Editor's Note: Commentary based on Moussa I, Klein LW, Shah B, et al. Consideration of a New Definition of Clinically Relevant Myocardial Infarction after Coronary Revascularization. J Am Coll Cardiol 2013; 62:1563-1570.
Supplemental Reference: White H. Avatar of the universal definition of periprocedural myocardial infarction. J Am Coll Cardiol 2013;62:1571-4.

Introduction

In 2007, a "universal definition" for MI following coronary revascularization was proposed,¹ and was recently revised.² According to the revised universal definition, a PCI-related MI (type 4a) was defined as an increase in cTn to >5× the 99th percentile of the URL during the first 48 h following PCI (in patients with normal baseline cTn concentrations), plus either: 1) evidence of prolonged ischemia as demonstrated by prolonged chest pain; or 2) ischemic ST-segment changes or new pathological Q waves; or 3) angiographic evidence of a flow limiting complication; or 4) imaging evidence of new loss of viable myocardium or new regional wall motion abnormality. cTn was considered the preferred biomarker for detection of myonecrosis. The writing committee noted, however, that these definitions were arbitrary and not grounded on substantial scientific evidence linking their occurrence to subsequent adverse outcomes.¹

Applying significance to peri-procedural biomarker elevations without prognostic relevance will result in unintended consequences on patient care, physician and systems quality evaluation, and comparative effectiveness research. Elevated cardiac biomarkers even after successful revascularization can lead to prolonged hospital stay and unnecessary interventions. Hence, the concept of "post PCI clinically relevant MI" has been proposed. The most contemporary evidence to date does not support use of the universal definition as the optimal criterion to identify clinically relevant post-PCI MI events. The expert Consensus Document from the Society for Cardiovascular Angiography and Interventions (SCAI) proposed the following criteria to diagnose post PCI clinically relevant MI³:

1. In patients with normal baseline CK-MB: peak CK-MB to ≥10× ULN 48 hours after PCI is used as a criterion. A lower threshold (≥5× ULN) may be accepted in the patient in whom new pathologic Q-waves in ≥2 contiguous leads (or new persistent LBBB) develop post-PCI. If CK-MB levels are unavailable AND cTn are normal at baseline, a reasonable cTn (I or T) value is measured 48 hours after PCI and a cTn of ≥70× ULN, or ≥35× ULN, with new pathologic Q-waves in ≥2 contiguous leads or new persistent LBBB is valid.

2. In patients with elevated baseline cardiac biomarkers: Accurate diagnosis of post-PCI MI is problematic, and requires assessment of serial biomarker levels. The following recommendations are made to diagnose post-PCI MI in ACS patients in whom the baseline level has not returned to normal:

   • In patients with elevated cTn (or CK-MB) in whom the biomarker levels are stable or falling, there should be a new CK-MB elevation by an absolute increment of ≥10× ULN (or ≥70× ULN for cTn I or T) from the previous nadir level;
   • In patients with elevated cTn (or CK-MB) in whom the biomarker levels have not been shown to be stable or falling, there should be a further rise in CK-MB or cTn beyond the most recently measured value by an absolute increment of ≥10× ULN in CK-MB or ≥70× ULN in cTn 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). Chest pain alone is not specific enough for substantial myonecrosis to be used as a criterion.

Practical Recommendations for Diagnosis of Post-PCI MI

The assessment of post-PCI MI is dependent on knowledge of whether biomarker levels are elevated at baseline, both in patients with ACS and those undergoing elective PCI, in whom cTn may be asymptomatically elevated. Ideally, cardiac biomarkers should be tested at least twice within 24 hours post-PCI. However, most interventionalists currently do not routinely measure cardiac biomarkers after an uncomplicated PCI, either because of cost considerations, planned early discharge, or lack of evidence that the knowledge of elevated biomarkers after an uncomplicated PCI affects prognosis or should change clinical management. In the most recent ACCF/AHA/SCAI PCI guidelines, routine assessment of cardiac biomarker levels after PCI is supported with a class I recommendation in the patient with angiographic complications during PCI or clinical symptoms or ECG changes after PCI, but with only a class IIb recommendation after an uncomplicated PCI.⁴

In the absence of routine testing we recommend the following: If cardiac biomarker levels were not elevated (or were not measured) pre-PCI, the PCI procedure is uncomplicated, and the patient is pain-free post procedure, a 12-lead electrocardiogram should be obtained within one to four hours post-PCI. If the ECG is un-changed cardiac biomarkers do not need to be drawn. If either clinical symptoms are present post-PCI, and/or transient or sustained angiographic complications occurred, and/or the post-PCI ECG shows new ST-segment depression or elevation, then CK-MB (or cTn in hospitals where CK-MB is not available) should be measured 8-12 hours post the procedure. If post-PCI cardiac biomarker elevation >ULN is noted, then serial levels should be drawn q8-12 hours until they are falling. An ECG should also be repeated in 24 hours, or earlier if symptoms develop.

If a clinically relevant MI is diagnosed, an echocardiogram may be considered to assess left ventricular function, and other routine post-MI medical measures may be initiated, including beta-blockers and angiotensin converting enzyme inhibitors (absent contraindications). Repeat cardiac catheterization might be considered if there were no overt angiographic complications to explain this level of myonecrosis and new left ventricular function is present. Conversely, if lesser levels of CK-MB elevation occur and/or Q-waves have not developed, and the patient is ambulating without symptoms or signs of ischemia or heart failure, the patient may be discharged on the day after the procedure. For classification purposes this might be considered "myonecrosis without clinically relevant MI."

The currently recommended definition of a "clinically relevant MI" is not perfect; however, it is clinically more useful and is based on the best scientific evidence presently available. Utilization of this definition in future randomized clinical trials of PCI would provide an opportunity to validate its premise.

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References

1. Thygesen K, Alpert JS, White HD, et al. Universal definition of myocardial infarction. Circulation 2007; 116:2634-2653.
2. Thygesen K, Alpert JS, Allan S, et al. Third universal definition of myocardial infarction. J Am Coll Cardiol 2012; 60:1581-1598.
3. Moussa I, Klein LW, Shah B, et al; Consideration of a New Definition of Clinically Relevant Myocardial Infarction after Coronary Revascularization. J Am Coll Cardiol 2013; 62:1563-1570.
4. Levine GN, Bates ER, Blankenship JC, et al. 2011 ACCF/AHA/ SCAI guideline for percutaneous coronary intervention: a report of the American College of Cardiology Foundation/American Heart Association Task Force on Practice Guidelines and the Society for Cardiovascular Angiography and Interventions. J Am Coll Cardiol 2011;58:e44–122.

Keywords: Chest Pain, Percutaneous Coronary Intervention, Myocardial Infarction, Myocardium

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