Computed tomography-derived myocardial extracellular volume in patients with severe aortic stenosis: correlation with markers of ventricular dysfunction

Abstract

Abstract Funding Acknowledgements Type of funding sources: None. Background Myocardial fibrosis is a potential adverse prognostic marker in patients with severe aortic stenosis (AS) and can be quantified using non-invasive imaging measures, such as the extracellular volume fraction (ECV). Although computed tomography (CT) for transcatheter aortic valve replacement (TAVR) planning was originally developed to assess the aortic valve complex and access routes, it has evolved to include the measurement of ECV for myocardial tissue characterization. Aim This study aimed to determine associations between CT-derived ECV (ECVCT) and clinical and echocardiographic markers of ventricular function in patients with severe AS referred for TAVR-planning CT. Methods Single-center prospective study enrolling all consecutive patients with severe symptomatic AS referred for TAVR-planning CT between April and November 2022. CT was performed on a 192-slice dual-source 3rd generation scanner (Siemens Somatom Force) and ECVCT was acquired during TAVR-planning using an additional 5-minute post-contrast low-radiation-dose prospective acquisition. ECVCT was calculated as the ratio of change in CT attenuation (Hounsfield units [HU]) of the septal myocardium and the left ventricle (LV) blood pool before and after contrast administration, according to the equation: ECVCT = (1 – hematocrit) x (DHUmyo/DHUblood) – Figure 1A. Results A total of 102 patients were included (mean age 81 ± 7 years; 46% male; mean valvular transaortic gradient 51 ± 14 mmHg; mean aortic valve area 0.7 ± 0.2 cm2; mean LV ejection fraction (EF) by 2D echocardiogram 57 ± 11%). No patient had a clinical diagnosis of cardiac amyloidosis. Overall, the mean ECVCT value was 33.4 ± 7.0%. Myocardial ECVCT values significantly differed between AS subtypes, with higher values in patients with low-gradient AS (n=13, 13%; ECVCT 40.3 ± 4.8% vs 32.4 ± 6.7%, p<0.001) - Figure 1B. Additionally, myocardial ECVCT values correlated with markers of LV and right ventricular (RV) dysfunction, including lower LV EF (r = -0.354, p<0.001), worse LV global longitudinal strain (r = 0.420, p = 0.002), reduced TAPSE (r = -0.230, p = 0.043) and RV S wave by tissue doppler imaging (r = -0.321, p = 0.010) and higher NT-proBNP values (r = 0.347, p = 0.002). Conclusions In patients with severe AS scheduled for TAVR-planning CT, ECVCT values are significantly higher in those with low-gradient AS and correlated with several measures of biventricular dysfunction. This CT parameter may be useful to identify a subgroup of patients with higher risk of adverse prognosis.