Myocardial ultrastructure of human heart failure with preserved ejection fraction

Over half of patients with heart failure have a preserved ejection fraction (>50%, called HFpEF), a syndrome with substantial morbidity/mortality and few effective therapies¹. Its dominant comorbidity is now obesity, which worsens disease and prognosis^1–3. Myocardial data from patients with morbid obesity and HFpEF show depressed myocyte calcium-stimulated tension⁴ and disrupted gene expression of mitochondrial and lipid metabolic pathways^5,6, abnormalities shared by human HF with a reduced EF but less so in HFpEF without severe obesity. The impact of severe obesity on human HFpEF myocardial ultrastructure remains unexplored. Here we assessed the myocardial ultrastructure in septal biopsies from patients with HFpEF using transmission electron microscopy. We observed sarcomere disruption and sarcolysis, mitochondrial swelling with cristae separation and dissolution and lipid droplet accumulation that was more prominent in the most obese patients with HFpEF and not dependent on comorbid diabetes. Myocardial proteomics revealed associated reduction in fatty acid uptake, processing and oxidation and mitochondrial respiration proteins, particularly in very obese patients with HFpEF.