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Cardiac MRI as Living Histology: Tissue‐Based Risk Stratification After STEMI

Year: 2026
Type: article
Abstract: In the Cardiac MRI reading room, we frequently encounter a disquieting pattern: a STEMI patient with “successful” primary PCI [1] with TIMI-3 flow, minimal residual stenosis, preserved LVEF—who nevertheless progresses to heart failure within months. This clinical scenario highlights the limitations of conventional angiographic and functional metrics. Angiographic assessment of epicardial flow, while essential for guiding acute therapy, does not capture the full spectrum of reperfusion injury. Cardiac magnetic resonance (MRI) provides a noninvasive window into the pathophysiological processes that angiography cannot capture [2]. Over the past decade, investigations have sought to quantify these “invisible” injuries—encompassing infarcted myocardium, salvageable myocardium, microvascular obstruction (MVO), intramyocardial hemorrhage (IMH), and the remote myocardium—to refine risk prediction by adding tissue-level information to established parameters. Cardiac MRI tissue characterization reveals tissue-level injury patterns strongly associated with long-term prognosis. Late gadolinium enhancement (LGE) identifies irreversible myocardial injury [2]. Infarct size assessed by Cardiac MRI within 1 month after primary PCI is strongly associated with 1-year mortality and heart failure hospitalization, with a > 7-fold increase in events between smallest and largest infarct quartiles [3]. While this establishes the necrotic core as a fundamental prognostic anchor, the extent of salvageable myocardium and the severity of microvascular damage provide critical additional dimensions for risk refinement. Complementing the assessment of irreversible injury, Cardiac MRI offers a critical prognostic dimension by evaluating the salvage potential of the myocardium at risk. This concept assesses the proportion of ischemic tissue that remains viable, providing a direct measure of therapeutic efficacy and tissue resilience. Techniques such as calculating the myocardial salvage index (MSI) from early and late gadolinium enhancement (EGE/LGE) images have validated this approach. In a recent study, this measurement proved to be a potent prognostic indicator: during a median follow-up of 3.2 years, every 10% increase in MSI was associated with a 32% reduction in the risk of major adverse cardiovascular events (MACE) (HR = 0.68, 95% CI: 0.53–0.86, p = 0.001), demonstrating that the capacity for myocardial salvage is an independent determinant of long-term outcomes [4]. However, even among patients with successful epicardial reperfusion, microvascular injury may persist, manifested as microvascular obstruction (MVO) and intramyocardial hemorrhage (IMH)—progressive stages of severe tissue damage now codified in the Canadian Cardiovascular Society classification [5]. While infarct size is strongly prognostic, MVO and IMH provide additional dimensions. Initially evaluated dichotomously, subsequent studies demonstrated that the extent and pattern of microvascular injury offer substantially greater prognostic information than presence alone: in a pooled analysis of 1688 STEMI patients, each 1% increase in MVO extent was associated with higher risks of death (HR 1.14, 95% CI 1.09–1.19) and heart failure hospitalization (HR 1.08, 95% CI 1.05–1.12), with MVO remaining predictive of mortality even after adjustment for infarct size [6]. More recently, the relative importance of MVO and IMH has been clarified by contemporary cohorts. In a multicenter study of 1109 patients, Lechner et al. [7] demonstrated that an IMH-positive phenotype independently predicted major adverse cardiovascular events (HR 3.88; 95% CI: 1.93–7.80), whereas isolated MVO without IMH conferred comparable risk to patients without microvascular injury. These findings establish IMH as a distinct, high-risk tissue phenotype—supporting the conceptual shift from binary to continuous microvascular injury assessment in prognostic modeling. A comprehensive risk stratification model must extend its view beyond the necrotic core to encompass the state of the entire myocardial substrate. The ischemic and reperfusion insult triggers a diffuse pathological response, altering the tissue composition of remote and noninfarcted myocardium. Quantitative mapping techniques have revealed abnormal tissue characteristics in noninfarcted myocardium that are associated with adverse clinical outcomes, independent of infarct severity [8, 9]. These observations indicate that the myocardium outside the infarct zone contributes to post-STEMI prognosis. At the same time, the biological interpretation and clinical application of remote myocardial abnormalities remain areas of active investigation. Elevated mapping values may reflect transient edema, systemic inflammatory activation, or early diffuse fibrosis, and their temporal evolution is incompletely understood. Advanced Cardiac MRI-based approaches, including quantitative tissue mapping and extracellular volume assessment, have therefore been proposed primarily as tools for prognostic assessment, monitoring ventricular remodeling, and defining surrogate endpoints in clinical trials [10]. Despite the consistency of these associations, important limitations merit consideration. Quantification of MVO and IMH is sensitive to imaging timing, sequence parameters, and threshold definitions; detection of IMH by T2* mapping may be influenced by susceptibility artifacts and inter-vendor variability. For remote myocardial assessment, lack of standardized thresholds, inter-platform variability, and limited external validation similarly constrain broader clinical implementation. Consequently, current evidence most strongly supports the use of Cardiac MRI tissue phenotyping for risk stratification and trial enrichment, rather than for directing specific therapeutic interventions in individual patients. Taken together, accumulating evidence supports a shift from purely functional assessment toward tissue-informed risk stratification after STEMI. Cardiac MRI-derived phenotypes—particularly the extent and pattern of microvascular injury and the condition of the noninfarcted myocardium—provide biologically plausible and prognostically meaningful insights beyond conventional markers. At present, their greatest clinical value lies in identifying high-risk patient subsets, informing post-infarction surveillance strategies, and enriching clinical trials targeting inflammation, microvascular injury, or adverse ventricular remodeling. Future progress will depend on methodological standardization, prospective validation, and demonstration that tissue-based stratification can meaningfully influence patient management and outcomes. From my perspective, the “living histology” vision is now within reach—one that promises to transform risk stratification after STEMI, provided we advance with the scientific rigor that clinical translation demands. The authors declare no conflicts of interest.
DOI: 10.1002/jmri.70317
Language: English
Field: Medicine
Open Access status: green
OpenAlex ID: W7140165840
FWCI:
Cites: 7
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