Myocardial histopathology by cardiac biopsy enhances phenotyping of heart failure with preserved ejection fraction

In patients with heart failure with preserved ejection fraction (HFpEF), studies have described different HFpEF phenogroups based on medical comorbidities and variable echocardiographic, invasive hemodynamic, and biomarker data. We hypothesized that myocardial histopathologic findings may define phenogroups with differing clinical features and outcomes in patients with HFpEF.

We analyzed consecutive patients with left HF and EF ≥50% who underwent right ventricular septal endomyocardial biopsy (EMB) at our institution between 2001 and 2022 to investigate HF etiology. Patients with infiltrative or hypertrophic cardiomyopathy, sarcoidosis, myocarditis, primary valvular heart disease, constrictive pericarditis, isolated right HF, or insufficient EMB samples were excluded. Clinical, echocardiographic, and invasive hemodynamic data were collected. The severity of hypertrophy and fibrosis on EMB specimens was characterized (semiquantitative grading) by experienced cardiac pathologists based on standard histologic stains. Patients were stratified into four phenogroups based on EMB findings: "mild" (none/mild hypertrophy and fibrosis), "hypertrophy" (moderate/marked hypertrophy, minimal/mild fibrosis), "fibrosis" (moderate/marked fibrosis, none/mild hypertrophy), and "severe" (moderate/marked hypertrophy and fibrosis).

Among the 121 patients analyzed, the median age was 67 years, 50% were female and cardiovascular conditions were common (Table 1). Fibrosis was graded as minimal in 21% (n=25), mild in 64% (n=77), moderate in 12% (n=15), and marked in 3% (n=4). Hypertrophy was graded as none in 4% (n=5), mild in 41% (n=50), moderate in 40% (n=48), and marked in 15% (n=18). Only one patient had the isolated "fibrosis" phenogroup and was excluded from further analysis, while 54 had the "mild", 48 had the "hypertrophy", and 18 had the "severe" phenogroup (Table 1). The "hypertrophy" phenogroup exhibited significantly higher rates of hypertension, diabetes, RV dilation, and higher pulmonary artery pressures. Over a median follow-up of 7.9 years (3.1–13.8), mortality rate varied according to the histopathologic phenogroups (Figure 1, p=0.034) with "severe" having the worst and "mild" having the best outcomes. Survival analyses based on fibrosis grades alone, hypertrophy grades alone, or echocardiographic hypertrophy did not reveal significant differences (all p = NS). Differences in survival remained significant adjusting for age (HR 3.39, 95% CI 1.20-9.58).

The integrated severity of histopathologic hypertrophic and fibrotic remodeling defined HFpEF phenogroups with variable prognosis. Clinical features did not reliably identify histopathologic phenogroups. These data suggest that advanced myocardial phenotyping (e.g., gene, protein, metabolism) may reveal unique HFpEF myocardial subtypes in need of specific therapies.Figure 1