The use of the block cycle length as a safe and efficient means of interrupting sustained ventricular tachycardia and its pharmacological modification

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.

Japanese randomized trial for investigation of a combined therapy of amiodarone and implantable cardioverter defibrillator in patients with ventricular tachycardia and fibrillation: the Nippon ICD Plus Pharmachologic Option Necessity study design

BACKGROUND

Implantable cardioverter-defibrillators (ICDs) are the most effective therapy in reducing the mortality of patients with life-threatening ventricular tachyarrhythmias. However, the ICD cannot prevent the recurrence of tachycarida attacks and that limits the clinical usefulness of them. The Nippon ICD Plus Pharmachologic Option Necessity (NIPPON) trial was designed as the first prospective randomized study to test the hypothesis whether amiodarone could improve the patient's clinical outcome by reducing the amount of ICD therapy in the Japanese patient population.

METHODS AND RESULTS

Approximately 400 patients with organic heart disease and spontaneous episode(s) of sustained ventricular tachycardia/fibrillation (VT/VF) will be randomly assigned to one of 2 groups; the amiodarone group and non-amiodarone group. Both groups of patients will be followed at least for 24 months. The end-point committee will adjudicate events in a blinded fashion. The primary end-points of this study are determination of the appropriate therapy from the ICD and alteration of the assigned treatment because of its harmful effects and/or frequent ICD therapies.

CONCLUSION

The NIPPON study is expected to confirm our understanding of the prognostic and therapeutic usefulness of adjuvant amiodarone therapy for patients with an ICD and with a history of sustained VT/VF.

Indications for an implantable cardioverter defibrillator (ICD)

Since the first clinical use of implantable defibrillator in human, the technology and the function of implantable cardioverter-defibrillator (ICD) have been much improved and now, ICD can be implanted within the chest wall. ICD is the most reliable therapy to prevent sudden cardiac death (SCD) in patients with documented VT/VF and the efficacy is most clear in patients with depressed heart function. It is now extended as a tool of the primary prevention of SCD in high risk patients after myocardial infarction. However, such beneficial effect is not applicable to DCM though patients might have depressed heart function. ICD is not free from procedure- or device-related problems which need to be resolved. From unknown causes, VT/VF might recur in an incessant form and an emergency admission is needed. Therefore, even during ICD therapy, patients often require antiarrhythmic drugs or catheter ablation.

Evaluation of post-repolarization refractoriness for conduction block in cardiac muscle: studies in an artificial isthmus in the canine right atrium

Post-repolarization refractoriness (PRR) is an important factor in determining conduction block and is the difference between the effective refractory period (ERP) and the duration of the monophasic action potential (MAPD). In the present study, conduction block in an artificial isthmus in the canine atrium was evaluated and the coupling interval of a premature beat, which caused the block, was defined as the block coupling interval (BCI). The usefulness of this value was also evaluated. Radiofrequency linear ablation was performed on the right atrial surface parallel to the atrioventricular groove in 5 mongrel dogs, and an artificial isthmus (8-10mm wide and 25-30mm long) was created. Fourteen simultaneous unipolar recordings were performed in the isthmus with a resolution of 1.2 mm. Single extra-stimuli with basic drive train were delivered to induce conduction block in the isthmus and when it occurred, the coupling interval at the recording site just proximal to the site of the block was defined as the BCI. At the site of the block, the ERP and MAPD at each drive cycle length were measured. The PRR was calculated using 2 different formulae: (1) [ERP-MAPD], and (2) [BCI-MAPD]. It was found that each value was shortened in accordance with the shortening of the basic drive cycle length. In all basic drive trains, BCI>ERP>MAPD, and [ERP-MAPD] was always shorter than [BCI-MAPD]. In the shorter cycle length of basic drives, the difference between [ERP-MAPD] and [BCI-MAPD] was more prominent. In the artificial isthmus model in the canine atrium, BCI was always longer than the ERP measured at the same site as the block. Because the ERP may not directly reflect the block phenomenon, the electrophysiologic evaluation should use the BCI instead, as in the PRR evaluation.

Antitachycardia burst pacing for pleomorphic reentrant ventricular tachycardias associated with non-coronary artery diseases: a morphology specific programming for ventricular tachycardias

To study the role of antitachycardia burst pacing in patients with reentrant pleomorphic ventricular tachycardia (VT) associated with non-coronary artery diseases, the efficacy of antitachycardia pacing and appropriate antitachycardia pacing cycle length were evaluated in each pleomorphic VT morphology of seven patients. Seven patients were included in this study. Clinically documented pleomorphic VTs were reproduced in an electrophysiologic study. For each VT, rapid ventricular pacing was attempted from the apex of the right ventricle at a cycle length which was 20 ms shorter than that of VT and repeated after a decrement of the cycle length in steps of 10 ms until the VT was terminated or accelerated. All 16 VTs could be entrained by the rapid pacing, and 13 of the 16 VTs (81%) were terminated, whereas pacing-induced acceleration was observed in the other 3 VTs of the 3 patients. VT cycle length (VTCL), block cycle length (BCL) which was defined as the longest VT interrupting paced cycle length, %BCL/VTCL and entrainment zone which was defined as VTCL minus BCL, varied in each VT morphology of each patient. In two patients, antitachycardia pacing was effective in all VT morphologies and the maximum difference of the %BCL/VTCL among the pleomorphic VTs was less than 10%. Thus, antitachycardia pacing seemed to be beneficial for these patients. In the other 5 patients, a difference of more than 10% in %BCL/VTCL was observed among the pleomorphic VT morphologies and/or at least one VT morphology showed pacing-induced acceleration. Compared to the 13 terminated VTs, three accelerated VTs had a wide entrainment zone [160 +/- 44 vs 90 +/- 48 ms, p < 0.04] and small %BCL/VTCL [61 +/- 6 vs 77 +/- 11%,p<0.03]. In pleomorphic VTs associated with non-coronary artery diseases, responses to rapid pacing was not uniform; VT might be terminable or accelerated even in the same patient. We need to pay close attention when programming antitachycardia pacing in patients with pleomorphic VT.