Discordant Diagnosis of Coronary Microvascular Dysfunction by Microvascular Resistance Reserve: Transthoracic Doppler Echocardiography vs Bolus Thermodilution Method

Background: Epicardial stenosis and coronary microvascular dysfunction (CMD) may coexist in patients with chronic coronary syndrome (CCS). Microvascular resistance reserve (MRR) has been demonstrated to be a valid cross-modality metric using continuous saline infusion thermodilution and intracoronary Doppler flow velocity methods. This study aimed to investigate the prevalence and diagnostic concordance of CMD defined by MRR using two methods-stress transthoracic Doppler echocardiography (S-TDE) and the invasive bolus thermodilution method (B-Thermo)-in patients with functionally significant epicardial stenosis.

Methods: We retrospectively investigated 204 left anterior descending artery (LAD) territories in CCS. All patients underwent physiological assessment using a pressure-temperature wire and S-TDE before elective fractional flow reserve (FFR)-guided percutaneous coronary intervention. The concordance rate was evaluated using κ values.

Results: In the final analysis, the median age was 72 years, and 72.5% of patients were male. The median FFR value was 0.69. MRR_S-TDE and MRR_B-Thermo were similar (3.41 vs. 3.48, P=0.877), whereas only a weak, albeit significant relationship was observed between these two metrics (r=0.167, P=0.017). CMD was diagnosed in 20.6% and 32.8% of patients using S-TDE and B-Thermo, respectively, when a cutoff MRR value of 2.7 was applied. The concordance rate of CMD diagnosis between the two methods was low (κ=0.079).

Conclusions: MRR_S-TDE and MRR_B-Thermo showed a very weak correlation in the LAD territory with functionally significant stenosis in patients with CCS. The prevalence of CMD diagnosed using MRR_S-TDE and MRR_B-Thermo was not comparable, and the diagnostic concordance of CMD using these two methods was very low.