Coronary microvascular resistance comparison of coronary arteries with and without considering vascular diameter: A retrospective, single‐center study

Figures

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  Figure 1. Calculation of coronary physiological values. Hyperemic microvascular resistance index (hMVRI) was calculated as distal coronary pressure (Pd) divided by distal average peak velocity (APV) at maximal hyperemia. Vessel diameter was analyzed by quantitative coronary angiography (QCA) at the site of blood flow measurement by wire (white arrow). QCA was performed with a validated densitometric analysis system (Pie Medical Imaging B.V, Maastricht, the Netherlands). Coronary blood flow (CBF) was calculated as πD2/4 (0.5 × APV), where D is vessel diameter. CBF as measured by QCA is described as CBFQCA, then hMVRIQCA is calculated as Pd divided by CBFQCA during maximal hyperemia. As CBFQCA will be overestimated, hMVRIQCA will be higher than the original HMR. (A) Coronary angiography. (B) Insertion of the Doppler flow guidewire into the left anterior descending artery. (C) Final position of the Doppler flow guidewire as confirmed by contrast injection. (D) Physiological measurements at rest. (E) Physiological measurements under hyperemic conditions. CFR, coronary flow reserve; HMR, hyperemic microvascular resistance; HSR, hyperemic stenosis resistance.

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  Figure 2. Evaluation of FFR, hMVRI, APV, and Pd in Groups A and B. In comparisons between LAD, LCX, and RCA, significant differences in FFR, hMVRI, and Pd are seen in Group A (A–D) and Group B (E–H). (A) FFR is significantly lower in the LAD than in the LCX or RCA (p < 0.001) in Group A. (B) hMVRI is significantly lower in the LAD than in the LCX or RCA (p = 0.003) in Group A. (C) No significant differences in APV are seen between the three coronary branches in Group A. (D) Pd is significantly lower in the LAD than in the RCA (p < 0.001) in Group A. (E) FFR is significantly lower in the LAD than in the LCX or RCA (p < 0.001) in Group B. (F) hMVRI is significantly lower in the LAD than in the RCA (p = 0.019) in Group B. (G) No significant differences in APV are seen between the three coronary branches in Group B. (H) Pd is significantly lower in the LAD and LCX than in the RCA (p = 0.004) in Group B. † p < 0.05; †† p < 0.001. FFR, fractional flow reserve; hMVRI, hyperemic microvascular resistance index; LAD, left anterior descending coronary artery; LCX, left circumflex; Pd, mean distal coronary pressure; RCA, right coronary artery.

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  Figure 3. DQCA, CBFQCA, and HMRQCA corrected for vessel diameter by QCA. (A) DQCA in the LAD, LCX, and RCA are 2.27, 2.81, and 2.91 mm, respectively. DQCA is significantly larger in the LCX and RCA than in the LAD (LCX, p = 0.029; RCA, p < 0.001), but no significant difference is seen between the LCX and RCA (p = 0.152). (B, C) No significant differences in CBFQCA or hMVRIQCA are seen between LAD, LCX, and RCA. † p < 0.05; †† p < 0.001. FFR, fractional flow reserve; hMVRI, hyperemic microvascular resistance index; LAD, left anterior descending coronary artery; LCX, left circumflex; Pd, mean distal coronary pressure; RCA, right coronary artery.

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  Figure 4. Correlation between APV and CBFQCA in Group B. (A) No collinearity between DQCA and APV is seen in scattergrams (p = 0.225). (B) CBFQCA and APV in Group B show a weak correlation (p < 0.001, R 2 = 0.34; APV = 19.59 + 0.15 × CBFQCA). We divided Group B into three equal groups according to the DQCA: small diameter group (C), 1.57–2.29 mm; middle diameter group (D), 2.31–2.9 mm; and large diameter group (E), 2.92–3.94 mm. (C–E). The correlations between CBFQCA and APV in the small, middle and large diameter groups are strong (small diameter group: R 2 = 0.85, p < 0.001, APV = 8.6 + 0.48 × CBFQCA; middle diameter group: R 2 = 0.87, p < 0.001, APV = 6.4 + 0.30 × CBFQCA; large diameter group: R 2 = 0.80, p < 0.001, APV = 4.0 + 0.21 × CBFQCA). The slope of the straight line between APV and CBFQCA for small, middle, and large diameters is 0.48, 0.30, and 0,21, respectively, decreasing as diameter increases.