Comparative Assessment of CMR-Determined Extracellular Volume Metrics in Predicting Adverse Outcomes

<b>Background:</b> Extracellular volume (ECV) by cardiovascular magnetic resonance (CMR) imaging is associated with disease burden and clinical outcomes. Recent studies in patients with valvular heart disease (VHD) have suggested that the indexed total ECV (iECV) = ECVx(LV_mass/1.05)/body surface area may supersede ECV in terms of prognostication. In this study, we aimed to compare the prognostic capability of conventional ECV and iECV in an all-comer CMR cohort. <b>Methods:</b> From January 2012 to 2023, ECV and iECV were measured in consecutive CMR patients. Adverse outcomes were defined as a composite of hospitalization for heart failure (HF) and/or death. All patients underwent transthoracic echocardiography within 3 weeks of CMR. <b>Results:</b> Overall, 1525 patients (44% female, mean age 65 ± 18 years) were included. The mean ECV was 29 ± 9% and the mean iECV was 21 ± 13 mL/m². During 52 ± 36 months of follow-up, 414 (27%) events occurred. Both ECV (HR = 1.04, 95% CI = 1.04-1.05, <i>p</i> < 0.001) and iECV (HR = 1.03, 95% CI = 1.02-1.03, <i>p</i> < 0.001) were significantly associated with outcomes. Having been stratified for ECV and iECV tertiles, Kaplan-Meier analyses showed a significant association with event-free survival for both parameters (log-rank, <i>p</i> < 0.001 for both; central illustration). Regarding multivariate analysis, adjusted for age, sex, left ventricular function, and NT-proBNP, both ECV and iECV remained independently associated with the composite endpoint (ECV: HR = 1.31, 95% CI = 1.20-1.44, <i>p</i> < 0.001; iECV: HR = 1.17, 95% CI = 1.06-1.29, <i>p</i> = 0.002). In addition, ECV was significantly associated with aortic valve velocity (<i>p</i> < 0.001) pertaining to echocardiography, whereas iECV did not show an association (<i>p</i> = 0.41). <b>Conclusions:</b> Both conventional ECV and iECV provided profound prognostic information regarding the risk of HF hospitalizations and death. However, iECV, which is more complex to determine, did not add value.