Early onset of Ca ²⁺ waves and synchronization in multicellular clusters facilitate focal arrhythmogenesis in human heart failure

Background

Spontaneous Ca ²⁺ release events and waves are frequent in isolated ventricular cardiomyocytes from failing hearts (HF) and are proposed to initiate arrhythmias in the intact heart. However, evidence supporting whether single-cell Ca ²⁺ waves trigger tissue-wide depolarization in the intact heart is scarce, particularly in human HF. We characterized Ca ²⁺ waves at single-cell resolution within the multicellular network of the intact heart and identified propagating dynamics and mechanisms facilitating arrhythmogenesis at tissue level.

Methods

Living myocardial slices (LMS) from HF and non-HF human hearts were prepared from left ventricular tissue and paced at 2 Hz under adrenergic stimulation. Ca ²⁺ transients and waves were recorded by wide-field imaging of Fluo-8. Ca ²⁺ waves in relation to single-cell structures within each LMS were identified using custom algorithms. Computational modelling assessed whether experimentally observed HF Ca ²⁺ waves dynamics can lead to focal excitation in tissue models.

Results

Following pacing, early onset Ca ²⁺ waves, initiating within the first 2 seconds, were more frequent in HF compared to non-HF, and HF cardiomyocytes had more foci, where Ca ²⁺ waves originate, than non-HF. Spatial mapping showed that early onset waves in HF occurred frequently in clusters of neighboring cells. Although early onset Ca ²⁺ waves propagated similar distances in HF and non-HF cardiomyocytes, they more frequently crossed cell boundaries in HF. Particularly, HF LMS exhibited more side-to-side Ca ²⁺ propagation, correlating with increased connexin 43 distribution to lateral membranes. Furthermore, HF LMS exhibited more local and global triggered Ca ²⁺ activities compared to non-HF LMS, correlating with local tissue depolarization. Simulations of HF Ca ²⁺ wave dynamics in remodeled tissue demonstrated a greater capacity to elicit focal excitation.

Conclusions

In human HF, a higher incidence of early onset Ca ²⁺ waves combines with altered intercellular connectivity to create synchrony in clusters of nearby cells that can overcome the current sink, thereby increasing arrhythmia susceptibility.

GRAPHICAL ABSTRACT