This study shows that spiral waves in atrial cardiomyocyte monolayers can be terminated effectively by a light-induced depolarizing current, produced by the arrhythmogenic substrate itself, upon optogenetic engineering. These results provide proof-of-concept for shockless defibrillation.

Arrhythmogeneity of fibrotic myocardial cultures is mediated by Cx43 expression in MFBs. Reduced expression of Cx43 causes a more negative MDP of CMCs. This preserves CMC excitability, limits prolongation of repolarization and thereby strongly reduces the incidence of spontaneous re-entrant tachyarrhythmias.

Background— Atrial fibrillation is the most common cardiac arrhythmia. Ventricular proarrhythmia hinders pharmacological atrial fibrillation treatment. Modulation of atrium-specific Kir3.x channels, which generate a constitutively active current ( I K,ACh-c ) after atrial remodeling, might circumvent this problem. However, it is unknown whether and how I K,ACh-c contributes to atrial fibrillation induction, dynamics, and termination. Therefore, we investigated the effects of I K,ACh-c blockade and Kir3.x downregulation on atrial fibrillation. Methods and Results— Neonatal rat atrial cardiomyocyte cultures and intact atria were burst paced to induce reentry. To study the effects of Kir3.x on action potential characteristics and propagation patterns, cultures were treated with tertiapin or transduced with lentiviral vectors encoding Kcnj3 - or Kcnj5 -specific shRNAs. Kir3.1 and Kir3.4 were expressed in atrial but not in ventricular cardiomyocyte cultures. Tertiapin prolonged action potential duration (APD; 54.7±24.0 to 128.8±16.9 milliseconds; P <0.0001) in atrial cultures during reentry, indicating the presence of I K,ACh-c . Furthermore, tertiapin decreased rotor frequency (14.4±7.4 to 6.6±2.0 Hz; P <0.05) and complexity (6.6±7.7 to 0.6±0.8 phase singularities; P <0.0001). Knockdown of Kcnj3 or Kcnj5 gave similar results. Blockade of I K,ACh-c prevented/terminated reentry by prolonging APD and changing APD and conduction velocity restitution slopes, thereby altering the probability of APD alternans and rotor destabilization. Whole-heart mapping experiments confirmed key findings (eg, >50% reduction in atrial fibrillation inducibility after I K,ACh-c blockade). Conclusions— Atrium-specific Kir3.x controls the induction, dynamics, and termination of fibrillation by modulating APD and APD/conduction velocity restitution slopes in atrial tissue with I K,ACh-c . This study provides new molecular and mechanistic insights into atrial tachyarrhythmias and identifies Kir3.x as a promising atrium-specific target for antiarrhythmic strategies.

Proliferation of MFBs in myocardial cultures gives rise to spontaneous, sustained reentrant tachyarrhythmias. Antiproliferative treatment of such cultures prevents the occurrence of arrhythmias by limiting MFB-induced depolarization, conduction slowing, and ectopic activity. This study could provide a rationale for a new treatment option for cardiac arrhythmias.