Influence of Percutaneous Coronary Intervention on Coronary Microvascular Resistance Index

Background—Coronary microvascular resistance during maximal hyperemia is generally assumed to be unaffected by percutaneous coronary interventions (PCIs). We assessed a velocity-based index of hyperemic microvascular resistance (h-MRv) by using prototypes of a novel, dual-sensor (Doppler velocity and pressure)–equipped guidewire before and after PCI to test this hypothesis. Methods and Results—Aortic pressure, flow velocity (h-v), and pressure (h-Pd) distal to 24 coronary lesions were measured simultaneously during maximal hyperemia induced by intracoronary adenosine. Measurements were obtained in the reference vessel before PCI and in the target vessel before and after PCI, stenting, and ultrasound-guided, upsized stenting. h-Pd increased from 57.9±17.0 to 85.5±15.6 mm Hg, and h-MRv (ie, h-Pd/h-v) decreased from 2.74±1.40 to 1.58±0.61 mm Hg · cm−1 · s after stenting (both P<0.001). The reduction in h-MRv accounted for 34% of the decrease in total coronary resistance achieved by PCI. h-MRv of the target vessel after PCI was lower than that of the corresponding reference vessel despite a higher h-Pd in the reference vessel (P<0.01). Post-PCI baseline MRv was correlated with baseline Pd before PCI (P<0.01). Conclusions—PCI-induced restoration of Pd resulted in a reduction of h-MRv in accordance with the pressure dependence of h-MRv. The decrease in h-MRv to a level below that of the corresponding reference vessel in the immediate post-PCI period and a lowered baseline MRv suggest microvascular remodeling induced by long-term exposure to a low-pressure environment.