A novel method for measuring absolute coronary blood flow and microvascular resistance in patients with ischaemic heart disease

Abstract

Aims Ischaemic heart disease is the reduction of myocardial blood flow, caused by epicardial and/or microvascular disease. Both are common and prognostically important conditions, with distinct guideline-indicated management. Fractional flow reserve (FFR) is the current gold-standard assessment of epicardial coronary disease, but is only a surrogate of flow and only predicts percentage flow changes. It cannot assess absolute (volumetric) flow or microvascular disease. The aim of this study was to develop and validate a novel method that predicts absolute coronary blood flow and microvascular resistance (MVR) in the catheter laboratory. Methods and Results A computational fluid dynamics (CFD) model was used to predict absolute coronary flow (QCFD) and coronary microvascular resistance (MVR) using data from routine invasive angiography and pressure-wire assessment. QCFD was validated in an in vitro flow circuit which incorporated patient-specific, 3-D printed coronary arteries; and then in vivo, in patients with coronary disease. In vitro, QCFD agreed closely with the experimental flow over all flow rates (bias +2.08 mL/min; 95% CI (error range) -4.7 to + 8.8 mL/min; R2=0.999, p < 0.001; variability coefficient <1%). In vivo, QCFD and MVR were successfully computed in all 40 patients under baseline and hyperaemic conditions, from which coronary flow reserve (CFR) was also calculated. QCFD-derived CFR correlated closely with pressure-derived CFR (R2=0.92, P < 0.001). This novel method was significantly more accurate than Doppler-wire-derived flow both in vitro (±6.7 vs ± 34 mL/min) and in vivo (±0.9 vs ± 24.4 mmHg). Conclusions Absolute coronary flow and MVR can be determined alongside FFR, in absolute units, during routine catheter laboratory assessment, without the need for additional catheters, wires or drug infusions. Using this novel method, epicardial and microvascular disease can be discriminated and quantified. This comprehensive coronary physiological assessment may enable a new level of patient stratification and management. Translational Perspective Current pressure wire-based methods of assessing coronary disease cannot assess absolute flow or microvascular disease. Our novel QCFD method, using only angiography-based CFD and a pressure wire, simultaneously measures FFR, absolute coronary blood flow rate, microvascular resistance and coronary flow reserve. QCFD is suitable for use in the catheter laboratory and requires no dedicated catheters, wires or infusions. QCFD measures blood flow and microvascular resistance in absolute units and allows microvascular and epicardial disease to be differentiated, quantified and separately assessed, with the potential to improve diagnostic accuracy and clinical management.

The Impact of Virtual Fractional Flow Reserve and Virtual Coronary Intervention on Treatment Decisions in the Cardiac Catheter Laboratory

“…Previous work demonstrates that VCI based on invasive pressure wire data is not only more accurate but can also generate absolute flow and microvascular data. 20 …”

“…In addition, vFFR allied to VCI may offer the non-interventional cardiologist appreciation of the possibilities for treatment. Previous work demonstrates that VCI based on invasive pressure wire data is not only more accurate but can also generate absolute flow and microvascular data 20 .…”

Virtual (Computed) Fractional Flow Reserve: Future Role in Acute Coronary Syndromes

“…The greatest advantage is that vFFR could bring the advantage of coronary physiology to many more patients with ACS than at present. Finally, recent CFD-based modelling innovations are able to predict microvascular resistance which is known to be of prognostic significance in ACS (81). Examples of vFFR application in patients with ACS are shown in Figure 4.…”

The new role of diagnostic angiography in coronary physiological assessment

“…41 Ultimately, the CFD methods behind CAG-FFR may also enable quantification of absolute (volumetric) blood flow and other parameters, such as microvascular resistance, providing a more comprehensive coronary physiological assessment. 42 In the future, intravascular ultrasound and optical coherence tomography, coregistered with CAG, may augment anatomical reconstruction, and this may improve CAG-FFR accuracy.…”

“…The other is that FFR, while being accurate as regards the contribution of the lesion to blood flow limitation, provides no information about the state of the microvasculature. 42 Indeed, disease in this compartment may explain some of the 'false positive' results of non-invasive tests like pMRI when compared with CAG and FFR. Although primarily an anatomical test, like CAG, CTCA is the basis of CTFFR.…”