# Exploratory Characterization of Coronary Thrombi by Integrated Mass Spectrometry and Elemental Imaging in Acute Coronary Syndrome

## TL;DR

This study uses advanced imaging techniques to explore the molecular and elemental makeup of coronary blood clots in heart attack patients, revealing differences based on clot type.

## Contribution

The paper introduces an exploratory multimodal approach combining MALDI-MSI and SEM/EDS to characterize thrombus heterogeneity in acute coronary syndrome.

## Key findings

- Cholesterol distribution varied across thrombus types and was influenced by statin exposure in plaque rupture cases.
- Phosphatidylcholine and sphingomyelin showed distinct spatial patterns, while heme b was abundant in erythrocyte-rich thrombi.
- SEM/EDS confirmed calcium accumulation in calcified nodules and structural differences matching IVUS classifications.

## Abstract

Background

The molecular composition of coronary thrombi varies according to the underlying pathophysiology of acute coronary syndrome (ACS); however, exploratory, spatially resolved analyses integrating molecular and elemental information across intravascular ultrasound (IVUS)-defined thrombus types remain limited.

Objectives

This study aims to exploratorily and descriptively characterize, as a proof-of-concept, thrombus-type-specific molecular and elemental features by combining matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS), and to assess associations with clinical background factors, including statin exposure as a contextual modifier rather than an intervention.

Methods

A total of 11 coronary thrombi aspirated during percutaneous coronary intervention (PCI) for ACS were collected consecutively, and seven representative samples were analyzed. Thrombi were classified into five IVUS-based categories: plaque rupture (PR), lotus-root-like organized thrombus (LR), calcified nodule (CN), thromboembolism (TE), and plaque erosion (E). Serial cryosections were subjected to MALDI-MSI in the positive-ion mode (m/z 120-1000) to visualize representative molecules, including cholesterol, phosphatidylcholine (PC), sphingomyelin (SM), flavin mononucleotide (FMN), and heme b. Adjacent sections were evaluated by SEM/EDS to assess thrombus structure and elemental distribution.

Results

Cholesterol was detected in all thrombus types. Within PR lesions, higher cholesterol signal intensities were observed in statin-naïve cases compared with statin-treated cases, representing an observed association rather than evidence of direct therapeutic modulation. LR lesions exhibited relatively low cholesterol signals despite statin-naïve status, consistent with characteristics of more organized thrombi. In contrast, TE and E lesions showed abundant and diffusely distributed cholesterol irrespective of statin exposure. PC and SM displayed heterogeneous distribution patterns across thrombus types, with PC prominently detected in LR lesions and variable SM signals across clinical backgrounds. Heme b was strongly detected in PR and TE, in line with erythrocyte-rich thrombi, whereas LR and CN showed low levels compatible with platelet-dominant compositions. FMN showed heterogeneous patterns across thrombus types, which should be regarded as hypothesis-generating. SEM/EDS revealed pathology-consistent findings, including prominent calcium accumulation in CN and distinct structural architectures corresponding to IVUS-based classifications. Exploratory principal component analysis of MSI data suggested overall patterns of variability across thrombus types, without inferential or classificatory interpretation.

Conclusions

Integrated molecular and elemental imaging revealed heterogeneous, thrombus-type-specific features across intravascular ultrasound-defined acute coronary syndrome phenotypes, representing descriptive, spatially resolved associations rather than causal relationships. This exploratory, hypothesis-generating multimodal approach using MALDI-MSI and SEM/EDS provides an initial framework for characterizing coronary thrombi in situ, with further validation in larger, prospectively enrolled cohorts required to determine potential clinical relevance.