The definition of heart attack is undergoing a transformation. Technically termed myocardial infarction or MI, heart attacks have been diagnosed in the past based on the presence or history of chest pain and characteristic changes in the wave patterns on an electrocardiograph (ECG). More recently, the results of the creatine kinase (CK and CK-MB) blood tests have been used in diagnosis. And within the last year, the European Society of Cardiology and the American College of Cardiology have proposed that there should be a new gold standard for defining a heart attack: cardiac troponin.

With new and more sensitive blood assays for troponin recently becoming available, this cardiac marker has been receiving a lot of attention recently. Its main advantage is that it is very sensitive to even minor damage to the heart.

Troponin , a protein that has three isotypes (I, T, and C), is released from dead and injured cells in heart muscle, so elevated levels can indicate that there has been injury, such as would occur during a heart attack, even a mild one. Other advantages of troponin, particularly TnI and TnT, over the CK-MB test are that it will remain in the blood stream for days following a cardiac event, allowing more time for diagnosis, and, while CK and CK-MB are only released from muscle cells that have died (the definition of infarction), troponin is released from dead and severely injured muscle cells. A number of studies have shown that people who have elevated troponin but normal CK and CK-MB suffer similar consequences to those who meet the more traditional diagnostic criteria for diagnosing a heart attack.

As a result, the American College of Cardiology and the European Society of Cardiology released recommendations essentially redefining MIs. This definition requires evidence of elevated cardiac markers (such as troponin or CK-MB and total CK) and one other positive criterion (such as pathologic exam or ECG results). However, there is a clear preference for troponin over CK-MB, and it is expected that troponin will become the new gold standard. Recently, other organizations, such as the American Heart Association, began working this new conceptualization into their own guidelines for the management of patients with heart disease.

This new emphasis on troponin will clearly impact patient care, for what may in the past have been considered severe or unstable angina might now be classified as a mild heart attack, allowing for more appropriate and timely monitoring and treatment. One challenge, however, will be determining the appropriate cut-off values in serum troponin for confirming a heart attack. This will be difficult because of the lack of standardization of troponin assays; different laboratories, depending on the particular assay they use, may have different cut-offs.

The American Association for Clinical Chemistry (AACC) appointed a Troponin I Standardization Subcommittee to address this critical need for standardization (‘close agreement’) between different Troponin I tests. Working with diagnostic companies, this group is performing complex technical studies to help improve the clinical utility of this very important test by identifying a single reference material that all assays can use to assign troponin I values for their own company’s test. But it will still be left to the global laboratory community to effectively use and validate all the currently available troponin assays in providing optimal patient care.

Sources:
New Heart Technologies Will Save Thousands More Lives. AdvaMed’s Medical Technology & Innovation. Vol. 2, Issue 35, November 26, 2001.

American Heart Association, November 14, 2001 Meeting Report.

Clinical Laboratory News, December 2000, Vol. 26, Number 12.