Introduction: Ischemia without obstructive coronary artery disease (INOCA) is an often underdiagnosed form of coronary artery disease associated with an increased risk of cardiovascular events. In stress cardiac magnetic resonance imaging (CMR), INOCA may appear as localized ischemic areas; however, the mechanisms underlying this localized presentation of INOCA is unclear. Thus, the aim of our study was to investigate if there is a relationship between coronary microvascular dysfunction and ischemic areas in patients with INOCA.

Methods: The study cohort included 54 vessels from 18 patients with INOCA with localized ischemia as determined by CMR but without relevant coronary stenosis in coronary angiography. In order to assess microvascular dysfunction in these vessels, an angiography based index of microvascular resistance (aIMR) was calculated offline using a commercially available software (QFR, Medis Software, Leiden, NL) and a previously published protocol.

Results: In 4 cases (22.2%), ischemia was localized in the LAD territory, in 7 cases (38.9%) in the LCX territory, in further 7 cases (38.9%) in RCA territory. QFR values were comparable between vessels with vs without ischemic areas (0.91±0.06 vs 0.92±0.09 , p=0.782). In contrast, aIMR was significantly higher (115.0±61.2 vs 79.8±40.5, p=0.004) and flow velocity significantly lower in vessels with vs without ischemia (0.10±0.04 vs 0.16±0.06 cm/s, p<0.001).

Conclusion: We conclude that coronary microvascular dysfunction co-localizes with ischemia in patients without obstructive coronary artery disease. Further studies are needed to investigate if the presence of microvascular dysfunction in INOCA may explain the increased cardiovascular risk of these patients.