Impact of coronary hyperemia on collateral flow correction of coronary microvascular resistance indices

Recently, a novel method to estimate wedge pressure (P-w)-corrected minimal microvascular resistance (MR) was introduced. However, this method has not been validated since, and there are some theoretical concerns regarding the impact of different physiological conditions on the derivation of P-w measurements. This study sought to validate the recently introduced method to estimate P-w-corrected MR in a Doppler-derived study population and to evaluate the impact of different physiological conditions on the P-w measurements and the derivation of P-w-corrected MR. The method to derive "estimated" hyperemic microvascular resistance (HMR) without the need for P-w measurements was validated by estimating the coronary fractional flow reserve (FFRcor) from myocardial fractional flow reserve (FFRmyo) in a Doppler-derived study population (N = 53). From these patients, 24 had hyperemic P-w measurements available for the evaluation of hyperemic conditions on the derivation of P-w and its effect on the derivation of both "true" (with measured P-w) and "estimated" P-w-corrected HMR. Nonhyperemic P-w differed significantly from P-w measured in hyperemic conditions (26 +/- 14 vs. 35 +/- 14 mmHg, respectively, P < 0.005). Nevertheless, there was a strong linear relationship between FFRcor and FFRmyo in nonhyperemic conditions (R-2 = 0.91, P < 0.005), as well as in hyperemic conditions (R-2 = 0.87, P < 0.005). There was a strong linear relationship between "true" HMR and "estimated" HMR using either nonhyperemic (R-2 = 0.86, P < 0.005) or hyperemic conditions (R-2 = 0.85, P < 0.005) for correction. In contrast to a modest agreement between nonhyperemic P-w-corrected HMR and apparent HMR (R-2 = 0.67, P < 0.005), hyperemic P-w-corrected HMR showed a strong agreement with apparent HMR (R-2 = 0.88, P < 0.005). We validated the calculation method for P-w-corrected MR in a Doppler velocity-derived population. In addition, we found a significant impact of hyperemic conditions on the measurement of P-w and the derivation of P-w-corrected HMR.
NEW & NOTEWORTHY The following are what is known: 1) wedge-pressure correction is often considered for the derivation of indices of minimal microvascular resistance, and 2) the Yong method for calculating wedge pressure-corrected index of microvascular resistance (IMR) without balloon inflation has never been validated in a Doppler-derived population and has not been tested under different physiological conditions. This study 1) adds validation for the Yong method for calculated wedge-pressure correction in a Doppler-derived study population and 2) shows significant influence of the physiological conditions on the derivation of coronary wedge pressure.