Differences in Myocardial Remodeling and Tissue Characteristics in Chronic Isolated Aortic and Mitral Regurgitation.

Background: The left ventricular hemodynamic load differs between aortic regurgitation (AR) and primary mitral regurgitation (MR). We used cardiac magnetic resonance to compare left ventricular remodeling patterns, systemic forward stroke volume, and tissue characteristics between patients with isolated AR and isolated MR.
Methods: We assessed remodeling parameters across the spectrum of regurgitant volume. Left ventricular volumes and mass were compared against normal values for age and sex. We calculated forward stroke volume (planimetered left ventricular stroke volume-regurgitant volume) and derived a cardiac magnetic resonance-based systemic cardiac index. We assessed symptom status according to remodeling patterns. We also evaluated the prevalence of myocardial scarring using late gadolinium enhancement imaging, and the extent of interstitial expansion via extracellular volume fraction.
Results: We studied 664 patients (240 AR, 424 primary MR), median age of 60.7 (49.5-69.9) years. AR led to more pronounced increases in ventricular volume and mass compared with MR across the spectrum of regurgitant volume ( P <0.001). In ≥moderate regurgitation, AR patients had a higher prevalence of eccentric hypertrophy (58.3% versus 17.5% in MR; P <0.001), whereas MR patients had normal geometry (56.7%) followed by myocardial thinning with low mass/volume ratio (18.4%). The patterns of eccentric hypertrophy and myocardial thinning were more common in symptomatic AR and MR patients ( P <0.001). Systemic cardiac index remained unchanged across the spectrum of AR, whereas it progressively declined with increasing MR volume. Patients with MR had a higher prevalence of myocardial scarring and higher extracellular volume with increasing regurgitant volume ( P value for trend <0.001), whereas they were unchanged across the spectrum of AR ( P =0.24 and 0.42, respectively).
Conclusions: Cardiac magnetic resonance identified significant heterogeneity in remodeling patterns and tissue characteristics at matched degrees of AR and MR. Further research is needed to examine if these differences impact reverse remodeling and clinical outcomes after intervention.