SCAI Proposes New Definition for Heart Attack After Angioplasty or Bypass Surgery

October 14, 2013—The Society for Cardiovascular Angiography and Interventions (SCAI) announced publication of an expert consensus document that proposes new, more meaningful criteria for identifying patients who experience a heart attack after coronary angioplasty or bypass surgery. SCAI noted that leading physicians representing both interventional cardiology and cardiac surgery developed the proposed new criteria and their implications for patient care.

The document, “Consideration of a New Definition of Clinically Relevant Myocardial Infarction After Coronary Revascularization” by Issam D. Moussa, MD, is available online ahead of print in SCAI's Catheterization and Cardiovascular Interventions. The document was also published in the Journal of the American College of Cardiology (2013;62:1563–1570).

According to SCAI, by focusing specifically on postprocedure heart attacks that have the potential to influence a patient's clinical outcomes—“prognostically important” heart attacks—the new definition may improve not only patient care, but also the way heart procedures are evaluated for quality and effectiveness.

As summarized by SCAI, the new criteria differ from the existing criteria in several ways. Both diagnose a heart attack primarily by detecting a protein in the blood that is released when the heart muscle is damaged. However, the definitions differ by which protein is the preferred marker, how high the protein level must rise to signal a heart attack, and under what circumstances additional evidence from an electrocardiogram (ECG), imaging test, or symptoms is needed to confirm the diagnosis.

The existing definition calls for a relatively small increase in the blood level of cardiac troponin to five times the normal level, plus confirmation by an ECG, an imaging test, or symptoms.

In most cases, the new definition calls for a large increase in the blood level of the protein CK-MB to at least 10 times the normal level. If CK-MB is not available, the new definition calls for a troponin level that is 70 times normal. If the ECG tracing provides strong evidence of a heart attack, then the new definition allows for blood levels of CK-MB and troponin that are five times and 35 times normal, respectively.

The SCAI statement advises that the disparities between the two definitions highlight critical differences in their diagnostic goals. The existing definition, by relying on small protein leaks from the heart muscle, can detect even minimal heart damage. However, this information does not necessarily help doctors determine a patient's prognosis, because minimal heart damage is unlikely to influence short- and long-term survival, the likelihood of having another heart attack, and other important clinical outcomes. In contrast, the new definition focuses on detecting prognostically meaningful heart attacks that can be expected to affect a patient's heart function, wellbeing, and future health.

SCAI outlined four other advantages of the new definition. For one, it focuses on the link between a large rise in CK-MB levels and poor long-term outcomes after angioplasty or bypass surgery, an association that has been validated in numerous clinical studies. Although troponin is the preferred protein marker to use in diagnosing a spontaneous heart attack, its role in diagnosing prognostically important heart attacks after stenting or bypass surgery has not been well validated, particularly at the levels specified in the existing definition. Two, it would bring uniformity to the criteria used to diagnose heart attack after percutaneous coronary intervention and bypass surgery (the existing definition uses different standards for the two types of procedures). Three, by focusing on clinically relevant outcomes, the new criteria would allow for more meaningful assessment of physician and program quality. Four, the focus on clinically relevant outcomes would aid clinical research by enabling better comparison between various methods of treating coronary artery disease.

In SCAI's press release, Dr. Moussa commented, “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.”

He continued, “If you tell a patient, ‘You have had a heart attack,' it should mean something about clinical outcomes, not microscopic injury to the heart muscle. This diagnosis has important implications. It could lead to longer hospital stays, more blood tests, and repeat imaging procedures. It could even affect a patient's job.”

In conclusion, Dr. Moussa stated, “This is not about semantics by any means. How we define a heart attack after angioplasty or bypass surgery can have a significant impact on patient perception, health care resource utilization, and how we measure the quality of these procedures.”