Progesterone pretreatment reduces the incidence of drug-induced torsades de pointes in atrioventricular node-ablated isolated perfused rabbit hearts.

INTRODUCTION: Higher progesterone concentrations are protective against drug-induced prolongation of ventricular repolarization. We tested the hypothesis that pretreatment with progesterone reduces the incidence of drug-induced torsades de pointes (TdP). METHODS AND RESULTS: Female New Zealand white rabbits (2.5-3.2 kg) underwent ovariectomy and were randomized to undergo implantation with subcutaneous 21-day sustained release pellets containing progesterone 50 mg (n = 22) or placebo (n = 23). After 20 days, hearts were excised, mounted, and perfused with modified Krebs-Henseleit solution. The atrioventricular (AV) node was destroyed manually. Following a 15-minute equilibration period, hearts were perfused with dofetilide 100 nM for 30 minutes, during which the electrocardiogram was recorded continuously. Incidences of spontaneous TdP, other ventricular arrhythmias and mean QTc intervals were compared. Median serum progesterone concentrations were higher in progesterone vs placebo-treated rabbits (3.8 [range, 2.8-5.1] vs 0.7 [0.4-1.7] ng/mL, P < 0.0001). Median serum estradiol concentrations were similar (58 [22-72] vs 53 [34-62] pg/mL), P = 0.79). The incidence of TdP was lower in hearts from progesterone-treated rabbits (27% vs 61%, P = 0.049). The incidences of bigeminy (36% vs 74%, P = 0.03) and trigeminy (18% vs 57%, P = 0.01) were also lower in hearts from progesterone-treated rabbits. There was no significant difference between groups in incidence of couplets (59% vs 74%, P = 0.54) or monomorphic ventricular tachycardia (14% vs 30%, P = 0.28). Maximum QT c interval and short-term beat-to-beat QT interval variability during dofetilide perfusion were significantly shorter in hearts from progesterone-treated rabbits. CONCLUSIONS: Pretreatment with progesterone reduces the incidence of drug-induced TdP, bigeminy, and trigeminy in isolated perfused AV node-ablated rabbit hearts.

Investigation of potential mechanisms of sex differences in quinidine-induced torsade de pointes risk.

INTRODUCTION: The electrocardiographic index Tpeak-Tend has been proposed as a marker of dispersion of repolarization and may be a stronger predictor of torsade de pointes risk than QTc prolongation. METHODS AND RESULTS: We assessed whether quinidine-induced Tpeak-Tend prolongation is greater in women than men. The relationship between QTc prolongation and quinidine concentration was greater in women than men (38 ± 10 vs. 28 ± 9 ms/µg/ml, p=0.02), but there was no difference for Tpeak-Tend prolongation (39 ± 13 vs. 32 ± 13 ms/µg/ml, p=0.21). There was a delay (hysteresis) between peak concentration and both maximum QTc and Tpeak-Tend prolongation and a trend toward higher serum quinidine concentration in men than women. Analysis controlling for hysteresis showed no sex difference for QTc (55 ± 18 vs. 43 ± 19 ms/µg/ml, p=0.14), without changing the lack of sex difference with Tpeak-Tend (61 ± 22 vs. 55 ± 21 ms/µg/ml, p=0.49). CONCLUSIONS: Women do not have a greater quinidine-induced Tpeak-Tend prolongation than men. Sex differences in hysteresis and serum quinidine concentration in this study may have contributed to sex differences in quinidine-induced QTc prolongation.

Torsade de pointes--a rare presentation of primary hyperaldosteronism.

Primary aldosteronism was the most common form of endocrine hypertension resulting in hypertension, metabolic alkalosis, and hypokalemia. Ventricular arrhythmia in association with primary hyperaldosteronism is an uncommon presentation that has previously been described in literature. We presented one case of torsades de pointes due to primary hyperaldosteronism.

In vivo Analysis of the Anti-atrial Fibrillatory, Proarrhythmic and Cardiodepressive Profiles of Dronedarone as a Guide for Safety Pharmacological Evaluation of Antiarrhythmic Drugs.

Anti-atrial fibrillatory, proarrhythmic and cardiodepressive profiles of dronedarone were analyzed using the halothane-anesthetized beagle dogs (n = 4) to create a standard protocol for clarifying both efficacy and adverse effects of anti-atrial fibrillatory drugs. Intravenous administration of dronedarone hydrochloride in doses of 0.3 and 3 mg/kg over 30 s attained the peak plasma concentrations of 61 and 1248 ng/mL, respectively, reflecting sub- to supra-therapeutic ones. The low dose decreased the left ventricular contraction and mean blood pressure, which were enhanced at the high dose. The high dose also decreased the heart rate and cardiac output, but increased the total peripheral resistance and left ventricular end-diastolic pressure, showing its potent cardiodepressive profile. Moreover, the high dose delayed the atrioventricular nodal and intraventricular conductions in addition to the ventricular repolarization, suggesting its inhibitory action on the Ca2+, Na+ and K+ channels in the in situ heart, respectively. The high dose also prolonged the effective refractory period 1.9 times greater in the atrium than in the ventricle, explaining its clinically demonstrated efficacy against the atrial arrhythmias. Dronedarone significantly prolonged the Tpeak-Tend in a dose-related manner with a tendency to prolong the terminal repolarization period and J-Tpeakc, indicating considerable risk to induce torsade de pointes. No significant change was detected in the P-wave duration by either dose, indicating the lack of effect on the atrial Na+ channel in vivo. The current experimental protocol and the results of dronedarone can be used as a guide for safety pharmacological evaluation of new anti-atrial fibrillatory drugs.

Systemic inflammation as a novel QT-prolonging risk factor in patients with torsades de pointes.

OBJECTIVE: Increasing evidence indicates systemic inflammation as a new potential cause of acquired long QT syndrome (LQTS), via cytokine-mediated changes in cardiomyocyte ion channels. Torsade de pointes (TdP) is a life-threatening polymorphic ventricular tachycardia occurring in patients with LQTS, usually when multiple QT-prolonging factors are simultaneously present. Since classical risk factors cannot fully explain TdP events in a number of patients, we hypothesised that systemic inflammation may represent a currently overlooked risk factor contributing to TdP development in the general population. METHODS: Forty consecutive patients who experienced TdP (TdP cohort) were consecutively enrolled and circulating levels of C-reactive protein (CRP) and proinflammatory cytokines (interleukin-6 (IL-6), tumour necrosis factor alpha (TNFα), interleukin-1 (IL-1)) were compared with patients with active rheumatoid arthritis (RA), comorbidity or healthy controls. An additional 46 patients with different inflammatory conditions (acute infections, n=31; immune-mediated diseases, n=12; others, n=3) and elevated CRP (inflammatory cohort) were prospectively enrolled, and corrected QT (QTc) and cytokine levels were measured during active disease and after a CRP decrease of >75% subsequent to therapy. RESULTS: In the TdP cohort, 80% of patients showed elevated CRP levels (median: ~3 mg/dL), with a definite inflammatory disease identifiable in 18/40 cases (acute infections, n=12; immune-mediated diseases, n=5; others, n=1). In these subjects, IL-6, but not TNFα and IL-1, was ~15-20 times higher than in controls, and comparable to RA patients. In the inflammatory cohort, where QTc prolongation was common (mean values: 456.6±30.9 ms), CRP reduction was associated with IL-6 level decrease and significant QTc shortening (-22.3 ms). CONCLUSION: The data are first to show that systemic inflammation via elevated IL-6 levels may represent a novel QT-prolonging risk factor contributing to TdP occurrence in the presence of other classical risk factors. If confirmed, this could open new avenues in antiarrhythmic therapy.

Arrhythmogenicity of Anti-Ro/SSA Antibodies in Patients With Torsades de Pointes.

BACKGROUND: In patients with autoimmune disease, anti-Ro/SSA antibodies (anti-Ro/SSA) are responsible for a novel autoimmune-associated long-QT syndrome by targeting the hERG potassium channel and inhibiting the related current (IKr). Because anti-Ro/SSA are also present in a significant proportion of healthy subjects and may be associated with torsades de pointes (TdP) arrhythmia, we tested the hypothesis that anti-Ro/SSA may represent a silent risk factor in patients developing TdP. METHODS AND RESULTS: Twenty-five consecutive patients who experienced TdP were prospectively collected independent of ongoing therapies and concomitant diseases. Anti-Ro/SSA were detected by fluoroenzyme immunoassay, immuno-Western blotting, and line-blot immunoassay. Purified IgGs from anti-Ro/SSA-positive and anti-Ro/SSA-negative patients were tested on IKr using HEK293 cells stably expressing the hERG channel. As expected, in TdP patients, many known corrected QT interval-prolonging risk factors were simultaneously present, including hypokalemia that was the most common (52%). Anti-Ro/SSA were present in 60% of the subjects, mostly the anti-Ro/SSA-52-kD subtype detected by immuno-Western blotting only. A history of autoimmune disease was found in only 2 of anti-Ro/SSA-positive patients. Experimental data demonstrated that purified anti-Ro/SSA-positive IgGs significantly inhibited IKr and cross reacted with hERG-channel proteins. Moreover, anti-Ro/SSA-positive sera exhibited high reactivity with a peptide corresponding to the hERG-channel pore-forming region. CONCLUSIONS: Anti-Ro/SSA may represent a clinically silent novel risk factor for TdP development via an autoimmune-mediated electrophysiological interference with the hERG channel. We propose that TdP patients may benefit from specific anti-Ro/SSA testing even in the absence of autoimmune diseases as immunomodulating therapies may be effective in shortening corrected QT interval and reducing TdP recurrence risk.

Torsade de pointes with an antihistamine metabolite: potassium channel blockade with desmethylastemizole.

OBJECTIVES: Proarrhythmic effects have been observed with the selective histamine1 (H1) receptor antagonist drug astemizole, a widely prescribed antihistamine. The metabolites of astemizole and those of other antihistamine compounds have not been implicated as causative agents of cardiac arrhythmias. The purpose of this study was to examine whether desmethylastemizole, the principal metabolite of astemizole, blocks delayed rectifier potassium (K+) channels. BACKGROUND: QT interval prolongation and torsade de pointes are associated with astemizole intake and have been ascribed to block the repolarizing K+ currents, specifically the rapidly activating component of the delayed rectifier iKr. Astemizole undergoes extensive first-pass metabolism, and its dominant metabolite, desmethylastemizole, has a markedly prolonged elimination time. We report the clinical observation of QT prolongation and torsade de pointes in a patient with undetectable serum concentrations of astemizole (< 0.5 ng/ml) and "therapeutic" concentrations of desmethylastemizole (up to 7.7 ng/ml or 17.3 nmol/liter). METHODS: The perforated patch clamp recording technique was used to study the effects of desmethylastemizole (20 nmol/liter) on action potentials and iKr in isolated rabbit ventricular myocytes. RESULTS: Desmethylastemizole produced action potential prolongation and the induction of plateau early afterdepolarizations. Under voltage clamp conditions, desmethylastemizole suppressed iKr amplitude by approximately 65%. The drug E-4031 (100 nmol/liter), which selectively blocks iKr, had a similar effect on current amplitude. CONCLUSIONS: Desmethylastemizole, the major astemizole metabolite, blocks the repolarizing K+ current iKr with high affinity. The clinical observation of QT prolongation and torsade de pointes found with astemizole intake may principally be caused by the proarrhythmic effects of its metabolite desmethylastemizole.

Alcoholic liver cirrhosis complicated with torsade de pointes during plasma exchange and hemodiafiltration.

A 36-year-old man with severe alcoholic hepatitis was treated with plasma exchange combined with hemodiafiltration to remove endotoxins and inflammatory cytokines. During the treatment, he had critical arrhythmia (torsade de pointes [TdP]). His laboratory data showed hypomagnesemia, which was suspected to be responsible for the development of TdP. Patients with alcoholic liver disease tend to have hypomagnesemia and Q-T interval prolongation. Furthermore, hemodiafiltration may cause hypomagnesemia. Careful observation for electrolytic imbalance is necessary when clinicians treat patients with alcoholic liver failure with a liver support system.

Dose-related effects of methadone on QT prolongation in a series of patients with torsade de pointes.

STUDY OBJECTIVE: To investigate the relationship between the daily dose of the synthetic opioid methadone and the corrected QT (QTc) interval in a series of methadone-treated patients who developed torsade de pointes. DESIGN: Retrospective case series analysis. SETTING: Outpatient pain management center and methadone maintenance treatment programs. PATIENTS: Seventeen patients who developed torsade de pointes while receiving very high daily doses of methadone. MEASUREMENTS AND MAIN RESULTS: The QTc intervals were calculated for each patient. The relationship between daily methadone dose and QTc interval was assessed and adjusted for clinical characteristics that may have independently prolonged cardiac repolarization. The mean QTc interval was 615 +/- 77 msec. Multiple linear regression indicated that only the daily methadone dose was predictive of the QTc interval (r = +0.51, p = 0.03). All other variables examined, such as age, sex, presence of hypokalemia or structural heart disease, and presence of QT-prolonging drugs, were not predictive of the QTc interval (minimum p = 0.28). CONCLUSION: In this series, the daily methadone dose correlated positively with the QTc interval. This finding supports the possibility that methadone contributed to the development of arrhythmia.

Torsades de pointes associated with high dose levomethadyl acetate (ORLAAM).

A patient undergoing management of heroin dependency with high dosages of the long-acting methadone derivative, levomethadyl acetate HCl (LAAM; ORLAAM) developed a prolonged QTc interval and polymorphic QRS complexes on EKG consistent with torsades de pointes (TdP). The patient was taking other drugs known to prolong the QTc interval (fluoxetine and IV cocaine), and those known to antagonize the activity of the P450 enzymes responsible for the metabolism of LAAM and its active metabolite (fluoxetine, cocaine and marijuana). No previous reports have appeared in the literature attributing this adverse event to LAAM therapy; however, five similar cases have been reported to the manufacturer. Animal studies indicate that LAAM and metabolites prolong the action potential duration of myocardial cells. We propose that predisposed patients on high doses of LAAM may be at risk for developing TdP. Patients being treated with LAAM should receive dosages consistent with guidelines and be evaluated for concomitant diseases, interacting drug therapies, and EKG abnormalities.

[Bepridil: importance of serum level in treatment surveillance]. / Bépridil: intérêt du dosage sérique dans la surveillance du traitement.

OBJECTIVE: Despite precise recommendations for prescription and monitoring, tosades de pointes is still observed with bepridil. The purpose of this study was to demonstrate the contribution of bepridil serum assay in therapeutic supervision. PATIENTS AND METHODS: Seventy-five patients over 70 years of age were included. Prolongation of the QT interval was observed in 23 patients. RESULTS: The potential prognostic factors for increased QT interval as demonstrated by univariate logistic regression were hypokaliemia, bradycardia, renal failure and bepridil serum level. After multivariate logistic regression, the persisting causal factors for increased QT interval were hypokaliemia, bradycardia and bepridil serum level. CONCLUSION: Prolongation of the QT interval remains dependent on several variables. Bepridil determination during treatment is insufficient alone.

Pharmacometabolomic approach to predict QT prolongation in guinea pigs.

Drug-induced torsades de pointes (TdP), a life-threatening arrhythmia associated with prolongation of the QT interval, has been a significant reason for withdrawal of several medicines from the market. Prolongation of the QT interval is considered as the best biomarker for predicting the torsadogenic risk of a new chemical entity. Because of the difficulty assessing the risk for TdP during drug development, we evaluated the metabolic phenotype for predicting QT prolongation induced by sparfloxacin, and elucidated the metabolic pathway related to the QT prolongation. We performed electrocardiography analysis and liquid chromatography-mass spectroscopy-based metabolic profiling of plasma samples obtained from 15 guinea pigs after administration of sparfloxacin at doses of 33.3, 100, and 300 mg/kg. Principal component analysis and partial least squares modelling were conducted to select the metabolites that substantially contributed to the prediction of QT prolongation. QTc increased significantly with increasing dose (r = 0.93). From the PLS analysis, the key metabolites that showed the highest variable importance in the projection values (>1.5) were selected, identified, and used to determine the metabolic network. In particular, cytidine-5'-diphosphate (CDP), deoxycorticosterone, L-aspartic acid and stearic acid were found to be final metabolomic phenotypes for the prediction of QT prolongation. Metabolomic phenotypes for predicting drug-induced QT prolongation of sparfloxacin were developed and can be applied to cardiac toxicity screening of other drugs. In addition, this integrative pharmacometabolomic approach would serve as a good tool for predicting pharmacodynamic or toxicological effects caused by changes in dose.

Multifactorial QT interval prolongation.

Acquired long QT interval has been widely reported to be a consequence of drug therapy and electrolyte disturbances. We describe two cases of multifactorial acquired QT interval prolongation and torsades de pointes. In the first case, the drugs venlafaxine, amiodarone and domperidone may have contributed to QT interval prolongation in a patient with hypokalemia and hypomagnesaemia. In the second case, QT interval prolongation occurred in a patient taking quetiapine and citalopram, and whose use of hydrocholorothiazide and history of chronic alcohol abuse likely contributed by rendering the patient hypokalemic. These cases highlight the potential risks associated with polypharmacy and demonstrate that though torsades de pointes is an uncommon arrhythmia, the combination of multiple factors known to prolong QT interval may precipitate this life-threatening arrhythmia.

[Early onset of torsades de Pointes and elevated levels of serum troponin I due to acute arsenic poisoning]. / Torsades de Pointes precoces y elevación sérica de la troponina I debidas a intoxicación aguda por arsénico.

Most cases of acute arsenic poisoning occur through accidental or voluntary ingestion of pesticides or insecticides, and all body systems are affected. Arsenic can prolong the QT interval and lead to torsades of Pointes, a crucial type of arrhythmia characteristic of such QT interval prolongation. In our revision of the literature, there have been found only 5 cases of torsades of Pointes due to acute arsenic poisoning. Recently, there have been published four additional cases in patients with refractory or recurrent acute promyelocytic leukemia being treated with arsenic trioxide. In all nine cases, torsades of pointes appeared slowly after poisoning. Herein is described a case of acute arsenic poisoning which led to an early onset of torsades of Pointes, hypopotasemia and high levels of serum troponin I.

[Polymorphic ventricular tachycardia of torsade de pointes type in patient with schizophrenia treated with thioridazine]. / Wieloksztaltny czestoskurcz komorowy typu torsade de pointes u pacjentki ze schizofrenia leczonej tiorydazyna.

A case of 82 year-old female with schizophrenia treated with thioridazine with a long QT syndrome and polymorphic ventricular tachycardia of torsade de pointes type was presented. Additional predisposing factor for cardiac arrhythmia was diarrhea with subsequent hypokalemia. Infusion of magnesium sulphate, potassium supplementation and thioridazine discontinuation was effective management of the pathient.

Clinical evaluation of adverse effects during bepridil administration for atrial fibrillation and flutter.

BACKGROUND: Bepridil hydrochloride (Bpd) has attracted attention as an effective drug for atrial fibrillation (AF) and atrial flutter (AFL). However, serious adverse effects, including torsade de pointes (Tdp), have been reported. METHODS AND RESULTS: Adverse effects of Bpd requiring discontinuation of treatment were evaluated. Bpd was administered to 459 patients (361 males, 63+/-12 years old) comprising 378 AF and 81 AFL cases. Mean left ventricular ejection fraction and atrial dimension (LAD) were 66+/-11% and 40+/-6 mm, respectively. Adverse effects were observed in 19 patients (4%) during an average follow-up of 20 months. There was marked QT prolongation greater than 0.55 s in 13 patients, bradycardia less than 40 beats/min in 6 patients, dizziness and general fatigue in 1 patient each. In 4 of 13 patients with QT prolongation, Tdp occurred. The major triggering factors of Tdp were hypokalemia and sudden decrease in heart rate. There were no differences in the clinical backgrounds of the patients with and without Tdp other than LAD and age, which were larger and older in the patients with Tdp. CONCLUSION: Careful observation of serum potassium concentration and the ECG should always be done during Bpd administration, particularly in elderly patients.

Optimal administration dosage of magnesium sulfate for torsades de pointes in children with long QT syndrome.

BACKGROUND: Intravenous administration of magnesium sulphate (MgSO(4)) is a very effective and safe treatment for torsades de pointes (TdP) associated with acquired long QT syndrome (LQTS) in adults. Discussed here is the efficacy of MgSO(4) for TdP in children with congenital and acquired LQTS. METHODS: The optimal MgSO(4) dosage and serum magnesium (SMg) was determined in six consecutive children with TdP; four had congenital LQTS and two had acquired LQTS. A bolus injection of MgSO(4) was given intravenously over 1 to 2 minutes followed by continuous infusion for the next 2 to 7 days. RESULTS: Of the six patients, five responded completely to the initial bolus of 6.1 +/- 4.2 mg/kg (range, 2.3-12 mg/kg). One (a neonate with congenital LQTS) required a total of 30 mg/kg until complete TdP elimination. Continuous infusion was given at rates of 0.3 to 1.0 mg/kg/hr with no recurrence of TdP. SMg concentration was 3.9 +/- 1.0 mg/dL (2.9-5.4 mg/dL) immediately after bolus injection. CONCLUSION: Intravenous MgSO(4) infusion effectively treated TdP in children with LQTS. Optimal bolus dosage, infusion rates and SMg concentration were 3 to 12 mg/kg, 0.5 to 1.0 mg/kg/hr and 3 to 5 mg/dL, respectively.

Abnormal function of platelet G proteins in long QT syndrome.

Several hypotheses have been proposed for the pathophysiology of the congenital long QT syndrome, however, the underlying mechanism has not yet been elucidated. This study evaluated G protein function in patients with congenital long QT syndrome (LQTS) and compared it with that of normal subjects. Platelet-rich plasma was collected and the cyclic AMP (cAMP) level of platelets was measured in three conditions utilizing radioimmunoassay: the basal state (Basal cAMP), after stimulation by PGE1 (PGE1-cAMP), and after stimulation by PGE1 followed by inhibition by adrenaline (Adr-cAMP), and the results were compared between 7 LQTS patients and 10 healthy volunteers (control). Gs function was defined as (PGE1-cAMP)/(Basal cAMP) and Gi function as ¿(PGE1-cAMP)-(Adr-cAMP)¿/(PGE1-cAMP). Basal cAMP was lower in patients than in the controls: 2.9 +/- 0.6 pmol/ 10(8) cells vs. 4.2 +/- 0.7 pmol/10(8) cells (p < 0.05). The increase in cAMP after PGE1 was similar in the two groups but the peak was lower in the patients: 16.8 +/- 6.2 pmol/10(8) cells vs. 24.8 +/- 7.4 pmol/10(8) cells (PGE1-cAMP). After addition of adrenaline, cAMP decreased to 14.2 +/- 5.8 pmol/10(8) cells vs. 16.2 +/- 7.6 pmol/10(8) cells and the change was significantly smaller in the patients than in the controls: 0.17 +/- 0.12 vs. 0.38 +/- 0.16 (p < 0.05). Basal cAMP was weakly correlated with sinus cycle length (r = -0.48, p > 0.3) and QTc was correlated with Gs function (r = 0.52, p > 0.3) but not with Gi function. Patients with associated Torsade de Pointes had a significantly lower Gi function compared to those without (p < 0.05). In LQTS patients, G protein function was abnormal and the abnormality was associated with clinical characteristics of long QT syndrome. The relationship between the abnormal G protein function and the regulation of the repolarization of the ventricular myocardium needs to be studied further.

Effective use of magnesium for acquired torsade de pointes in a 4-month-old infant.

We report a 4-month-old infant with torsade de pointes secondary to procainamide treatment. The infant presented with atrial flutter and converted to normal sinus rhythm with intravenous procainamide. Oral procainamide therapy was initiated as the infusion was tapered, and the patient subsequently developed incessant torsade de pointes. Once the proarrhythmia was recognized, procainamide was withheld, and intravenous magnesium was administered. The torsade de pointes resolved after one bolus of magnesium sulfate. An infusion regimen of magnesium was given until the procainamide and N-acetylprocainamide concentrations became undetectable. Intravenous magnesium should be administered to newborns with acquired torsade de pointes; dosing guidelines for its use are suggested.