Abstract Body (Do not enter title and authors here): Background: Titin truncating variants (TTNtv) are present in ~1% of the population and increase risk for cardiovascular complications like early onset atrial fibrillation (AF), dilated cardiomyopathy (DCM), and ventricular arrhythmias. Many TTNtv patients who present with AF may have normal or only modestly impaired ventricular function, and the relationship between AF and DCM in TTNtv has been challenging to study owing to the lack of suitable models.

Hypothesis: TTNtv increase the susceptibility to arrhythmia-induced cardiomyopathy in the context of AF in a clinically-relevant pig model.

Methods: A heterozygous TTNtv model (+/K16648X) was generated in Yucatan minipigs by introducing the mutation in fetal fibroblasts using homologous recombination, followed by somatic cell nuclear transfer. K16648X creates an A band truncation in titin. Genotype was confirmed by long-range PCR, Southern blot, and DNA sequencing (Fig. A). One year-old TTNtv (n=4) and littermate controls (n=3) were used for the study. A single-chamber atrial pacemaker was inserted and used for atrial tachypacing (ATP) for 5 weeks. Pacing was only briefly interrupted to determine AF burden, thus providing balanced exposure to tachycardia. Echocardiograms were obtained at baseline, after 2 and 5 weeks. A terminal EP study determined ventricular ERP and VT/VF inducibility by programmed stimulation. Ventricular tissue was embedded in OCT and frozen. Cryosections were stained with Masson Trichrome.

Results: At baseline, ventricular function was similar between control and TTNtv piglets by echo (Fig. B). While both groups developed arrhythmia-induced cardiomyopathy, TTNtv had significantly reduced LV ejection fraction (LVEF) compared to wild-type controls after ATP. While right and left ventricular ERPs were not different between groups, programmed stimulation induced VT/VF in 40% of attempts in TTNtv animals while control animals never developed VT/VF (Fig. C). Trichrome stain showed low overall fibrosis, with a small but non significant increase of fibrosis in TTNtv LV myocardium (Fig. D, arrows).

Conclusion: TTNtv increases the susceptibility to arrhythmia-induced cardiomyopathy in a porcine model, with worse LV systolic function and increased propensity to ventricular arrhythmias after 5 weeks of ATP. This clinically-relevant porcine model will support the identification of the molecular mechanisms of TTNtv-dependent cardiomyopathy and the future development of mechanism-guided treatments.