Effects of Late Sodium Current Blockade on Ventricular Refibrillation in a Rabbit Model

BACKGROUND

After defibrillation of initial ventricular fibrillation (VF), it is crucial to prevent refibrillation to ensure successful resuscitation outcomes. Inability of the late Na⁺ current to inactivate leads to intracellular Ca²⁺ dysregulation and arrhythmias. Our aim was to determine the effects of ranolazine and GS-967, inhibitors of the late Na⁺ current, on ventricular refibrillation.

METHODS AND RESULTS

Long-duration VF was induced electrically in Langendorff-perfused rabbit hearts (n=22) and terminated with a defibrillator after 6 minutes. Fibrillating hearts were randomized into 3 groups: treatment with ranolazine, GS-967, or nontreated controls. In the treated groups, hearts were perfused with ranolazine or GS-967 at 2 minutes of VF. In control experiments, perfusion solution was supplemented with isotonic saline in lieu of a drug. Inducibility of refibrillation was assessed after initial long-duration VF by attempting to reinduce VF. Sustained refibrillation was successful in fewer ranolazine-treated (29.17%; P=0.005) or GS-967-treated (45.83%, P=0.035) hearts compared with that in nontreated control hearts (84.85%). In GS-967-treated hearts, significantly more spontaneous termination of initial long-duration VF was observed (66.67%; P=0.01). Ca²⁺ transient duration was reduced in ranolazine-treated hearts compared with that in controls (P=0.05) and also Ca²⁺ alternans (P=0.03).

CONCLUSIONS

Late Na⁺ current inhibition during long-duration VF reduces the susceptibility to subsequent refibrillation, partially by mitigating dysregulation of intracellular Ca²⁺. These results suggest the potential therapeutic use of ranolazine and GS-967 and call for further testing in cardiac arrest models.

In silico approach towards lipase mediated chemoenzymatic synthesis of (S)-ranolazine, as an anti-anginal drug

An in silico modelling based biocatalytic approach for the synthesis of drugs and drug intermediates in enantiopure forms is a rationalized methodology over the organo-chemical routes.

Selective and non-selective non-steroidal anti-inflammatory drugs differentially regulate pulmonary vein and atrial arrhythmogenesis

BACKGROUND

Non-steroidal anti-inflammatory drugs (NSAIDs) increase the risk of atrial fibrillation (AF). This study investigated whether selective and non-selective NSAIDs differentially regulate the arrhythmogenesis of pulmonary veins and atria.

METHODS

Conventional microelectrodes were used to record action potentials (APs) in isolated rabbit PVs, sinoatrial node (SAN), left atrium (LA), and right atrium (RA) preparations before and after celecoxib or indomethacin administration. A whole-cell patch clamp was used to record the sodium-calcium exchanger (NCX) current, L-type calcium current (ICa-L), and late sodium current (INa-late) before and after celecoxib administration in isolated PV cardiomyocytes.

RESULTS

Celecoxib (0.3, 1, and 3 μM) reduced PV spontaneous beating rates, and induced delayed afterdepolarizations and burst firings in four of eight PV preparations (50%, p<0.05). Celecoxib also reduced SAN beating rates and decreased AP durations (APDs) in RA and LA, but did not change the resting membrane potential. Indomethacin (0.3, 1, 3, and 10 μM) changed neither the PV or SAN beating rates nor RA APDs, but it reduced LA APDs. Celecoxib (3 μM) significantly increased the NCX current and decreased the ICa-L, but did not change the INa-late. Ranolazine (10 μM) suppressed celecoxib (3 μM)-induced PV burst firings in 6 (86%, p<0.05) of 7 PVs. KB-R7943 (10 μM) suppressed celecoxib (3 μM)-induced PV burst firings in 5 (71%, p<0.05) of 7 PVs.

CONCLUSIONS

Selective and non-selective NSAIDs differentially modulate PV and atrial electrophysiological characteristics. Celecoxib increased PV triggered activity through enhancement of the NCX current, which contributed to its arrhythmogenesis.

Mechanisms of ranolazine's dual protection against atrial and ventricular fibrillation

Coronary artery disease and heart failure carry concurrent risk for atrial fibrillation and life-threatening ventricular arrhythmias. We review evidence indicating that at therapeutic concentrations, ranolazine has potential for dual suppression of these arrhythmias. Mechanisms and clinical implications are discussed.

Nitric oxide/reactive oxygen species generation and nitroso/redox imbalance in heart failure: from molecular mechanisms to therapeutic implications

Adaptation of the heart to intrinsic and external stress involves complex modifications at the molecular and cellular levels that lead to tissue remodeling, functional and metabolic alterations, and finally to failure depending upon the nature, intensity, and chronicity of the stress. Reactive oxygen species (ROS) have long been considered as merely harmful entities, but their role as second messengers has gradually emerged. At the same time, our comprehension of the multifaceted role of nitric oxide (NO) and the related reactive nitrogen species (RNS) has been upgraded. The tight interlay between ROS and RNS suggests that their imbalance may implicate the impairment in physiological NO/redox-based signaling that contributes to the failing of the cardiovascular system. This review initially provides basic concepts on the role of nitroso/oxidative stress in the pathophysiology of heart failure with a particular focus on sources of ROS/RNS, their downstream targets, and endogenous modulators. Then, the role of NO/redox regulation of cardiomyocyte function, including calcium homeostasis, electrogenesis, and insulin signaling pathways, is described. Finally, an overview of old and emerging therapeutic opportunities in heart failure is presented, focusing on modulation of NO/redox mechanisms and discussing benefits and limitations.

First Direct Comparison of the Late Sodium Current Blocker Ranolazine to Established Antiarrhythmic Agents in an Ischemia/Reperfusion Model

Introduction: There are few safe antiarrhythmics for ischemic heart disease. Whereas ranolazine is a promising late INa blocker with antiarrhythmic effects, and devoid of pro-arrhythmic properties, there are no direct comparisons between ranolazine and other antiarrhythmic agents in an ischemia/reperfusion setting. Hypothesis and methods: To determine whether ranolazine was as effective as sotalol and lidocaine to reduce ischemia/reperfusion-induced arrhythmias, anesthetized rats were subjected to 5 minutes of proximal left coronary artery occlusion plus 5 minutes of reperfusion, which causes severe ventricular arrhythmias. At 21 minutes prior to coronary occlusion, rats (n = 20 per group) were randomized to receive either sotalol (intravenous [IV] bolus 5 mg/kg, 10 mg/kg per hour infusion), lidocaine (IV bolus 2.5 mg/kg, 2.5 mg/kg/hr infusion), ranolazine (IV bolus 3.3 mg/kg, 3.2 mg/kg per hour infusion), or saline (control). Results: The incidence of ventricular arrhythmias in the sotalol (S), lidocaine (L), ranolazine (R), and control (C) groups was 7/20, 10/20, 9/20, and 16/20, respectively (P = .01 S vs C, P = .10 L vs C, and P = .048 R vs C). Duration of ventricular tachycardia (VT) episodes was reduced from 15.5 seconds (mean) in C to 1.3 seconds in S, 1.4 sec in L and 0.09 sec in R (P < .05 for S vs C and R vs C by Wilcoxon test). The number of rats with any (≥10 seconds) sustained VT was 3 in C versus 1, 0, and 0 in the S, L, and R groups, respectively. Two rats in C had reversible ventricular fibrillation versus 0 in the S, L, and R groups. The number of ventricular premature beats (VPBs) per rat was 10.9 in C, 2.3 in S, 4.9 in L, and 5.7 in R (P < .05 for S, L, or R vs C). P = NS for R versus L or S for all analyses. Conclusion: In this first head-to-head comparison of R vs other antiarrhythmic agents at therapeutic doses in an ischemia/reperfusion model, ranolazine (which lacks pro-arrhythmic effects) was as effective as either sotalol or lidocaine to reduce reperfusion-induced ventricular arrhythmias.

Antifibrillatory effect of ranolazine during severe coronary stenosis in the intact porcine model

BACKGROUND

Clinical evidence suggests that the antianginal agent ranolazine has antiarrhythmic properties, but its effects on vulnerability to ventricular fibrillation (VF) and T-wave alternans (TWA) during coronary artery stenosis have not been measured.

OBJECTIVE

We investigated whether the antiarrhythmic effect of ranolazine during acute coronary stenosis could be quantified by measuring VF threshold and TWA magnitude.

METHODS

Electrode catheters placed in the left ventricular apex were used to determine VF threshold during ventricular pacing at 130 beats/min, and TWA was quantified from epicardial electrograms using modified moving average method (N = 18). Left anterior descending coronary flow was reduced with a balloon occluder by 75% for 10 minutes. The I(Kr) blocker E-4031 was used to distinguish effects of late I(Na) and I(Kr) inhibition by ranolazine.

RESULTS

Before stenosis, ranolazine and E-4031 increased VF threshold from 32 ± 4 mA to 46 ± 4 mA (mean ± SEM), P = .02, and from 33 ± 5 mA to 40 ± 9 mA, P = .02, respectively. During stenosis, ranolazine increased VF threshold from 19 ± 2 mA to 33 ± 3 mA (P = .02), whereas E-4031 decreased VF threshold from 21 ± 3 mA to 15 ± 3 mA (P = .02). The ischemia-induced increase in TWA was suppressed by ranolazine but not by E-4031, consistent with effects of these agents on VF threshold.

CONCLUSION

Ranolazine exerts significant antifibrillatory effects during coronary stenosis through direct effects on cardiac electrical properties independent of coronary flow. Ranolazine's antifibrillatory action during myocardial ischemia does not appear to be mediated by blockade of I(Kr) but rather by inhibition of late I(Na). TWA changes paralleled vulnerability to VF as indicated by VF threshold testing.