SCAI proposes new definition for MI after revascularization

The Society for Cardiovascular Angiography and Interventions has proposed a new definition for clinically relevant MI after PCI and CABG that diverges from previous definitions, including the one used by WHO. The new SCAI criteria define it as “an event associated with worsened prognosis.”

Previous definitions have not taken into account prognosis, according to the authors. The universal definition “designates post procedural biomarker thresholds for defining [PCI]-related MI (type 4a) and [CABG]-related MI (type 5), which are of uncertain prognostic importance,” they wrote, adding that cardiac troponin (cTn) is the most important biomarker in this definition. They suggested that CK-MB carries more clearly defined prognostic significance than cTn.

For the SCAI group, failing to link MI to subsequent adverse events may affect not only how devices and therapies are evaluated, but clinical pathways as well. This could, in turn, result in “misinterpretation of physician competence,” they wrote.

A definition sensitive for small degrees of myonecrosis — which is unlikely to be associated with important clinical consequences, according to the SCAI authors — may not be as effective as one that provides a threshold level of biomarker elevation indicating adverse events.

“We believe something should have a clinical impact in the intermediate to long term to be called a complication,” Issam D. Moussa, MD,FSCAI, co-author of the paper and chair of the division of cardiovascular diseases at Mayo Clinic in Jacksonville, Fla., said in an interview with Cardiology Today’s Intervention. “If you label someone as having a MI after the procedure, they may have to go back for a repeat angiogram, stay in the hospital longer or be given additional medication. So there is the potential for overutilization of services [with the presently used definition].”

Issam D. Moussa

Besides affecting the patient, a new definition that more adequately accounts for long-term outcome would also have a significant influence on the design of future clinical trials, Moussa said.

“In clinical trials, a primary endpoint should have proven clinical and prognostic significance,” Moussa said. “In clinical trials evaluating coronary revascularization procedures, an endpoint of MI should be as clinically meaningful as other endpoints (stroke and death). The clinical relevance of post-PCI MI as defined by the universal definition remains unproven, and therefore should not qualify for inclusion in the composite endpoint of those trials.”

Proposed new definition

In the suggested definition for clinically relevant MI after revascularization, the authors write that in patients with normal baseline CK-MB, it should be defined as, “The peak CK-MB measured within 48 hours of the procedure rises to ≥10 [times] the local laboratory [upper limit of normal (ULN)], or to ≥5 [times] 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 cTn, a cTn (I or T) level measured within 48 hours of the PCI rises to ≥70 [times] the local laboratory ULN, or ≥35 [times] ULN with new pathologic Q-waves in ≥2 contiguous leads or new persistent LBBB.”

For patients with CK-MB elevations at baseline, and who have stable or falling biomarkers, it is defined as “CK-MB or cTn rising by an absolute increment equal to those levels recommended above from the most recent pre-procedure level,” they wrote.

And for patients with elevated CK-MB or cTn with biomarkers that may not be stable or falling, they suggest the following definition: “The 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.”

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The authors said cardiac catheterization is performed after clinicians obtain only one biomarker or when serial biomarkers demonstrated continued escalation, adding that diagnosing MI after PCI in this setting on the basis of biomarker information is “impossible.”

Although the SCAI authors said chest pain is not a sufficient enough signal for substantial myonecrosis, more data will be needed to clearly define diagnostic criteria in patients demonstrating elevations in baseline biomarkers.

New definition ‘should not supplant universal definition’

Harvey White, DSc, co-chairman for the Task Force for the Universal Definition of Myocardial Infarction with Green Lane Cardiovascular Service and Auckland City Hospital in New Zealand, wrote in an accompanying editorial that whether post-procedural myonecrosis is a risk marker of atherosclerotic burden and PCI complexity or a risk factor is an unresolved question.

“New definitions of periprocedural MI will of necessity be arbitrary,” he wrote.

White said the SCAI group effectively articulated the reasons for the new definition. However, the rationale “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.”

For White, more rigorous and systematic implementation of the standard definition may allow equally rigorous assessment of new interventions in the post-PCI MI setting. He said emphasizing troponin levels at baseline could increase the specificity of the standard definition. Documenting angiographic complications in the universal definition is important for defining the clinical relevance of biomarkers and understanding how those biomarkers impact prognosis. However, he added that this will present challenges for clinicians.

“There is a need to have high sensitivity to identify all clinically important type 4a MIs and to differentiate them from an index MI with high specificity,” White wrote. “Further modification of the universal definition of MI associated with PCI should await substantial data that may well be forthcoming in the near future.” – by Rob Volansky, with additional reporting by Brian Ellis

For more information:

Moussa ID. J Am Coll Cardiol. 2013;62:1563-1570.

White M. J Am Coll Cardiol. 2013;62:1571-1574.

Disclosure: The SCAI authors report a number of relationships with companies, including Abbott Vascular, AstraZeneca, BMS/Sanofi, BridgePoint Medical/Boston Scientific, Daiichi Sankyo, Eli Lilly, Guerbet, Janssen Pharmaceuticals, Maya Medical, Medtronic, Merck, Regado Biosciences and The Medicines Company. See the editorial for a full list of White’s relevant financial disclosures.