BackgroundLipoprotein(a) (Lp[a]) is a risk factor for cardiovascular disease. The burden of thrombus in ST-segment elevation myocardial infarction (STEMI) has implications on treatment and outcomes. However, the association between Lp(a) and atherothrombosis in STEMI remains unclear.ObjectivesThe aim of the study was to determine the association between Lp(a) and culprit artery thrombus burden in younger patients with STEMI.MethodsThis was a single-center study of 83 patients aged <65 years with STEMI between 2016–2018 who underwent percutaneous coronary intervention and measurement of Lp(a); those receiving thrombolytic therapy were excluded. Thrombus burden in the culprit artery was determined angiographically using the Thrombolysis In Myocardial Infarction score and classified as absent-to-small, moderate, or large. Elevated Lp(a) was defined as plasma mass concentration >30 mg/dL. Multivariate analysis was performed adjusting for cardiovascular risk factors.ResultsThe mean age was 48.0 ± 8.4 years, and 78.3% were male. Thirteen (16%), 9 (11%), and 61 (73%) patients had small, moderate, or large thrombus burden, respectively, and 34 (41%) had elevated Lp(a). Elevated Lp(a) was associated with greater thrombus burden compared to normal Lp(a) (large burden 85% vs. 65%;p= 0.024). Elevated Lp(a) was associated with moderate or large thrombus in univariate (OR 10.70 [95% CI 1.32–86.82];p= 0.026) and multivariate analysis (OR 10.33 [95% CI 1.19–89.52];p= 0.034). Lp(a) was not associated with culprit artery or stenosis location according to culprit artery.ConclusionsElevated Lp(a) is associated with greater thrombus burden in younger patients with STEMI. The finding of this observational study accords with the thrombotic and anti-fibrinolytic properties of Lp(a). A causal relationship requires verification.