Value of a short non-contrast CMR protocol in MINOCA

Abstract

Objectives: To evaluate the diagnostic performance of a short non-contrast CMR (ShtCMR) protocol relative to a matched standard comprehensive CMR (StdCMR) protocol in patients with myocardial infarction with non-obstructive coronary arteries (MINOCA).

Methods: This multicenter retrospective study included patients with a working diagnosis of MINOCA who underwent a StdCMR between January 2019 and December 2020. An expert and a non-expert reader performed a blinded reading with the ShtCMR (long-axis cine images, T2w-STIR, T1- and T2-mapping). A consensus reading of the StdCMR (reference standard) was performed at least 3 months after the ShtCMR reading session. Readers were asked to report the following: (1) diagnosis; (2) level of confidence in their diagnosis with the ShtCMR; (3) number of myocardial segments involved, and (4) functional parameters.

Results: A total of 179 patients were enrolled. The ShtCMR lasted 21 ± 9 min and the StdCMR 45 ± 11 min (p < 0.0001). ShtCMR allowed reaching the same diagnosis as StdCMR in 85% of patients when interpreted by expert readers (rising from 66% for poor confidence to 99% for good, p = 0.0001) and in 73% (p = 0.01) by non-expert ones (60% for poor vs 89% for good confidence, p = 0.0001). Overall, the ShtCMR overestimated the ejection fraction, underestimated cardiac volumes (p < 0.01), and underestimated the number of segments involved by pathology (p = 0.0008) when compared with the StdCMR.

Conclusion: The ShtCMR was found to be a debatable alternative to the StdCMR in patients with MINOCA. Nevertheless, when an experienced reader reaches a good or very good diagnostic confidence using the ShtCMR, the reader may choose to stop the examination, reducing the length of the CMR without affecting the patient's diagnosis.

Clinical relevance statement: A short non-contrast CMR protocol may be a viable alternative to standard protocols in selected CMR studies of patients with MINOCA, allowing for faster diagnosis while reducing time and resources and increasing the number of patients who can be scanned.

Key points: • The ShtCMR lasted 21 ± 9 min and the StdCMR 45 ± 11 min (p < 0.0001). • In 57% of patients with MINOCA, the experienced reader considers that contrast medium is probably not necessary for diagnosis without affecting the patient's diagnosis (99% of agreement rate between ShtCMR and StdCMR).

Keywords: Chest pain; MINOCA; Myocardial infarction; Myocarditis; Takotsubo cardiomyopathy.

Fig. 1

Enrollment flowchart

Fig. 2

A 67-year-old male patient was admitted to the emergency department with acute chest pain, elevated troponin (troponin T 21 ≥ 280 ng/mL, normal value < 34 ng/mL), and non-ST elevation on the electrocardiogram. In the absence of significant stenosis, invasive coronary angiography revealed 50% stenosis of the anterior descending artery, 50% stenosis of a secondary branch of the first diagonal branch, and irregularities of the right and circumflex coronary arteries. CMR was performed 3 days later. Images from the short protocol are shown on the left panel (A, 3ch-view diastolic frame; B, 3ch-view systolic frame; C and D, 3ch and short-axis short tau inversion recovery (STIR) image; E, T1 native map; and F, T2 map), and contrast-enhanced cine-SSFP (G–H), late gadolinium enhancement (LGE) sequences (I–K), and postcontrast T1 map (L) are shown on the right. On the short protocol, CMR systolic function was normal (EF: 56%), with focal areas of hypokinesis in the inferolateral segment (A, B). A focal area of subepicardial edema in the infero-lateral wall is associated with increased native T1 (E) and T2 (F) values. As a result, the expert reader’s short protocol diagnosis was myocarditis albeit with a score of 4 for the presence of hypokinesia. However, post-contrast cine-SSFP images revealed a slight transmural enhancement in the infero-lateral wall, as well as a small area of hypointensity, indicating microvascular obstruction. These findings were clearly visible on 3ch-view LGE (I), 2ch-view LGE (J, K), and post-contrast T1 mapping (L), demonstrating a transmural scar associated with the no-reflow phenomenon. As a result, acute myocardial infarction without obstructive coronary arteries was the correct diagnosis. The presence of subendocardial myocardial hemorrhage on STIR images was responsible for a misdiagnosis in the short non-contrast protocol

Fig. 3

ROC curves for the expert (blue line) and the non-expert reader (red line)

Fig. 4

Number of segments detected with short (vertical axis) and standard protocol (horizontal axis by the expert radiologist (blue dots) and the non-expert radiologist (empty red squares). The bisector corresponds to the ideal situation of parity in the number of segments detected with the two protocols