Clinical significance of elevated troponin levels
The introduction of troponin (cTn) testing in the early 1990s has led to many questions about the clinical significance of elevated values. What has become clear in the past several years is that an elevated troponin in and of itself does not indicate myocardial infarction (MI); rather it is a finding that represents the likely occurrence of myocardial necrosis and of itself does not provide any indication of the etiology. It is extremely important for all practitioners to fully understand the implications of an elevated troponin in order to initiate the appropriate treatment and optimize outcomes.
The term MI should only be used when there is evidence of myocardial necrosis in a clinical setting consistent with acute myocardial ischemia. The definition should include a rise and/or fall of cardiac markers (preferably cardiac troponin cTn) with at least one value above the 99th percentile upper reference limit (URL) and at least one of the following:
- Symptoms of ischemia
- New ST segment changes or new left bundle branch block (LBBB)
- Development of pathological Q waves
- Imaging evidence of new loss of viable myocardium or new regional wall abnormalities
- Identification of an intracoronary thrombus by angiography or autopsy
A 2012 expert consensus document, developed by the European Society of Cardiology, American College of Cardiology, American Heart Association, and World Heart Foundation, maintains the pathological definition of acute MI as myocardial cell death due to prolonged myocardial ischemia. Their definition also classified AMI into 5 types, based on pathological, clinical and prognostic differences:
- Type 1: Ischemic myocardial necrosis secondary to plaque rupture (ACS)
- Type 2: Ischemic myocardial necrosis not due to ACA (i.e. supply/demand mismatch, coronary spasm, embolism, hypertension or hypotension, anemia, arrhythmia)
- Type 3: Cardiac death with symptoms of ischemia and new ECG changes or new LBBB, but death occurring before cardiac biomarkers were drawn
- Type 4: MI related to percutaneous coronary intervention (PCI) or stent thrombosis: cTn must be more than five times the 99th percentile URL and also requires one of the following events: symptoms suggestive of myocardial ischemia, new ischemic ECG changes, angiographic findings consistent with a regional wall motion abnormality, stent thrombosis when detected by angiography in the setting of myocardial ischemia and with a rise or fall of cardiac biomarker values.
- Type 5: MI related to coronary artery bypass graft surgery is defined as an elevation of cTn values more than 10 times the 99th percentile and requires one of the following: new pathological Q waves or new LBBB, angiographically documented new graft or new native coronary artery occlusion, or imaging evidence of new loss of viable myocardium or new regional wall motion abnormality.
For further assistance in determining the etiology of the elevated troponin level (ischemic versus non-ischemic) and appropriate patient diagnosis (myocardial infarction versus non-myocardial infarction), please refer to Figure 1 in the reference listed below.
Remember, any time an MI diagnosis is documented, all AMI core measures must be met, including:
- Aspirin given during first 24 hours of admission and at discharge
- Beta-blocker prescribed at discharge
- ACE inhibitor or Angiotensin Receptor Blocker given at discharge for those patients with an ejection fraction < 40%
- Statin prescribed at discharge
- Smoking cessation counseling if tobacco use within past year
References: American College of Cardiology Foundation 2012 Expert Consensus Document on Practical Clinical Considerations in the Interpretation of Troponin Elevations: A Report of the American College of Cardiology Foundation Task Force on clinical expert consensus documents.