The American Heart Association estimates approximately 785,000 Americans will have a heart attack in 2010. With the signs and symptoms of a heart attack varying widely, it is imperative for physicians to have a multitude of ways to diagnose ongoing attacks and prevent impending cardiac damage. A common method of confirming the presence of damage to the heart muscle is to check for elevations in cardiac-specific enzymes.
Cardiac Enzymes
Biomarkers are physiological parameters that can help measure, or quantify, the presence of biological process. Cardiac enzymes are a type of biomarker that specifically identify processes occurring within the heart muscle. These enzymes can provide critical information for the diagnosis and treatment of patients incurring a heart attack. In fact, cardiac enzymes are so important that in 2002, the American College of Cardiology and the European Society of Cardiology included the presence of specific cardiac enzymes in their new definition of a heart attack.
The Rise In Enzymes
Cardiac enzymes are used as the biomarkers of heart attack because these specific enzymes are housed within the heart muscle itself. When that muscle begins to die as a result of a heart attack, the muscle's contents begin to spill out and filter into the blood stream. Cardiac enzymes and proteins are generally not found in significant quantities in the blood, so a sharp increase presents a red flag to alert the physician that tissue damage has occurred.
Creatine Kinase
Creatine kinase is an enzyme, or catalyst, that helps muscles generate energy and is found in all muscle types throughout the body. Because of the widespread nature of creatine kinase, heart attacks are confirmed by looking for a rise in the cardiac-specific creatine kinase, known as CK-MB. According to a 2010 report in "Coronary Artery Disease," CK-MB levels usually increase four to six hours after the onset of a heart attack, peak within 10 to 24 hours and return to normal within three days. These time frames are approximations, however, and depend on the severity of the heart attack. To reach the peak level and return to normal takes longer the larger the heart attack is and the greater the damage to the heart muscle.
Cardiac Troponins
Troponin is a triad of regulatory proteins essential for cardiac and skeletal muscle contraction. TnC has the same characteristics regardless of what type of muscle it is found in, and therefore cannot be used as a cardiac-specific marker. The varying characteristics of TnI and TnT, on the other hand, allow them to be identified as coming from cardiac muscle or skeletal muscle. Because of this, physicians can look specifically for a rise in the cardiac form of TnI and TnT to determine the presence of damaged heart tissue. Elevations in troponin can be identified in as little as four to eight hours after the start of a heart attack. Unlike CK-MB, however, troponin levels tend to remain elevated for as long as 10 to 14 days after the initial attack. A rise in cardiac troponin has generally been held as the gold standard for identifying the occurrence of a heart attack because, unlike CK-MB, increases can be detected even in instances of minor heart damage.
Future Biomarkers
A number of potential biomarkers of heart disease are currently under investigation, but thus far, none have withstood the tests of time and reliability as well as troponin and CK-MB. Finding new markers that will alert a physician to an impending heart attack and potential sudden cardiac death earlier in the disease process is key to advancing the diagnosis, risk stratification and treatment of cardiac patients.
References
- "Circulation"; Heart Disease and Stroke Statistics 2010 Update; Donald Lloyd-Jones, M.D.; 2010
- "European Heart Journal"; A Consensus Document - Myocardial Infarction Redefined; Kristian Thygesen, Ph.D.; 2002
- "Coronary Artery Disease"; Cardiac Biomarkers - the old and the new; Vikas Singh, Ph.D.; 2010
