The hypothesis to be tested is that RyR2 hyperactivity in patients with structural heart disease drives proarrhythmic changes in refractoriness and conduction, and decreases cardiac contractility, which promotes VT/VF. Dantrolene, a currently available drug that inhibits RyR2, but has no Na or K channel activity, will be used as a tool to study RyR2 modulation. The investigators propose a randomized controlled trial of dantrolene versus placebo in patients with structural heart disease referred for VT ablation to evaluate electrophysiologic, hemodynamic, and arrhythmia prevention endpoints. Dantrolene's inhibition of RyR1 will also be studied to define its effect on muscle and respiratory strength in this clinical population, which will be important if dantrolene is to be considered for repurposing as an antiarrhythmic drug.~The two aims are:~Aim 1: To conduct a randomized, placebo-controlled trial of dantrolene to study the effect of RyR inhibition on cardiac electrophysiology, hemodynamics, arrhythmia inducibility, muscle strength, and respiratory mechanics in patients with structural heart disease referred for VT ablation.~Aim 2: To explore the pharmacokinetic/pharmacodynamic relationship of I.V. dantrolene and its short-term effect on cardiac electrophysiology, hemodynamics, and muscle and respiratory strength.
This is a randomized, placebo controlled trial of Dantrolene (N= 84 participants) to demonstrate the feasibility of using I.V. dantrolene to study the effect of RyR2 inhibition on cardiac electrophysiology, hemodynamics and ventricular arrhythmia inducibility in patients with structural heart disease referred for VT ablation. The investigators will also explore the pharmacokinetic/pharmacodynamic relationship of I.V. dantrolene and it short-term effect on specific cardiac electrophysiologic and hemodynamic parameters.