Innervated human cardiac muscle model reveals sympathetic drivers of KCNH2-associated arrhythmias.

Cardiac autonomic neurons regulate contractility. Autonomic nervous system dysregulation can cause sympathetic overdrive, leading to heart failure, and fatal arrhythmias. Here, we introduce innervated engineered human myocardium (iEHM), a model of neuro-cardiac junctions, constructed by fusing sympathetic neuronal organoids (SNO) and engineered human myocardium (EHM). Projections of sympathetic neurons formed presynaptic terminals in close proximity to cardiomyocytes and to the extensive vascular network co-developing in iEHM. Contractile responses to optogenetic stimulation of the accordingly engineered neuronal component demonstrated functional neuro-cardiac junctions. Modeling long-QT 2 in iEHM revealed sympathetic neuron hyperactivity and after depolarizations, underscoring a central role for sympathetic drive in KCNH2-associated arrhythmias. β-adrenoreceptor blockade was insufficient to rescue the pro-arrhythmic phenotype, while mexiletine targeting both neurons and cardiomyocytes, proved to be more effective. Collectively, our data establishes iEHM as a New Approach Methodology that provides a human-relevant, physiologically integrated model for mechanistic investigations and pharmacological testing.