New Definition of "MI" Poised for World Domination

October 23, 2007 — A new consensus report [1] sponsored jointly by four cardiology societies refines and expands on the definition of "myocardial infarction" last updated seven years ago [2] and — in a bold move — recognizes five separate myocardial infarction (MI) categories based on differences in pathophysiology and whether percutaneous coronary intervention (PCI) or coronary artery bypass graft (CABG) surgery is involved.
The new definition's components reflect knowledge and skills gained since the last time, much of which has been commonly used in clinical practice and research, though inconsistently and without a formal mandate.
"What's not different is that troponin together with clinical information from the patient history and the electrocardiogram are still the gold standard," Dr Joseph S Alpert (University of Arizona, Tucson) told heartwire.
The document notes that troponin is the "preferred" biomarker but that others, such as the MB fraction of creatinine kinase (CK-MB), can suffice when troponin testing is unavailable. Other innovations include criteria for MI as the cause of sudden death and unprecedented weight given to findings from echocardiography, perfusion scans, and other imaging techniques.
One goal for the consensus document is to nail down specific criteria for making an MI diagnosis that will be modern, useful, and relevant most everywhere.
"What we're trying to do is standardize the definition so that all clinical trials and people at hospitals around the world will on the same page," said Alpert, a cochair of the task force behind the "expert consensus document" jointly sponsored by the American College of Cardiology (ACC), American Heart Association (AHA), European Society of Cardiology (ESC), and the World Heart Federation (WHF).
The report was published October 19, 2007 on the ACC, AHA, and ESC web sites, appears in the second October, 2007 edition of the European Heart Journal, and is scheduled for the November 27, 2007 issues of the Journal of the American College of Cardiology and Circulation.
Usually key to the diagnosis, with some notable exceptions, is an elevation in levels of troponin or other biomarkers exceeding the 99th percentile of the upper reference limit (URL), combined with the familiar clinical syndrome, electrocardiogram (ECG) signs, or imaging evidence of new myocardial ischemia.
The new criteria's effects may take some getting used to. Even in the absence of ECG changes, "if you have a syndrome consistent with myocardial infarction or acute coronary syndrome, with [such] a troponin elevation, then those two alone are sufficient to make the diagnosis," according to Dr Keith Fox (University of Edinburgh, UK). With troponin's specificity for myocardial necrosis at the specified concentration threshold, he observed, a great many more patients who would be missed by "previously conventional markers like CK and CK-MB" will be classified as having an MI.
"It will increase by about a quarter the prevalence of myocardial infarction," he said.
Fox made the remarks during a Cardiology Panel discussion sponsored by theheart.org [3] that was recorded in September after the new MI definition was described at the European Society of Cardiology 2007 Scientific Meeting.
The new definition also formally recognizes myocardial necrosis associated with PCI or CABG as an MI as long as a biomarker threshold is met, and allows the diagnosis in the absence of biomarker elevations in the setting of sudden cardiac death as long as there is evidence of myocardial ischemia.
With the MI definition's increased complexity comes a classification system to sort out the variations, starting with the syndrome's classic pathophysiology.
New clinical classification of MI
Classification
Description
1
Spontaneous MI related to ischemia due to a primary coronary event, such as plaque erosion and/or rupture, fissuring, or dissection
2
MI secondary to ischemia due to an imbalance of O2 supply and demand, as from coronary spasm or embolism, anemia, arrhythmias, hypertension, or hypotension
3
Sudden unexpected cardiac death, including cardiac arrest, often with symptoms suggesting ischemia with new ST-segment elevation; new left bundle branch block; or pathologic or angiographic evidence of fresh coronary thrombus — in the absence of reliable biomarker findings
4a
MI associated with PCI
4b
MI associated with documented in-stent thrombosis
5
MI associated with CABG surgery
The system goes far beyond the long-outmoded distinctions of transmural vs nontransmural or Q-wave vs non-Q-wave MI, and even the contemporary terms ST-elevation and non-ST-elevation MI (STEMI and non-STEMI). "The distinction between STEMI and non-STEMI is becoming clinically less interesting," Alpert said. "We hope, and we recommend, that in the future in clinical trials and routinely in the hospital, people will begin to characterize infarction by the different categories."
The classifications and updated diagnostic criteria could ultimately improve patient care and outcomes, he predicted. With a broader range of patients classified as having an MI, many who might have been labeled with "unstable angina" will get more aggressive management, said Alpert, "which should result in a decrease in mortality."
When speaking to heartwire, Alpert gave primary credit for the classification system and its inclusion in the document to task-force cochair Dr Harvey E White (Auckland City Hospital, New Zealand).
A detailed listing of disclosure information for members of the "Task Force for the Redefinition of Myocardial Infarction" appears at the end of the document, which also notes contributions of "unrestricted educational grants" from several companies, "none of whom were involved in the development of this publication and in no way influenced its contents." They are AstraZeneca, Beckman-Coulter, Dade Behring, GlaxoSmithKline, Roche Diagnostics, Sanofi-Aventis, and Servier.
Sources
Thygesen K, Alpert JS, White HD, et al. Universal definition of myocardial infarction. Circulation, published online before print October 19, 2007. DOI: 10.1161/CIRCULATIONAHA.107.187397
Alpert JS, Thygesen K, Antman E, et al. Myocardial infarction redefined — a consensus document of The Joint European Society of Cardiology/American College of Cardiology Committee for the redefinition of myocardial infarction. J Am Coll Cardiol 2000;36:959-969. PMID: 10987628
Are we ready for a troponin-based definition of MI?. theheart.org. [Editorial series > Cardiology panels]; October 17, 2007. Accessed at http://www.theheart.org/article/819427.do on October 19, 2007.