutaneous coronary intervention (PCI) and coronary artery bypass graft (CABG) surgery applicable to clinical trials, patient care and the assessment of quality outcomes. The definition primarily uses the protein creatine kinase-myocardial band (CK-MB) as the primary cardiac biomarker for the diagnosis of MI after coronary revascularization.

Published Oct. 14 in the Journal of the American College of Cardiology, the new definition differs from previous definitions according to three patient characteristics:

• In patients with normal baseline CK-MB, the definition is based on when the peak CK-MB measured within 48 hours of the procedure rises to ≥10 x the local laboratory upper limit of normal (ULN) or to ≥5 ULN with new pathologic Q-waves in ≥2 contiguous leads or new persistent left bundle branch block (LBBB), or in the absence of CK-MB measurements and a normal baseline cardiac troponin (cTn), a cTn (I or T) level measured within 48 hours of the PCI rises to ≥70 x the local laboratory ULN, or ≥35 x ULN with new pathologic Q-waves in ≥2 contiguous leads, or new persistent LBBB.
• In patients with elevated baseline CK-MB (or cTn) in whom the biomarkers are stable or falling, the definition is based on when CK-MB (or cTn) rises by an absolute increment equal to those levels recommended above from the most recent pre-procedure level.
• In patients with elevated baseline CK-MB (or cTn) in whom the biomarker levels have not been shown to be stable or falling, the definition is based on when CK-MB (or cTn) rises by an absolute increment equal to those levels recommended above plus new ST-segment elevation or depression plus signs consistent with a clinically relevant MI, such as new onset or worsening heart failure or sustained hypotension.

Additional Resources Third Universal Definition of MI Interventional Membership Section CardioSmart for Your Patients: About Heart Attack

The SCAI consensus group maintains that the current universal definition for MI after revascularization recommends using cTn as the biomarker of choice, but its prognostic significance is not as well validated as that for CK-MB and it is not clearly linked to subsequent adverse events, such as mortality or heart failure. They add that the new definition "would bring uniformity to the criteria used to diagnose MI after PCI and bypass surgery," and "by focusing on clinically relevant outcomes, the new criteria would allow for more meaningful assessment of physician and program quality" which would then aid clinical research "by enabling better comparison between various methods of treating coronary artery disease."

"This definition of heart attack would better identify those patients with true complications after angioplasty or bypass surgery who require urgent action, better reflect the quality of these procedures and inform future research designed to identify the best preventive strategies," said Issam D. Moussa, MD, FACC, chair of the Division of Cardiovascular Diseases at Mayo Clinic Florida in Jacksonville. He adds that the definition will have a significant impact "on patient perception, health care resource utilization and how we measure the quality of these procedures."

An accompanying editorial by Harvey White, DSC, FACC, from the Green Lane Cardiovascular Service, Auckland City Hospital, New Zealand, argues that there may be negative unintended consequences for having different definitions. He adds that "CK-MB is now unavailable in an increasing number of hospitals. With CK-MB becoming obsolete, troponin will become the gold standard, and CK-MB will no longer have a role in defining PCI injury and infarction in clinical practice."

In addition, "it is an unresolved question whether post-procedural 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 notes. "Further modification of the universal definition of MI associated with PCI should await substantial data that may well be forthcoming in the near future."

Keywords: Depression, Coronary Artery Disease, Myocardial Infarction, Infarction, Patient Care, Creatine Kinase, MB Form, Hypotension, Risk Factors, Angioplasty, Percutaneous Coronary Intervention, Biomarkers, Heart Failure, Bundle-Branch Block, Coronary Artery Bypass, United States, Troponin

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