Clinician Satisfaction With Advanced Clinical Decision Support to Reduce the Risk of Torsades de Pointes

OBJECTIVES

Clinical decision support (CDS) can potentially help clinicians identify and manage patients who are at risk for torsades de pointes (TdP). However, computer alerts are often ignored and might contribute to alert fatigue. The goals of this project were to create an advanced TdP CDS advisory that presents patient-specific, relevant information, including 1-click management options, and to determine clinician satisfaction with the CDS.

METHODS

The advanced TdP CDS was developed and implemented across a health system comprising 29 hospitals. The advisory presents patient-specific information including relevant risk factors, laboratory values, and 1-click options to help manage the condition in high-risk patients. A short electronic survey was created to gather clinician feedback on the advisory.

RESULTS

After implementation, an email invitation to complete the anonymous advisory-related survey was sent to 442 clinicians who received the advisory. Among the 38 respondents, feedback was generally positive, with 79% of respondents reporting that the advisory helps them care for their patients and 87% responding that alternative actions for them to consider were clearly specified. However, 46% of respondents indicated the alert appeared too frequently.

CONCLUSIONS

Advanced TdP risk CDS that provides relevant, patient-specific information and 1-click management options can be generally viewed favorably by clinicians who receive the advisory.

Short-term Variability of Repolarization Is Superior to Other Repolarization Parameters in the Evaluation of Diverse Antiarrhythmic Interventions in the Chronic Atrioventricular Block Dog

Short-term variability (STV), to quantify beat-to-beat variability of repolarization, is a surrogate parameter that reliably identifies proarrhythmic risk in preclinical models. Examples include not only the use in the chronic atrioventricular block (CAVB) dog model whereby it was developed but also in vulnerable patients with heart failure or drug-induced long QT syndrome. In the CAVB dog model, STV can specifically distinguish between safe and unsafe drugs in proarrhythmic screening. Conversely, this dog model also offers the possibility to evaluate antiarrhythmic strategies in a setting of Torsades de Pointes (TdP) induction with a standard IKr inhibitor. The different antiarrhythmic interventions studied in suppression and prevention of drug-induced TdP in vivo in the CAVB dog model and in vitro in canine ventricular cardiomyocytes are described in this overview. We provide evidence that STV predicts the magnitude of antiarrhythmic effect against TdP better than other repolarization parameters in both suppression and prevention conditions. Moreover, suppression and prevention experiments revealed the same level of antiarrhythmic efficacy, whereas cellular experiments seem more sensitive in comparison with drug testing in vivo. Together, these observations suggest that STV could be used as a consistent indicator to rank efficacy of antiarrhythmic interventions in a number of conditions.

Antiarrhythmic and Proarrhythmic Properties of QT-Prolonging Antianginal Drugs

In recent years there has been a major reorientation of drug therapy for cardiac arrhythmias, its changing role, and above all, a radical change in the class of arrhythmia drugs because of their impact on mortality. The decline in the use of sodium-channel blockers has led to an expanding use of β-blockers and simple or complex class III agents for controlling cardiac arrhythmias. Success with these agents in the context of their side effects has spurred the development of compounds with simpler ion-channel blocking properties that have less complex adverse reactions. The resulting so-called pure class III agents, such as dofetilide or ibutilide, were found to have antifibrillatory effects in atrial fibrillation and flutter and in ventricular tachyarrhythmias. Such agents are effective and have diversity, but they have come into therapeutics with a price: the sometimes-fatal torsades de pointes. The drug amiodarone, a complex compound that was synthesized as an antianginal agent, has been an exception in this regard. Its therapeutic use is associated with a negligibly low incidence of torsades de pointes, even though the drug produces significant bradycardia and QT lengthening to 500 to 700 msec. Recent electrophysiologic studies suggest that this paradox is likely due to the differential block of ion channels in endocardium, epicardium, midmyocardial (M) cells, and Purkinje fibers in the ventricular myocardium. There is also clinical evidence suggesting that amiodarone reduces the “torsadogenic” effects of pure class III agents. Ranolazine was also synthesized for the development of antianginal properties that stem from a partial inhibition of fatty acid oxidation; it too has been found to have electrophysioloigic properties. These are somewhat similar to those of amiodarone on ion channels in endocardium, epicardium, M cells, and Purkinje fibers in the ventricular myocardium, but the drug does not prolong the QT interval to the same extent as amiodarone does. Thus, the drug produces modest increases in repolarization as judged by its effects on the action potential duration (APD) without the potential for the development of torsades de pointes. By virtue of its suppressant action on early afterdepolarizations and triggered activity in Purkinje fibers and M cells, the drug appears to have a powerful potential for reducing the torsadogenic proclivity of conventional class III antiarrhythmic compounds. The rationale for the therapeutic niche for amiodarone, and especially in the case of ranolazine, in the prevention of drug-induced torsades de pointes is discussed.

Computer-assisted interventions to improve QTc documentation in patients receiving QT-prolonging drugs

BACKGROUND

Many medications commonly used in hospitals can cause prolonged corrected QT interval (QTc), putting patients at risk for torsade de pointes (TdP), a potentially fatal arrhythmia. However, documentation of QTc for hospitalized patients receiving QT-prolonging medications is often not consistent with American Heart Association standards.

OBJECTIVE

To examine effects of education and computerized documentation enhancements on QTc documentation.

METHODS

A quasi-experimental multisite study among 4011 cardiac-monitored patients receiving QTc-prolonging medications within a 10-hospital health care system was conducted to compare QTc documentation before (n=1517), 3 months after (n = 1301), and 4 to 6 months after (n = 1193) an intervention. The intervention included (1) online education for 3232 nurses, (2) electronic notifications to alert nurses when a patient received at least 2 doses of a QT-prolonging medication, and (3) computerized calculation of QTc in electronic health records after nurses had documented heart rate and QT interval.

RESULTS

QTc documentation for inpatients receiving QTc-prolonging drugs increased significantly from baseline (17.3%) to 3 months after the intervention (58.2%; P < .001) within the 10 hospitals and had increased further 4 to 6 months after the intervention (62.1%, P = .75). Patients at larger hospitals were significantly more likely to have their QTc documented (46.4%) than were patients at smaller hospitals (26.2%; P < .001).

CONCLUSION

A 3-step system-wide intervention was associated with an increase in QTc documentation for patients at risk for drug-induced TdP, and improvements persisted over time. Further study is needed to assess whether increased QTc documentation decreases occurrence of drug-induced TdP. (American Journal of Critical Care. 2015;24:e6-e15).

QT interval prolongation and the risk of torsades de pointes: essentials for clinicians

OBJECTIVE

QT interval prolongation signifies an increased risk of the life-threatening arrhythmia torsades de pointes (TdP). The purpose of this paper is to review the diverse methods for assessing and monitoring the risk of TdP, discuss risk factors for TdP, and recommend interventions that may mitigate the risk of TdP.

METHODS

A non-systematic search of PubMed (through March 2013) was conducted to determine the optimal approach to assessing and monitoring QT interval, prevention of TdP, and to identify risks factors for TdP. Papers known to the authors were included, as were scientific statements. Articles were chosen based on the judgment of the authors.

RESULTS

Risk factors for drug-induced TdP include hypokalemia, female sex, drug-drug interactions, advancing age, genetic predisposition, hypomagnesemia, heart failure, bradycardia, and corrected QT (QTc) interval prolongation. Many risk factors, including hypokalemia, use of QT-interval-prolonging drugs, and drug interactions are potentially modifiable and should be corrected in persons at risk for QT interval prolongation. Given the variable onset of TdP following initiation of QT-interval-prolonging drugs, careful and regular monitoring of electrocardiography (EKG) and electrolytes are necessary. Patients at risk for QT interval prolongation should be educated to go directly to the emergency room if they experience palpitations, lightheadedness, dizziness or syncope. When the QTc interval is 470-500 ms for males, or 480-500 ms for females, or the QTc interval increases 60 ms or more from pretreatment values, dose reduction or discontinuation of the offending drug should be considered where possible, and electrolytes corrected as needed. Furthermore, if the QTc interval is ≥500 ms, the offending drug should be discontinued, and continuous EKG telemetry monitoring should be performed, or the 12-lead EKG should be repeated every 2-4 hours, until the QT interval has normalized.

CONCLUSIONS

Close monitoring for QTc prolongation is necessary to prevent TdP. The recommendations in this paper are limited by the available evidence and additional studies are needed to better define the approach to monitoring.

[Magnesium metabolism and therapeutic strategy in cardiovascular disease]

Many epidemiological and clinical analysis have reported the relation between Mg and cardiovascular disease. Hypomagnesemia may be triggering mechanisms for ischemic heart disease, arrhythmias after open heart surgery, serious arrhythmias such as Torsades de Pointes (TdP) , and the negative feed back in congestive heart failure. Supplemental and therapeutic Mg infusion have been reported to reduce the mortality in acute myocardial infarction and having the cardioprotective effect after infarction (controversial) . It is also reported to reduce the incidence of arrhythmias after heart surgery, terminate the serious arrhythmias such as TdP, and improve the negative feed back in congestive heart failure. Magnesium metabolisms in cardiovascular disease are not necessarily clear. We expect the precise analysis of Mg actions and attractive Mg therapy in clinical literature.

Quasi-experimental study to improve nurses' QT-interval monitoring: results of QTIP study

BACKGROUND

A collaboration led by the American Heart Association recently released the scientific statement "Prevention of Torsade de Pointes in Hospital Settings." Patients receiving proarrhythmic drugs, who have electrolyte disturbances, or who have bradyarrhythmias require QT-interval monitoring. Prior studies have demonstrated that physicians have a poor level of proficiency at calculating QT intervals. The ability of nurses at calculating QT intervals remains untested.

OBJECTIVES

To evaluate nurses' knowledge and ability to perform QT/QTc interval monitoring.

METHODS

At a single institution, 47 QT-education classes were provided to 480 eligible nurses who regularly perform cardiac monitoring. All nurses completed a researcher-developed knowledge test at baseline and after the QT-related education intervention.

RESULTS

Overall 379 nurses participated (mean age 39 [SD, 10] years), 71% had more than 5 years' nursing experience. Total test scores increased after intervention (46% vs 77%, P < .001). Education significantly improved marking of the QT/RR intervals (QT: 65% vs 91%, RR: 83% vs 90%, P ≤ .001 and P = .02) and measurement of the QT/RR intervals (QT: 47% vs 84%, RR: 35% vs 71% P ≤ .001 and P ≤ .001). Calculation of the QTc interval also increased significantly (6% vs 52%, P ≤ .001).

CONCLUSIONS

Our study results demonstrate that nurses' baseline ability to perform QT interval monitoring is extremely poor. An unacceptable amount of error persists after an educational intervention. Accurate computer-assisted methods are needed to reduce the error associated with manual QT-interval monitoring.

The ketogenic diet and the QT interval

Cardiac complications have been rarely reported associated with the ketogenic diet. Prolonged QT interval in the electrocardiogram and torsades de pointes arrhythmias have been described in a few cases. The effect of the ketogenic diet on QT interval has not been systematically evaluated. We obtained serial electrocardiograms in our patients on the ketogenic diet to look for changes in the mean QT interval. Twenty seven children aged 6 months to 5 years with refractory epilepsy were enrolled. Classic ketogenic diet was introduced using a non-fasting gradual initiation protocol. All patients were supplemented with oral calcium and selenium. Electrocardiograms were obtained at baseline and after 1, 3, 6, and 12 months on the ketogenic diet. There was no statistically significant change in the corrected QT interval over time. There were no ST segment changes or dysrhythmias in any of the electrocardiograms.

QT interval screening in methadone maintenance treatment: report of a SAMHSA expert panel

In an effort to enhance patient safety in opioid treatment programs, the Substance Abuse and Mental Health Saervices Administration convened a multi-disciplinary Expert Panel on the Cardiac Effects of Methadone. Panel members (Appendix A) reviewed the literature, regulatory actions, professional guidances, and opioid treatment program experiences regarding adverse cardiac events associated with methadone. The Panel concluded that, to the extent possible, every opioid treatment program should have a universal Cardiac Risk Management Plan (incorporating clinical assessment, electrocardiogram assessment, risk stratification, and prevention of drug interactions) for all patients and should strongly consider patient-specific risk minimization strategies (such as careful patient monitoring, obtaining electrocardiograms as indicated by a particular patient's risk profile, and adjusting the methadone dose as needed) for patients with identified risk factors for adverse cardiac events. The Panel also suggested specific modifications to informed consent documents, patient education, staff education, and methadone protocols.

[First experience of clinical use of new class III antiarrhythmic agent niferidil in patients with persistent atrial fibrillation and flutter]

The aim of the study was to evaluate the efficacy and safety of administered intravenously niferidil in doses 10, 20 and 30 mkg per kg in patients with persistent atrial fibrillation (AF) and flutter (AFL) for pharmacological cardioversion. The study included 30 patients (22 male) with persistent AF (n = 28) and AFL (n = 2) without structural heart diseases with median arrhythmia duration 6.1 +/- 4.8 months (2 weeks to 24 months). Niferidil was administered as 3 bolus injections (10 mkg per kg each) performed with the interval of 15 minutes. Antiarrhythmic efficacy of niferidil in dose of 10 mkg per kg was 60%, in dose of 20 mkg per kg it was 70%, and in dose of 30 mkg per kg reached 90% prespectively. The part of the patients, in whom QTc prolongation exceeded potentionally dangerous value of 500 mc, was 22.2% (6 of 27). None of the patients developed proarrhythmic side effect as torsade de pointes.

Torsades: adjacent and triggering electrocardiographic events

Torsades de pointes (TdP) is a particular variant of ventricular arrhythmia associated with the long QT syndrome. The background of the latter is essentially 2-fold: patients under treatment with QT-prolonging drugs and subjects with congenital ionopathies. A third category is composed of subjects with both of these backgrounds. The fundamental feature of TdP is its provocation by pause-related augmentation of the repolarizing TU wave. The substrate electrocardiogram (ECG) shows prominent U waves in regular rhythm. The exaggeration of the U wave voltage following a pause is more marked the longer the pause and, for a given pause, more marked the faster the prepause rate. The pause-related sequences figure frequently adjacent to that which actually triggers the attack of TdP and continues to be seen after the event, serving to advise the physician as to the diagnosis, even following cardiac resuscitation, so that preventive measures can be taken (pacing, intravenous magnesium sulfate, or infusion with isoproterenol). The U wave of the regular rhythm ECG may show amplitude instability: an especially tall U triggering a premature ventricular complexe (PVC) that then in turn generates a pause-related sequence. TU alternans is common. Because these patients may not be in a monitored bed, recognition of pause-related phenomena in a patient with a long QT requires the ECG reader of the day to alert the floor as to the running danger. The mechanism of the pause-related TU augmentation is the generation of early afterdepolarizations.

Effect of high doses of magnesium on converting ibutilide to a safe and more effective agent

Ibutilide is a class III antiarrhythmic agent indicated for cardioversion of atrial fibrillation and atrial flutter to sinus rhythm (SR). The most serious complication of ibutilide is torsades de pointes (TdP). Magnesium has been successfully used for the treatment of TdP, but its use as a prophylactic agent for this arrhythmia has not yet been established. The present study investigated whether high dose of magnesium would increase the safety and efficacy of ibutilide administration. A total of 476 patients with atrial fibrillation or atrial flutter who were candidates for conversion to SR were divided into 2 groups. Group A consisted of 229 patients who received ibutilide to convert atrial fibrillation or atrial flutter to SR. Group B consisted of 247 patients who received an intravenous infusion of 5 g of magnesium sulfate for 1 hour followed by the administration of ibutilide. Then, another 5 g of magnesium were infused for 2 additional hours. Of the patients in groups A and B, 154 (67.3%) and 189 (76.5%), respectively, were converted to SR (p = 0.033). Ventricular arrhythmias (sustained, nonsustained ventricular tachycardia, and TdP) occurred significantly more often in group A than in group B (7.4% vs 1.2%, respectively, p = 0.002). TdP developed in 8 patients (3.5%) in group A and in none (0%) in group B (p = 0.009). The administration of magnesium (despite the high doses used) was well tolerated. In conclusion, the administration of high doses of magnesium probably makes ibutilide a much safer agent, and magnesium increased the conversion efficacy of ibutilide.

Drug-induced QT-interval prolongation and proarrhythmic risk in the treatment of atrial arrhythmias

Despite the large number of available antiarrhythmic agents, significant QT-interval prolongation and risk of severe proarrhythmia, including torsade de pointes, limit pharmacological opportunities in the management of atrial arrhythmias. The risk of proarrhythmia has been demonstrated in class I and class III drugs, but significant variability has been observed between agents of the same class. Electrophysiological drug effects found to be important in the etiology of proarrhythmia include QT-interval prolongation through selective blockade of the delayed rectifying potassium current (I(Kr)), early afterdepolarizations, transmural dispersion of repolarization, and a reverse rate dependence. Interestingly, less proarrhythmic potential is seen or anticipated with agents that are able to block multiple ion channels and those with atrial selectivity, despite moderate QT prolongation. This observation has helped steer the development of newer drugs, with some promising preliminary results.

Increasing gap junction coupling reduces transmural dispersion of repolarization and prevents torsade de pointes in rabbit LQT3 model

INTRODUCTION

Increased transmural dispersion of repolarization (TDR) contributes importantly to the development of torsades de pointes (TdP) in long QT syndrome (LQTS). Intercellular electrical coupling via gap junctions plays an important role in maintaining TDR in both normal and diseased hearts. This study examined the effects of antiarrhythmic peptide AAP10, a gap junction enhancer, on TDR and induction of TdP in a rabbit LQT3 model.

METHODS AND RESULTS

An arterially perfused rabbit left ventricular preparation and sea anemone toxin II (ATX-II, 20 nM) were used to establish a LQT3 model. Transmural ECG as well as action potentials from both endocardium and epicardium were simultaneously recorded. Changes in nonphosphorylated connexin43 (Cx43) were measured by immunoblotting. Compared with the control group, the QT interval, TDR, early afterdepolariztion (EAD), R-on-T extrasystole, and TdP increased sharply with augmented nonphosphorylated Cx43 in the LQT3 group (P < 0.001 for both). Interestingly, compared with the LQT3 group, 500 nM AAP10 reduced QT interval, TDR (P < 0.001 for both), and prevented EAD, R-on-T extrasystole, and TdP (P = 0.003, P = 0.001, P = 0.02) with a parallel decrease in nonphosphorylated Cx43 in the presence of ATX-II (P < 0.001).

CONCLUSION

Gap junction enhancer AAP10 is capable of abbreviating the QT interval, reducing TDR, and suppressing TdP in a rabbit LQT3 model probably via its effect by preventing dephosphorylation of Cx43. These data suggest that increasing intercellular coupling may reduce TDR and, therefore, prevent TdP in LQTS.

Calcium antagonist property of CPU228, a dofetilide derivative, contributes to its low incidence of torsades de pointes in rabbits

1. Torsades de pointes (TDP) is a severe adverse effect during the clinical use of dofetilide, a selective blocker of the rapid component of the delayed rectifier potassium channel (I(Kr)). The present study was designed to test whether CPU228, a derivative of dofetilide with calcium (Ca(2+)) antagonist properties, could reduce TDP without reducing the blockade of I(Kr). 2. The incidence of TDP in a rabbit model and the effective refractory period (ERP) were measured and compared for dofetilide and CPU228. Suppression of I(Kr) and the L-type Ca(2+) current (I(Ca,L)) and the Ca(2+) transients of isolated cardiomyocytes were investigated by whole-cell patch-clamp and Fluo-3 dye spectrophotometry. 3. The incidence of TDP was greatly reduced by CPU228 relative to dofetilide, occurring in only one of six rabbits compared with five of six rabbits following dofetilide (P < 0.05). In isolated atria, prolongation of ERP by CPU228 was less than that of dofetilide and no reverse frequency dependence was observed. Negative inotropism by CPU228 was significant against positive inotropism by dofetilide. CPU228 inhibited both I(Kr) and I(Ca,L) currents and the IC(50) for I(Ca,L) inhibition was 0.909 micromol/L. At 3 micromol/L, CPU228 significantly suppressed the Ca(2+) transients. 4. CPU228 is able to block I(Ca,L), contributing to decreased TDP, while also blocking I(Kr) activity. By combined blockade of I(Kr) and I(Ca,L), CPU228 shares the property of complex Class III anti-arrhythmic agents.

Points to consider emerging from a mini-workshop on cardiac safety: assessing torsades de pointes liability

A mini-workshop on cardiac safety focusing on assessing drug-induced Torsades de Pointes (TdP) liability was convened as part of the 6th Annual Meeting of the Safety Pharmacology Society. The purpose of this brief publication is to disseminate the salient points emanating from this workshop as a means of engaging the scientific community in the appropriate discussions needed to advance this important field of human safety. The recommendations in this publication extend those of the workshop on "Moving Towards Better Predictors of Drug-Induced Torsades de Pointes" held in November 2005 under the auspice of the International Life Sciences Institute, Health and Environmental Sciences Institute; they fall into four key areas: molecular and cellular biology underlying TdP, dynamics of periodicity, models of TdP proarrhythmia and key considerations for demonstrating utility of non-clinical models. The reader is encouraged to consider the recommendations emanating from the two workshops and align these with ongoing studies in their laboratories. The authors intend to convene a workshop in 2009/2010 to judge advancements in the field of study of drug-induced TdP and make recommendations for a focused validation of those methods holding the greatest promise of improving the predictivity of this unwanted human cardiac risk.

[Reduction of prolonged QTc-interval related risks in treatment with neuropharmacological drugs. Recommendations for clinical practice]

A prolonged QTc-interval may cause potentially life-threatening arrhythmias. Almost all drugs used in psychiatric practice are able to prolong the QTc-interval. There are some indications that clinicians are not sufficiently aware of the risks of QTc-interval prolongation in clinical practice. By drawing up a list of risk factors associated with prolonged QTc-interval and by correcting for these factors as far as possible, one should be able to reduce the overall risk of potentially lethal arrhythmias and administer more appropriate pharmacological treatment.

Efficacy and Safety of the Additional Bepridil Treatment in Patients With Atrial Fibrillation Refractory to Class I Antiarrhythmic Drugs

BACKGROUND

Bepridil has multiple ion-channel blocking effects and is expected to be useful for managing atrial fibrillation (AF). The purpose of this study was to clarify the efficacy and safety of additional treatment with bepridil in patients with AF who had been treated with class I antiarrhythmic drugs (AADs).

METHODS AND RESULTS

Bepridil (50-200 mg/day) was given to 76 patients with either paroxysmal (n=49) or persistent AF (n=27). All patients had been treated with class I AADs (1.9+/-0.9 drugs/patient) that failed to control the AF. With the addition of bepridil, the frequency of symptomatic AF episodes decreased to less than 10% in 38 (78%) patients with paroxysmal AF, and sinus rhythm was restored within 3 months and maintained during the follow-up in 20 (74%) patients with persistent AF. Efficacy was usually obtained with a small to moderate dose (50-150 mg/day) of bepridil. During a mean follow-up period of 27+/-22 months, no potential complications occurred in any of the patients.

CONCLUSIONS

The addition of bepridil to class I AADs is effective and safe for AF, but careful observation using periodic ECG recordings is essential for avoiding torsades de pointes caused by QT prolongation.

Genotype-specific onset of arrhythmias in congenital long-QT syndrome: possible therapy implications

BACKGROUND

The identification of the molecular-genetic substrate underlying the various forms of the congenital long-QT syndrome (LQTS) has sparked studies into possible genotype-phenotype correlations with the aim of developing genotype-tailored therapy. The onset of torsade de pointes (TdP) may differ among LQTS patients, being pause dependent in some but not all. This disparity may point to different arrhythmia mechanisms and may affect therapy strategies. We studied whether the proportion of pause-dependent TdP onset varies among LQTS genotypes.

METHODS AND RESULTS

We studied all LQT1 (n=10), LQT2 (n=34), and LQT3 (n=6) patients from 4 centers for whom ECGs of TdP onset were available and analyzed whether pauses preceded TdP onset (first available ECG per patient). Pauses preceded TdP significantly more often in LQT2 (68%) than in LQT1 (0%), and the interval immediately before TdP (pause interval) was significantly longer in LQT2 than in LQT1. The proportion of pause dependence in LQT3 (33%) appeared intermediate, but this group was too small for statistical analysis.

CONCLUSIONS

Pause dependence of TdP onset is predominant in LQT2 but absent or rare in LQT1. It is suggested that disparities in pause dependence of TdP onset may reflect different arrhythmia mechanisms.

K201, a multi-channel blocker, inhibits clofilium-induced torsades de pointes and attenuates an increase in repolarization

K201 (JTV519) is a 1,4-benzothiazepine derivative that exhibits a strong cardioprotective action and acts as a multiple-channel blocker, including as a K+ channel blocker. An experimental model of prolongation of the QT interval and torsades de pointes can be induced in rabbits by treatment with clofilium in the presence of the alpha1-adrenoreceptor agonist methoxamine. In this study we examined the effects of K201 with and without methoxamine on the QT and QTc intervals, and determined whether K201 inhibits clofilium-induced torsades de pointes in the presence of methoxamine (15 microg/kg/min) in rabbits (n=74). Administration of K201 (0, 40, 100, 200 and 400 microg/kg/min) with and without methoxamine prolonged the QT interval in a dose-dependent manner, and torsades de pointes did not occur in any animals. However, clofilium (50 microg/kg/min) with methoxamine induced torsades de pointes in all animals (6/6). Torsades de pointes occurred at rates of 100%, 67%, 40% and 0% at K201 concentrations of 0, 50, 200 and 400 microg/kg/min, respectively, in the clofilium-infused torsades de pointes model. Therefore, 400 microg/kg/min of K201 completely inhibited clofilium-induced torsades de pointes and attenuated the increase of repolarization caused by clofilium; the inhibitory effects of K201 may be related to its pharmacological properties as an alpha1-adrenoceptor blocker. Overall, our results show that K201 causes prolongation of the QT and QTc intervals, but does not induce torsades de pointes, with and without alpha1-adrenoceptor stimulation. Furthermore, K201 inhibits clofilium-induced torsades de pointes, despite QT prolongation, suggesting that QT prolongation alone is not a proarrhythmic signal.

Pharmacokinetic-pharmacodynamic modelling of QT interval prolongation following citalopram overdoses

AIMS

To develop a pharmacokinetic-pharmacodynamic model describing the time-course of QT interval prolongation after citalopram overdose and to evaluate the effect of charcoal on the relative risk of developing abnormal QT and heart-rate combinations.

METHODS

Plasma concentrations and electrocardiograph (ECG) data from 52 patients after 62 citalopram overdose events were analysed in WinBUGS using a Bayesian approach. The reported doses ranged from 20 to 1700 mg and on 17 of the events a single dose of activated charcoal was administered. The developed pharmacokinetic-pharmacodynamic model was used for predicting the probability of having abnormal combinations of QT-RR, which was assumed to be related to an increased risk for torsade de pointes (TdP).

RESULTS

The absolute QT interval was related to the observed heart rate with an estimated individual heart-rate correction factor [alpha = 0.36, between-subject coefficient of variation (CV) = 29%]. The heart-rate corrected QT interval was linearly dependent on the predicted citalopram concentration (slope = 40 ms l mg(-1), between-subject CV = 70%) in a hypothetical effect-compartment (half-life of effect-delay = 1.4 h). The heart-rate corrected QT was predicted to be higher in women than in men and to increase with age. Administration of activated charcoal resulted in a pronounced reduction of the QT prolongation and was shown to reduce the risk of having abnormal combinations of QT-RR by approximately 60% for citalopram doses above 600 mg.

CONCLUSION

Citalopram caused a delayed lengthening of the QT interval. Administration of activated charcoal was shown to reduce the risk that the QT interval exceeds a previously defined threshold and therefore is expected to reduce the risk of TdP.

Calmodulin antagonist W-7 prevents sparfloxacin-induced early afterdepolarizations (EADs) in isolated rabbit purkinje fibers: importance of beat-to-beat instability of the repolarization

INTRODUCTION

The occurrence of early afterdepolarizations (EADs) has been related to the incidence of torsades de pointes in drug-induced long QT (LQT). The generation of EADs may be facilitated by Ca(2+)/calmodulin-dependent protein kinase II (CaM kinase).

METHODS AND RESULTS

In the present study, we investigated a possible involvement of Ca(2+)/Calmodulin dependent protein kinase in the generation of sparfloxacin-induced EADs in isolated rabbit Purkinje fibers by means of a calmodulin antagonist W-7. EADs were evident in 8 of the 10 preparations perfused with sparfloxacin at 1 x 10(-4) M and stimulated at 0.2 Hz. The induction of EADs by sparfloxacin was associated with a large prolongation of the duration of the action potential (APD), an increase in the triangulation, and the short-term instability of the repolarization. CaM kinase blockade with the calmodulin antagonist W-7 inhibited sparfloxacin-induced EADs in a concentration-dependent manner (EADs were induced in 3 of 10, 1 of 10, and 0 of 8 preparations in the presence of W-7 at 5 x 10(-7) M, 5 x 10(-6) M, and 5 x 10(-5) M, respectively; P < 0.01 at 5 x 10(-6) M and 5 x 10(-5) M). The inhibition of sparfloxacin-induced EADs by W-7 at 5 x 10(-7) M and 5 x 10(-6) M was associated with a significant decrease in the beat-to-beat instability but not associated with a significant shortening of the APD and reduction of V(max).

CONCLUSION

The present findings support the hypothesis that CaM kinase may be a proarrhythmic signaling molecule and demonstrate that CaM kinase may be involved in the generation of EADs in drug-induced LQT and enhanced beat-to-beat instability of repolarization is essential for the genesis of EADs in rabbit in vitro.

Beat-to-Beat variability of repolarization determines proarrhythmic outcome in dogs susceptible to drug-induced torsades de pointes

OBJECTIVES

We investigated whether increasing or decreasing beat-to-beat variability of repolarization (BVR) would change drug-induced proarrhythmic outcome accordingly.

BACKGROUND

Increased variability of repolarization has been suggested as a prelude to proarrhythmic circumstances in experimental and clinical situations.

METHODS

The non-cardiovascular, I(Kr)-blocking drug sertindole was administered to anesthetized dogs with chronic atrioventricular block. Three interventions were used to prevent or suppress sertindole-induced torsades de pointes (TdP).

RESULTS

Supratherapeutic doses of sertindole (1.0 mg/kg intravenously) induced TdP in 10 of 13 dogs whereas 0.2 mg/kg induced no TdP, despite increases in QT intervals by both doses. The BVR, quantified as short-term variability (STV) from Poincaré plots, was the only parameter that predicted TdP outcome (1.0 mg/kg sertindole: 2.3 +/- 0.7 ms to 5.1 +/- 2.1 ms, p < 0.05; 0.2 mg/kg sertindole: 2.3 +/- 0.8 ms to 3.2 +/- 1.1 ms, p= NS).

INTERVENTIONS

1) KCl, intravenous, reduced the incidence of sertindole-induced TdP from 6 of 7 to 1 of 7 dogs (p<0.05) and prevented sertindole-related increase of STV: 3.0 +/- 1.1 ms vs. 4.5 +/- 1.3 ms (p < 0.05); 2) levcromakalim (I(K,ATP) activator) reduced sertindole-induced TdP and decreased STV from 4.9 +/- 2.1 ms to 2.6 +/- 0.9 ms (p < 0.05); 3) steady-state ventricular pacing (60 beats/min) abolished sertindole-induced TdP and decreased STV from 4.9 +/- 1.5 to 3.2 +/- 1.0 (p < 0.05). Torsades de pointes reappeared upon return to non-paced idioventricular rhythm. None of the 3 interventions reduced the sertindole-induced prolonged QT interval.

CONCLUSIONS

Proarrhythmic intervention is related to an increase in BVR, whereas antiarrhythmic treatment is associated with a decrease in BVR. The BVR is superior to QT interval prolongation in the prediction and prevention of drug-induced TdP in this experimental model.

Atrial-specific drug AVE0118 is free of torsades de pointes in anesthetized dogs with chronic complete atrioventricular block

BACKGROUND

The novel compound AVE0118 has been shown to prevent and terminate persistent atrial fibrillation. AVE0118 blocks I(Kur), I(KAch), and I(to), leading to prolongation of atrial repolarization with no change in ventricular repolarization. This finding suggests that AVE0118 may be devoid of proarrhythmic side effects. Experimentally, AVE0118 has been antiarrhythmic against some specific ventricular arrhythmias.

OBJECTIVES

The purpose of this study was to investigate the proarrhythmic and antiarrhythmic effects of AVE0118 in anesthetized dogs with chronic complete AV block, known for a high proclivity for torsades de pointes (TdP).

METHODS

AVE0118 was administered intravenously as a fast infusion (0.5 mg/kg/5 min) and a slow infusion (3 or 10 mg/kg/60 min). Dofetilide was given to induce TdP. ECG and monophasic action potentials were recorded. Short-term beat-to-beat variability (STV) of the left ventricular monophasic action potential duration (MAPD) was calculated. We examined whether AVE0118 (1) caused ventricular proarrhythmia (both infusions), (2) prevented dofetilide-induced TdP (slow infusion + dofetilide after 30 minutes), and (3) abolished TdP (fast infusion).

RESULTS

At 0.55 +/- 0.10 microg/mL (fast infusion at 10 minutes), AVE0118 did not increase ventricular repolarization or induce TdP; however, right atrial MAPD(50) and MAPD(90) were significantly increased by 26% +/- 9% and 10% +/- 5%, respectively (P <.05 vs baseline). At 1.9 +/- 0.5 microg/mL and 6.1 +/- 1.2 microg/mL (30 minutes of 3 or 10 mg/kg/h), AVE0118 did not induce TdP (0/6 and 0/4) nor prevent dofetilide-induced TdP (6/6 and 2/2). Dofetilide significantly increased all repolarization parameters, including STV from 2.1 +/- 0.4 ms to 4.6 +/- 1.8 ms (P <.05 vs baseline), which were not changed by AVE0118 (to 2.1 +/- 0.3 ms after 30 minutes). Rapid infusion of AVE0118 did not suppress dofetilide-induced TdP.

CONCLUSION

In the anesthetized chronic complete AV block dog, the atrial-specific drug AVE0118 is free of TdP and has no antiarrhythmic properties against dofetilide-induced torsades de pointes.

An overview of QT interval assessment in safety pharmacology

Medicinal products that prolong cardiac repolarization unintentionally, as assessed in terms of prolongation of the QT interval of the electrocardiogram, may trigger a potentially fatal arrhythmia called torsade de pointe (TDP). This lethal risk necessitates a detailed preclinical evaluation before initiating clinical trials. There are two different and complementary approaches to assess the potential of drugs to cause QT interval prolongation. The in vivo approach provides information on the potential of the compound to prolong the QT interval under near-physiological conditions. It is mostly descriptive and not explanatory in terms of mechanisms of action. The in vitro approach provides much more mechanistic information, but is far removed from the clinical situation. While both approaches appear to possess reasonable predictive value, the results may depend largely on the experimental conditions employed. This unit reviews these issues and discusses a strategy aimed at understanding the problems associated with this cardiovascular risk.

Drug-induced q-T prolongation

Drug therapy may induce Q-T prolongation by alteration of potassium ion currents in cardiac cells, resulting in abnormal repolarization. Q-T prolongation, whether congenital or acquired, has been associated with the development of the malignant dysrhythmia Torsade de Pointes (TdP), which may result in sudden death. Re-cent regulatory actions and drug withdrawals due to Q-T prolongation or TdP have focused attention on this issue. Although our understanding of the pathophysiology continues to evolve, both patient and medication factors contribute to the individual risk of drug-induced Q-T prolongation or TdP. The clinician should be aware of these issues when prescribing new drugs and should weigh the risks and benefits carefully when prescribing drugs known to prolong the Q-T interval.

Verapamil prevents torsade de pointes by reduction of transmural dispersion of repolarization and suppression of early afterdepolarizations in an intact heart model of LQT3

BACKGROUND

In long QT syndrome (LQTS), prolongation of the QT-interval is associated with sudden cardiac death resulting from potentially life-threatening polymorphic tachycardia of the torsade de pointes (TdP) type. Experimental as well as clinical reports support the hypothesis that calcium channel blockers such as verapamil may be an appropriate therapeutic approach in LQTS. We investigated the electrophysiologic mechanism by which verapamil suppresses TdP, in a recently developed intact heart model of LQT3.

METHODS AND RESULTS

In 8 Langendorff-perfused rabbit hearts, veratridine (0.1 microM), an inhibitor of sodium channel inactivation, led to a marked increase in QT-interval and simultaneously recorded monophasic ventricular action potentials (MAPs) (p < 0.05) thereby mimicking LQT3. In bradycardic (AV-blocked) hearts, simultaneous recording of up to eight epi- and endocardial MAPs demonstrated a significant increase in total dispersion of repolarization (56%, p < 0.05) and reverse frequency-dependence. After lowering potassium concentration, veratridine reproducibly led to early afterdepolarizations (EADs) and TdP in 6 of 8 (75%) hearts. Additional infusion of verapamil (0.75 microM) suppressed EADs and consecutively TdP in all hearts. Verapamil significantly shortened endocardial but not epicardial MAPs which resulted in significant reduction of ventricular transmural dispersion of repolarization.

CONCLUSIONS

Verapamil is highly effective in preventing TdP via shortening of endocardial MAPs, reduction of left ventricular transmural dispersion of repolarization and suppression of EADs in an intact heart model of LQT3. These data suggest a possible therapeutic role of verapamil in the treatment of LQT3 patients.

Sex Modulates the Arrhythmogenic Substrate in Prepubertal Rabbit Hearts with Long QT 2

Females have a greater susceptibility to Torsade de Pointes in congenital and drug-induced long QT syndrome (LQTS) that has been attributed to the modulation of ion channel expression by sex hormones. However, little is known regarding sex differences in pre-puberty, that is, before the surge of sexual hormones. In patients with congenital LQTS types 1 and 2, male children tend to have a greater occurrence of adverse events, especially in 10-15 year olds, than their female counterpart. To evaluate whether the rabbit model of drug-acquired LQTS exhibits similar age dependences, hearts of prepubertal rabbits were perfused, mapped optically to record action potentials (APs) and treated with an I(Kr) blocker, E4031 to elicit LQTS2. As expected, AP durations (APD) were significantly longer in female (n = 18) than male hearts (n = 10), at long cycle length. Surprisingly, E4031 (50-250 nM) induced a greater prolongation of APDs in male than in female hearts, and in both genders reversed the direction of repolarization (apex --> base to base --> apex), enhancing dispersions of repolarization. Furthermore, in male hearts, E4031 (0.5 microM) elicited early afterdepolarizations (EADs) that progressed to polymorphic ventricular tachycardia (PVT) (n = 7/10) and were interrupted by isoproterenol (40 nM) and prevented by propranolol (0.5-2.5 microM). In female hearts, E4031 (0.5 microM) produced marked prolongations of APDs yet few EADs with no progression to PVT (n = 16/18). Thus, sex differences are opposite in prepubertal versus adult rabbits with respect to E4031-induced APD prolongation, EADs and PVT, underscoring the fact that APD prolongation alone is insufficient to predict arrhythmia susceptibility.

[Calmodulin antagonist inhibits torsade de pointes induced by d-sotalol in an isolated rabbit heart model]

OBJECTIVE

To evaluate the effects of W-7, a calmodulin inhibitor, on transmural dispersion of repolarization (TDR), early after depolarization (EAD) and torsade de pointes (TdP) induction after administration of d-sotalol in isolated rabbit heart.

METHODS

TdP was induced by d-sotalol (30 micromol/L), bradycardia, and hypokalemic (1.5 mmol/L)/hypomagnesaemic (0.35 mmol/L) solution in isolated female rabbit hearts. Thirty six rabbit hearts were divided into 4 groups (n = 9 each): d-sotalol alone, d-sotalol + W-7 (20 micromol/L), d-sotalol + W-7 (50 micromol/L), and d-sotalol + W-7 (100 micromol/L). Monophasic action potentials (MAPs) of the left ventricular epimyocardium (Epi), midmyocardium (M), and endomyocardium (Endo) were recorded simultaneously with ECG. The incidence of EAD and TdP were observed as well.

RESULTS

Treatment with d-sotalol alone prolonged ventricular MAP duration and QT interval, increased TDR, and evoked high incidence of EAD (9/9) and spontaneous TdP (7/9) in hypokalemic/hypomagnesaemic solution in female rabbit heart. W-7 concentration-dependently decreased incidence of TdP (4/9 in 20 micromol/L; 2/9 in 50 micromol/L; 1/9 in 100 micromol/L). This effect of W-7 coincided with the decreased incidence of EAD (5/9 in 20 micromol/L; 4/9 in 50 micromol/L; 1/9 in 100 micromol/L). However, the d-sotalol-induced prolongation of QT interval and TDR was not significantly altered by W-7 at the three concentration used.

CONCLUSIONS

In isolated female rabbit hearts, calmodulin antagonist W-7 suppresses d-sotalol-induced TdP without altering TDR but does suppress EAD. The effects observed with W-7 also suggest a possible important role for calmodulin-activated enzymes in the induction of TdP.

Cellular and ionic mechanism for drug-induced long QT syndrome and effectiveness of verapamil

OBJECTIVES

We examined the cellular and ionic mechanism for QT prolongation and subsequent Torsade de Pointes (TdP) and the effect of verapamil under conditions mimicking KCNQ1 (I(Ks) gene) defect linked to acquired long QT syndrome (LQTS).

BACKGROUND

Agents with an I(Kr)-blocking effect often induce marked QT prolongation in patients with acquired LQTS. Previous reports demonstrated a relationship between subclinical mutations in cardiac K+ channel genes and a risk of drug-induced TdP.

METHODS

Transmembrane action potentials from epicardial (EPI), midmyocardial (M), and endocardial (ENDO) cells were simultaneously recorded, together with a transmural electrocardiogram, at a basic cycle length of 2,000 ms in arterially perfused feline left ventricular preparations.

RESULTS

The I(Kr) block (E-4031: 1 micromol/l) under control conditions (n = 5) prolonged the QT interval but neither increased transmural dispersion of repolarization (TDR) nor induced arrhythmias. However, the I(Kr) blocker under conditions with I(Ks) suppression by chromanol 293B 10 micromol/l mimicking the KCNQ1 defect (n = 10) preferentially prolonged action potential duration (APD) in EPI rather than M or ENDO, thereby dramatically increasing the QT interval and TDR. Spontaneous or epinephrine-induced early afterdepolarizations (EADs) were observed in EPI, and subsequent TdP occurred only under both I(Ks) and I(Kr) suppression. Verapamil (0.1 to 5.0 micromol/l) dose-dependently abbreviated APD in EPI more than in M and ENDO, thereby significantly decreasing the QT interval, TDR, and suppressing EADs and TdP.

CONCLUSIONS

Subclinical I(Ks) dysfunction could be a risk of drug-induced TdP. Verapamil is effective in decreasing the QT interval and TDR and in suppressing EADs, thus preventing TdP in the model of acquired LQTS.

Seltene Ursache einer Prolongierung der QT-Zeit und reanimationspflichtigen Torsade-de-pointes-Tachykardie

A 62 year old patient underwent an intraoperative pancreas biopsy because of a pancreas head process. On 13(th) and 20(th) postoperative day a short syncope episode occurred. On that days calcium blood levels were 1,82 and 1,74 mmol/l, respectively. On 13(th) postoperative day QT(c) interval was 565 ms. On 26(th) postoperative day the patient was resuscitated because of torsade de pointes tachycardia. His actual calcium blood level was 1,47 mmol/l and QT(c) interval 627 ms. An extensive diagnostic work-up revealed no evidence of cardiac disease. After calcium substitution QT interval normalised. During a follow-up period of 16 months the patient remained without symptoms.

A patient with LQTS in whom verapamil administration and permanent pacemaker implantation were useful for preventing torsade de pointes

A 21-year-old woman with long QT syndrome and missense mutation in HERG (T613M), suffered from repeated attacks of pause dependent torsade de pointes, even though she was given beta-blockers and underwent stellate ganglion block twice at the age of eight. After she received permanent pacemaker implantation and administration of verapamil, no premature beats or pause dependent torsade de pointes was observed.

Initiation and monitoring of class III antiarrhythmic agents

Initiation and Monitoring of Class III Agents. Dofetilide is a Class III antiarrhythmic agent that is approved by the United States Food and Drug Administration (FDA) for use in the conversion of atrial fibrillation, as well as in the maintenance of normal sinus rhythm. Because of the risk of torsades de pointes associated with dofetilide, the FDA mandated in-hospital initiation of therapy and initially restricted dofetilide's availability to institutions and prescribers who completed appropriate educational forums. The use of dofetilide within health care systems requires specific procedures for prescribing, dispensing, and monitoring, as well as a format for educating personnel who will be involved in the care of these patients. Several models have demonstrated success in initiating dofetilide and are also used for sotalol, which also can cause torsades de pointes. The utilization of nonphysician personnel, such as nurse practitioners and clinical pharmacists, in conjunction with a team approach were essential components for the success of these models. Preprinted order forms or procedural guidelines, as well as computer-assisted dosing programs, can be utilized to prevent inappropriate or miscalculated dosing of these agents, which potentially can cause life-threatening ventricular arrhythmias.

Drug-induced torsades de pointes and implications for drug development

Torsades de pointes is a potentially lethal arrhythmia that occasionally appears as an adverse effect of pharmacotherapy. Recently developed understanding of the underlying electrophysiology allows better estimation of the drug-induced risks and explains the failures of older approaches through the surface ECG. This article expresses a consensus reached by an independent academic task force on the physiologic understanding of drug-induced repolarization changes, their preclinical and clinical evaluation, and the risk-to-benefit interpretation of drug-induced torsades de pointes. The consensus of the task force includes suggestions on how to evaluate the risk of torsades within drug development programs. Individual sections of the text discuss the techniques and limitations of methods directed at drug-related ion channel phenomena, investigations aimed at action potentials changes, preclinical studies of phenomena seen only in the whole (or nearly whole) heart, and interpretation of human ECGs obtained in clinical studies. The final section of the text discusses drug-induced torsades within the larger evaluation of drug-related risks and benefits.

Evaluation of the dofetilide risk-management program

BACKGROUND

Dose-dependent torsades de pointes has been shown to occur with dofetilide (Tikosyn) and sotalol HCl (Betapace AF); thus, detailed dosing and monitoring recommendations to minimize this risk are included in the product labeling for both drugs. Only dofetilide, however, has a mandated risk-management program that restricts distribution of the drug and requires prescriber education on the drug. We investigated whether this program improved adherence to dosing and monitoring recommendations for dofetilide as compared with sotalol.

METHODS

Charts for 47 patients taking dofetilide and 117 patients taking sotalol were reviewed.

RESULTS

The recommended starting dose was prescribed more frequently in the dofetilide group than in the sotalol group (79% vs 35%, P <.001). A higher number of patients in the dofetilide group compared with the sotalol group received the recommended baseline tests for potassium (100% vs 82%, P <.001), magnesium (89% vs 38%, P <.001), serum creatinine (100% vs 82%, P <.001), and electrocardiography (94% vs 67%, P <.001). A significantly greater proportion of patients in the dofetilide group received recommended electrocardiograms obtained after the first dose (94% for dofetilide vs 43% for sotalol, P <.001) and subsequent doses (80% for dofetilide vs 3.5% for sotalol, P <.001).

CONCLUSION

Better adherence to several dosing and monitoring recommendations in the dofetilide group may be caused by the presence of the risk-management program. However, low usage of dofetilide during the study period may signify an unintended, negative consequence of the risk-management program.

Mortality in patients after a recent myocardial infarction: a randomized, placebo-controlled trial of azimilide using heart rate variability for risk stratification

BACKGROUND

Depressed left ventricular function (LVF) and low heart rate variability (HRV) identify patients at risk of increased mortality after myocardial infarction (MI). Azimilide, a novel class III antiarrhythmic drug, was investigated for its effects on mortality in patients with depressed LVF after recent MI and in a subpopulation of patients with low HRV.

METHODS AND RESULTS

A total of 3717 post-MI patients with depressed LVF were enrolled in this randomized, placebo-controlled, double-blind study of azimilide 100 mg on all-cause mortality. Placebo patients with low HRV had a significantly higher 1-year mortality than those with high HRV (>20 U; 15% versus 9.5%, P<0.0005) despite nearly identical ejection fractions. No significant differences were observed between the 100-mg azimilide and placebo groups for all-cause mortality in either the "at-risk" patients identified by depressed LVF (12% versus 12%) or the subpopulation of "high-risk" patients identified by low HRV (14% versus 15%) or for total cardiac or arrhythmic mortality. Significantly fewer patients receiving azimilide developed atrial fibrillation than did patients receiving placebo (0.5% versus 1.2%, P<0.04). The incidences of torsade de pointes and severe neutropenia (absolute neutrophil count < or =500 cells/microL) were slightly higher in the azimilide group than in the placebo group (0.3% versus 0.1% for torsade de pointes and 0.9% versus 0.2% for severe neutropenia).

CONCLUSIONS

Azimilide did not improve or worsen the mortality of patients after MI. Low HRV independently identified a subpopulation at high risk of mortality.

Prevention of clofilium-induced torsade de pointes by prostaglandin E2 does not involve ATP-dependent K+ channels

Drugs that prolong the QT interval can trigger the life-threatening arrhythmia, torsade de pointes, but there is a poor correlation between the extent of QT prolongation and the occurrence of torsade de pointes. The clinical status of a patient may modify the arrhythmogenicity of drugs; thus, we have investigated whether a mediator of fever and inflammation, prostaglandin E(2), alters the proarrhythmic effects of clofilium. In pentobarbitone-anaesthetized, open-chest, alpha-adrenoceptor-stimulated rabbits, prostaglandin E(2) 0.28, 0.84 and 2.80 nmol kg(-1) min(-1), infused into the left ventricle, reduced the incidence of torsade de pointes from 50% in controls to 20%, 20% and 0%, respectively (n=10 per group). Pretreatment with glibenclamide (10 micromol kg(-1)) did not alter the antiarrhythmic effect of prostaglandin E(2) (2.80 nmol kg(-1) min(-1)). These results indicate that prostaglandin E(2) prevents drug-induced torsade de pointes and that this action of prostaglandin E(2) is not mediated via opening of ATP-dependent K(+) channels (K(ATP)).