Microvascular resistance reserve in the presence of functionally significant epicardial stenosis and changes after revascularization

In the presence of functionally significant epicardial lesions, microvascular resistance reserve (MRR) calculation needs incorporation of collateral flow. Coronary fractional flow reserve (FFR( cor )) requiring coronary wedge pressure (P( w )), which is an essential part of the true MRR calculation, is reportedly estimated by myocardial FFR (FFR( myo )) not requiring P( w ) measurement. We sought to find an equation to calculate MRR without the need for P( w ). Furthermore, we assessed changes in MRR after percutaneous coronary intervention (PCI). An equation to estimate FFR( cor ) was developed from a cohort of 230 patients who underwent physiological measurements and PCI. Corrected MRR was calculated using this equation and compared with true MRR in 115 patients of the different set of the validation cohort. True MRR was calculated using FFR( cor ). FFR( cor ) and FFR( myo ) showed a strong linear relationship (r (2) = 0.86) and an equation was FFR( cor ) = 1.36 × FFR( myo ) – 0.34. This equation provided no significant difference between corrected MRR and true MRR in the validation cohort. Pre‐PCI lower coronary flow reserve and higher index of microcirculatory resistance were independent predictors of pre‐PCI decreased true MRR. True MRR significantly decreased after PCI. In conclusion, MRR can be accurately corrected using an equation for FFR( cor ) estimation without P( w ).