Dynamic Changes of Distinct Compartmental LV Remodeling Following Septal Myectomy in Hypertrophic Obstructive Cardiomyopathy

BACKGROUND: In hypertrophic obstructive cardiomyopathy, left ventricular mass index (LVMi) regresses following septal myectomy, but the specific dynamics, mechanisms (involving cellular and extracellular compartments), and related factors remain unclear. METHODS: This prospective study included patients with hypertrophic obstructive cardiomyopathy who underwent septal myectomy. Cardiac magnetic resonance imaging was performed preoperatively and at 6, 12, and 24 months postoperatively. LVMi, indexed cellular volume, and indexed extracellular volume were analyzed using repeated measures ANOVA. Factors associated with LVMi regression, postoperatively, were identified using linear regression. RESULTS: The study included 27 patients (53.70±13.85 years; 17 female). LVMi significantly decreased from 105.76±25.22 g/m 2 , preoperatively, to 82.52±25.90 g/m 2 at 6 months, postoperatively, further declining to 78.86±24.73 g/m 2 at 12 months and 76.22±23.93 g/m 2 at 24 months ( P <0.05). The average percent decrease in LVMi from baseline was 22.97% at 6 months, 26.26% at 12 months, and 28.58% at 24 months postoperatively. This regression is primarily driven by indexed cellular volume regression (23.70%), with a smaller reduction in the indexed extracellular volume (18.40%) in the first 6 months. Both compartments exhibited sustained reductions through 12 months. But from 12 to 24 months, only indexed extracellular volume continued to decline (from 22.13±6.76 to 20.89±6.25 mL/m 2 ; P <0.001). Greater left ventricular outflow tract pressure gradient reduction (β=0.157; P =0.001) was associated with LVMi regression after septal myectomy. CONCLUSIONS: In patients with hypertrophic obstructive cardiomyopathy postseptal myectomy, early LVMi reduction involves both cellular and extracellular compartments, with slower reduction from 12 to 24 months, mainly driven by the extracellular component. This demonstrates rapid myocardial adaptability to afterload relief, with slower extracellular matrix remodeling. Greater left ventricular outflow tract pressure gradient reduction was associated with greater LVMi regression after surgery. REGISTRATION: URL: https://www.chictr.org.cn ; Unique identifier: ChiCTR2100043699.