A comparison of postoperative morphometric and hemodynamic changes between saphenous vein and left internal mammary artery grafts

Abstract

There is higher long-term failure of the saphenous vein graft (SVG) compared with the left internal mammary artery (LIMA) graft, which is affected by the hemodynamic environment. A comprehensive analysis of postoperative structure-function changes is important to study the atherogenesis in the SVG A comparison of morphometric and hemodynamic parameters was carried out between LIMA grafts and SVGs and between different time points postoperatively. Various parameters were obtained from the image reconstruction and flow simulation in patients, who underwent CT exams for ~1 year, 5 and 10 years after revascularization. Morphometric data showed a decrease in lumen size in the entire SVG and anastomosis of different patients in a sequence of ~1 year, 5 and 10 years postoperatively despite negligible changes of LIMA size. Computational results indicated the fourfold increased surface area ratio (SAR) of low time-averaged wall shear stress (TAWSS) in the SVG and anastomosis at postoperative 10 years than that at postoperative ~1 year. The SAR of high TAWSS gradient (TAWSSG) at the distal anastomosis between SVG and coronary arteries was significantly higher (14 ± 9% vs. 6 ± 8%) than that in the LIMA group at postoperative ~1 year. There were strong correlations between morphometric and hemodynamic parameters in the SVG and distal anastomosis at various time points postoperatively, which showed deterioration relevant to persistent diffuse diseases at postoperative ~10 years.

Keywords: CABG; LIMA; SVG; flow simulation; hemodynamics.

Figure 1

(A) 3‐dimensional (3D) geometric model of LIMA graft and SVG and coronary arteries reconstructed from CTA images of a representative patient; (B) schematic representative of geometric parameters in LIMA graft and SVG, and (C) schematic representative of geometric parameters at an anastomosis.

Figure 2

(A–B) plot of D_fit along normalized graft centerline in LIMA (A: n = 22 for ~1 year, n = 25 for ~5 years, and n = 22 for ~10 years postoperatively) and SVG (B: n = 21 for ~1 year, n = 21 for ~5 years, and n = 21 for ~10 years postoperatively) groups; (C‐D) plot of D_fit along normalized anastomotic centerline in LIMA (C: n = 22 for ~1 year, n = 25 for ~5 years, and n = 22 for ~10 years postoperatively) and SVG (D: n = 21 for ~1 year, n = 21 for ~5 years, and n = 21 for ~10 years postoperatively) groups, where error bars refer to the SDs of D_fit at various postoperative times. The centerlines were normalized by the accumulative length from A1 to A10 in Figure 1B and C.

Figure 3

(A–D) 3D geometric model of LIMA graft (A) and SVG (B) and TAWSS (Unit: Dynes∙cm⁻²) in LIMA graft (C) and SVG (D) of two representative patients, who underwent CTA for ~1 year after surgical revascularization; (E–H) 3D geometric model and TAWSS (Unit: Dynes∙cm⁻²) in LIMA graft and SVG of two representative patients, who underwent CTA for ~5 year after surgical revascularization; (I–L) 3D geometric model and TAWSS (Unit: Dynes∙cm⁻²) in LIMA graft and SVG of two representative patients, who underwent CTA for ~10 year after surgical revascularization.

Figure 4

(A) SAR‐TAWSS and (B) SAR‐OSI (n = 22 for ~1 year, n = 25 for ~5 years, and n = 22 for ~10 years postoperatively in the LIMA group; and n = 21 for ~1 year, n = 21 for ~5 years, and n = 21 for ~10 years postoperatively in the SVG group) in the entire graft except for the anastomotic regions. The histograms of light and dark textures refer to the mean values of the parameters averaged over patients in LIMA and SVG groups, respectively, at various postoperative times, where error bars refer to the SDs of the parameters and P‐value < 0.05 indicates statistical difference between LIMA and SVG groups.

Figure 5

(A) SAR‐TAWSS, (B) SAR‐OSI, and (C) SAR‐TAWSSG (n = 22 for ~1 year, n = 25 for ~5 years, and n = 22 for ~10 years postoperatively in the LIMA group; and n = 21 for ~1 year, n = 21 for ~5 years, and n = 21 for ~10 years postoperatively in the SVG group) at the anastomosis between the graft and coronary arteries. The histograms of light and dark textures refer to the mean values of the parameters averaged over patients in LIMA and SVG groups, respectively, at various postoperative times, where error bars refer to the SDs of the parameters and P‐value < 0.05 indicates statistical difference between LIMA and SVG groups.