Preclinical drug screens are not based on human physiology, possibly complicating predictions on cardiotoxicity. Drug screening can be humanised with in vitro assays using human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs). However, in contrast to adult ventricular cardiomyocytes, iPSC-CMs beat spontaneously due to presence of the pacemaking current I and reduced densities of the hyperpolarising current I. In adult cardiomyocytes, I finalises repolarisation by stabilising the resting membrane potential while also maintaining excitability. The reduced I density contributes to proarrhythmic traits in iPSC-CMs, which leads to an electrophysiological phenotype that might bias drug responses. The proarrhythmic traits can be suppressed by increasing I in a balanced manner. We systematically evaluated all studies that report strategies to mature iPSC-CMs and found that only few studies report I current densities. Furthermore, these studies did not succeed in establishing sufficient I levels as they either added too little or too much I. We conclude that reduced densities of I remain a major flaw in iPSC-CMs, which hampers their use for in vitro drug screening.

Background: Electronic cigarettes (e-cigarettes), the smokeless alternative to conventional tobacco cigarettes, have become increasingly popular. E-cigarettes vaporise e-liquid, a solution of highly concentrated nicotine, propylene glycol (PG) and vegetable glycerine (VG). With the popularity of e-cigarettes, e-liquid refills have become easily accessible and several cases of intoxication due to the ingestion of e-liquid have been reported. We provide an overview of these cases, their pathophysiology and patients' characteristics. Methods: We carried out a retrospective evaluation of the scientific literature reporting on cases of liquid nicotine intoxication, using the following inclusion criteria: (1) the article is or contains a case report, (2) describes an intoxication with e-liquid, (3) the substance contains nicotine, and (4) intake is oral, intravenous or subcutaneous. Results: We found 26 case reports describing a total of 31 patients who suffered from e-liquid intoxication. All intoxications up to the age of six were reported as unintentional, whereas nearly all cases from ages 13 to 53 were due to suicide attempts. The three most prevalent symptoms of e-liquid intoxication were tachycardia, altered mental status and vomiting. Eleven cases resulted in the death of the patient. In the survivors, the highest plasma concentration of nicotine was 800 mg L À1 , while the lowest concentration in the non-survivors was 1600 mg L À1 . Conclusions: There is a mismatch between the generally accepted lethal oral nicotine dose of 60 mg, resulting in approximately 180 mg L À1 plasma concentration, and the 4.4-to 8.9-fold higher lethal plasma concentrations we found in cases of e-liquid intoxication. In these severe intoxications, plasma cotinine concentration does not act as a more reliable indicator of nicotine intoxication than nicotine itself. The ages of the patients display a bimodal distribution. In patients above the age of 10, intoxication results mainly from suicide attempts rather than accidental ingestion. The role of PG and VG in e-liquid intoxications is remarkably unclear. However, the similarity across nicotine and PG toxicity symptoms leads us to believe a cumulative effect cannot be excluded. ARTICLE HISTORY

TdP can be driven by focal activity as well as by re-entry depending on the duration of the episode. NT episodes are always maintained by re-entry, which can be identified in local unipolar electrograms by shorter interbeat intervals and smaller deflection amplitude.

Background and PurposeEnhanced late sodium current (late I Na) in heart failure and long QT syndrome type 3 is proarrhythmic. This study investigated the antiarrhythmic effect and mode of action of the selective and potent late I Na inhibitor GS‐458967 (GS967) against Torsades de Pointes arrhythmias (TdP) in the chronic atrioventricular block (CAVB) dog.Experimental ApproachElectrophysiological and antiarrhythmic effects of GS967 were evaluated in isolated canine ventricular cardiomyocytes and CAVB dogs with dofetilide‐induced early afterdepolarizations (EADs) and TdP, respectively. Mapping of intramural cardiac electrical activity in vivo was conducted to study effects of GS967 on spatial dispersion of repolarization.Key ResultsGS967 (IC50~200nM) significantly shortened repolarization in canine ventricular cardiomyocytes and sinus rhythm (SR) dogs, in a concentration and dose‐dependent manner. In vitro, despite addition of 1μM GS967, dofetilide‐induced EADs remained present in 42% and 35% of cardiomyocytes from SR and CAVB dogs, respectively. Nonetheless, GS967 (787±265nM) completely abolished dofetilide‐induced TdP in CAVB dogs (10/14 after dofetilide to 0/14 dogs after GS967), while single ectopic beats (sEB) persisted in 9 animals. In vivo mapping experiments showed that GS967 significantly reduced spatial dispersion of repolarization: cubic dispersion was significantly decreased from 237±54ms after dofetilide to 123±34ms after GS967.Conclusion and ImplicationsGS967 terminated all dofetilide‐induced TdP without completely suppressing EADs and sEB in vitro and in vivo, respectively. The antiarrhythmic mode of action of GS967, through the reduction of spatial dispersion of repolarization, seems to predominantly impede the perpetuation of arrhythmic events into TdP rather than their initiating trigger.

Background and PurposeKv11.1 (hERG) channel blockade is an adverse effect of many drugs and lead compounds, associated with lethal cardiac arrhythmias. LUF7244 is a negative allosteric modulator/activator of Kv11.1 channels that inhibits early afterdepolarizations in vitro. We tested LUF7244 for antiarrhythmic efficacy and potential proarrhythmia in a dog model.Experimental ApproachLUF7244 was tested in vitro for (a) increasing human IKv11.1 and canine IKr and (b) decreasing dofetilide‐induced action potential lengthening and early afterdepolarizations in cardiomyocytes derived from human induced pluripotent stem cells and canine isolated ventricular cardiomyocytes. In vivo, LUF7244 was given intravenously to anaesthetized dogs in sinus rhythm or with chronic atrioventricular block.Key ResultsLUF7244 (0.5–10 μM) concentration dependently increased IKv11.1 by inhibiting inactivation. In vitro, LUF7244 (10 μM) had no effects on IKIR2.1, INav1.5, ICa‐L, and IKs, doubled IKr, shortened human and canine action potential duration by approximately 50%, and inhibited dofetilide‐induced early afterdepolarizations. LUF7244 (2.5 mg·kg−1·15 min−1) in dogs with sinus rhythm was not proarrhythmic and shortened, non‐significantly, repolarization parameters (QTc: −6.8%). In dogs with chronic atrioventricular block, LUF7244 prevented dofetilide‐induced torsades de pointes arrhythmias in 5/7 animals without normalization of the QTc. Peak LUF7244 plasma levels were 1.75 ± 0.80 during sinus rhythm and 2.34 ± 1.57 μM after chronic atrioventricular block.Conclusions and ImplicationsLUF7244 counteracted dofetilide‐induced early afterdepolarizations in vitro and torsades de pointes in vivo. Allosteric modulators/activators of Kv11.1 channels might neutralize adverse cardiac effects of existing drugs and newly developed compounds that display QTc lengthening.