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Published on: August 25, 2023
Validation of physiological principles of Non-Invasive fractional flow reserve derived from CT coronary angiography
Jasmine Chan1, Abdul R Ihdayhid2, Harsh V Thakkar1
1Victorian Heart Institute and Victorian Heart Hospital, Monash University, Monash Health, 631 Blackburn Road, Clayton, Victoria, 3168, Australia.
Background:
Coronary computed tomography angiography (CTA) simulation of fractional flow reserve (FFR) is derived from allometric and morphometric scaling principles, allowing inference of physiological parameters from anatomical measures like left-ventricular (LV) mass and coronary luminal dimensions. Validity of these assumptions in humans remains uncertain, with supporting data derived from animal models.
Methods:
Twenty-two patients with non-obstructive coronary artery disease underwent proximal-LAD intravascular ultrasound (IVUS) and Combowire assessment at rest and hyperemia. Coronary volumetric flow (Q, cm3/sec) was derived from average baseline peak-velocity (cm/sec) x IVUS cross-sectional-area (cm2). Baseline microvascular resistance (BMVR, mmHg/cm2) was calculated: distal coronary pressure (mmHg) - right atrial pressure (mmHg) divided by Q. Patients underwent same-day CTA to provide quantitative measures including LV mass (g), cumulative coronary luminal volume (mm3) and vessel length (mm). Relationships between quantitative CTA-derived metrics and invasive physiology were evaluated using Pearson's correlation.
Results:
Mean FFR was 0.94 ± 0.06; median coronary flow reserve velocity was 2.54 [IQR 2.1-3.1]. Baseline Q and BMVR were 2.30 ± 1.0 cm3/s and 44.6 ± 21.6 mmHg/cm2, respectively. Average LV-mass was 148.6 ± 30.6g, coronary luminal volume 1038.6 ± 485.2 mm3 and vessel length 184.5 ± 66.8 mm. LV mass correlated strongest with coronary flow (r = 0.87, p < 0.001) followed by vessel length (r = 0.75, p < 0.0001) and coronary luminal volume (r = 0.73, p < 0.001). The scaling coefficient (1.87) significantly differed from experimental data. CT-derived metrics demonstrated strong negative correlation with BMVR (LV mass -0.70, coronary luminal volume -0.70, vessel length -0.76; P < 0.0001 respectively).
Conclusion:
These findings support deriving coronary flow and microvascular resistance from CTA anatomical metrics. Revised scaling coefficients and hyperemic modelling could enhance CTA-derived FFR diagnostic performance.
