ABSTRACT: Objectives: Myocardial fibrosis in noninfarcted myocardium is emerging as a principal phenotype of vulnerability to adverse events such as mortality and hospitalization for heart failure (HHF), but its optimal noninvasive measurement remains uncertain despite consistently robust histologic validation data for extracellular volume fraction (ECV). We therefore compared ECV, native T1, post contrast T1, the gadolinium contrast partition coefficient (lambda), and the presence of nonischemic scar in their associations with mortality and HHF outcomes. Method: To quantify of myocardial fibrosis, we performed T1 mapping (MOLLI) in basal and mid short axis slices with cardiovascular magnetic resonance (CMR) before contrast and 12-30 minutes post contrast bolus in 1185 consecutive patients without amyloidosis, hypertrophic or stress cardiomyopathy. We assessed associations with outcomes using Kaplan-Meier plots and chi square values from univariable Cox regression models. All standard T1 mapping parameters were obtained: native and post contrast myocardial T1, the partition coefficient lambda, and ECV. ECV = (1-hematocrit) · [?R1myocardium]/[?R1bloodpool], where R1 = 1/T1 Late gadolinium enhancement imaging with phase sensitive reconstruction identified nonischemic scar. Results: Over a median of 1.7 years, 111 individuals experienced events after CMR: 55 HHF events and 74 deaths. ECV yielded better separation of Kaplan-Meier curves in a dose dependent fashion (Figure) and also stronger associations with the combined endpoint of death or HHF. The ECV chi square (77.3, p < 0.001) was at least twice as large as the Native T1 chi square (37.5, p < 0.001), the lambda chi square (34.8, p < 0.001) and nonischemic scar (chi square = 20.5, p<0.001). Post-contrast T1 was not associated with outcomes, even when adjusting further for time after contrast bolus, renal function, and patient weight (chi square <3, p >0.10). Conclusion: Analogous to histologic previously published validation data, quantitative ECV myocardial fibrosis measures associated with outcomes far stronger than other surrogate measures outcome measures such as native T1, post contrast T1 and nonischemic scar on LGE images. These data suggest that ECV is the noninvasive metric of choice to measure myocardial fibrosis. Figure. Kaplan-Meier Plots for T1 mapping parameters.
