Measurement of myocardial extracellular volume fraction and cardiomyocyte diameter before and 6 months after aortic valve replacement in patients with severe aortic stenosis.

BACKGROUND: Extracellular volume fraction (ECV) is an independent predictor of mortality in aortic stenosis (AS). ECV can be measured using myocardial T1 maps acquired before and after contrast administration. Standard ECV measurements do not consider the limited rate of water exchange (WX) between cardiomyocytes and the extracellular matrix which can result in underestimated ECV at higher contrast agent concentrations.

OBJECTIVES: The objective was to estimate ECV in patients with severe AS before and after surgical aortic valve replacement (AVR) using a 2-site exchange model (2SXM) that also enables estimates of the intracellular lifetime of water (τic; an indicator of the minor diameter of the cardiomyocytes).

METHODS: 20 patients (67±6 years) with severe AS, referred for AVR, underwent MRI on a 3 T MR system before and 6 months after AVR. T1 measurements were made using a multiparametric saturation-recovery single-shot acquisition before and at four time points post-injection of contrast agent. A 2SXM and standard linear model (LM) were used to estimate ECV and, when combined with indexed left ventricular mass (LVMI), to calculate cell and matrix volumes, (LVMI × (1-ECV)/1.05) and (LVMI × ECV/1.05), respectively. The 2SXM model was also used to estimate τic.

RESULTS: Data were acquired before and 174 (157 to 267) days after AVR. LVMI reduced following AVR, from 78±15 g/m2 to 63±11 g/m2 (p<0.001). ECV estimates increased from 22±3% to 28±5% (p<0.001) using the LM compared to 28±5% to 32±4% (p = 0.005) using the 2SXM. Indexed cell volume decreased from 58±12 cm3/m2 to 43±9 cm3/m2 (p<0.001; LM) and from 54±12 cm3/m2 to 41±8 cm3/m2 (p<0.001; 2SXM). Indexed matrix volume did not change significantly by either method (LM, 16±4 cm3/m2 to 17±3 cm3/m2; 2SXM, 20±5 cm3/m2 to 19±3 cm3/m2). τic decreased from 0.21±0.12 s to 0.12±0.09 s (p = 0.007).

CONCLUSION: Cellular hypertrophy regressed 6 months following AVR; the extracellular matrix volume did not change significantly. τic decreased post-AVR, indicating that the reduction in cell volume can be largely attributed to a reduction in cardiomyocyte diameter.