Electrocardiography ; Female ; Humans ; Syncope/etiology* ; Torsades de Pointes/etiology*

Diagnosis, Differential ; Electrocardiography ; Humans ; Tachycardia, Ventricular ; Torsades de Pointes

In 2005, the International Council for Harmonization (ICH) established cardiotoxicity assessment guidelines to identify the risk of Torsade de Pointes (TdP). It is focused on the blockade of the human ether-à-go-go-related gene (hERG) channel known to cause QT/QTc prolongation and the QT/QTc prolongation shown on the electrocardiogram. However, these biomarkers are not the direct risks of TdP with low specificity as the action potential is influenced by multiple channels along with the hERG channel. Comprehensive in vitro Proarrhythmia Assay (CiPA) initiative emerged to address limitations of the current model. The objective of CiPA is to develop a standardized in silico model of a human ventricular cell to quantitively evaluate the cardiac response for the cardiac toxicity risk and to come up with a metric for the TdP risk assessment. In silico working group under CiPA developed a standardized and reliable in silico model and a metric that can quantitatively evaluate cellular cardiac electrophysiologic activity. The implementation mainly consists of hERG fitting, Hill fitting, and action potential simulation. In this review, we explained how the in silico model of CiPA works, and briefly summarized current overall CiPA studies. We hope this review helps clinical pharmacologists to understand the underlying estimation process of CiPA in silico modeling.
Action Potentials ; Biomarkers ; Cardiotoxicity ; Computer Simulation ; Electrocardiography ; Hope ; Humans ; In Vitro Techniques ; Risk Assessment ; Sensitivity and Specificity ; Torsades de Pointes

K⁺ channels are key components of the primary and secondary basolateral Cl- pump systems, which are important for secretion from the salivary glands. Paroxetine is a selective serotonin reuptake inhibitor (SSRI) for psychiatric disorders that can induce QT prolongation, which may lead to torsades de pointes. We studied the effects of paroxetine on a human K⁺ channel, human ether-a-go-go-related gene (hERG), expressed in Xenopus oocytes and on action potential in guinea pig ventricular myocytes. The hERG encodes the pore-forming subunits of the rapidly-activating delayed rectifier K⁺ channel (I(Kr)) in the heart. Mutations in hERG reduce I(Kr) and cause type 2 long QT syndrome (LQT2), a disorder that predisposes individuals to life-threatening arrhythmias. Paroxetine induced concentration-dependent decreases in the current amplitude at the end of the voltage steps and hERG tail currents. The inhibition was concentration-dependent and time-dependent, but voltage-independent during each voltage pulse. In guinea pig ventricular myocytes held at 36℃, treatment with 0.4 µM paroxetine for 5 min decreased the action potential duration at 90% of repolarization (APD₉₀) by 4.3%. Our results suggest that paroxetine is a blocker of the hERG channels, providing a molecular mechanism for the arrhythmogenic side effects of clinical administration of paroxetine.
Action Potentials ; Animals ; Arrhythmias, Cardiac ; Guinea Pigs ; Heart ; Humans ; Long QT Syndrome ; Muscle Cells ; Oocytes ; Paroxetine ; Salivary Glands ; Serotonin ; Tail ; Torsades de Pointes ; Xenopus

Long QT syndrome is a cardiac repolarization disorder and is associated with an increased risk of torsades de pointes. The acquired form is most often attributable to administration of specific medications and/or electrolyte imbalance. This review provides insights into the risk for QT prolongation associated with drugs frequently used in the treatment of chronic pain. In the field of pain medicine all the major drug classes (i.e. NSAIDs, opioids, anticonvulsive and antidepressant drugs, cannabinoids, muscle relaxants) contain agents that increase the risk of QT prolongation. Other substances, not used in the treatment of pain, such as proton pump inhibitors, antiemetics, and diuretics are also associated with long QT syndrome. When the possible benefits of therapy outweigh the associated risks, slow dose titration and electrocardiography monitoring are recommended.
Analgesics ; Analgesics, Opioid ; Anti-Inflammatory Agents, Non-Steroidal ; Anticonvulsants ; Antidepressive Agents ; Antiemetics ; Cannabinoids ; Chronic Pain ; Diuretics ; Electrocardiography ; Long QT Syndrome ; Muscle Relaxants, Central ; Narcotics ; Proton Pump Inhibitors ; Torsades de Pointes

OBJECTIVES: To investigate the effect of taurine magnesium coordination compound (TMCC) on torsades de pointes (TdP) in isolated guinea pig hearts. METHODS: Healthy male guinea pigs weighting 250~300 g were randomly divided into 4 groups:①TdP model group (=7):Isolated hearts were perfused by normal K-H solution 20 minutes, then perfused by slowly activated delayed rectifier potassium current(IKs) blocker 10mol/L Chromanol 293B under hypokalemic solution(1.8 mmol/L) to establish TdP model;②~④ TdP model + TMCC group (=6):Isolated hearts were perfused by normal K-H solution for 20 minutes, then perfused by IKs blocker 10mol/L Chromanol 293B under hypokalemic solution(1.8 mmol/L) for 60 minutes, at the same time TMCC which concentration was 1, 2, 4 mmol/L was administered respectively by Langendorff retrograde aortic perfusion method. Cardiac surface electrocardiogram of guinea pigs was collected and recorded by Biopac electrophysiological recorder. Incidence of TdP, transmural dispersion of repolarization (TDR), instability of QT interval were acquired from Lead Ⅱ electrocardiograph (ECG) wave forms to describe the effect of TMCC on TdP model. Datas were acquired at the time of 20 min and pre-TdP, in case there was no TdP observed, a value of 60 min was entered for calculation purpose. RESULTS: Incidence of TdP in TdP model group was 6/7. TdP incidence could be decreased significantly by 1, 2, 4 mmol/L TMCC, and was 5/6, 1/6, 0/6 respectively. Compared with the pre-drug, Chromanol 293B under hypokalemic solution in TdP model group increased TDR(corrected) evidently(<0.01). Compared with the pre-drug, 1, 2, 4 mmol/L TMCC in TdP model + TMCC group could decrease the increased TDR(corrected) induced by Chromanol 293B under hypokalemic solution(>0.05). Compared with the TdP model group, 2, 4 mmol/L TMCC could evidently decrease the instability of QT interval induced by Chromanol 293B under hypokalemic solution(<0.05). During the establishment of TdP model, P waves in more than one cardiac cycle continuously were disappeared in ECG. However, P wave could always be seen independent in ECG acquired from TdP model + TMCC group. CONCLUSIONS TMCC can play the role against TdP through decreasing TDR and instability of QT interval, and inhibiting early after depolarization(EAD).
Animals ; Anti-Arrhythmia Agents ; pharmacology ; Electrocardiography ; Guinea Pigs ; In Vitro Techniques ; Long QT Syndrome ; Magnesium ; pharmacology ; Male ; Random Allocation ; Taurine ; pharmacology ; Torsades de Pointes ; drug therapy

BACKGROUND: The Htr3a antagonist, ondansetron, has been reported to prolong the QT interval and induce Torsades de pointes in the treatment of postoperative nausea and vomiting. To explore the mechanisms underlying these findings, we examined the effects of ondansetron on the mouse cardiac voltage-gated K⁺ (Kv) channel. METHODS AND RESULTS: Ondansetron increased QT intervals in late pregnant (LP) mice. We measured the Kv channels in freshly isolated left ventricular (LV) myocytes from non-pregnant (NP) and late pregnant (LP) mice, using patch-clamp electrophysiology. Ondansetron blocked Kv current at a dose of 50 µM, and reduced the amplitude of peak current densities in a dose-dependent manner (0, 1, 5, 50 µM), in LP but not in NP mice. In contrast, serotonin and the Htr3 agonist, m-CPBG, increased Kv current densities in NP, but not in LP mice. Interestingly, during pregnancy, serum serotonin levels were markedly increased, suggesting the saturation of the effect of serotonin. Immunostaning data showed that Kv4.3 protein and Htr3a co-localize at the membrane and t-tubule of cardiomyocytes. Moreover, Kv4.3 membrane trafficking was enhanced in response to Htr3a-mediated serotonin stimulation in NP, but not in LP mice. Membrane analysis showed that serotonin enhances Kv4.3 membrane trafficking in NP, but not LP mice. CONCLUSION: Ondansetron reduced Kv current densities, and reduced the Kv4.3 membrane trafficking in LP mouse ventricular cardiomyocytes. This data suggests that QT prolongation by ondansetron is mediated by the reduction of Kv current densities and Kv4.3 membrane trafficking.
Animals ; Electrophysiology ; Membranes ; Mice* ; Muscle Cells* ; Myocytes, Cardiac ; Ondansetron* ; Postoperative Nausea and Vomiting ; Pregnancy ; Serotonin ; Torsades de Pointes

Long QT syndrome (LQTS) is a rare cardiac channelopathy associated with syncope and sudden death due to torsades de pointes and ventricular fibrillation. Syncope and sudden death are frequently associated with physical and emotional stress. Management of patients with LQTS consists of life-style modification, β-blockers, left cardiac sympathetic denervation (LCSD), and implantable cardioverter-defibrillator (ICD) implantation. Prohibition of competitive exercise and avoidance of QT-prolonging drugs are important issues in life-style modification. Although β-blockers are the primary treatment modality for patients with LQTS, these drugs are not completely effective in some patients. Lifelong ICD implantation in young and active patients is associated with significant complications. LCSD is a relatively simple and highly effective surgical procedure. However, LCSD is rarely used.
Channelopathies ; Death, Sudden ; Defibrillators, Implantable ; Humans ; Long QT Syndrome* ; Stress, Psychological ; Sympathectomy ; Syncope ; Torsades de Pointes ; Ventricular Fibrillation

Flecainide acetate is a potent class IC anti-arrhythmic drug with a major sodium channel blocking effect. Flecainide toxicity can cause myocardial impairment and precipitate circulatory collapse. It may also result in life-threatening arrhythmia, although cases of flecainide-induced torsades de pointes are rare. Furthermore, the electrical and hemodynamic deteriorations observed during flecainide toxicity may not respond to conventional treatments. In the present study, we report the case of a 20-year-old Korean man with flecainide poisoning, who presented with hypotension. The patient was successfully treated with sodium bicarbonate, amiodarone, MgSO₄, and lidocaine, with no recourse to extracorporeal therapy. Although there is no standard therapy for flecainide toxicity, this report demonstrates that intensive pharmacological treatment is beneficial in cases of flecainide overdose.
Amiodarone ; Arrhythmias, Cardiac ; Drug-Related Side Effects and Adverse Reactions ; Flecainide ; Hemodynamics ; Humans ; Hypotension ; Lidocaine ; Poisoning ; Shock ; Sodium Bicarbonate ; Sodium Channels ; Torsades de Pointes* ; Young Adult

Humans ; Torsades de Pointes