Cardiac Markers - Facilitating Diagnosis and Exclusion of Patients with Acute Coronary Syndrome

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Abstract

The optimal use of cardiac markers depends upon what exactly the clinician is trying to use them for. Markers with high positive-predictive values are ideal to tailor aggressive care for patients who are at a high risk of cardiovascular complications. Patients most likely to benefit from early invasive care with a rapid transition to cardiac catheterization can be more expeditiously identified by markers with high positive-predictive values. Conversely, because the great majority of patients who present to the ED with potential ACS do not ultimately have a cardiac explanation for their symptoms, a marker with a high negative-predictive value is useful to allow expeditious evaluation (rule out ACS) and disposition from the ED. To that end, a panel of cardiac markers may ideally provide for both a rapid 'rule out' and a rapid identification of patients with high-risk ACS.
 

Citation
US Cardiology 2006;2005:2(1):61-64

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Ischemic heart disease is the leading cause of death among adults and one of the most common reasons for emergency department (ED) visits across the US. There are approximately five to seven million ED visits for acute chest pain syndromes annually; however, only 5% of these patients are ultimately diagnosed with acute myocardial infarction (AMI) and an additional 10% have non-AMI acute coronary syndromes (ACS). Thus, 85% of patients have non-ACS causes for their symptoms. From the ED perspective, it is important to expeditiously distinguish between these two groups of patients.

Although the standard 12-lead electrocardiogram (ECG) is the single best test to identify patients with AMI upon ED presentation, it still has relatively low sensitivity for detection of AMI (only 35% to 50%). Cardiac markers are the next most commonly used test to identify patients with potential ACS. They detect ACS in patients with normal and non-diagnostic ECGs.

The optimal use of cardiac markers depends upon what exactly the clinician is trying to use them for. Markers with high positive-predictive values are ideal to tailor aggressive care for patients who are at a high risk of cardiovascular complications. Patients most likely to benefit from early invasive care with a rapid transition to cardiac catheterization can be more expeditiously identified by markers with high positive-predictive values. Conversely, because the great majority of patients who present to the ED with potential ACS do not ultimately have a cardiac explanation for their symptoms, a marker with a high negative-predictive value is useful to allow expeditious evaluation (rule out ACS) and disposition from the ED. To that end, a panel of cardiac markers may ideally provide for both a rapid 'rule outÔÇÖ and a rapid identification of patients with high-risk ACS.

There are several cardiac markers in common practice that individually can assist the evaluation of patients with acute coronary syndromes, but combinations of cardiac markers are even more useful.

Creatine Kinase MB Fraction

In the setting of AMI, creatine kinase MB fraction (CK-MB) levels rise two-fold within six hours and peak within 12 to 24 hours. They have nearly 90% sensitivity six to eight hours after symptom onset (usually three to four hours after ED presentation) but are only 36% to 48% sensitive when utilized at or shortly after ED presentation.

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