Heart size distorts biomarker levels

The blood level of troponin, a complex of the three proteins troponin C, troponin I and troponin T, increases when heart muscle is damaged. Because of this, it can be used as a biomarker to tell the difference between an episode of angina and a heart attack (acute myocardial infarction), and estimate its severity. However, according to a study in the Journal of the American College of Cardiology, the size of the heart affects the levels of the protein and this could have an impact on how patients are treated, and also on outcomes in clinical trials.

The level of troponin in the blood after a heart attack, along with the levels of creatine kinase, correlate with the size of the area of damaged muscle in the heart, and with the clinical outcome for the patient. These levels are therefore used to estimate the extent of the damage. In some patients, a thickening of the heart wall (either as a response to high blood pressure, heart disease or exercise), known as left ventricular hypertrophy, increases the levels of troponins, and this could potentially confuse any tests for troponin levels after a heart attack.

To confirm this, the researchers looked at the levels of creatine kinase and troponin I, and the levels of thickening of the heart wall in the records of acute myocardial infarction patients admitted between 2004 and 2009. They found that levels of troponin I were significantly higher in patients with left ventricular hypertrophy, compared with people with no hypertrophy.

The most accurate ways of measuring the area of heart damage are MRI (magnetic resonance imaging) or SPECT (single-photon emission computed tomography), but these methods aren't always available. According to the researchers, this is the first time that a different pattern of creatine kinase and troponin I increase has been shown in heart attack patients with left ventricular hypertrophy. As these levels are widely used in determining treatments for patients, and in measuring outcomes in clinical trials, and they seem to be overestimating the size of the area of damage heart muscle, it is important that this retrospective analysis is validated using prospective studies to avoid patients being over-treated. Further, it is important to ensure that clinical trial results truly reflect the activity of investigational drugs.

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