Native T1-mapping is useful in detecting subtle, focal disease with sensitivity of 90%, specificity of 91%, and accuracy of 91%, which is superior to T2-weighted MRI and LGE techniques [115]. The updated Lake Louise criteria requires at least one T2-based criterion (global/regional elevation of myocardial T2 or increased T2 signal of myocardium) with at least one T1-based criterion (elevated myocardial T1, elevated ECV, or LGE) for diagnosing acute myocarditis with high specificity [139]. Having only one criterion will still support a diagnosis of acute myocarditis but has lower specificity than with two criteria [139]. Different LGE patterns have been reported based on the viral etiology, with parvovirus B19 showing subepicardial or mid myocardial distribution LGE in the LV inferolateral wall and recovering Nonischemic Myocardial Disease without serious damage, whereas HHV-6 infection involves the LV basilar septum in linear mid myocardial LGE pattern, often rapidly progressing to HF [140]. Myocardial edema without fibrosis indicates good potential for recovery, whereas a high amount of EGE and LGE indicate adverse prognosis, particularly if LGE is persistent at 4 weeks after onset [2]. LGE may not correlate with the clinical and lab markers, indicating it is an independent risk assessment tool [141]. A normal MRI in patients with suspected myocarditis indicates a good long-term prognosis, independent of clinical and other findings [142]. In Chagas disease, patients are typically not imaged in the acute phase, but the indeterminate phase may show changes including RWMA and diastolic dysfunction without overt systolic dysfunction. The chronic phase shows global systolic dysfunction, apical aneurysm, and thrombus. LGE is seen in up to 72% of patients [135] and in 100% of those with arrhythmias, more common in apical and basal inferolateral segments.
Nonischemic Myocardial Disease with Clinical Manifestations Ischemic Cardiomyopathy Already Excluded . Native T1-mapping is useful in detecting subtle, focal disease with sensitivity of 90%, specificity of 91%, and accuracy of 91%, which is superior to T2-weighted MRI and LGE techniques [115]. The updated Lake Louise criteria requires at least one T2-based criterion (global/regional elevation of myocardial T2 or increased T2 signal of myocardium) with at least one T1-based criterion (elevated myocardial T1, elevated ECV, or LGE) for diagnosing acute myocarditis with high specificity [139]. Having only one criterion will still support a diagnosis of acute myocarditis but has lower specificity than with two criteria [139]. Different LGE patterns have been reported based on the viral etiology, with parvovirus B19 showing subepicardial or mid myocardial distribution LGE in the LV inferolateral wall and recovering Nonischemic Myocardial Disease without serious damage, whereas HHV-6 infection involves the LV basilar septum in linear mid myocardial LGE pattern, often rapidly progressing to HF [140]. Myocardial edema without fibrosis indicates good potential for recovery, whereas a high amount of EGE and LGE indicate adverse prognosis, particularly if LGE is persistent at 4 weeks after onset [2]. LGE may not correlate with the clinical and lab markers, indicating it is an independent risk assessment tool [141]. A normal MRI in patients with suspected myocarditis indicates a good long-term prognosis, independent of clinical and other findings [142]. In Chagas disease, patients are typically not imaged in the acute phase, but the indeterminate phase may show changes including RWMA and diastolic dysfunction without overt systolic dysfunction. The chronic phase shows global systolic dysfunction, apical aneurysm, and thrombus. LGE is seen in up to 72% of patients [135] and in 100% of those with arrhythmias, more common in apical and basal inferolateral segments.