Proarrhythmia with class III antiarrhythmic drugs: types, risks, and management

Predictors of in-hospital ventricular fibrillation or torsades de pointes in patients with acute symptomatic bradycardia

Severe bradyarrythmias remain as an important cause for hospital urgent admission and these patients can suffer potentially lethal complications (such as ventricular fibrillation [VF] and torsades de pointes [TdP]) between hospital admission and final therapy. Incidence and predictors of these tachyarrhythmias have not been well established. We retrospectively studied all consecutive patients (N = 243, age 75 +/- 10 years; 47% men) admitted to the emergency department of a general hospital between January 1998 and July 2000 for symptomatic bradyarrhythmia. Concomitant therapy included diuretics (25%), digitalis (10%), beta-blockers (10%), amiodarone (2%), and verapamil or diltiazem (8%). Syncope was the most frequent symptom at admission (54%). The most prevalent inclusion bradyarrhythmia was > or =second-degree AV block (82%). Eleven patients (4.5%) presented VF or TdP. Univariate predictors for these complications were previous amiodarone or diuretic intake, presentation as syncope, low serum potassium level, and longer QTc at admission. Multivariate analysis with logistic regression showed only therapy with diuretics and/or amiodarone and QTc at admission as significant predictors for TdP or VF development. Incidence of VF or TdP in patients admitted for symptomatic bradyarrhythmia is relatively important. A prolonged QTc interval and/or therapy with amiodarone or diuretics can predict their presentation.

Sensitivity and specificity of isolated perfused guinea pig heart to test for drug-induced lengthening of QTc

INTRODUCTION

The purpose of this study was to determine the sensitivity and specificity for predicting the liability of a compound to lengthen QTc using isolated, perfused guinea pig hearts (Langendorff preparation).

METHODS

QTc (Fridericia correction) was calculated from bipolar transventricular electrograms. Hearts were exposed to escalating concentrations of 26 compounds thought to lengthen, and 13 compounds thought not to lengthen, QTc in humans.

RESULTS

In this preparation, QTc was found to lengthen in 26 of 26 compounds thought to be positive (sensitivity 1.00) and not to lengthen or to lengthen insignificantly in 13 of 13 compounds thought to be negative (specificity 1.0) in man. Probucol and ontazolast could not be studied because of limited solubility. Successful experiments were conducted on over 98% of guinea pigs anesthetized.

DISCUSSION

We believe that the isolated perfused guinea pig heart is an in vitro preparation that could be utilized early in preclinical testing for identifying a liability to lengthen QTc in humans, but we do not believe--as is true also for other in vitro methods--that the concentration at which the liability is demonstrated in vitro necessarily predicts the concentration at which a liability exists in man.

Clinical relevance and management of drug-related QT interval prolongation

Much attention recently has focused on drugs that prolong the QT interval, potentially leading to fatal cardiac dysrhythmias (e.g., torsade de pointes). We provide a detailed review of the published evidence that supports or does not support an association between drugs and their risk of QT prolongation. The mechanism of drug-induced QT prolongation is reviewed briefly, followed by an extensive evaluation of drugs associated with QT prolongation, torsade de pointes, or both. Drugs associated with QT prolongation are identified as having definite, probable, or proposed associations. The role of the clinician in the prevention and management of QT prolongation, drug-drug interactions that may occur with agents known to affect the QT interval, and the impact of this adverse effect on the regulatory process are addressed.

Prescription of QT-prolonging drugs in a cohort of about 5 million outpatients

Many drugs prolong the QT interval and increase the risk of torsade de pointes. Concurrent use of two or more of these drugs can further increase the risk, but the prevalence of concurrent prescription of QT-prolonging drugs is not known. Using the administrative claims database of a national pharmaceutical benefit manager, we conducted a retrospective cohort study in 4,825,345 subjects aged 18 years or older. After identifying 50 drugs with QT-prolonging potential, and an additional 26 drugs that inhibit the metabolic clearance of QT-prolonging drugs, we measured the frequency of overlapping prescriptions for two or more of these drugs in the outpatient setting in 1999. Nearly 1.1 million subjects (22.8%) filled 4.4 million prescriptions for QT-prolonging drugs. Of these, 103,119 subjects (9.4%) filled overlapping prescriptions for two or more of the drugs or for a QT-prolonging drug and another drug that inhibits its clearance; 7249 subjects (0.7%) filled overlapping prescriptions for three or more of these drugs. Twenty-two percent of subjects who filled overlapping prescriptions were aged 65 or older; 74% were women. Antidepressants were involved in nearly 50% of the cases. Concurrent prescription of QT-prolonging drugs is common in the outpatient setting, and antidepressants are involved in half of these cases. Large pharmaceutical claims databases are useful for detecting potentially harmful prescribing behaviors, but better clinical evidence on medication safety is needed before such a system can be implemented fully.

Repolarization measures and their relation to sex hormones in postmenopausal women with cardiovascular disease receiving hormone replacement therapy

Women are more susceptible to the development of Torsades de Pointes ventricular tachycardia and have a longer heart rate-corrected QT interval than men. A causal role for estrogen has been implicated. The purpose of this study was to investigate if hormone replacement therapy (HRT) resulted in any changes in noninvasive depolarization and repolarization measurements, and to study their relation to circulating concentrations of sex hormones. Sixty postmenopausal women with cardiovascular disease (mean age 59 +/- 7 years; range 44 to 75) were randomized to receive oral conjugated estrogens, transdermal estradiol-17-beta (both with addition of progestins), or placebo. QRS, QT, and JT intervals and their dispersion on 12-lead electrocardiograms were analyzed at baseline, and after 6 and 12 treatment cycles of HRT. Blood samples for analyses of serum concentration of estrogens and androgens were obtained on the same occasions. Neither mean RR, QT, QTc, JT, and JTc intervals, nor QT and JT dispersion changed during treatment. There was a significant inverse relation between the mean JTc interval and the serum concentration of estradiol-17-beta, independent of age, testosterone levels, and abdominal obesity. There was also a significant inverse relation between the change in androstenedione levels and the change in QT interval (Spearman -0.35, p = 0.028) or JT interval (Spearman -0.41, p = 0.009) at 6 treatment cycles compared with baseline. In conclusion, treatment with oral conjugated estrogens or transdermal estradiol-17-beta combined with progestins did not alter depolarization or repolarization measurements. However, the inverse relation between repolarization and androgens fits with an effect of androgens on repolarization in postmenopausal women.

Beta-blocker decreases the increase in QT dispersion and transmural dispersion of repolarization induced by bepridil

Bepridil is effective for intractable cardiac arrhythmia, but in rare cases will induce torsades de pointes (TdP) associated with QT interval prolongation. Beta-blockers will effectively prevent TdP in some clinical settings, so the effect of beta-blocker on the change in QT interval, QT dispersion and transmural dispersion of repolarization (TDR) induced by bepridil was investigated in 10 patients (7 male, 3 female; 62+/-6 years old) with intractable paroxysmal atrial fibrillation. The QTc interval, QTc dispersion and TDR were measured before and after 1 month of administration of bepridil, and then a beta-blocker was added and the QTc interval, QTc dispersion and TDR re-measured 1 month later. Bepridil significantly prolonged the QTc interval (0.42+/-0.05 to 0.50+/-0.08; p<0.01), and increased both the QT dispersion (0.07+/-0.05 to 0.14+/-0.08; p<0.01) and TDR (0.10+/-0.04 to 0.16+/-0.05; p<0.01). The addition of a beta-blocker decreased the QTc interval (0.50+/-0.08 to 0.47+/-0.04; p=0.09) and significantly decreased both the QTc dispersion (0.14 +/-0.08 to 0.06+/-0.02; p<0.01) and TDR (0.16+/-0.05 to 0.11+/-0.04; p<0.001). Compared with the control, the combination therapy significantly prolonged the QTc interval, but did not increase either QTc dispersion or TDR, and so was effective in all patients with intractable AF. The findings suggest that beta-blocker reduces the increase in QT dispersion and TDR induced by bepridil, and combined therapy with bepridil and beta-blocker might thus be useful for intractable atrial fibrillation.

[Myotonic dystrophy and bundle-branch re-entrant tachycardia]

We report the case of a 37-year-old man diagnosed with myotonic dystrophy who presented atrial fibrillation with high ventricular rate. While being treated with amiodarone, he suffered cardiac arrest. The electrophysiological study disclosed bundle-branch reentrant ventricular tachycardia and ventricular fibrillation. Catheter ablation of the right bundle branch was performed and a bicameral defibrillator was implanted. The mechanisms and treatment of arrhythmias in these patients are discussed.

Antipsychotic-related QTc prolongation, torsade de pointes and sudden death

Sudden unexpected deaths have been reported with antipsychotic use since the early 1960s. In some cases the antipsychotic may be unrelated to death, but in others it appears to be a causal factor. Antipsychotics can cause sudden death by several mechanisms, but particular interest has centred on torsade de pointes (TdP), a polymorphic ventricular arrhythmia that can progress to ventricular fibrillation and sudden death. The QTc interval is a heart rate-corrected value that represents the time between the onset of electrical depolarisation of the ventricles and the end of repolarisation. Prolongation of the QTc interval is a surrogate marker for the ability of a drug to cause TdP. In individual patients an absolute QTc interval of >500 msec or an increase of 60 msec from baseline is regarded as indicating an increased risk of TdP. However, TdP can occur with lower QTc values or changes. Concern about a relationship between QTc prolongation, TdP and sudden death applies to a wide range of drugs and has led to the withdrawal or restricted labelling of several. Among antipsychotics available in the UK, sertindole was voluntarily suspended, droperidol was withdrawn, and restricted labelling introduced for thioridazine and pimozide. The degree of QTc prolongation is dose dependent and varies between antipsychotics reflecting their different capacity to block cardiac ion channels. Significant prolongation is not a class effect. Among currently available agents, thioridazine and ziprasidone are associated with the greatest QTc prolongation. Virtually all drugs known to cause TdP block the rapidly activating component of the delayed rectifier potassium current (I(kr)). Arrhythmias are more likely to occur if drug-induced QTc prolongation coexists with other risk factors, such as individual susceptibility, presence of congenital long QT syndromes, heart failure, bradycardia, electrolyte imbalance, overdose of a QTc prolonging drug, female sex, restraint, old age, hepatic or renal impairment, and slow metaboliser status. Pharmacodynamic and pharmacokinetic interactions can also increase the risk of arrhythmias. Further research is needed to quantify the risk of sudden death with antipsychotics. The risk should be viewed in the context of the overall risks and benefits of antipsychotic treatment. It seems prudent, where possible, to select antipsychotics that are not associated with marked QTc prolongation. If use of a QTc-prolonging drug is warranted, then measures to reduce the risk should be adopted.

Comparison of the in vivo electrophysiological and proarrhythmic effects of amiodarone with those of a selective class III drug, sematilide, using a canine chronic atrioventricular block model

Amiodarone effectively blocks both the sodium and calcium channels and beta-adrenoceptors, in addition to blocking several potassium currents including IKr, IKs, Ito, IK1, IKACh and IKNa. The incidence of clinical torsade de pointes (TdP) associated with amiodarone has been reported to be low and the present study compared the proarrhythmic potential of amiodarone with that of a selective IKr channel blocker, sematilide, using a canine chronic atrioventrucular block model. Amiodarone or sematilide (3 and 30 mg/kg; n=4 for each group) was administered orally without anesthesia under continuous ECG monitoring. Both drugs prolonged the QT interval, although the onset was faster for sematilide. The high dose of sematilide induced TdP in 3 of 4 animals, which caused their death, but neither the low dose of sematilide nor the 2 dosages of amiodarone induced lethal ventricular arrhythmias. These results suggest that IKr channel inhibition by amiodarone with its additional ion channel blocking action may contribute to the prevention of TdP.

Electrocardiographic and hemodynamic effects of Panax ginseng

OBJECTIVE

To determine whether Panax ginseng ingestion can acutely or chronically alter electrocardiographic parameters: PR, QRS, QT, QTc, and RR intervals, and QT and QTc interval dispersion. Effects of P. ginseng on blood pressure and heart rate also were evaluated.

METHODS

This is a prospective, randomized, double-blind, placebo-controlled study of healthy adults at the University of Connecticut. Thirty subjects were randomly allocated to receive 28 days of therapy with either P. ginseng extract 200 mg or placebo. Baseline 12-lead electrocardiograms (ECGs) were obtained. Subsequent ECGs were performed following study drug ingestion at 50 minutes, 2 hours, and 5 hours on days 1 and 28. Blood pressure readings were taken with each ECG.

RESULTS

P. ginseng ingestion increased the QTc interval by 0.015 seconds on day 1 at 2 hours compared with the placebo group (p = 0.03). It also reduced diastolic blood pressure from 75 +/- 5 mm Hg at baseline to 70 +/- 6 mm Hg at the same time point (p = 0.02). The observed effects are not believed to be clinically significant. No other statistically significant changes were found in electrocardiographic or hemodynamic variables on days 1 or 28.

CONCLUSIONS

P. ginseng, at doses of 200 mg of the extract daily, increases the QTc interval and decreases diastolic blood pressure 2 hours after ingestion in healthy adults on the first day of therapy.

Sotalol: the mechanism of its antiarrhythmic-defibrillating effect

This minireview deals with the role of intercellular communication and synchronization in the initiation and maintenance of ventricular fibrillation. It is proposed that myocardial cell junctions might represent a therapeutic substrate for the prevention of this fatal arrhythmia. This hypothesis is supported by the results of recent experimental studies involving elucidation of the mechanism of antiarrhythmic-defibrillating effects of sotalol. Enhancement of intercellular communication and myocardial synchronization are thought to play critical role in the mechanism of action of this drug.

Synthesis and activity of novel and selective I(Ks)-channel blockers

Since the discovery of the I(Ks)-potassium channel as the slowly activating component of the delayed rectifier current (I(k)) in cardiac tissue, the search for blockers of this current has been intense. During the screening of K(ATP)-channel openers of the chromanol type we found that chromanol 293B was able to block I(Ks). Chromanol 293B is a sulfonamide analogue of the K(ATP)-channel openers but had no activity on this target. Experiments were initiated to improve the activity and properties based on this lead compound. As a screening model we used Xenopus oocytes injected with human minK (KCNE1). Variations of the aromatic substituent and the sulfonamide group were prepared, and their activity was evaluated. We found that the greatest influence on activity was found in the aromatic substituents. The most active compounds were alkoxy substituted. We chose HMR1556 ((3R, 4S)-(+)-N-[-3-hydroxy-2,2-dimethyl-6-(4,4,4-trifluorobutoxy)chroman-4-yl]-N-methyl-ethanesulfonamide) 10a for development as an antiarrhythmic drug. The absolute configuration, resulting from an X-ray single-crystal structure analysis, was determined.

Evaluation of drug-induced QT interval prolongation: implications for drug approval and labelling

Assessment of proarrhythmic toxicity of newly developed drugs attracts significant attention from drug developers and regulatory agencies. Although no guidelines exist for such assessment, the present experience allows several key suggestions to be made and an appropriate technology to be proposed. Several different in vitro and in vitro preclinical models exist that, in many instances, correctly predict the clinical outcome. However, the correspondence between different preclinical models is not absolute. None of the available models has been demonstrated to be more predictive and/or superior to others. Generally, compounds that do not generate any adverse preclinical signal are less likely to lead to cardiac toxicity in humans. Nevertheless, differences in likelihood offer no guarantee compared with entities with a preclinical signal. Thus, the preclinical investigations lead to probabilistic answers with the possibility of both false positive and false negative findings. Clinical assessment of drug-induced QT interval prolongation is crucially dependent on the quality of electrocardiographic data and the appropriateness of electrocardiographic analyses. An integral part of this is a precise heart rate correction of QT interval, which has been shown to require the assessment of QT/RR relationship in each study individual. The numbers of electrocardiograms required for such an assessment are larger than usually obtained in pharmacokinetic studies. Thus, cardiac safety considerations need to be an integral part of early phase I/II studies. Once proarrhythmic safety has been established in phase I/II studies, large phase III studies and postmarketing surveillance can be limited to less strict designs. The incidence of torsade de pointes tachycardia varies from 1 to 5% with clearly proarrhythmic drugs (e.g. quinidine) to 1 in hundreds of thousands with drugs that are still considered unsafe (e.g. terfenadine, cisapride). Thus, not recording any torsade de pointes tachycardia during large phase III studies offers no guarantee, and the clinical premarketing evaluation has to rely on the assessment of QT interval changes. However, since QT interval prolongation is only an indirect surrogate of predisposition to the induction of torsade de pointes tachycardia, any conclusion that a drug is safe should be reserved until postmarketing surveillance data are reviewed. The area of drug-related cardiac proarrhythmic toxicity is fast evolving. The academic perspective includes identification of markers more focused compared with simple QT interval measurement, as well as identification of individuals with an increased risk of torsade de pointes. The regulatory perspective includes careful adaptation of new research findings.

A comparison of the QT and QTc dispersion among patients with sustained ventricular tachyarrhythmias and different etiologies of heart disease

OBJECTIVES

To determine if etiology of heart disease is associated with differences in QT and QTc dispersion among patients with ventricular tachyarrhythmias.

METHODS

This study was undertaken in 145 patients undergoing electrophysiological testing for sustained ventricular tachycardia or ventricular fibrillation. Patients were divided into groups based on etiology of heart disease determined by history, ECG, coronary angiography, and echocardiography. The groups included patients with: dilated cardiomyopathy (n = 29), myocardial infarction (n = 90), established coronary artery disease without a myocardial infarction (n = 11), or hypertension induced left ventricular hypertrophy (n = 15). The QT intervals on a 12--lead ECG were determined and Bazett's formula was used to derive the QTc intervals. The QT and QTc dispersion were determined by subtracting the shortest QT(c) interval from the longest on each 12-lead recording.

RESULTS

The patients with dilated cardiomyopathy had significantly higher QT and QTc dispersion values as compared to any of the other three groups (P < 0.05 for both). No other differences in electrocardiographic variables were found between groups.

CONCLUSIONS

In a group of patients with a history of ventricular tachycardia or ventricular fibrillation, QT and QTc dispersion are significantly greater among patients with dilated cardiomyopathy than for patients with a previous myocardial infarction, established coronary artery disease without a myocardial infarction, or hypertensive left ventricular hypertrophy.

Evaluation of electrocardiographic and hemodynamic effects of caffeine with acute dosing in healthy volunteers

STUDY OBJECTIVE

To evaluate the effects of moderate, single-dose caffeine consumption on electrocardiographic variables: PR, QRS, QT, QTc, and RR intervals, and QT and QTc interval dispersion. Effects of caffeine on blood pressure and heart rate also were evaluated.

DESIGN

Randomized, double-blind, placebo-controlled, crossover study.

SETTING

University school of pharmacy.

PATIENTS

Ten healthy volunteers aged 17 years or older.

INTERVENTION

Participants abstained from caffeinated products for at least 2 days before the study began and were randomly designated to receive placebo or caffeine 400 mg on various days. For each of the study phases, a baseline 12-lead electrocardiogram (ECG) was performed and a subsequent 12-lead ECG performed 3 hours after ingesting the study drug. Blood pressure readings were taken with each ECG.

MEASUREMENTS AND MAIN RESULTS

No significant changes in any intragroup or intergroup electrocardiographic variables occurred. Caffeine increased blood pressure (systolic blood pressure [SBP]/diastolic blood pressure [DBP]) from 118+/-5/75+/-6 mm Hg to 128+/-8/77+/-7 mm Hg versus baseline (p=0.0022 and p=0.0368 for SBP and DBP, respectively). After drug dosing, SBP in the caffeine group was significantly higher than in the placebo group (128+/-8 mm Hg versus 119+/-7 mm Hg, p=0.0174).

CONCLUSION

Moderate caffeine consumption by healthy young adults does not acutely affect PR, QRS, QT, QTc, and RR intervals, or QT and QTc interval dispersion. Caffeine-naive subjects experienced persistent elevations in SBP and DBP 3 hours after caffeine ingestion, indicating that longer caffeine abstinence than that which is recommended is necessary for blood pressure determination in the clinical setting.

Cardioselective K(ATP) channel blockers derived from a new series of m-anisamidoethylbenzenesulfonylthioureas

Sulfonylthioureas exhibiting cardioselective blockade of ATP-sensitive potassium channels (K(ATP) channels) were discovered by stepwise structural variations of the antidiabetic sulfonylurea glibenclamide. As screening assays, reversal of rilmakalim-induced shortening of the cardiac action potential in guinea pig papillary muscles was used to probe for activity on cardiac K(ATP) channels as the target, and membrane depolarization in CHO cells stably transfected with hSUR1/hKir6.2 was used to probe for unwanted side effects on pancreatic K(ATP) channels. Changing glibenclamide's para-arrangement of substituents in the central aromatic ring to a meta-pattern associated with size reduction of the substituent at the terminal nitrogen atom of the sulfonylurea moiety was found to achieve cardioselectivity. An additional change from a sulfonylurea moiety to a sulfonylthiourea moiety along with an appropriate substituent in the ortho-position of the central aromatic system was a successful strategy to further improve potency on the cardiac K(ATP) channel. Among this series of sulfonylthioureas HMR1883, 1-[5-[2-(5-chloro-o-anisamido)ethyl]-2-methoxyphenyl]sulfonyl-3-methylthiourea, and its sodium salt HMR1098 were selected for development and represent a completely new therapeutic approach toward the prevention of life-threatening arrhythmias and sudden cardiac death in patients with coronary heart disease.

The clinician's approach to evaluating patients with dysrhythmias

As cardiac arrhythmia services and the ability to perform electrophysiologic testing become more prevalent in the hospital setting, advanced practice nurses (APNs) are continually challenged to keep their skills in evaluating patients with dysrhythmias sharp and current. The experienced APN evaluates the patient's history, recognizes physical findings, and uses noninvasive data to help diagnose, anticipate, and even prevent dysrhythmias. This article reviews the essential components of a systematic evaluation of patients with a known or potential rhythm disturbance.

Cardiac arrhythmias: drugs and devices

This review focuses on the important role played by the various types of remedial therapy in the prevention and treatment of perioperative cardiac arrhythmias. It discusses the new concepts of arrhythmogenesis and pro-arrhythmia; the long QT interval syndrome; newer, more selective class 3 antiarrhythmic drugs; cardiac rhythm management devices; drugs or devices used as prophylaxis for postoperative atrial arrhythmias; intravenous amiodarone for destabilizing ventricular arrhythmias; and preoperative potassium imbalance.

Pharmacogenetics of cardiac K(+) channels

A number of commonly prescribed drugs belonging to various therapeutic classes (antiarrhythmic, antibiotic, antifungal, antihistamine, antipsychotic, prokinetic drugs...) possess, in common, the adverse property to prolong cardiac repolarization [prolonged QT interval duration on surface electrocardiogram (ECG)], exposing patients to a risk of torsade-de-pointes arrhythmias, syncope, and sudden death. Arrhythmias related to drug-induced QT prolongation do not occur in every patient treated with these drugs but most likely occur in a subset of susceptible patients. These patients have a high risk of recurrence of arrhythmias upon exposure to any of the other drugs that broaden the QT interval. It is currently suspected (though not yet proven) that susceptible individuals carry a silent mutation in one of the genes responsible for the congenital long QT syndrome. Indeed, it appears more and more clear that a large proportion of congenital long QT syndrome gene carriers, have a normal QT interval and a normal phenotype and therefore, remain undiagnosed. Therefore, a much larger than previously thought proportion of the general population may be affected by asymptomatic mutations in cardiac ion channel encoding genes. No routine technology is currently available in identifying these patients preventively.

Antiarrhythmic and electrophysiological effects of GYKI-16638, a novel N-(phenoxyalkyl)-N-phenylalkylamine, in rabbits

The effect of N-[4-[2-N-methyl-N-[1-methyl-2-(2, 6-dimethylphenoxy)ethylamino]-ethyl]-phenyl]-methanesulfonamide. hydrochloride (GYKI-16638; 0.03 and 0.1 mg/kg, i.v.), a novel antiarrhythmic compound, was assessed and compared to that of D-sotalol (1 and 3 mg/kg, i.v.) on arrhythmias induced by 10 min of coronary artery occlusion and 10 min of reperfusion in anaesthetized rabbits. Also, its cellular electrophysiological effects were studied in rabbit right ventricular papillary muscle preparations and in rabbit single isolated ventricular myocytes. In anaesthetized rabbits, intravenous administration of 0.03 and 0.1 mg/kg GYKI-16638 and 1 and 3 mg/kg D-sotalol significantly increased survival during reperfusion (GYKI-16638: 82% and 77%, D-sotalol: 75% and 83% vs. 18% in controls, P<0.05, respectively). GYKI-16638 (0.1 mg/kg) significantly increased the number of animals that did not develop arrhythmias during reperfusion (46% vs. 0% in controls, P<0.05). In isolated rabbit right ventricular papillary muscle, 2 microM GYKI-16638, at 1 Hz stimulation frequency, lengthened the action potential duration at 50% and 90% repolarization (APD(50-90)) without influencing the resting membrane potential and action potential amplitude (APA). It decreased the maximal rate of depolarization (V(max)) in a use-dependent manner. This effect was statistically significant only at stimulation cycle lengths shorter than 700 ms. The offset kinetics of this V(max) block were relatively rapid, the corresponding time constant for recovery of V(max) was 328.2+/-65.0 ms. In patch-clamp experiments, performed in rabbit ventricular myocytes, 2 microM GYKI-16638 markedly depressed the rapid component of the delayed rectifier outward and moderately decreased the inward rectifier K(+) current without significantly altering the slow component of the delayed rectifier and transient outward K(+) currents. These results suggest that in rabbits, GYKI-16638 has an in vivo antiarrhythmic effect, comparable to that of D-sotalol, which can be best explained by its combined Class I/B and Class III actions.

Alternans and the onset of ventricular fibrillation

Ventricular fibrillation (VF) remains a major cause of death in the industrialized world. Alternans (a period-doubling bifurcation of cardiac electrical activity) have recently been causally linked to the progression from ventricular tachycardia (VT) to VF, a more spatiotemporally disorganized electrical activity. In this paper, we show how alternans and thus VT degenerate to chaos via multiple, specific dynamical routes, largely associated with spatial components of VF dynamics, explaining failures of many recently proposed antiarrhythmic drugs. Identification of dynamical mechanisms for the onset of VF should lead to the design of future experiments and consequently to more effective antiarrhythmic drugs.

Predictive factors of ventricular fibrillation triggered by pause-dependent torsades de pointes associated with acquired long QT interval: role of QT dispersion and left ventricular function

INTRODUCTION

Death due to acquired torsades de pointes usually is caused by ventricular fibrillation (VF), but the contributing factors to VF triggered by pause-dependent torsades de pointes are not understood.

METHODS AND RESULTS

We evaluated 91 patients who fulfilled four criteria: (1) pause-dependent torsades de pointes; (2) prolonged QT interval and/or corrected QT (QTc) (>0.44 sec); (3) long-short initiation sequence; and (4) conditions known to induce pause-dependent torsades de pointes. There were 38 patients with a documented VF (group I) and 53 without VF (group II). Absolute and relative dispersions of QT and QTc were calculated based on the 12-lead standard ECG. Group I differed from group II with regard to myocardial infarction history (32% vs 13%; P = 0.035), left ventricular ejection fraction (44% +/- 14% vs 65% +/- 9%; P < 0.0001), presence of structural heart disease (100% vs 20.8%; P < 0.0001), QT mean (591 +/- 73 msec vs 514 +/- 78 msec; P < 0.0001), QTc mean (563 +/- 76 msec vs 508 +/- 90 msec; P = 0.002), absolute QT dispersion (166 +/- 56 msec vs 84 +/- 49 msec; P < 0.0001), relative QT dispersion (9.9% +/- 3.5% vs 6.3% +/- 3.2%; P < 0.0001), absolute QTc dispersion (158 +/- 57 msec vs 81 +/- 44 msec; P < 0.0001), and relative QTc dispersion (9.9% +/- 3.6% vs 6.2% +/- 3%; P < 0.0001). Multiple regression analysis showed that ejection fraction (P = 0.0001), presence of structural heart disease (P < 0.0001), and relative QTc dispersion (P = 0.038) were the only independent predictors of VF.

CONCLUSION

Left ventricular function, presence of structural heart disease, and QTc relative dispersion should be evaluated carefully in patients with conditions susceptible to inducing torsades de pointes.

A prospective, randomized controlled trial comparing the efficacy and safety of sotalol, amiodarone, and digoxin for the reversion of new-onset atrial fibrillation

STUDY OBJECTIVE

A prospective, randomized controlled trial of new-onset atrial fibrillation was conducted to compare the efficacy and safety of sotalol and amiodarone (active treatment) with rate control by digoxin alone for successful reversion to sinus rhythm at 48 hours.

METHODS

We prospectively randomly assigned 120 patients with atrial fibrillation of less than 24 hours' duration to treatment with sotalol, amiodarone, or digoxin using a single intravenous dose followed by 48 hours of oral treatment. Patients had ECG monitoring for 48 hours, and time of reversion, adequacy of rate control, and numbers of adverse events were compared. After 48 hours, those still in atrial fibrillation underwent cardioversion according to a standardized protocol. After 48 hours of therapy and attempted cardioversion, the number of patients whose rhythms had successfully reverted were compared.

RESULTS

There was a significant reduction in the time to reversion with both sotalol (13. 0+/-2.5 hours, P <.01) and amiodarone (18.1+/-2.9 hours, P <.05) treatment compared with digoxin only (26.9+/-3.4 hours). By 48 hours, the active treatment group was significantly more likely to have reverted to sinus rhythm than the rate control group (95% versus 78%, P <.05; risk ratio 5.4, 95% confidence interval [CI] 1.5 to 19.2 ). In those patients whose rhythms did not revert to sinus rhythm, there was superior ventricular rate control in the sotalol group at both 24 and 48 hours compared with those who received either amiodarone or digoxin. There were also fewer adverse events in the active treatment group compared with the rate control group.

CONCLUSION

Immediate pharmacologic therapy for new-onset atrial fibrillation with class III antiarrhythmic drugs (sotalol or amiodarone) improves complication-free 48-hour reversion rates compared with rate control with digoxin.

Bone marrow granulomas possibly associated with amiodarone

Amiodarone is a class III antiarrhythmic agent that is effective in treating different types of cardiac dysrhythmias. It was approved only for treatment of life-threatening ventricular dysrhythmias refractory to other therapy; however, its use for atrial dysrhythmias such as atrial fibrillation is well accepted. Adverse effects associated with amiodarone include pulmonary, hepatic, thyroid, ocular, and neurologic toxicities. Our patient experienced intermittent fever, night sweats, and fatigue while taking the drug for treatment of atrial fibrillation. Bone marrow biopsy showed granuloma formation after 17 months of therapy with amiodarone. Amiodarone was discontinued due to significant hypotension and shortness of breath. To our knowledge, this is the third case report of granuloma formation in bone marrow possibly associated with this agent.

Review of common adverse effects of selected antiarrhythmic drugs

The management of cardiac arrhythmias has changed dramatically over the past several years. New drugs and devices are now available to treat various arrhythmias. Many new agents have been developed that rely on different electrophysiologic mechanisms to elicit their effect on the heart rhythm. Though often effective, these drugs also pose a risk because all of them have a variety of potential adverse effects associated with their use. Many of these adverse reactions are common to all antiarrhythmic drugs, whereas others are unique to particular agents. This review discusses the notable adverse effects of selected antiarrhythmic drugs.

Effects of K+ channel modulators on the relationship between action potential duration and Ca2+ transients in single ventricular myocytes of the guinea pig

Effects of K+ channel modulators, cromakalim and E4031 [1-[2-(6-methyl-2-pyridyl)-ethyl]-4-(4-methylsulfonylaminobenzoyl) piperidine], on the relationship between the action potential duration (APD) and Ca2+ transients were examined in single myocytes isolated from guinea pig cardiac left ventricle. Application of cromakalim decreased APD at 90% repolarization (APD90) and Ca2+ transient elicited at 0.5 Hz (IC50s=0.6 and 3 microM, respectively). Application of 0.3 microM E4031 increased these parameters by 110% and 45%, respectively. Under voltage-clamp, the relation between the duration of depolarization to 0 mV and Ca2+ transients could be described by the sum of two exponential components; the time constants were approximately 5 and 280 msec, respectively. The first component was abolished by 10 microM ryanodine, suggesting the involvement of Ca2+-induced Ca2+ release (CICR). Neither cromakalim nor E4031 directly affected Ca2+ current and Ca2+ transients under voltage clamp. When APD was changed by K+ channel modulators, the relation between APD90 and Ca2+-transients was almost similar to that obtained by changing the depolarization duration under voltage-clamp. CICR was changed significantly only when APD90 was markedly shortened by cromakalim. The extensively prolonged AP and Ca2+ transient in the presence of E4031 were reduced by an addition of cromakalim. It is concluded that these two K+ channel modulators can significantly alter the AP-induced Ca2+ transient mainly by changing APD, which regulates both Ca2+ influx and extrusion.

Recurrent Torsades de Pointes After Sotalol Therapy for Symptomatic Paroxysmal Atrial Fibrillation in a Patient with End-Stage Renal Disease

BACKGROUND: In recent years there has been ain increase in the use of class III antiarrhythmic drugs such as sotalol, amiodarone, and the so-called pure class III compound for the control of cardiac arrhythmias. It appears there has been a corresponding increase in the frequency of torsades de pointes (TdP). METHODS AND RESULTS: The case reported here, a patient on daily renal dialysis for end-stage renal disease, has important implications for class III agents, which are excreted largely by the kidneys. A relatively low dose of sotalol administered for the prevention of recurrences of atrial fabrillation, with a fast ventricular response producing angina, led to modest increases in the QT interval and moderate bradycardia. This culminated in the development of TdP, which deteriorated into ventricular fibrillation, from which the patient could be resuscitated with considerable difficulty. Dialysis after the occurrence of TdP led to further and striking prolongation of the QT interval associated with numerous episodes of TdP for several days before control was achieved. The atrial fibrillation and recurrences of TdP were eventually controlled with oral amiodarone. CONCLUSIONS: This case emphasizes that in the absence of significant renal function, use of sotalol may not be safe because drug accumulation may not be controlled adequately with renal dialysis. In view of this, in patients with end-stage renal disease, the use of sotalol for arrhythmia control appears contraindicated and alternative agents, the excretion of which does not occur by the renal route, should be used.

Effects of Sotalol on the Circadian Rhythmicity of Heart Rate and QT Intervals With a Noninvasive Index of Reverse-Use Dependency

BACKGROUND: The effects of sotalol on the 24-hour profile of the QT interval relative to that of the heart rate (HR) may be helpful in determining the time course of the drug's action in controlling cardiac arhythmias. This has not been previously determined. Thus, the objective of the current study was to evaluate the influence of the drug on the circadian rhythmicity of HR and QT intervals from Holter recordings in ambulatory patients. Reverse-use dependency (RUD) of sotalol was also studied noninvasively from Holter recordings. METHODS AND RESULTS: Holter recordings of 18 patients with ventricular arrhythmias were analyzed before and after 3-7 days of treatment with sotalol. We developed and used a signal processing system. A new noninvasive index to evaluate RUD was defined and applied to sotalol as a test agent. Sotalol significantly reduced HR from 76.9 +/- 3.2 to 60.0 +/- 1.1 (P <.001). The mean QT interval increased from 393 +/- 11 ms to 489 +/- 9 ms, whereas the mean normalized QT (QTc) interval increased from 415 +/- 5 ms to 487 +/- 5 ms (P <.001) during the drug treatment. Circadian rhythmicity of RR interval was abolished, but the circadian rhythms of the QT and QTc intervals were maintained during continuous treatment with sotalol. This finding is in contrast to amiodarone, which abolished the circadian rhythmicity of QTc interval while maintaining that of RR interval. RUD index was increased from 0.13 +/- 0.08 to 0.24 +/- 0.10 (P <.001) after sotalol, consistent with increased RUD with sotalol. CONCLUSIONS: The effects of sotalol on the circadian rhythmicity of HR and QTc interval are dissociated. They are in direct contrast to those reported for amiodarone, a difference that may be of clinical significance. The RUD index introduced here provides a noninvasive parameter for comparing short-term as well as long-term effects of class III antiarrhythmic drugs on RUD.

Cardiac and hemodynamic effects of the sinus node inhibitor tedisamil dihydrochloride in patients with congestive heart failure due to dilated cardiomyopathy

Clinical and experimental investigations have demonstrated an inverse relation between heart rate and myocardial performance in patients with congestive heart failure. Accordingly, this study was designed to investigate the hemodynamic effect of the novel bradycardic compound tedisamil in patients with heart failure. We hypothesized that tedisamil would reduce heart rate and thereby improve hemodynamic parameters of failing hearts with an inverse force-frequency relation. Tedisamil was administered intravenously in nine patients with dilated cardiomyopathy (NYHA II-III). Hemodynamic measurements by right heart catheterization were carried out at time points -30, 10, 20 min, 1, 2, 4, and 6 h. Tedisamil decreased heart rate significantly from 84 +/- 6 beats/min to 73 +/- 4 beats/min (at 10 min; p < 0.05). Stroke volume index remained unchanged, and cardiac index tended to decrease transiently. Mean blood pressure increased from 98 +/- 5 to 104 +/- 6 mm Hg (p < 0.05) because of an increase in systemic vascular resistance from 1,619 +/- 145 to 2,079 +/- 198 dyn x s x cm(-5) (at 20 min; p < 0.05). Diastolic pulmonary pressure and pulmonary vascular resistance showed similar changes. Pulmonary capillary wedge pressure increased from 12 +/- 3 to 16 +/- 4 mm Hg (at 20 min; p < 0.05). Although tedisamil resulted in a significant heart-rate reduction, this was not associated with an improvement of hemodynamics. This may be due to increased afterload of the left and right ventricle. In these patients, tedisamil increased vascular resistance, which is unwanted in the treatment of congestive heart failure.

General principles of antiarrhythmic therapy for ventricular tachyarrhythmias

Sudden cardiac death due to ventricular arrhythmias is a significant cause of mortality in patients with structural heart disease. Over the past several decades, the introduction of new pharmacologic and nonpharmacologic therapy has expanded the treatment options available. This article will focus on the use of antiarrhythmic medication for the treatment of ventricular arrhythmias and will review the following: (1) treatment goals for various clinical populations, (2) the mechanisms of antiarrhythmic and proarrhythmic actions of antiarrhythmic medications, and (3) empiric versus guided pharmacologic therapy.

The side effect profile of class III antiarrhythmic drugs: focus on d,l-sotalol

Class III antiarrhythmic drugs have been under extensive clinical investigation as safer, more effective alternatives to class I drugs, which have recognized risks in selected populations. Class III drugs prolong the action potential duration of myocardial cells, resulting in a lengthening of the effective refractory period. This pharmacologic activity has antiarrhythmic properties, but it may induce a distinctive form of proarrhythmia known as torsades de pointes. Amiodarone and d,l-sotolol are class III drugs that have been available for many years. In addition to their ability to prolong refractoriness, these drugs have other pharmacodynamic properties. Recent antiarrhythmic drug discovery has focused on the identification and development of selective or so-called pure class III drugs that are devoid of additional actions. Investigators have hoped that these drugs would be as effective as sotalol and amiodarone but have fewer adverse effects. Accumulating data, however, indicate that complex compounds exhibiting antiadrenergic and other electrophysiologic properties may be superior to pure class III agents.