Post-hoc diagnosis of congenital long QT syndrome in patients with tetralogy of Fallot

Human ether‑à‑go‑go‑related gene mutation L539fs/47‑hERG leads to cell apoptosis through the endoplasmic reticulum stress pathway

Congenital long QT syndrome (LQTS) is a cardiac channelopathy that often results in fatal arrhythmias. LQTS mutations not only lead to abnormal myocardial electrical activities but are associated with heart contraction abnormalities, cardiomyopathy and congenital heart defects. In vivo and in vitro studies have found that LQTS mutations are associated with cardiomyocyte apoptosis, cardiac developmental disorders and even embryonic mortality. Cardiac delayed rectifier potassium channel dysfunction due to the human ether‑à‑go‑go‑related gene (hERG) mutation causes congenital LQTS type 2. The majority of LQTS 2 mutations are characterized by mutant protein accumulation in the endoplasmic reticulum (ER). Unfolded or misfolded protein retention in the ER causes an unfolded protein reaction, which is characteristic of ER stress (ERS). Therefore, the present study hypothesized that LQTS mutations can cause cardiac structural abnormalities via ERS‑mediated cardiomyocyte apoptosis. To test this hypothesis, 293 cells were transiently transfected with an L539fs/47‑hERG plasmid to generate an LQTS 2 model. L539fs/47‑hERG is an LQTS 2 mutation, which consists of a 19‑bp deletion at 1619‑1637 and a point mutation at 1692. Using confocal laser scanning microscopy analysis, it was verified that the L539fs/47‑hERG protein was retained in the ER. Hoechst 33342 apoptosis staining indicated that apoptosis was increased in the L539fs/47‑hERG‑transfected cells, and this be reversed by treatment with 4‑phenyl butyric acid. Western blot analysis revealed increased expression levels of the ERS chaperone glucose regulated protein 78 and pro‑apoptotic ERS‑induced factors, including protein kinase R‑like endoplasmic reticulum kinase, eukaryotic translation‑initiation factor‑2α and C/EBP homologous protein, in the L539fs/47‑hERG‑transfected cells. The B‑cell lymphoma (Bcl‑2)‑associated X protein/Bcl‑2 ratio and caspase‑12 were also increased in the mutated cells. These results demonstrate that L539fs/47‑hERG induces cell apoptosis and the potential molecular mechanism involves the activation of ERS and ERS‑mediated cell apoptosis.

Ondansetron and teratogenicity in rats: Evidence for a mechanism mediated via embryonic hERG blockade

The potent hERG channel blocking drug ondansetron is used off-label for treatment of nausea and vomiting in early pregnancy. Some human epidemiological studies have associated ondansetron with fetal cardiovascular defects and orofacial clefts. This study investigated the effects of ondanestron on embryonic heart rhythm of gestational day (GD) 13 rat embryos in vitro and then integrated the results with published animal teratology, and animal and human pharmacokinetic studies to perform a risk evaluation. Ondansetron caused concentration dependent bradycardia and arrhythmia. Cardiovascular malformations in rats occurred at exposures slightly higher than those in early human pregnancy. Together the results suggest that ondansetron can have teratogenic potential in rats and humans mediated via hERG block and severe heart rhythm disturbances in the embryo. The risk may be increased in human pregnancy if additional risk factors are present such as hypokalemia.

Refractory ventricular fibrillations after surgical repair of atrial septal defects in a patient with CACNA1C gene mutation - case report

BACKGROUND

Congenital long QT syndrome (LQTS) can cause ventricular arrhythmic events with syncope and sudden death resulting from malignant torsades de pointes (TdP) followed by ventricular fibrillations (VFs). However, the syndrome is often overlooked prior to the development of arrhythmic events in patients with congenital heart diseases demonstrating right bundle branch block on electrocardiogram (ECG). We present a case of an adult patient with congenital heart disease who developed VFs postoperatively, potentially due to his mutation in a LQTS related gene, which was not identified on preoperative assessment due to incomplete evaluation of his family history.

CASE PRESENTATION

A 64-year-old man was diagnosed as having multiple atrial septal defects. He presented with no symptoms of heart failure. His preoperative ECG showed complete right bundle branch block (CRBBB) with a corrected QT interval time of 478 ms. He underwent open-heart surgery to close the defects through median sternotomy access. Three hours after the operation, he developed multiple events of TdP and VFs in the intensive care unit. Cardiopulmonary resuscitation and multiple cardioversions were attempted for his repetitive TdP and VFs. He eventually reverted to sinus rhythm, and intravenous beta-blocker was administered to maintain the sinus rhythm. After this event, his family history was reviewed, and it was confirmed that his daughter and grandson had a medical history of arrhythmia. A genetic test confirmed that he had a missense mutation in CACNA1C, p.K1580 T, which is the cause for type 8.

CONCLUSIONS

This case highlights the importance of paying attention to other ECG findings in patients with CRBBB, which can mask prolonged QT intervals.

Role of Mutation and Pharmacologic Block of Human KCNH2 in Vasculogenesis and Fetal Mortality

Background—

N629D KCNH2 is a human missense long-QT2 mutation. Previously, we reported that the N629D/N629D mutation embryos disrupted cardiac looping, right ventricle development, and ablated I Kr activity at E9.5. The present study evaluates the role of KCNH2 in vasculogenesis.

Methods and Results—

N629D/N629D yolk sac vessels and aorta consist of sinusoids without normal arborization. Isolated E9.5 +/+ first branchial arches showed normal outgrowth of mouse ERG–positive/α-smooth muscle actin coimmunolocalized cells; however, outgrowth was grossly reduced in N629D/N629D. N629D/N629D aortas showed fewer α-smooth muscle actin positive cells that were not coimmunolocalized with mouse ERG cells. Transforming growth factor-β treatment of isolated N629D/N629D embryoid bodies partially rescued this phenotype. Cultured N629D/N629D embryos recapitulate the same cardiovascular phenotypes as seen in vivo. Transforming growth factor-β treatment significantly rescued these embryonic phenotypes. Both in vivo and in vitro, dofetilide treatment, over a narrow window of time, entirely recapitulated the N629D/N629D fetal phenotypes. Exogenous transforming growth factor-β treatment also rescued the dofetilide-induced phenotype toward normal.

Conclusions—

Loss of function of KCNH2 mutations results in defects in cardiogenesis and vasculogenesis. Because many medications inadvertently block the KCNH2 potassium current, these novel findings seem to have clinical relevance.

Preoperative diagnosis of long QT syndrome in an infant with tetralogy of Fallot

Long QT syndrome is a well-described entity in infants. Its presentation in the context of congenital heart disease is rare and is almost exclusively diagnosed postoperatively. For patients undergoing surgical intervention, preoperative knowledge of the diagnosis and appropriate perioperative management can be life-saving. We present the rare case of an infant with tetralogy of Fallot who was preoperatively diagnosed with long QT syndrome and discuss the implications of this diagnosis for his perioperative management.

Homozygous missense N629D hERG (KCNH2) potassium channel mutation causes developmental defects in the right ventricle and its outflow tract and embryonic lethality

Loss-of-function mutations in the human ERG1 potassium channel (hERG1) frequently underlie the long QT2 (LQT2) syndrome. The role of the ERG potassium channel in cardiac development was elaborated in an in vivo model of a homozygous, loss-of-function LQT2 syndrome mutation. The hERG N629D mutation was introduced into the orthologous mouse gene, mERG, by homologous recombination in mouse embryonic stem cells. Intact homozygous embryos showed abrupt cessation of the heart beat. N629D/N629D embryos die in utero by embryonic day 11.5. Their developmental defects include altered looping architecture, poorly developed bulbus cordis, and distorted aortic sac and branchial arches. N629D/N629D myocytes from embryonic day 9.5 embryos manifested complete loss of I(Kr) function, depolarized resting potential, prolonged action potential duration (LQT), failure to repolarize, and propensity to oscillatory arrhythmias. N629D/N629D myocytes manifest calcium oscillations and increased sarcoplasmic reticulum Ca(+2) content. Although the N629D/N629D protein is synthesized, it is mainly located intracellularly, whereas +/+ mERG protein is mainly in plasmalemma. N629D/N629D embryos show robust apoptosis in craniofacial regions, particularly in the first branchial arch and, to a lesser extent, in the cardiac outflow tract. Because deletion of Hand2 produces apoptosis, in similar regions and with a similar final developmental phenotype, Hand2 expression was evaluated. Robust decrease in Hand2 expression was observed in the secondary heart field in N629D/N629D embryos. In conclusion, loss of I(Kr) function in N629D/N629D cardiovascular system leads to defects in cardiac ontogeny in the first branchial arch, outflow tract, and the right ventricle.