Elevated troponin levels are a frequent finding in patients presenting with atrial fibrillation or atrial flutter (AF) to the emergency department but are seldom caused by myocardial infarction (MI). The current high‐sensitivity cTnT (cardiac troponin T) assay measures both the intact and highly fragmented cTnT forms (total cTnT) and detects cTnT elevations in conditions causing myocardial injury or MI without distinction between the 2.

The SuperTROPO (Better Diagnostics of Myocardial Infarction With a Test for Special Forms of Troponin) study included 521 consecutive patients with AF only and 188 patients with MI only (139 Type 1 MI), all with a total cTnT value ≥14 ng/L at emergency department admission. Intact and long forms of cTnT (long cTnT) were analyzed from the first plasma samples using a novel immunoassay. The diagnostic performance of long cTnT and total cTnT assays was compared in these cases with elevated total cTnT.

Long cTnT was superior to total cTnT in discriminating troponin elevations in patients with MI from those in patients with AF (area under the curve for type 1 MI: 0.879 versus 0.783; for any MI: 0.864 versus 0.779; both P<0.001) when measured from the first blood sample without a significant effect of sex, age, estimated glomerular filtration rate, or total cTnT <200 ng/L. The difference in long cTnT levels was most notable in patients presenting within 12 hours of symptom onset.

The long cTnT immunoassay shows that the troponin release in AF is composed mainly of smaller troponin fragments. This novel test holds promise that measuring long cTnT forms could help to separate troponin elevations caused by AF from those of acute Type 1 MI from a single sample with better accuracy than the commercial high‐sensitivity cTnT test.