Ryanodine receptor inhibition with acute dantrolene treatment reduces arrhythmia susceptibility in human hearts.

Ryanodine receptor 2 (RyR2) hyperactivity is observed in structural heart diseases that are a result of ischemia or heart failure. It causes abnormal calcium handling and calcium leaks that cause metabolic, electrical, and mechanical dysfunction, which can trigger arrhythmias. Here, we tested the antiarrhythmic potential of dantrolene (RyR inhibitor) in human hearts. Human hearts not used in transplantation were obtained, and right ventricular outflow tract (RVOT) wedges and left ventricular (LV) slices were prepared. Pseudo-ECGs were recorded to determine premature ventricular contraction (PVC) incidences. Optical mapping was performed to determine arrhythmogenic substrates. After baseline optical recordings, tissues were treated with 1) isoproterenol (250 nM), 2) caffeine (200 mM), and 3) dantrolene (2 or 10 mM). Optical recordings were obtained after each treatment. Isoproterenol and caffeine treatment increased PVC incidence, whereas dantrolene reduced the PVC burden. Isoproterenol shortened action potential duration (APD) in the RV, RVOT, and LV regions and shortened calcium transient duration (CaTD) in the LV. Caffeine further shortened APD in the RV, did not modulate APD in the RVOT, and prolonged APD in the LV. In addition, in the LV, CaTD prolongation was also observed. More importantly, adding dantrolene did not alter APD in the RV or RVOT regions but produced a trend toward APD prolongation and significant CaTD prolongation in the LV, restoring these parameters to baseline values. In conclusions, dantrolene treatment suppresses triggers and reverses arrhythmogenic substrates in the human heart and could be a novel antiarrhythmic therapy in patients with structural heart disease.NEW & NOTEWORTHY Ryanodine receptor 2 hyperactivity is observed in structural heart diseases caused by ischemia or heart failure. It causes abnormal calcium leaks, which can trigger arrhythmias. To prevent arrhythmias, we applied dantrolene in human hearts ex vivo. Isoproterenol and caffeine treatment increased PVC incidence, whereas dantrolene reduced the PVC burden. Dantrolene treatment suppresses triggers and reverses arrhythmogenic substrates and could be a novel antiarrhythmic therapy in patients with structural heart disease.

Coordinated Tbx3 / Tbx5 transcriptional control of the adult ventricular conduction system.

The cardiac conduction system (CCS) orchestrates the electrical impulses that enable coordinated contraction of the cardiac chambers. The T-box transcription factors TBX3 and TBX5 are required for cardiac conduction system development and associated with overlapping and distinct human cardiac conduction system diseases. We evaluated the coordinated role of Tbx3 and Tbx5 in the murine ventricular conduction system (VCS). We engineered a compound Tbx3:Tbx5 conditional knockout allele for both genes located in cis on mouse chromosome 5. Conditional deletion of both T-box transcriptional factors in the ventricular conduction system, using the VCS-specific Mink:Cre, caused loss of VCS function and molecular identity. Combined Tbx3 and Tbx5 deficiency in the adult VCS led to conduction defects, including prolonged PR and QRS intervals and elevated susceptibility to ventricular tachycardia. These electrophysiologic defects occurred prior to detectable alterations in cardiac contractility or histologic morphology, indicative of a primary conduction system defect. Tbx3:Tbx5 double knockout VCS cardiomyocytes revealed a transcriptional shift towards non-CCS-specialized working myocardium, suggesting reprogramming of their cellular identity. Furthermore, optical mapping revealed a loss of VCS-specific conduction system propagation. Collectively, these findings indicate that Tbx3 and Tbx5 coordinate to control VCS molecular fate and function, with implications for understanding cardiac conduction disorders in humans.