Change in coronary blood flow after percutaneous coronary intervention in relation to baseline lesion physiology: results of the JUSTIFY-PCI study

Abstract

Background: Percutaneous coronary intervention (PCI) aims to increase coronary blood flow by relieving epicardial obstruction. However, no study has objectively confirmed this and assessed changes in flow over different phases of the cardiac cycle. We quantified the change in resting and hyperemic flow velocity after PCI in stenoses defined physiologically by fractional flow reserve and other parameters.

Methods and results: Seventy-five stenoses (67 patients) underwent paired flow velocity assessment before and after PCI. Flow velocity was measured over the whole cardiac cycle and the wave-free period. Mean fractional flow reserve was 0.68±0.02. Pre-PCI, hyperemic flow velocity is diminished in stenoses classed as physiologically significant compared with those classed nonsignificant (P<0.001). In significant stenoses, flow velocity over the resting wave-free period and hyperemic flow velocity did not differ statistically. After PCI, resting flow velocity over the wave-free period increased little (5.6±1.6 cm/s) and significantly less than hyperemic flow velocity (21.2±3 cm/s; P<0.01). The greatest increase in hyperemic flow velocity was observed when treating stenoses below physiological cut points; treating stenoses with fractional flow reserve ≤0.80 gained Δ28.5±3.8 cm/s, whereas those fractional flow reserve >0.80 had a significantly smaller gain (Δ4.6±2.3 cm/s; P<0.001). The change in pressure-only physiological indices demonstrated a curvilinear relationship to the change in hyperemic flow velocity but was flat for resting flow velocity.

Conclusions: Pre-PCI physiology is strongly associated with post-PCI increase in hyperemic coronary flow velocity. Hyperemic flow velocity increases 6-fold more when stenoses classed as physiologically significant undergo PCI than when nonsignificant stenoses are treated. Resting flow velocity measured over the wave-free period changes at least 4-fold less than hyperemic flow velocity after PCI.

Keywords: angioplasty; blood flow velocity; percutaneous coronary intervention.

Figure 1

Flow velocity across a stenosis before percutaneous coronary intervention (PCI). Simultaneous trans-stenotic pressure and flow velocity measurements permit assessment of hemodynamic change before and after PCI. Flow velocity can be measured during adenosine-mediated hyperemia over the entire cardiac cycle (Hyperemic Flow_{whole cycle}). It can also be measured under basal conditions, over the whole cardiac cycle (Rest Flow_{whole cycle}) or over the specific part in diastole known as the wave-free period (Rest Flow_{wave-free period}).

Figure 2

A, Paired mean flow velocity shown before and after percutaneous coronary intervention (PCI) measured during hyperemia (blue) and the wave-free period (red). Fractional flow reserve (FFR) ≤0.60 had 28 stenoses; FFR 0.61 to 0.70: 10 stenoses; FFR 0.71 to 0.80: 14 stenoses; FFR >0.80: 23 stenoses. Hyperemic flow increases most for highly physiologically significant lesions (FFR≤0.70). Flow over the iFR-window is remarkably stable throughout all levels of lesion severity and changes little after PCI. Rest Flow_{wave-free period} has little variability between FFR categories of stenosis severity. B, The change in flow velocity after PCI. Hyperemic Flow_{whole cycle} increases significantly more than the increases in Rest Flow_{wave-free period} for every FFR category of stenosis severity. *P≤0.01.

Figure 3

The change in hyperemic flow after percutaneous coronary intervention (PCI) according to different pre-PCI indices. Coronary flow reserve (CFR), fractional flow reserve (FFR), instantaneous wave-free ratio measured at rest (iFR), or during adenosine-mediated hyperemia (iFRa), basal stenosis resistance (BSR), and hyperemic stenosis resistance (HSR) were used to classify stenoses as physiologically significant (⊕) or physiologically nonsignificant (Ө) according to their respective cut points, as described in the Methods section of this article. The change in hyperemic flow velocity after PCI (top) was significantly higher when stenoses were physiologically significant (⊕) than when nonsignificant (Ө), regardless of the index used. *P=0.01, **P<0.001. Bottom, The change in resting wave-free period flow using the same annotation.

Figure 4

The relationship between pre-percutaneous coronary intervention (PCI) pressure-only physiological indices and the increase in hyperemic flow velocity after PCI. Hyperemic flow increases significantly following PCI. A ratio of pre-PCI and post-PCI hyperemic flow velocity was plotted using a third-order polynomial against the pre-PCI fractional flow reserve (FFR) value. Ratios above 1 suggest an increase in flow velocity, whereas those below 1 suggest a fall. iFR indicates instantaneous wave-free ratio.

Figure 5

Estimating the change in hyperemic flow velocity based on the δ or change in pressure-only index after percutaneous coronary intervention (PCI). Pressure-only indices increase after PCI and demonstrate a curvilinear relationship with the change in resting and hyperemic flow velocity. For a change in instantaneous wave-free ratio (iFR), the change in wave-free flow velocity was predicted by the curve y=7.522x³−2.863x²+0.6754x+1.1943, whereas the change in hyperemic flow velocity was predicted by the curve y=18.96x³−11.94x²+5.6048x+1.304. For fractional flow reserve (FFR), the change in resting wave-free flow velocity was predicted by a curve y=20.7x³−9.1852x²+2.0422x+1.1019, whereas the change in hyperemic flow was y=17.175x³−0.1665x²−3.0192x+1.0898.

Figure 6

Change in microvascular resistance and flow reserve after percutaneous coronary intervention (PCI). Top, The capacity for hyperemia and the wave-free period to reduce resistance compared with the resting whole cycle was compared before and after PCI as a marker of microembolization. Post PCI, the hyperemic effect was not significantly blunted, suggesting no impact of embolization. Bottom, This was confirmed by assessing the capacity of coronary flow reserve (CFR) to increase after PCI. FFR indicates fractional flow reserve.