Introduction: CMR-based staging of myocardial infarction (MI) with or without contrast agents relies on the resolution of edema in the chronic phase, which is determined on the basis of T2-based imaging. However, whether T2 CMR is sufficient for staging all MI types has not been investigated.
Hypothesis: Prolonged inflammation associated with chronic iron deposits following hemorrhagic MIs promote incomplete resolution of edema in the chronic phase which limit the capability of T2 imaging to stage hemorrhagic MIs.
Material and Methods: Hemorrhagic (n=15) and non-hemorrhagic (n=9) MIs were created in dogs. Multi-parametric non-contrast mapping (T1, T2 and T2*) and late-gadolinium enhancement (LGE) were performed in the acute and chronic phases of MI. T1, T2 and T2* values of the hemorrhagic, infarcted areas surrounding the hemorrhage (peri-hemorrhagic), non-hemorrhagic and un-infarcted/remote territories were measured. The changes in T1, T2 and T2* between the MI territories from remote myocardium were compared with respect to infarct age and field strength. Histopathology and immunohistochemistry were performed to gain insight into CMR findings.
Results: Native T1, T2 and T2* of MI territories and their relative change from remote myocardium showed significant dependence on infarct age and type. Specifically, in the chronic phase of MI, T2 of non-hemorrhagic MI territories resolved to remote levels (% difference in T2=0.0±3.2%); however, T2 of peri-hemorrhagic zones remained elevated relative to remote territories (% difference in T2 =8.6±5.1%) and was associated with ongoing active inflammation.
Conclusion: Combined interpretation of T2 CMR with contrast-enhanced (LGE) or non-contrast-enhanced approaches can stage non-hemorrhagic MIs. However, given the persistent inflammation in the chronic phase of hemorrhagic MIs, both T2 and T2* CMR are required for accurate staging.