Vomiting, electrolyte disturbance, and medications; the perfect storm for acquired long QT syndrome and cardiac arrest: a case report

Background Acquired long QT syndrome is an important and preventable cause of cardiac arrest. Certain medications and electrolyte disturbance are common contributors, and often coexist. In this case, we report five contributors to cardiac arrest. Case presentation This case is of a 51-year-old Caucasian female patient who presented with vomiting associated with hypokalemia and hypomagnesemia. She subsequently received ondansetron and metoclopramide, on the background of chronic treatment with fluoxetine. She then suffered an in-hospital monitored cardiac arrest, with features of long QT and torsades de pointes retrospectively noted on her prearrest electrocardiogram. She was diagnosed with acquired long QT syndrome, and her QT interval later normalized after removal of offending causes. Conclusions This case highlights the importance of proper consideration prior to prescribing QT prolonging medications, especially in patients who have other risk factors for prolonged QT, such as electrolyte disturbances and pretreatment with QT prolonging medications.

Base Editing of Human Pluripotent Stem Cells for Modeling Long QT Syndrome

Human pluripotent stem cells (hPSCs) have great potential for disease modeling, drug discovery, and regenerative medicine as they can differentiate into many different functional cell types via directed differentiation. However, the application of disease modeling is limited due to a time-consuming and labor-intensive process of introducing known pathogenic mutations into hPSCs. Base editing is a newly developed technology that enables the facile introduction of point mutations into specific loci within the genome of living cells without unwanted genome injured. We describe an optimized stepwise protocol to introduce disease-specific mutations of long QT syndrome (LQTs) into hPSCs. We highlight technical issues, especially those associated with introducing a point mutation to obtain isogenic hPSCs without inserting any resistance cassette and reproducible cardiomyocyte differentiation. Based on the protocol, we succeeded in getting hPSCs carrying LQTs pathogenic mutation with excellent efficiency (31.7% of heterozygous clones, 9.1% of homozygous clones) in less than 20 days. In addition, we also provide protocols to analyze electrophysiological of hPSC-derived cardiomyocytes using multi-electrode arrays. This protocol is also applicable to introduce other disease-specific mutations into hPSCs. Graphical abstract

The N-linker region of hERG1a upregulates hERG1b potassium channels

A major physiological role of hERG1 (human Ether-a-go-go-Related Gene) potassium channels is to repolarize cardiac action potentials. Two isoforms, hERG1a and hERG1b, associate to form the native cardiac IKr current in vivo. Inherited mutations in hERG1a or hERG1b cause prolonged cardiac repolarization, Long QT Syndrome and sudden death arrhythmia. hERG1a subunits assemble with and enhance the number of hERG1b subunits at the plasma membrane, but the mechanism for the increase in hERG1b by hERG1a is not well understood. Here, we report that the hERG1a N-terminal PAS (Per-Arnt-Sim) domain-N-linker region expressed in trans with hERG1b markedly increased hERG1b currents and increased biotin-labelled hERG1b protein at the membrane surface. hERG1b channels with a deletion of the 1b domain did not have a measurable increase in current or biotinylated protein when co-expressed with hERG1a PAS domain-N-linker regions indicating that the 1b domain was required for the increase in hERG1b. Using a biochemical pull-down interaction assay and a FRET hybridization experiment, we detected a direct interaction between the hERG1a PAS domain-N-linker region and the hERG1b N-terminal 1b domain. Using engineered deletions and alanine mutagenesis, we identified a short span of amino acids at positions 216-220 within the hERG1a N-linker region that were necessary for the upregulation of hERG1b. Taken together, we propose that direct structural interactions between the hERG1a N-linker region and the hERG1b N-terminal 1b domain increase hERG1b at the plasma membrane. Mechanisms that enhance hERG1b current would be anticipated to shorten action potentials, which could be anti-arrhythmic, and may point toward hERG1b or the hERG1a N-linker as molecular targets for therapy for Long QT syndrome.