Is myocardial fibrosis a hallmark of paradoxical low gradient aortic stenosis?

Abstract

The pathophysiology and clinical significance of low gradient severe aortic stenosis [SAS] despite normal EF, also referred to as paradoxical low gradient [PLG]-SAS, is controversial. It has been suggested that PLG- SAS was associated with higher degree of interstitial myocardial fibrosis and worse outcome as compared to high-gradient (HG)-SAS. To verify this, we obtained myocardial biopsies and measured myocardial extravascular volume fraction (ECV, %) from cMR Modified Look-Locker imaging (MOLLI) T1 mapping at 3T in 155 consecutive patients with moderate to severe AS [22 moderate AS, 75 HG-SAS, 58 PLG-SAS, including 24 low flow (LF) and 34 normal flow (NF) PLG-SAS]. ECV values were compared to those measured in 33 normal age-matched controls. ECV correlated with the amount of interstitial fibrosis (IF) on histology ( r = 0.75, P < 0.01). By histology, the magnitude of IF was similar in all SAS subgroups (4.5 ± 3.3% in NFPLG-SAS, 6.2 ± 4.8% in LFPLG-SAS, 5.5 ± 5.3% in HG-SAS, P = 0.71). ECV was also similar in the different subgroups (29.1 ± 4.3% in moderate AS, 28.8 ± 4.0% in NFPLG-SAS, 29.6 ± 3.2% in LFPLG-SAS, 28.3 ± 5.5% in HG-SAS, P = 0.69), and was not different from that measured in controls (27 ± 4%, P = 0.33). A similar number of SAS patients had ECV values above 95% CI of control subjects HV [2/22 (9%) MAS, 3/24 (13%) LFPLG-SAS, 5/34 (14%) NFPLG-SAS and 9/75 (12%) HG-SAS, P = 0.95; Fig. 1 ]. Our results demonstrate that the amount of IF, measured by histology or MOLLI is similar among controls and patients with SAS. These data do not support the contention that PLG-SAS is associated with higher degree of IF.