A small study of non-elite marathon runners has cast new light on cardiac troponins, with implications for diagnosing non-ST elevation myocardial infarction (MI).

International recommendations of raised troponin T value as an indicator of acute MI are not definitive, it seems, if the subject has engaged in prolonged exercise.

Cardiac troponin T (cTnT) values in blood rose to >0.01 μg/l from below 0.01 μg/l—the detection limit of the assay—among more than three quarters of 72 non-elite runners in the London marathon. In almost 60% of them values were >0.03 μg/l; in 36% >0.05 μg/l—the current recommended cut off for acute MI—and in 11% >0.1 μg/ml. Ischaemia was not evident on electrocardiography (ECG), but after the race the ratio of early to late left ventricular filling (E:A) dropped significantly. Raised cTnT was unaffected by age, race time, or changes in ventricular filling. Such results, when combined with dyspnoea, chest tightness, and abnormal ECG findings sometimes seen in highly trained athletes, may confuse the picture further, so caution is advised.

Data came from 2002/3 London marathons, from reputedly healthy runners with no cardiovascular disease. Each provided samples for cTnT assay and had 12 lead ECG and echocardiography 24 hours before the race and within 30 minutes after finishing.

Cardiac troponins have become linchpins of diagnosis of acute MI. Much less is known about their behaviour in the ever growing numbers competing in city marathons than in highly trained endurance athletes, and this merits further investigation, along with long term effects and changed diastolic function.