Distinguishing Epicardial and Microvascular Disease Using Combined Functional and Anatomical Endpoints in a Porcine Model

For a better treatment of coronary artery disease in a catheterization lab, detection of the relative contributions of the epicardial stenosis (ES) and concomitant microvascular disease (MVD) is important. To diagnose ES, fractional flow reserve (FFR), the hyperemic stenosis resistance index (hSRv) and to diagnose MVD, hyperemic microvascular resistance index (hMRv) have been tested in cath labs. However, for concurrent assessment of ES and MVD, functional parameter utilizing flow and pressure values, pressure drop coefficient (CDP) and combined functional and anatomical parameter, lesion flow coefficient (LFC) are defined. To test the ability of CDP and LFC to account for ES and MVD, they were correlated with the hSRv and hMRv. We hypothesize that CDP and LFC will have a better combined correlation with hSRv and hMRv. Simultaneous pressure and flow readings were obtained in 11 Yorkshire swine. Single and multiple linear regression analyses were conducted between the FFR, CDP and LFC vs hSRv and hMRv. The correlation coefficient (r) was used to check the strength of correlation. The individual correlation between hSRv and hMRV with CDP (r = 0.90; r = 0.78) and LFC (r = 0.89; r = 0.95) was stronger compared to FFR (r = 0.63; r = 0.32). The combined correlation between hSRv and hMRv with CDP (r = 0.95) and LFC (r = 0.95) increased from the individual correlation. Therefore, we conclude that CDP and LFC can diagnose ES and MVD concurrently and might prove to be improved diagnostic parameters than FFR.

Functional and Anatomical Diagnosis of Coronary Artery Stenoses: A Retrospective Study in Humans

Fractional flow reserve (FFR: ratio of distal to proximal pressure of a stenotic section) is used to evaluate hemodynamic significance of epicardial stenosis. However, FFR and coronary flow reserve (CFR: ratio of hyperemic blood velocity to that of resting condition) are used in conjunction to evaluate combination of both epicardial and microvascular disease. It has been proposed that optimization of cutoff values for diagnostic parameters in determining stenosis severity depends on coupling functional (pressure and velocity) and anatomical data (% area stenosis). We hypothesize that, pressure drop coefficient (CDP: the ratio of trans-stenotic pressure drop to distal dynamic pressure) which has the functional information of pressure and velocity in its formulation correlates significantly with FFR and CFR, and lesion flow coefficient (LFC: ratio of % area stenoses to CDP at throat region) which combines both functional and anatomical (% area stenoses) information in its formulation correlates significantly with FFR, CFR and % area stenosis. We retrospectively analyzed the hemodynamic information from Meuwissen et al [3] to test this hypothesis. It was observed that, CDP, a functional index based on pressure drop and velocity, correlated linearly and significantly with FFR and CFR. And, LFC (combined functional and anatomic parameter) also correlated significantly with FFR, CFR (both hemodynamic endpoints) and % area stenosis (anatomic endpoint).

Influence of heart rate on fractional flow reserve, pressure drop coefficient, and lesion flow coefficient for epicardial coronary stenosis in a porcine model

A limitation in the use of invasive coronary diagnostic indexes is that fluctuations in hemodynamic factors such as heart rate (HR), blood pressure, and contractility may alter resting or hyperemic flow measurements and may introduce uncertainties in the interpretation of these indexes. In this study, we focused on the effect of fluctuations in HR and area stenosis (AS) on diagnostic indexes. We hypothesized that the pressure drop coefficient (CDPe, ratio of transstenotic pressure drop and distal dynamic pressure), lesion flow coefficient (LFC, square root of ratio of limiting value CDP and CDP at site of stenosis) derived from fluid dynamics principles, and fractional flow reserve (FFR, ratio of average distal and proximal pressures) are independent of HR and can significantly differentiate between the severity of stenosis. Cardiac catheterization was performed on 11 Yorkshire pigs. Simultaneous measurements of distal coronary arterial pressure and flow were performed using a dual sensor-tipped guidewire for HR < 120 and HR > 120 beats/min, in the presence of epicardial coronary lesions of <50% AS and >50% AS. The mean values of FFR, CDPe, and LFC were significantly different ( P < 0.05) for lesions of <50% AS and >50% AS (0.88 ± 0.04, 0.76 ± 0.04; 62 ± 30, 151 ± 35, and 0.10 ± 0.02 and 0.16 ± 0.01, respectively). The mean values of FFR and CDPe were not significantly different ( P > 0.05) for variable HR conditions of HR < 120 and HR > 120 beats/min (FFR, 0.81 ± 0.04 and 0.82 ± 0.04; and CDPe, 95 ± 33 and 118 ± 36). The mean values of LFC do somewhat vary with HR (0.14 ± 0.01 and 0.12 ± 0.02). In conclusion, fluctuations in HR have no significant influence on the measured values of CDPe and FFR but have a marginal influence on the measured values of LFC. However, all three parameters can significantly differentiate between stenosis severities. These results suggest that the diagnostic parameters can be potentially used in a better assessment of coronary stenosis severity under a clinical setting.