Definition

The Importance of Coronary Microcirculation

Angina pectoris is a chest pain syndrome caused by myocardial ischemia. It not only reduces quality of life but also leads to events including acute coronary syndrome and sudden death due to fatal arrhythmias. Traditionally, atherosclerotic organic stenosis in large coronary arteries was considered a major cause of angina, leading to the development of percutaneous coronary intervention (PCI) using stents and balloons. However, while PCI has become a widely adopted effective treatment for angina caused by organic coronary artery stenosis, it presents various challenges.

Specifically, approximately half of patients with symptoms suggestive of angina show no significant stenotic lesions even after coronary angiography. Furthermore, even after treating significant stenosis with PCI, chest pain persists in about 40% of patients. Furthermore, recent results from large-scale clinical trials such as the ORBITA study (Reference 1) and the ISCHEMIA study (Reference 2) have been published. These studies demonstrated that even when visible organic coronary artery stenosis is treated with PCI, exercise tolerance and long-term prognosis do not necessarily improve compared to groups treated with optimal medical therapy. Against this backdrop, the importance of coronary artery function as a cause of myocardial ischemia has gained attention. Coronary artery dysfunction includes not only organic atherosclerosis and coronary spasm in large vessels but also angina caused by dysfunction in small vessels (coronary microvessels) that cannot be observed with conventional coronary angiography (Figure 1; Reference 3).

A recent prospective registry study centered at Tohoku University (Reference 4) revealed that, contrary to conventional understanding, coronary microvascular dysfunction occurs frequently not only in women but also in men (male-to-female ratio approximately 1:2). the annual incidence of cardiovascular events is approximately 7.7%, which is by no means low, and that coronary microcirculatory dysfunction frequently coexists even in patients with organic stenosis or spasm of large coronary arteries. Consequently, the focus on coronary microcirculatory dysfunction is increasing. Elucidating the pathophysiology of coronary microcirculatory dysfunction and developing effective treatments represent important challenges for future cardiovascular medicine.

Figure 1: Mechanisms of three types of myocardial ischemia in angina pectoris (from Reference 3):
The etiology of stable angina involves various degrees of involvement of the following mechanisms:
Structural stenosis caused by atherosclerosis, Functional narrowing of the lumen associated with diffuse coronary artery spasm on the heart surface, Functional abnormalities of the microcoronaryarteries (hypercontractility and reduced relaxation capacity).

References
Lancet 2018;391:31-40
N Engl J Med 2020;382:1395-407
tohokuuniv-press20210527_01web_angina.pdf
EurHeart J 2021;42:4592-4600