Myocardial injury is defined by an elevation of cardiac troponin values above the 99th percentile upper reference limit. It is considered a prerequisite for the diagnosis of myocardial infarction but also an entity in itself and can arise from non-ischemic or non-cardiac conditions 1,2.
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Terminology
The term 'myocardial injury' might be used in the setting of direct cardiac damage such as cardiac contusion but it might also occur in diverse other clinical scenarios such as myocardial infarction, myocardial inflammation, sepsis, and iatrogenic injury 1-3.
Clinical presentation
A myocardial injury might present with cardiac symptoms like chest pain and/or dyspnea. Depending on the etiology and extent there will be characteristic changes on the electrocardiogram. It can be reliably detected biochemically with serologic markers and is defined by an elevation of cardiac troponin values above the 99th percentile upper reference limit 1. The creatine kinase MB isoform is another serologic marker 4,5.
Pathology
Presumed mechanisms of myocardial injury include the following 4:
direct cardiac damage with cardiomyocyte injury
myocardial strain as a result of excessive wall stress
myocardial ischemia due to myocardial oxygen supply and demand mismatch
Myocardial injury might be irreversible and is often associated with myocardial necrosis or apoptosis 4. However, the concept of troponin release in the setting of reversible injury such as extreme exercise has been suggested 4.
Etiology
Myocardial injury can have the following causes 1-4, 6,7:
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primary myocardial ischemia / myocardial infarction
atherosclerotic plaque rupture with thrombosis
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mismatch in myocardial oxygen supply and demand
coronary embolism / microembolism / dissection
sustained bradyarrhythmias/tachyarrhythmias
hypovolemic shock
respiratory failure / severe anemia
severe hypertension
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non-ischemic myocardial injury
cardiomyopathies (e.g. takotsubo cardiomyopathy)
iatrogenic (revascularization, cardiac surgery, ablation, pacing, cardioversion, defibrillation)
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multifactorial and systemic causes
sepsis / critical illness
cardiotoxicity (drugs)
infiltrative disease (cardiac amyloidosis, cardiac sarcoidosis)
acute or chronic renal disease
Radiographic features
Due to the excellent sensitivity and fast availability of serologic biomarkers, imaging methods have no real role in the detection of myocardial necrosis but the localization and the search for the etiology for non-ischemic or indeterminate cases.
MRI
Myocardial injury is associated with myocardial necrosis and myocardial edema. Therefore it can be depicted on MRI with cardiac tissue characterization techniques including T2-weighted imaging/STIR, late gadolinium enhancement and myocardial mapping techniques 2.
Signal characteristics
T2/STIR: hyperintensity
T2-mapping: increased T2 [ms]
T1-mapping: increased T1 [ms]
ECV: increased
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IRGRE/PSIR:
typically subendocardial to transmural late gadolinium enhancement in case of an acute myocardial infarction
no enhancement in the no-reflow zone in case of microvascular obstruction
focal subepicardial or patchy mid-wall enhancement in the setting of myocardial inflammation or direct cardiac damage such as cardiac contusion
Radiology report
The radiological report should include a description and localization of the following:
late gadolinium enhancement and no-reflow zones