A transmural t-tubule gradient in the human left ventricle is lost in heart failure: implications for myocardial...

The transverse tubular system (t-system) of ventricular cardiomyocytes is essential for excitation-contraction coupling and disrupted in chronic heart failure (HF). Whether physiological transmural gradients of t-tubule density exist in the non-failing human left ventricle (LV), and how representative small myocardial samples and biopsies are of the whole LV in HF, is unknown, limiting the translational use of t-tubules.

We performed quantitative microscopic imaging of transmural LV slices created from 8 non-failing donor hearts and 13 end-stage failing HFrEF hearts (HTx/LVAD), generating a total of >400 confocal volumes and > 100 confocal area scans. Established image processing pipelines extracted t-tubule skeleton volume density, intracellular t-tubule and sarcolemma distance (ΔTT, ΔSL), extracellular matrix (ECM) fraction, and a cell-width proxy. LV endomyocardial-forceps biopsies were obtained ex vivo from a subset of samples to model clinical biopsy procedures.

In non-failing hearts, t-tubule skeleton density was 45% higher at the subepicardium than the subendocardium (0.16 ± 0.01% vs 0.11 ± 0.01%, p < 0.001), with correspondingly lower ΔTT (0.89 vs 1.05 μm, p < 0.001) and ΔSL. Failing hearts showed ~40% lower t-tubule density, increased ECM (~28% vs ~20%), and ~ 50% wider myocytes. The transmural gradient was lost. Apical regions showed the most pronounced TT remodeling but predicted the remaining LV t-tubule parameters with mean relative errors of ~10%. Mean ΔSL in endomyocardial biopsies correlated best with the corresponding wall section (R² = 0.62, p = 0.0003), allowing samples with and without t-system remodeling to be distinguished using a threshold.

A subendo-to-subepicardial t-tubule gradient exists in the non-failing human LV and is abolished in HFrEF. These findings define the sampling constraints under which myocardial specimens may be used to stratify advanced t-system remodeling in human heart failure.