According to the fourth universal definition of myocardial infarction (UDMI), myocardial infarction with non-obstructive coronary artery disease (MINOCA) is define by classical criteria of myocardial infarction (MI), the absence of stenosis ≥50% in a major epicardial artery demonstrated on coronary angiography1 and no clinically overt specific cause for the acute presentation other than acute MI2. Since the knowledge of underlying pathophysiological mechanisms of MINOCA has developed significantly over the last decade, a key role is mainly occupied by the coronary microvascular disease (CMD)3. The coronary microcirculation has a fundamental role in the regulation of coronary blood flow in response to cardiac oxygen requirements. As a matter of fact, endothelial and smooth muscle cell dysfunction are commonly present in patients with MINOCA and CMD. In this setting, the functional assessment of the microcirculation has become one of the most interesting techniques in the evaluation of MINOCA, as CMD is highly prevalent and has significant unmet clinical need.
As shown in the Lindahl et al’s review, the invasive tests of coronary artery function should be used more often whenever possible in Cath labs, as they represent the true gold-standard4 in the evaluation of CMD. Both the use of guidewire-based measurement of coronary flow reserve (CFR) and intracoronary Acetylcholine testing for endothelium-dependent coronary microvascular spasm, should be used to assess CMD dysfunction5. Given the limitations of these techniques such as their time-consuming complexity and their invasiveness, we encourage the usage of positron emission tomography (PET) and cardiac magnetic resonance imaging (CMR) as discussed in this review. Through the measurements of myocardial blood flow and coronary flow reserve, PET is the reference standard for non-invasive assessment of CMD6. As shown in scientific Literature, CMR imaging and PET has a satisfactory concordance regarding vascular territories7. In our opinion, CT coronary angiography could be a future tool for evaluation of CMD, as myocardial first-pass dynamic CT allows for semi-quantitative assessment of Myocardial blood flow and Myocardial perfusion reserve8-9. However, there have been very few studies investigating its ability to detect CMD and it has not been validated. The main advantage of CT would be the ability to combine anatomical and functional imaging in one imaging examination, reducing the need for additional investigations.
There is no published randomised clinical trial on treatment of MINOCA, although there is one ongoing randomised clinical trial evaluating the usage of beta-blockers and ACE-inhibitor/angiotensin receptor blocker (MINOCA-BAT trial) 10. Nowadays, the medical treatment is based on low-dose aspirin4-14 and statins, which are associated with a reduction of MACE and mortality11-14, as well as ACE-I and ARB 12-14, while there is not any strong evidence that support the use of DAPT, beta-blockers or calcium channel blockers. As shown in the Lindahl et al’s review, the benefits of non-pharmacological treatments are even more uncertain; however, He et al showed the beneficial effect of moderate continuous training program on long term all-cause mortality. 13 Moreover, it’s fundamental to treat risk factors in any MINOCA patients. The deep and complete knowledge of pathophysiological pathways of MINOCA patients with CMD, could led to new and effective therapies that could help to cure this pathology.
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