Long-term effect of mexiletine on left ventricular function and relation to suppression of ventricular arrhythmia

Relevance of mexiletine in the era of evolving antiarrhythmic therapy of ventricular arrhythmias

Despite impressive developments in the field of ventricular arrhythmias, there is still a relevant number of patients with ventricular arrhythmias who require antiarrhythmic drug therapy and may, e.g., in otherwise drug and/or ablation refractory situations, benefit from agents known for decades, such as mexiletine. Through its capability of blocking fast sodium channels in cardiomyocytes, it has played a minor to moderate antiarrhythmic role throughout the recent decades. Nevertheless, certain patients with structural heart disease suffering from drug-refractory, i.e., mainly amiodarone refractory ventricular arrhythmias, as well as those with selected forms of congenital long QT syndrome (LQTS) may nowadays still benefit from mexiletine. Here, we outline mexiletine's cellular and clinical electrophysiological properties. In addition, the application of mexiletine may be accompanied by various potential side effects, e.g., nausea and tremor, and is limited by several drug-drug interactions. Thus, we shed light on the current therapeutic role of mexiletine for therapy of ventricular arrhythmias and discuss clinically relevant aspects of its indications based on current evidence.

Effectiveness and safety of mexiletine in patients at risk for (recurrent) ventricular arrhythmias: a systematic review

While mexiletine has been used for over 40 years for prevention of (recurrent) ventricular arrhythmias and for myotonia, patient access has recently been critically endangered. Here we aim to demonstrate the effectiveness and safety of mexiletine in the treatment of patients with (recurrent) ventricular arrhythmias, emphasizing the absolute necessity of its accessibility. Studies were included in this systematic review (PROSPERO, CRD42020213434) if the efficacy or safety of mexiletine in any dose was evaluated in patients at risk for (recurrent) ventricular arrhythmias with or without comparison with alternative treatments (e.g. placebo). A systematic search was performed in Ovid MEDLINE, Embase, and in the clinical trial registry databases ClinicalTrials.gov and ICTRP. Risk of bias were assessed and tailored to the different study designs. Large heterogeneity in study designs and outcome measures prompted a narrative synthesis approach. In total, 221 studies were included reporting on 8970 patients treated with mexiletine. Age ranged from 0 to 88 years. A decrease in ventricular arrhythmias of >50% was observed in 72% of the studies for pre-mature ventricular complexes, 64% for ventricular tachycardia, and 33% for ventricular fibrillation. Electrocardiographic effects of mexiletine were small; only in a subset of patients with primary arrhythmia syndromes, a relative (desired) QTc decrease was reproducibly observed. As for adverse events, gastrointestinal complaints were most frequently observed (33% of the patients). In this systematic review, we present all the currently available knowledge of mexiletine in patients at risk for (recurrent) ventricular arrhythmias and show that mexiletine is both effective and safe.

Pharmacologic Management for Ventricular Arrhythmias: Overview of Anti-Arrhythmic Drugs

Ventricular arrhythmias (Vas) are a life-threatening condition and preventable cause of sudden cardiac death (SCD). With the increased utilization of implantable cardiac defibrillators (ICD), the focus of VA management has shifted toward reduction of morbidity from VAs and ICD therapies. Anti-arrhythmic drugs (AADs) can be an important adjunct therapy in the treatment of recurrent VAs. In the treatment of VAs secondary to structural heart disease, amiodarone remains the most well studied and current guideline-directed pharmacologic therapy. Beta blockers also serve as an important adjunct and are a largely underutilized medication with strong evidentiary support. In patients with defined syndromes in structurally normal hearts, AADs can offer tailored therapies in prevention of SCD and improvement in quality of life. Further clinical trials are warranted to investigate the role of newer therapeutic options and for the direct comparison of established AADs.

Inhibition of cardiac Kv4.3 (Ito) channel isoforms by class I antiarrhythmic drugs lidocaine and mexiletine

Transient outward K⁺ current, I_to, contributes to cardiac action potential generation and is primarily carried by K_v4.3 (KCND3) channels. Two K_v4.3 isoforms are expressed in human ventricle and show differential remodeling in heart failure (HF). Lidocaine and mexiletine may be applied in selected patients to suppress ventricular arrhythmias, without effects on sudden cardiac death or mortality. Isoform-dependent effects of antiarrhythmic drugs on K_v4.3 channels and potential implications for remodeling-based antiarrhythmic management have not been assessed to date. We sought to test the hypotheses that K_v4.3 channels are targeted by lidocaine and mexiletine, and that drug sensitivity is determined in isoform-specific manner. Expression of KCND3 isoforms was quantified using qRT-PCR in left ventricular samples of patients with HF due to either ischemic or dilated cardiomyopathies (ICM or DCM). Long (K_v4.3-L) and short (K_v4.3-S) isoforms were heterologously expressed in Xenopus laevis oocytes to study drug sensitivity and effects on biophysical characteristics activation, deactivation, inactivation, and recovery from inactivation. In the present HF patient cohort KCND3 isoform expression did not differ between ICM and DCM. In vitro, lidocaine (IC₅₀-K_v4.3-L: 0.8 mM; IC₅₀-K_v4.3-S: 1.2 mM) and mexiletine (IC₅₀-K_v4.3-L: 146 μM; IC₅₀-K_v4.3-S: 160 μM) inhibited K_v4.3 with different sensitivity. Biophysical analyses identified accelerated and enhanced inactivation combined with delayed recovery from inactivation as primary biophysical mechanisms underlying K_v4.3 current reduction. In conclusion, differential effects on K_v4.3 isoforms extend the electropharmacological profile of lidocaine and mexiletine. Patient-specific remodeling of K_v4.3 isoforms may determine individual drug responses and requires consideration during clinical application of compounds targeting K_v4.3.

Different electrophysiological effects of the levo- and dextro-rotatory isomers of mexiletine in isolated rabbit cardiac muscle

Racemic mexiletine is a widely used antiarrhythmic agent that blocks sodium channels. The effects of R-(-) and S-(+) mexiletine stereoisomers on maximum rate of depolarization ([Formula: see text]), conduction time, and repolarization have not yet been investigated in isolated cardiac preparations. We studied the effect of the R-(-) and S-(+) mexiletine on rabbit cardiac action potential parameters by using the conventional microelectrode technique. Both enantiomers at 20 μmol/L of therapeutically and experimentally relevant concentration, significantly depressed the [Formula: see text] at fast heart rates (BCLs 300-700 ms). R-(-) mexiletine has more potent inhibitory effect than S-(+) mexiletine. Both R-(-) and S-(+) mexiletine significantly inhibited the [Formula: see text] of early extrasystoles measured at 70 ms diastolic interval induced by S1-S2 stimuli. R-(-) mexiletine has more pronounced inhibitory effect than S-(+) mexiletine. Both R-(-) and S-(+) mexiletine increased significantly the ERP/APD₉₀ ratio. The time constant (τ) of recovery of [Formula: see text] was found to be τ = 376.0 ± 77.8 ms for R-(-) mexiletine and τ = 227.1 ± 23.4 ms for S-(+) mexiletine, which indicates a slower offset kinetics for R-(-) mexiletine from sodium channels than that of the S-(+) enantiomer. These data suggest that R-(-) mexiletine might be a more potent antiarrhythmic agent than S-(+) mexiletine.

Congestive heart failure and arrhythmias: therapeutic modalities

Congestive heart failure affects millions of Americans, and thousands of new cases are reported each year. The prognosis continues to be grim. Most deaths in heart failure patients can be attributed to low-output states (pump failure) and arrhythmias (sudden). Attempts have been made to decrease the incidence of pump failure deaths by using contractility agents that, in most cases, have been shown to be detrimental. The results of trials using beta blockers are encouraging. Vasodilators have made a positive impact on outcome. However, the use of pharmacologic antiarrhythmic agents to decrease sudden death has failed to improve survival. Studies with implantable devices are ongoing and will provide an answer to the question of whether a reduction in sudden death will translate into a reduction of all-cause mortality. Antiplatelet and antithrombotic agents appear to be favorable, and revascularization is recommended when feasible.

Comparative hemodynamic effects of mexiletine and quinidine in patients with severe left ventricular dysfunction

Mexiletine and quinidine are often administered to patients with severe congestive heart failure, but their hemodynamic effects have not been adequately studied in these individuals. In a randomized, crossover study, the hemodynamic responses to single oral doses of quinidine (600 mg) and mexiletine (400 mg) were compared in 20 patients with marked left ventricular dysfunction. Quinidine predominantly caused vasodilation, with mean arterial, left ventricular filling, and right atrial pressures all decreasing (-7 +/- 2, -2.3 +/- 1.0, and -1.1 +/- 0.5 mm Hg, respectively) and the systemic vascular resistance also declining (-308 +/- 84 dynes.sec.cm5). In contrast, the systemic vascular resistance increased (314 +/- 84 dynes.sec.cm-5) and the mean arterial, left ventricular filling, and right atrial pressures also increased (+2 +/- 2, +6.1 +/- 1.8, and +1.8 +/- 0.6 mm Hg, respectively) after mexiletine. Cardiac performance declined with mexiletine (cardiac and stroke work indexes decreasing -0.3 +/- 0.1 L/min/m2 and -5 +/- 1 gm.m/m2, respectively), but there was no significant change in cardiac or stroke work indexes with quinidine (+0.1 L/min/m2 and -0.3 +/- 0.9 gm.m/m2, respectively). The response to the two agents significantly differed for all parameters measured (p less than 0.005). These hemodynamic changes were accompanied by clinical effects. Mexiletine induced increased dyspnea in five patients and quinidine led to symptomatic hypotension in two patients. Plasma concentrations of mexiletine and serum concentrations of quinidine were within or below the therapeutic range in all patients. In conclusion, mexiletine and quinidine exert different hemodynamic effects when given to patients with severe congestive heart failure.(ABSTRACT TRUNCATED AT 250 WORDS)