The evolving role of cardiac imaging in patients with myocardial infarction and non-obstructive coronary arteries
Introduction
Myocardial infarction (MI) with non-obstructive coronary arteries (MINOCA) represents about 6%–8% of all patients presenting with acute MI referred for coronary angiography.1,2 MINOCA is defined by the clinical evidence of MI with normal or near normal coronary arteries on angiography (stenosis severity < 50% in major epicardial coronary arteries), in absence of obvious systemic causes of a Type 2 MI (i.e. sepsis, myocarditis, pulmonary embolism).1 Despite MINOCA has been historically considered a benign condition, several studies have shown that MINOCA patients have a guarded prognosis. Indeed, MINOCA patients have a disconcerting 1-year mortality/re-infarction rate, which is less than those who have MI with obstructive coronary artery disease (MI-CAD) but much worse than those without MI.3, 4, 5, 6 Furthermore, approximately 25% of patients with MINOCA experience angina at follow-up similarly to those patients with MI-CAD, with a subsequent significant impact on quality of life, healthcare and socioeconomic related costs.3
Notably, the causes of MINOCA are multiple, including coronary plaque disruption, epicardial or microvascular spasm, coronary thromboembolism or spontaneous coronary artery dissection (SCAD) not angiographically obstructive.1,7 Therefore, MINOCA should not be considered as a single entity but a heterogeneous working diagnosis that requires a comprehensive evaluation to elucidate the underlying cause. Multimodality assessment aiming at uncovering the aetiology of MINOCA should be pursued. For this reason, advanced imaging techniques beyond coronary angiography and transthoracic echocardiography, the “gatekeeper” imaging exams performed in every MI patient, need to be considered in MINOCA patients for risks stratification as well as for a tailored therapeutic approach targeted to the underlying mechanism of disease.8 In particular, intracoronary imaging techniques, such as optical coherence tomography (OCT) and intravascular ultrasound (IVUS), and cardiac magnetic resonance (CMR) have been shown to be able to give important insights into the comprehension of the mechanism underlying MINOCA.1
In this review article, we analyse the role of cardiac imaging techniques in MINOCA, highlighting how this information guides patient management.
Section snippets
Coronary angiography and left ventriculography
Coronary angiography represents a “gatekeeper” imaging exam in MINOCA patients, enabling to exclude significant epicardial coronary artery stenoses or recent thrombotic occlusive or sub-occlusive lesions. The angiographic criteria for ‘non-obstructive coronary arteries’ detailed in the MINOCA definition utilizes the conventional cut-off of <50% stenosis. This threshold is somewhat arbitrary and suffers from several limitations, as the angiographic severity of a lesion can change as a result of
Coronary computed tomography angiography (CCTA)
CCTA has been demonstrated to be effective in ruling-out significant CAD in patients with chronic coronary syndromes,11 and a possible role of CCTA in intermediate-to-high risk patients presenting with acute coronary syndrome (ACS)12 has been suggested, although the recent RAPID-CTCA trial failed to demonstrate a benefit of CCTA in this subset pf patients.13 CCTA exhibits several strengths and limitations. It allows the detection and characterization of coronary atherosclerotic plaques with
Intracoronary imaging
Intracoronary imaging by IVUS or OCT is a cornerstone for confirmation of coronary artery pathology as the underlying aetiology in patients with the working diagnosis of MINOCA and has been suggested previously as part of a diagnostic algorithm.1,2 Intravascular imaging can identify thrombus, coronary dissection as well as a culprit lesion (i.e. plaque rupture, erosion, or calcified nodules; Fig. 1, Fig. 2).17 Several groups have investigated the role of IVUS and OCT in identifying the
Echocardiography
Echocardiography may play a pivotal role in the evaluation of multifaceted phenotypes of MINOCA. Indeed, the echocardiographic hallmark of myocardial infarction remains RWMA in the acute phase, even though transthoracic echocardiography (TTE) is unable to distinguish between MI with obstructive CAD and MINOCA. However, the pattern and distribution of RWMA may in part help physicians to understand the pathogenic mechanism underlying MINOCA. In particular, an epicardial pattern may suggest the
CMR
In the last ten years, CMR has emerged as a key diagnostic test in patients with a working diagnosis of MINOCA23,38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 (Fig. 5, Table 2). CMR provides an accurate assessment of cardiac structure and function due to its high tissue contrast, high resolution and unique non-invasive tissue characterization.51 Long- and short-axis cine images allow the visual and quantitative assessment of regional and global left and right ventricular systolic function;
Cardiac imaging techniques in clinical practise: what, how and when?
The implementation of a comprehensive approach with multimodality cardiac imaging is of utmost importance in the management of patients presenting with MINOCA (Fig. 6). Different cardiac imaging techniques are currently available, and the comprehensions of their strengths and limitations are required for their effective use in clinical practice (Table 3). Moreover, pathogenic mechanisms that may lead to MINOCA are multiple and clarifying the specific mechanism of disease is crucial to achieve
Conclusions
MINOCA is a clinical entity that gained a growing recognition in recent years. Multiple pathogenic mechanisms may lead to MINOCA and the comprehension of the specific underlying cause is of crucial importance in order to obtain a final diagnosis and establish an effective management. In this context, a multimodality cardiac imaging approach, combining different techniques, has been shown to be essential for the identification of the underlying process in the large majority of patients
Funding
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Declaration of Competing Interest
None.
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