Non-invasive and invasive diagnostic modalities for the assessment of coronary vasomotor dysfunction in ANOCA patients

In patients who have angina with non-obstructive coronary artery disease (ANOCA), invasive coronary function testing (ICFT) is the gold standard to comprehensively diagnose coronary dysfunction. Coronary dysfunction is divided into the endotypes coronary vasospasm, coronary endothelial dysfunction, and coronary microvascular dysfunction (i.e., an abnormal reduced coronary flow reserve [CFR] and/or enhanced microvascular resistance [MR]). However, because of the inherently invasive nature of ICFT, it is important to investigate non-invasive approaches for the diagnosis of coronary dysfunction. Several non-invasive modalities have been proposed as alternative techniques to measure different endotypes of coronary dysfunction. This is promising, given their higher availability and easier applicability. As such, an important clinical question is whether these non-invasive methods are equivalent to invasive tests. In this review, we provide an overview of the invasive and non-invasive diagnostic modalities available to assess coronary dysfunction. Our findings indicate that only CFR can be reliably measured non-invasively, using positron emission tomography (PET), transthoracic Doppler echocardiography (TTDE), and possibly stress cardiac magnetic resonance (CMR) imaging, although the latter has shown conflicting results. Reliable non-invasive techniques to measure coronary vasospasm, coronary endothelial dysfunction, or MR are scarce. Since most patients suffer from more than one coronary dysfunction entity, the added value of non-invasive techniques is still limited. To date, ICFT is the only method capable of investigating all endotypes of coronary dysfunction. Studies investigating the performance of non-invasive modalities for the diagnosis of all components of coronary dysfunction in ANOCA patients are warranted.