Summary of the original article:
The aim of this study was to assess the diagnostic yield of cardiac magnetic resonance (CMR) including high-resolution (HR) late gadolinium enhancement (LGE) imaging in patients with myocardial infarction with nonobstructed coronary arteries (MINOCA). A well selected population of patients with MINOCA (n=172) underwent conventional CMR including LGE imaging using usual breath-held methods. In the same patients, free-breathing HR LGE imaging was systematically added to the protocol in patients with inconclusive findings after conventional CMR and was optional otherwise, depending on the clinical work flow.
The conventional CMR returned a definite diagnosis in 86 patients (50%): infarction in 39 (23%), myocarditis in 32 (19%), takotsubo cardiomyopathy in 13 (8%), and other diagnoses in 2 (1%). In the remaining 86 patients (50%), results of CMR were inconclusive: negative in 54 (31%) and consistent with multiple diagnoses in 32 (19%). HR LGE imaging led to changes in final diagnosis in 45 patients (26%) and to a lower rate of inconclusive final diagnosis (29%). HR LGE imaging was particularly useful when the results of transthoracic echocardiography, ventriculography, and conventional CMR were negative, with a 48% rate of modified diagnosis in this subpopulation. The results show that the addition of HR LGE imaging has high diagnostic value in patients with MINOCA and inconclusive findings on conventional CMR.
Comments to the Article:
MINOCA represents a major diagnostic and therapeutic challenge in everyday practice. Among the non-invasive imaging modalities, CMR plays a pivotal role, being able to provide the definitive aetiology of MINOCA in a significant number of patients. LGE imaging is the cornerstone technique for differential diagnosis, indicating the disease by localizing the fibrous scar in different strata of the myocardium (i.e. subendocardial, mid-myocardial, subepicardial or transmural). Differentiating among various aetiologies is crucial, as it results in different treatment strategies and prognostic.
However, the CMR imaging in patients with MINOCA is not always straightforward as many of the examinations may be negative or inconclusive. The negative examinations (i.e. normal CMR despite definite myocardial injury on clinical, electrical and biological parameters) may be explained by the fact that the myocardial necrosis in MINOCA is usually of small size and can be missed by conventional LGE. On the other hand, the inconclusive CMR examinations may result from the incapacity of discerning the subendocardial or subepicardial origin of transmural injuries; practically, this will preclude the discrimination between myocardial infarction and myocarditis.
These setbacks may be overcome by employing a HR LGE technique as it was demonstrated in this study. The spatial resolution is improved, with voxel size decreased by 4-fold compared with conventional breath-held methods (from 15.1 to 3.9 mm3). This sequence is free-breathing, may be performed after conventional LGE imaging, and the acquisition time is of 10 minutes. In other words, the HR sequence does not replace the conventional technique, but it adds value to it with minimal discomfort for the patient.
Overall, the addition of HR LGE imaging led to a modification of the final diagnosis, either because of improved detection of myocardial injuries or because of improved assessment of LGE transmural location. The patients that benefit the most from the HR LGE were those with negative findings on transthoracic echocardiography, ventriculography, and cine magnetic resonance, and the pattern of hyperenhancement on conventional LGE imaging was more frequently uncertain. Especially in these categories of patients, HR LGE may be added in the clinical CMR workflow for increased diagnostic accuracy. The studied technique is already available on many scanners worldwide and thus may be included in daily practice.
As authors mention, the CMR protocol in this study did not include quantitative techniques such as T1 and T2 mapping. The potential role of these techniques for increasing the CMR diagnostic accuracy in MINOCA is a hypothesis which deserves attention for the future studies. Nevertheless, the results of this paper make an important step forward toward a better characterization of this difficult population of patients.