A pattern of disperse plaque microcalcifications identifies a subset of plaques with high inflammatory burden in patients with acute myocardial infarction

Aims: Inflammation plays a crucial role in plaque vulnerability. Calcifications can be detected by means of in vivo imaging techniques. The study purpose is to assess a potential association between tissue localization of calcifications and the inflammatory biomarkers, C-reactive protein (CRP), osteopontin and lipoprotein-associated phospholipase A2 (Lp-PLA2), in plaque tissue of patients with acute myocardial infarction (AMI).

Methods and results: Thrombectomy materials obtained from patients with electrocardiographically documented ST-segment elevation type of AMI (STEMI) were histologically screened for presence of thrombus, plaque tissues and calcifications. Size of calcifications was measured morphometrically, and their colocalization with the inflammatory biomarkers macrophages, CRP, osteopontin and Lp-PLA2 was assessed with immunostaining. A total of 171 samples containing plaque tissues were obtained from 562 thrombectomy procedures. Calcifications were observed in 67 (39%) plaque fragments, with diameters ranging from 4 to 170 μm. Plaque tissues with calcifications contained more frequently extracellular CRP and intracellular CRP in macrophages than those without calcifications (85%, 59% vs. 64%, 32%, P=0.012 and 0.005 respectively). Similar results were obtained with osteopontin immunostaining (98%, 76% vs. 56%, 40%; P<0.001 both). Furthermore, samples with calcifications were immunostained for CRP more intensely than those without calcifications (P=0.001). Finally, 96% of the plaque tissues stained positively for Lp-PLA2, but there was no association with presence of microcalcifications.

Conclusions: A pattern of disperse microcalcifications is positively associated with presence of the inflammatory biomarkers macrophages, CRP and osteopontin in thrombectomy materials of STEMI patients. Based on these findings, we speculate that such microcalcifications could have the potential to serve as a surrogate marker for plaques with high inflammatory burden.