Samuel Chauveau

Stem cell-based biological pacemakers from proof of principle to therapy: a review.

Electronic pacemakers are the standard therapy for bradycardia-related symptoms but have shortcomings. Over the past 15 years, experimental evidence has demonstrated that gene and cell-based therapies can create a biological pacemaker. Recently, physiologically acceptable rates have been reported with an adenovirus-based approach. However, adenovirus-based protein expression does not last more than 4 weeks, which limits its clinical applicability. Cell-based platforms are potential candidates for longer expression. Currently there are two cell-based approaches being tested: (i) mesenchymal stem cells used as a suitcase for delivering pacemaker genes and (ii) pluripotent stem cells differentiated down a cardiac lineage with endogenous pacemaker activity. This review examines the current achievements in engineering a biological pacemaker, defines the patient population for whom this device would be useful and identifies the challenges still ahead before cell therapy can replace current electronic devices.

Induced Pluripotent Stem Cell–Derived Cardiomyocytes Provide In Vivo Biological Pacemaker Function

Background— Although multiple approaches have been used to create biological pacemakers in animal models, induced pluripotent stem cell–derived cardiomyocytes (iPSC-CMs) have not been investigated for this purpose. We now report pacemaker function of iPSC-CMs in a canine model. Methods and Results— Embryoid bodies were derived from human keratinocytes, their action potential characteristics determined, and their gene expression profiles and markers of differentiation identified. Atrioventricular blocked dogs were immunosuppressed, instrumented with VVI pacemakers, and injected subepicardially into the anterobasal left ventricle with 40 to 75 rhythmically contracting embryoid bodies (totaling 1.3–2×106 cells). ECG and 24-hour Holter monitoring were performed biweekly. After 4 to 13 weeks, epinephrine (1 &mgr;g kg−1 min−1) was infused, and the heart removed for histological or electrophysiological study. iPSC-CMs largely lost the markers of pluripotency, became positive for cardiac-specific markers. and manifested If-dependent automaticity. Epicardial pacing of the injection site identified matching beats arising from that site by week 1 after implantation. By week 4, 20% of beats were electronically paced, 60% to 80% of beats were matching, and mean and maximal biological pacemaker rates were 45 and 75 beats per minute. Maximum night and day rates of matching beats were 53±6.9 and 69±10.4 beats per minute, respectively, at 4 weeks. Epinephrine increased rate of matching beats from 35±4.3 to 65±4.0 beats per minute. Incubation of embryoid bodies with the vital dye, Dil, revealed the persistence of injected cells at the site of administration. Conclusions— iPSC-CMs can integrate into host myocardium and create a biological pacemaker. Although this is a promising development, rate and rhythm of the iPSC-CMs pacemakers remain to be optimized.

Increased Late Sodium Current Contributes to the Electrophysiological Effects of Chronic, but Not Acute, Dofetilide Administration

Background—Drugs are screened for delayed rectifier potassium current (IKr) blockade to predict long QT syndrome prolongation and arrhythmogenesis. However, single-cell studies have shown that chronic (hours) exposure to some IKr blockers (eg, dofetilide) prolongs repolarization additionally by increasing late sodium current (INa-L) via inhibition of phosphoinositide 3-kinase. We hypothesized that chronic dofetilide administration to intact dogs prolongs repolarization by blocking IKr and increasing INa-L. Methods and Results—We continuously infused dofetilide (6–9 &mgr;g/kg bolus+6–9 &mgr;g/kg per hour IV infusion) into anesthetized dogs for 7 hours, maintaining plasma levels within the therapeutic range. In separate experiments, myocardial biopsies were taken before and during 6-hour intravenous dofetide infusion, and the level of phospho-Akt was determined. Acute and chronic dofetilide effects on action potential duration (APD) were studied in canine left ventricular subendocardial slabs using microelectrode techniques. Dofetilide monotonically increased QTc and APD throughout 6.5-hour exposure. Dofetilide infusion during ≥210 minutes inhibited Akt phosphorylation. INa-L block with lidocaine shortened QTc and APD more at 6.5 hours than at 50 minutes (QTc) or 30 minutes (APD) dofetilide administration. In comparison, moxifloxacin, an IKr blocker with no effects on phosphoinositide 3-kinase and INa-L prolonged APD acutely but no additional prolongation occurred on chronic superfusion. Lidocaine shortened APD equally during acute and chronic moxifloxacin superfusion. Conclusions—Increased INa-L contributes to chronic dofetilide effects in vivo. These data emphasize the need to include time and INa-L in evaluating the phosphoinositide 3-kinase inhibition–derived proarrhythmic potential of drugs and provide a mechanism for benefit from lidocaine administration in clinical acquired long QT syndrome.

Interventricular dispersion in repolarization causes bifid T waves in dogs with dofetilide-induced long QT syndrome

BACKGROUND Long QT2 (LQT2) syndrome is characterized by bifid (or notched) T waves, whose mechanism is not understood. OBJECTIVE The purpose of this study was to test whether increased interventricular dispersion of repolarization induces bifid T waves. METHODS We simultaneously recorded surface ECG and unipolar electrograms at baseline and after dofetilide in a canine model of dofetilide-induced LQT2 (6 male mongrel dogs). Standard ECG variables, T-wave duration, and moments of peaks of bifid T waves (Tp1 and Tp2) were correlated with moments of local repolarization. Epicardial electrograms were recorded over the left ventricular (LV) and right ventricular (RV) anterior walls (11 × 11 electrode grid, 5-mm interelectrode distance). In 5 of the 6 hearts, we also recorded intramural unipolar electrograms (n = 4-7 needles per heart). In each unipolar recording, we determined activation time, repolarization time (RTs), and activation-recovery interval. In addition, we studied RT response to heart rate changes. RESULTS Dofetilide prolonged QT and QTc, induced bifid T waves in 4 of 6 animals, and prolonged RT heterogeneously in LV and RV, resulting in increased interventricular and LV intraventricular RT dispersion. Dofetilide did not induce a disparate response in activation-recovery interval across the transmural axis. Dofetilide-induced separation of RT across the RV-LV interface concurred with the moments of T-wave peaks. Dofetilide-induced steepening of restitution slopes was larger in LV than RV. CONCLUSION Dofetilide-induced bifid T waves result from interventricular RT dispersion.

Delayed diagnosis of Brugada syndrome in a patient with aborted sudden cardiac death and initial negative flecainide challenge

A negative flecainide challenge does not rule out Brugada syndrome even in the presence of nonfatal cardiac arrest as the first manifestation of the disease. This should prompt clinicians to ensure long‐term ECG follow‐up and consider repeating a drug test with another sodium channel blocker.

A heartless brain.

A 81-year-old woman was admitted for right-sided hemiplegia. She had a one-month history of palpitations related to atrial tachycardia treated with oral anticoagulants and sotalol (80 mg twice daily). Brain magnetic resonance imaging demonstrated left middle cerebral artery territory infarct …

First identification of homozygous truncating CSRP3 variants in two unrelated cases with hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disease with an estimated prevalence of 1/500. More than 40 genes have been reported to cause HCM. Among them, CSRP3 is usually included on HCM gene panels used for molecular diagnosis by next-generation sequencing (NGS). To provide new insights into the pathophysiology of hypertrophic cardiomyopathy, a NGS workflow based on a panel of 48 cardiomyopathies-causing genes was analyzed on a cohort of 542 HCM patients. As expected, this molecular approach led to identify most pathogenic or likely pathogenic variants into prevalent HCM-causing genes: MYBPC3 (123/542; 22.7%), MYH7 (48/542; 8.9%), TNNT2 (12/542; 2.2%), and TNNI3 (10/542; 1.8%). Among MYBPC3 variants, 96 led to a premature stop codon (78%). More surprisingly, our molecular study led also to detect, for the first time, homozygous CSRP3 truncating variants in two unrelated HCM probands. Meta-analysis of rare previously reported CSRP3 variants on HCM probands using ACMG guidelines indicate that only one variation (p.Cys58Gly) could be considered as likely pathogen. By combining meta-analysis results and identification of two unrelated HCM patients with homozygous CSRP3 truncating variants, we suggest that the association of CSRP3 as a validated HCM-causing gene require additional studies and those CSRP3 variants could result in HCM with an autosomal recessive inheritance rather than with an autosomal dominant transmission as usually reported on HCM (OMIM 612124).

Atrial Structural Remodeling Gene Variants in Patients with Atrial Fibrillation

Atrial fibrillation (AF) is a common arrhythmia for which the genetic studies mainly focused on the genes involved in electrical remodeling, rather than left atrial muscle remodeling. To identify rare variants involved in atrial myopathy using mutational screening, a high-throughput next-generation sequencing (NGS) workflow was developed based on a custom AmpliSeq™ panel of 55 genes potentially involved in atrial myopathy. This workflow was applied to a cohort of 94 patients with AF, 76 with atrial dilatation and 18 without. Bioinformatic analyses used NextGENe® software and in silico tools for variant interpretation. The AmpliSeq custom-made panel efficiently explored 96.58% of the targeted sequences. Based on in silico analysis, 11 potentially pathogenic missense variants were identified that were not previously associated with AF. These variants were located in genes involved in atrial tissue structural remodeling. Three patients were also carriers of potential variants in prevalent arrhythmia-causing genes, usually associated with AF. Most of the variants were found in patients with atrial dilatation (n=9, 82%). This NGS approach was a sensitive and specific method that identified 11 potentially pathogenic variants, which are likely to play roles in the predisposition to left atrial myopathy. Functional studies are needed to confirm their pathogenicity.

Early repolarization syndrome caused by de novo duplication of KCND3 detected by next-generation sequencing

From the *Service de Rythmologie, Hôpital Cardiologique Louis-Pradel, Bron, France, Centre de référence des troubles du rythme héréditaires, Hôpital Cardiologique Louis-Pradel, Bron, France, Laboratoire de Cardiogénétique Moléculaire, Centre de Biologie et Pathologie Est, Hospices Civils de Lyon, Lyon, France, xInstitut NeuroMyoG ene, CNRS UMR 5310, INSERM U1217, Université Claude Bernard Lyon 1, Lyon, France, kUniversité de Lyon 1, Lyon, France, and {Cytogenetics, Hospices Civils de Lyon, & Centre de Recherche en Neurosciences de Lyon, INSERM U1028; CNRS UMR5292; UCBL1; Equipe GENDEV, Lyon, France.

Additional coronary sinus shocking lead as rescue therapy after multiple internal and external defibrillation failures

High defibrillation threshold (DFT) and defibrillation failure can lead to intractable ventricular arrhythmias. Additional coronary sinus coil is an effective strategy to achieve marked reduction in DFT. However, physicians should retain this might prevent future coronary sinus lead placement in case the patient would develop complete left bundle branch block.