High levels of troponin, a sign of acute stress to the heart, in the blood reveal whether someone recently experienced a heart attack. Advances in testing have made it possible to detect much lower levels of troponin — but still elevated above zero. For example, elevated troponin can be detected after strenuous exercise, even in healthy young athletes.
With that exercise-induced response in mind, Emory Clinical Cardiovascular Research Institute investigators have been studying whether high-sensitivity troponin measurements might be used to replace cardiac stress tests. These procedures are expensive and sometimes involve nuclear imaging, which exposes patients to radiation.
A new paper in American Journal of Cardiology shows how elevated high-sensitivity troponin levels in response to exercise on a treadmill can predict future outcomes in patients with coronary artery disease — better than stress tests with imaging.
The data came from a large Emory study of mental stress-induced ischemia, with ischemia meaning a restriction of blood flow in the heart. In this group, ECCRI director Arshed Quyyumi and colleagues had already shown that elevated high-sensitivity troponin at rest — a sign of chronic, rather than acute cardiac stress — can be used by itself as a risk predictor.
Quyyumi comments that the Emory study was done in people with known coronary artery disease, but most people have stress tests when their CAD status is unknown. If they do, high-sensitivity troponin (with or without exercise) could be a good triage test, he says.
High-sensitivity troponin assays are already widely used in Europe, notes the study’s first author, ECCRI fellow Bruno Lima.
“We and others showed previously that very low resting levels were very useful for excluding ischemic disease, but a subset of patients might have chronically elevated high-sensitivity troponin levels without ischemia,” Lima says. “Here, we showed that measuring troponins before and after provocative testing can help further discriminate these patients.”
The new analysis included 365 people with coronary artery disease. They were followed for three years for MACE (major adverse cardiac events): in this group, 11 heart attacks, 26 hospitalizations and 3 deaths occurred.
The combination of higher than average baseline troponin, plus exercise-induced augmentation by 20 percent or more, meant someone had a 4.6-fold higher risk of MACE. Measuring troponin before and after exercise added discriminatory power, beyond what researchers would get from traditional risk factors such as age, BMI, cholesterol, hypertension etc. In contrast, cardiac imaging did not improve risk prediction, the researchers found.
The authors suggest that resting and post-exercise high-sensitivity troponin measurements could be used to triage CAD patients before more invasive tests or expensive imaging. It also could identify patients who should receive more intensive prevention strategies with cholesterol-lowering agents beyond statins.
The Emory researchers are not alone in their interest in high-sensitivity troponin; two recent TCT-MD articles explore how adding it to other cardiovascular risk factors can help reclassify heart disease patients into more appropriate categories, or that troponin measurements could become part of initial evaluation of patients with intermittent chest pain, but who are not having an acute heart attack.