Changes in absolute coronary blood flow and myocardial resistance after percutaneous coronary intervention.

BACKGROUND: Treating a coronary stenosis by percutaneous coronary intervention (PCI) aims to relieve myocardial ischaemia by improving coronary blood flow. The evolution of coronary flow and resistance post-PCI is not fully understood. AIMS: This study aimed to investigate the immediate impact of PCI on absolute coronary flow (Q), and epicardial and microvascular resistance (Repi and Rμ). METHODS: In a two-centre cohort including 52 patients, pre- and post-PCI physiological assessments were performed using continuous thermodilution, via a combination of a pressure-temperature sensor wire and a dedicated infusion microcatheter. RESULTS: Resting Q remained similar before and after PCI (Δ +2 [interquartile range [IQR] -9 to 21] mL/min; p=0.21), as a 193 Wood unit (WU) reduction in resting Repi (Δ -193 [IQR -400 to -59] WU; p<0.001) was offset by a 267 WU increase in resting Rμ (Δ +267 [IQR -20 to 474] WU; p=0.002). Conversely, hyperaemic Q rose significantly (Δ +44 [IQR 16 to 92] mL/min; p<0.001), reflecting a 195 WU reduction in hyperaemic Repi (Δ -195 [IQR -379 to -82] WU; p<0.001), while hyperaemic Rμ remained stable (Δ +3 [IQR -96 to 75] WU; p=0.87). The median microvascular resistance reserve (MRR) did not change significantly after PCI (Δ -0.2 [IQR -0.7 to 0.6]; p=0.301). Pre- and post-PCI fractional flow reserve (FFR) were strongly and inversely associated with Repi and predicted the improvement of hyperaemic Q. CONCLUSIONS: PCI significantly reduces epicardial resistance, leading to a pronounced increase in hyperaemic flow, which can be predicted by FFR. Resting Q remained unchanged because of compensatory increases in microvascular resistance, providing direct evidence of coronary flow autoregulation in humans. The MRR was unaffected by PCI, confirming its specificity as an index of microvascular function.