Introduction

Approximately 50–70% of all patients with angina have no angiographically demonstratable obstructive coronary disease. A significant proportion of these patients will have undiagnosed microvascular dysfunction and/or vasospastic angina. The microcirculation is not visualized during coronary angiography but is important, patients can have ischemia without demonstratable angiographically visible obstructive macrovascular disease.

While we focus commonly on epicardial coronary artery disease due to obstructive atherosclerosis, other disease phenotypes must be considered. Causes of chronic coronary syndrome may also include myocardial bridging, epicardial vasospasm, endothelial impairment and microvascular dysfunction. In chronic coronary syndromes, ischemia with non-obstructive coronary artery disease (INOCA) often remains undiagnosed, or uninvestigated. INOCA, due to vasospastic angina and microvascular dysfunction requires invasive testing for confirmation in the coronary catheterization lab. To evaluate INOCA coronary flow reserve (CFR) and the index of microcirculatory resistance (IMR) are used to assess microvascular dysfunction before acetylcholine provocation testing for coronary spasm. In many cardiac catheterization laboratories these tests are not routinely performed outside of research settings.

Microvascular dysfunction and/or vasospastic angina, collectively known as ischaemia with non-obstructive coronary arteries (INOCA), are not benign conditions, they are associated at long term follow up with high morbidity, poor quality of life, increased hospitalisation, depresson, and increased risk of subsequent major adverse cardiac events when compared to people without symptoms of angina.