Predicting Patients With Troponin Positive Chest Pain and Unobstructed Coronary Arteries With Electrocardiogram, Troponin Kinetics and GRACE Score.

BACKGROUND: Troponin positive chest-pain with unobstructed coronary arteries (TPCP-UCA), occurs in 6% of cases of patients presenting with acute coronary syndrome (ACS). Whilst TPCP-UCA patients are known to be younger with less cardiovascular risk factors when compared to obstructive coronary disease (MICAD), no validated methods exist to reliably delineate these two conditions prior to coronary angiography.

METHODS: We analysed 142 patients with MICAD and 127 patients with TPCP-UCA from 2015 to 2019. Several key predetermined clinical, biochemical and electrocardiograph (ECG) parameters, as well as Global Registry of Acute Coronary Events (GRACE) score, were collected for all patients. All TPCP-UCA patients underwent cardiac magnetic resonance imaging (cMRI).

RESULTS: Patients with TPCP-UCA were younger than MICAD (44 vs 68 yrs, p<0.01), and with less cardiac risk factors of hypertension (31% vs 68%, p<0.01), hypercholesterolaemia (23% vs 56%, p<0.01), diabetes (11% vs 45%, p<0.01), prior ischaemic heart disease (8% vs 42%, p<0.01) and smoking history (29% vs 50%, p<0.01). Peak troponin (MICAD 2,084.5 ng/L vs TPCP-UCA 847.0 ng/L, p=0.02), serial-to-initial troponin ratio (MICAD 13.5 vs TPCP-UCA 5.1, p<0.01), and peak-to-initial troponin ratio (MICAD 69.6 vs TPCP-UCA 14.0, p<0.01) were all higher in the MICAD group. GRACE scores were significantly different across the two cohorts (TPCP UCA 74 vs MICAD 106, p<0.01), with a receiver operator characteristic (ROC) curve statistic of 0.794 (95% CI 0.739-0.850). On ECG analysis, MICAD had greater prevalence and sum of ST depression (40% vs 19% p<0.01; 1.6 mm vs 0.44 mm, p<0.01) and T wave inversion (37% vs 17%, p<0.01), whilst TPCP-UCA had greater presence of PR depression (20% vs 3% p<0.01), and longer repolarisation (T wave peak to end 89 ms vs 83 ms, p=0.04; T wave peak to end/corrected QT 0.208 ms vs 0.193 ms, p=0.03). All TPCP-UCA patients underwent cMRI. Aetiology was found in 82% of cases, with the leading diagnosis being myocarditis (58%), followed by infarction (8%), whilst 18% had a normal cMRI.

CONCLUSIONS: TPCP-UCA is an important differential for patients presenting with ACS, and has several key demographic, biochemical and electrocardiographic differences. The present findings are hypothesis generating, thus prospective studies are required to determine and validate potential clinical utility.