Acute effects of a mavacamten-like myosin-inhibitor (MYK-581 in a feline model of obstructed hypertrophic cardiomyopathy: evidence of improved ventricular filling (beyond obstruction reprieve)

Abstract Introduction Hypertrophic cardiomyopathy (HCM) is a progressive disease characterized by cardiac remodeling, hyperdynamic contraction, and impaired ventricular filling that can lead to dynamic left-ventricular outflow-track (LVOT) obstruction and exertional intolerance. Direct myosin-inhibition with mavacamten can normalize contractility and improve exercise capacity in patients with oHCM, providing sustained symptomatic relief. However, mavacamten can also improve ventricular filling by limiting residual cross-bridges during diastole, and therefore, may offer cardiac benefits beyond obstruction reprieve. This study leveraged a feline model of oHCM, cats with the A31P MYBPC3 variant, to study the acute in vivo effects of MYK-581, a mavacamten surrogate, on cardiac hemodynamics and filling. Methods A31P-homozygous cats with HCM (A31P, n=10) and wild-type healthy controls (CTRL, n=9) were anesthetized and instrumented for invasive pressure-volume (PV) measurements as well as trans-thoracic echocardiographic recording. A subset of cats were assigned to receive either vehicle (VEH, n=7) or MYK-581 (MYK, n=8) with a short IV infusion. Cardiac hemodynamics, function, and geometry were assessed at steady state before and during dobutamine challenges (2.5 μg/kg/min IV). Results A31P cats had thicker ventricular walls (6.4±0.1 vs. 5.2±0.2 mm, P