Table 1

Clinical classification of coronary microvascular dysfunction

Coronary microvascular dysfunction in the absence of obstructive coronary artery disease (CAD) and myocardial diseases	This type represents the functional counterpart of traditional coronary risk factors (smoking, hypertension, hyperlipidaemia, and diabetes and insulin resistant states). It can be identified by non-invasive assessment of coronary flow reserve (CFR). This type is at least partly reversible, and CFR can also be used as a surrogate end point to assess efficacy of treatments aimed at reducing the burden of risk factors.
Coronary microvascular dysfunction in the presence of myocardial diseases	This type is sustained in most instances by adverse remodelling of intramural coronary arterioles. It can be identified by invasive or non-invasive assessment of CFR and may be severe enough to cause myocardial ischaemia. It has independent prognostic value. It remains unclear whether medical treatment may reverse some cases. It is found with primary (genetic) cardiomyopathies (eg, dilated and hypertrophic) and secondary cardiomyopathies (eg, hypertensive and valvular).
Coronary microvascular dysfunction in the presence of obstructive CAD	This type may occur in the context of either stable CAD or acute coronary syndromes with or without ST segment elevation and can be sustained by numerous factors. It is more difficult to identify than the first two types and may be identified through the use of an integrated approach that takes into account the clinical context with the use of a combination of invasive and non-invasive techniques. There is some early evidence that specific interventions might prevent it or limit the resultant ischaemia.
Iatrogenic coronary microvascular dysfunction	This type occurs after coronary recanalisation and seems to be caused primarily by vasoconstriction or distal embolisation. It can be identified with the use of either invasive or non-invasive means on the basis of a reduced CFR, which seems to revert spontaneously in the weeks after revascularisation. Pharmacologic treatment has been shown to restore CFR promptly, and it may also change the clinical outcome. The likelihood of distal embolisation can be reduced by the use of appropriate devices during high risk procedures.