Introduction: Coronary microvascular dysfunction (CMD) is a common condition contributing to heterogenous cardiac diseases, such as myocardial ischemia and heart failure. However, little is known regarding the natural history of CMD, as most studies assessing this condition were performed cross-sectionally. Therefore, we investigated the evolution over time of microvascular function in an all-comer population, to assess the natural history of CMD.

Methods: 273 patients undergoing elective coronary angiography at two timepoints at least 6 months apart were included; average time between the two coronary angiographies was 34±21 months. Microvascular function was measured retrospectively by means of angiography-based index of microvascular resistance (aIMR) at both timepoints in the same vessel (LAD in 93.4% of cases, LCx in 1.5%, RCA in 4.8%), in order to assess variation of microvascular function over time. An aIMR ≥25 was considered indicative of CMD.

Results: Of the included 273 patients, 107 presented CMD at inclusion (39.2%); average aIMR at baseline was 23.2±8.0. At the second timepoint, after an average of 34±21 months, average aIMR was significantly increased compared to baseline (24.4±8.6, p=0.013). Interestingly, in spite of this overall increase in average aIMR reflecting a deteriorating microvascular function over time, of the 107 patients with CMD at inclusion only 61 (22.3% of the total population) still presented CMD at follow-up. Specifically, 46 patients with CMD at inclusion (16.8%) showed an improved coronary microvascular function with an aIMR<25. On the other hand, 60 patients (22.0%) with initially normal aIMR developed de novo CMD at the second timepoint.

Conclusion: Microvascular function generally deteriorates over time. However, our data demonstrate in an all-comer population that CMD is a highly dynamic condition with an also frequently observed improvement over time. This adds to the understanding of the natural history of CMD.