Polymorphous ventricular tachycardia: clinical characterization, therapy, and the QT interval

Catecholaminergic Polymorphic Ventricular Tachycardia Presented As Generalized Tonic-Clonic Seizure: A Case Report

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited, highly malignant cardiac channelopathy that causes autopsy-negative sudden deaths and sudden infant deaths. The symptoms of CPVT range from asymptomatic to syncopal. We present a patient who has had sporadic seizures for the last four years and was diagnosed with focal seizures. Genetic testing revealed heterozygosity for a variant of uncertain significance in the cardiac ryanodine receptor (RYR2). Pathogenic variants are known to be associated with CPVT. A subcutaneous implantable cardioverter-defibrillator (ICD) was placed and is being closely followed in the cardiology clinic.

Catecholaminergic Polymorphic Ventricular Tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is an inherited arrhythmia syndrome characterised by adenergically mediated bidirectional and/or polymorphic ventricular tachycardia. CPVT is a significant cause of autopsy-negative sudden death in children and adolescents, although it can also affect adults. It is often caused by pathogenic variants in the cardiac ryanodine receptor gene as well as other rarer genes. Early identification and risk stratification is of major importance. β-blockers are the cornerstone of therapy. Sodium channel blockers, specifically flecainide, have an additive role. Left cardiac sympathetic denervation is playing an increasing role in suppression of arrhythmia and symptoms. Concerns have been raised, however, about the efficacy of implantable cardioverter defibrillator therapy and the risk of catecholamine driven proarrhythmic storms. In this review, we summarise the clinical characteristics, genetics, and diagnostic and therapeutic strategies for CPVT and describe recent advances and challenges.

Modeling genetic cardiac channelopathies using induced pluripotent stem cells - Status quo from an electrophysiological perspective

Long QT syndrome (LQTS), Brugada syndrome (BrS), and catecholaminergic polymorphic ventricular tachycardia (CPVT) are genetic diseases of the heart caused by mutations in specific cardiac ion channels and are characterized by paroxysmal arrhythmias, which can deteriorate into ventricular fibrillation. In LQTS3 and BrS different mutations in the SCN5A gene lead to a gain-or a loss-of-function of the voltage-gated sodium channel Nav1.5, respectively. Although sharing the same gene mutation, these syndromes are characterized by different clinical manifestations and functional perturbations and in some cases even present an overlapping clinical phenotype. Several studies have shown that Na⁺ current abnormalities in LQTS3 and BrS can also cause Ca²⁺-signaling aberrancies in cardiomyocytes (CMs). Abnormal Ca²⁺ homeostasis is also the main feature of CPVT which is mostly caused by heterozygous mutations in the RyR2 gene. Large numbers of disease-causing mutations were identified in RyR2 and SCN5A but it is not clear how different variants in the SCN5A gene produce different clinical syndromes and if in CPVT Ca²⁺ abnormalities and drug sensitivities vary depending on the mutation site in the RyR2. These questions can now be addressed by using patient-specific in vitro models of these diseases based on induced pluripotent stem cells (iPSCs). In this review, we summarize different insights gained from these models with a focus on electrophysiological perturbations caused by different ion channel mutations and discuss how will this knowledge help develop better stratification and more efficient personalized therapies for these patients.

Reining in the QTc: reducing the risk of Torsades de Pointes across a major health system

Hospitalized patients have a high prevalence of prolonged QTc and are a high-risk population for Torsades de Pointes (TdP). One modifiable risk factor for TdP is the use of QT prolonging drugs. Electronically alerting providers who are ordering QT prolonging drugs in at-risk patients may help to achieve safer prescribing practices. Our previous study decreased inappropriate prescription of IV haloperidol by 36% using a targeted "smart" electronic alert. We wanted to assess an approach to expanding this type of electronic alert to commonly used QT prolonging medications and evaluate how this would affect prescribing practice. This retrospective cohort study evaluated the impact of these alerts for 12 frequently prescribed high-risk medications across a major health system. Between October 2016 and June 2017, a total of 6453 alerts fired and resulted in 3020 (46.8%) orders being cancelled by the provider. Our focused electronic alert significantly decreased prescribing of QT prolonging medications in high-risk patients.

Polymorphic Wide QRS Complex Tachycardia: Differential Diagnosis

Polymorphic wide QRS complex tachycardia is defined as a tachyarrhythmia showing variable and frequently alternating morphologies of the QRS complex with irregular R-R intervals. It may present with a specific and reproducible pattern including torsade de pointes and bidirectional ventricular tachycardia or with a nonspecific and very irregular pattern, different from ventricular fibrillation. Polymorphic ventricular tachycardia is a challenging diagnosis and is associated with a high risk for sudden cardiac death. Although rare, preexcited atrial fibrillation over multiple accessory pathways can also generate a polymorphic wide QRS complex tachycardia mimicking polymorphic ventricular tachycardia.

Importance of QT interval in clinical practice

Long QT interval is an important finding that is often missed by electrocardiogram interpreters. Long QT syndrome (inherited and acquired) is a potentially lethal cardiac channelopathy that is frequently mistaken for epilepsy. We present a case of long QT syndrome with multiple cardiac arrests presenting as syncope and seizures. The long QTc interval was aggravated by hypomagnesaemia and drugs, including clarithromycin and levofloxacin. Multiple drugs can cause prolongation of the QT interval, and all physicians should bear this in mind when prescribing these drugs.

QTc prolongation with antipsychotics: is routine ECG monitoring recommended?

Whether or not QTc interval should be routinely monitored in patients receiving antipsychotics is a controversial issue, given logistic and fiscal dilemmas. There is a link between antipsychotic medications and prolongation of QTc interval, which is associated with an increased risk of torsade de pointes (TdP). Our goal is to provide clinically practical guidelines for monitoring QTc intervals in patients being treated with antipsychotics. We provide an overview of the pathophysiology of the QT interval, its relationship to TdP, and a discussion of the QT prolonging effects of antipsychotics. A literature search for articles relevant to the QTc prolonging effects of antipsychotics and TdP was conducted utilizing the databases PubMed and Embase with various combinations of search words. The overall risk of TdP and sudden death associated with antipsychotics has been observed to be low. Medications, genetics, gender, cardiovascular status, pathological conditions, and electrolyte disturbances have been found to be related to prolongation of the QTc interval. We conclude that, while electrocardiogram (ECG) monitoring is useful when administering antipsychotic medications in the presence of co-existing risk factors, it is not mandatory to perform ECG monitoring as a prerequisite in the absence of cardiac risk factors. An ECG should be performed if the initial evaluation suggests increased cardiac risk or if the antipsychotic to be prescribed has been established to have an increased risk of TdP and sudden death.

Mechanisms, risk factors, and management of acquired long QT syndrome: a comprehensive review

Long QT syndrome is characterized by prolongation of the corrected QT (QTc) interval on the surface electrocardiogram and is associated with precipitation of torsade de pointes (TdP), a polymorphic ventricular tachycardia that may cause sudden death. Acquired long QT syndrome describes pathologic excessive prolongation of the QT interval, upon exposure to an environmental stressor, with reversion back to normal following removal of the stressor. The most common environmental stressor in acquired long QT syndrome is drug therapy. Acquired long QT syndrome is an important issue for clinicians and a significant public health problem concerning the large number of drugs with this adverse effect with a potentially fatal outcome, the large number of patients exposed to these drugs, and our inability to predict the risk for a given individual. In this paper, we focus on mechanisms underlying QT prolongation, risk factors for torsades de pointes and describe the short- and long-term treatment of acquired long QT syndrome.

Amiodarone (Nexterone) injection for the treatment and prophylaxis of frequently recurring ventricular fibrillation

INTRODUCTION

Intravenous (IV) amiodarone is the most used and effective drug to manage life-threatening ventricular arrhythmias. However, its administration is associated with important adverse effects, the most frequent of which is hypotension. Nexterone® is a novel IV amiodarone formulation, proved to be devoid of hypotensive effects in clinical studies and may represent an improved and safer instrument in this setting.

AREAS COVERED

The Medline Database was searched for articles on the efficacy and safety of IV amiodarone in ventricular arrhythmias and cardiac arrest. This article summarizes the key findings of the most relevant studies conducted so far, with a special attention to the limitations of the currently available IV amiodarone and the potential advantages of the recently approved Nexterone. The role given to IV amiodarone in the guidelines on Advanced Cardiovascular Life Support is also reported and discussed.

EXPERT OPINION

Available studies demonstrated a convincing efficacy of IV amiodarone in ventricular arrhythmias and cardiac arrest. The new formulation seems to resolve concerns about tolerability. However, despite proven antiarrhythmic efficacy of the drug, no improved survival was showed in different settings. The search for an antiarrhythmic drug able to impact on hard endpoint as survival to hospital discharge is therefore far from being concluded.

Electrical therapies in cardiac arrest

Recognition and appropriate treatment of ventricular fibrillation or pulseless ventricular tachycardia is an essential skill for healthcare providers. Appropriate defibrillation can improve survival and benefit patient outcome. Similarly, increased public access to automatic electronic defibrillators has been shown to improve out-of-hospital survival for cardiac arrest. When combined with high-quality cardiopulmonary resuscitation, electrical therapies are an important aspect of resuscitation in the patient with cardiac arrest. This article focuses on the use of electrical therapies, including defibrillation, cardiac pacing, and automated external defibrillators, in cardiac arrest.

Self-terminating polymorphous ventricular tachycardia occurring at the peak of myocardial ischemia

Polymorphous ventricular tachycardia (PVT) is a unique arrhythmia that may occur during or shortly after acute myocardial ischemia. It is believed that the occurrence of PVT at the time of ischemia is due to differences in the shortening time of the myocardial potentials in the different layers of the myocardium, caused by the heterogenic blood supply at that time. We describe a case of a patient who developed two consecutive episodes of PVT, both induced by ventricular premature beats (VPBs) that occurred during the peak of myocardial ischemia as detected by the ST analyzing system while hospitalized in the intensive coronary care unit.

Strategies for the prevention and treatment of sudden cardiac death

Cardiovascular diseases account for 40% of all deaths in the West. Sudden cardiac death (SCD) is a major health problem affecting over 300,000 patients annually in the United States alone. Presence of coronary artery disease (CAD), usually in the setting of diminished left ventricular ejection fraction, is still the single major risk factor for SCD. Additionally, acute myocardial ischemia, structural cardiac defects, anomalous coronary arteries, cardiomyopathies, genetic mutations, and ventricular arrhythmias are all attributed to SCD, demonstrating the perplexity of this condition. With the recent advancements in cardiovascular medicine, the incidence of SCD is expected to increase steeply as the prevalence of CAD and heart failure is uprising in general population. Considering SCD, the major challenge confronting contemporary cardiology, multiple strategies for prevention against SCD have been developed. β-blockers have been shown to reduce the risk of SCD, whereas implantable cardioverter-defibrillator devices are found to be effective at terminating the malignant arrhythmias. In recent years, multiple clinical trials were carried out to identify patients who may benefit from preventive intervention, including medical therapy and automatic cardioverter-defibrillator implantations. This review article provides insight into the advanced strategies for the prevention and treatment of SCD based on the data available in medical literature to date.

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.

Atrial fibrillation: a review of mechanism, etiology, and therapy

The prevalence of elderly individuals in the populations of developed countries is increasing rapidly, and atrial fibrillation (AF) is quite common in these elderly patients: currently, 11% of the U.S. population is between the ages of 65 and 85 years; 70% of people with AF are between the ages of 65 and 85 years. AF causes symptoms secondary to hemodynamic derangements that are the result of increased ventricular response and loss of atrial booster function. AF can lead to reversible impairment of left ventricular function, cardiac chamber dilatation, clinical heart failure, and thromboembolic events. AF requires treatment in order to prevent these potential complications. Type Ia, Ic, and III antiarrhythmics are capable of converting AF to normal sinus rhythm (NSR). Amiodarone has the greatest efficacy and safety for converting AF and maintaining NSR while digoxin and verapamil are ineffective in restoring NSR. Quinidine, flecainide, disopyramide, and sotalol have also been shown to maintain NSR after conversion of AF. Proarrhythmia is a definite concern with the latter four agents. Alternative therapy for AF includes anticoagulation with warfarin or aspirin for the prevention of thromboembolic events, and a variety of agents to control the ventricular response. All medications used to treat AF carry significant risks in the elderly, whether from proarrhythmia, overdosing because of compliance errors, or hemorrhage secondary to anticoagulation. Treatment of AF must be based on a careful risk-benefit evaluation. The physician must know the capability of the particular patient as well as drug mechanisms and effects in the elderly. The decision to convert patients from AF to NSR or to leave the patient in AF and control the ventricular response represents a complex intellectual challenge. Factors favoring one or the other of these two clinical strategies are discussed. Multicenter clinical trials, for example, the Atrial Fibrillation Follow-up Investigation Rhythm Management (AFFIRM) trial, are currently underway to assess various clinical strategies for maintenance of NSR following conversion from AF. Amiodarone is one of the drugs under investigation.

The canine virtual ventricular wall: A platform for dissecting pharmacological effects on propagation and arrhythmogenesis

We have constructed computational models of canine ventricular cells and tissues, ultimately combining detailed tissue architecture and heterogeneous transmural electrophysiology. The heterogeneity is introduced by modifying the Hund-Rudy canine cell model in order to reproduce experimentally reported electrophysiological properties of endocardial, midmyocardial (M) and epicardial cells. These models are validated against experimental data for individual ionic current and action potential characteristics, and their rate dependencies. 1D and 3D heterogeneous virtual tissues are constructed, with detailed tissue architecture (anisotropy and orthotropy, due to fibre orientation and sheet structure) of the left ventricular wall wedge extracted from a diffusion tensor imaging data set. The models are used to study the effects of tissue heterogeneity and class III drugs on transmural propagation and tissue vulnerability to re-entry. We have determined relationships between the transmural dispersion of action potential duration (APD) and the vulnerable window in the 1D virtual ventricular wall, and demonstrated how changes in the transmural heterogeneity, and hence tissue vulnerability, can lead to generation of re-entry in the 3D ventricular wedge. Two class III drugs with opposite qualitative effects on transmural APD heterogeneity are considered: d-sotalol that increases transmural APD dispersion, and amiodarone that decreases it. Simulations with the 1D virtual ventricular wall show that under d-sotalol conditions the vulnerable window is substantially wider compared to amiodarone conditions, primarily in the epicardial region where unidirectional conduction block persists until the adjacent M cells are fully repolarised. Further simulations with the 3D ventricular wedge have shown that ectopic stimulation of the epicardial region results in generation of sustained re-entry under d-sotalol conditions, but not under amiodarone conditions or in control. Again, APD increase in M cells was identified as the major contributor to tissue vulnerability--re-entry was initiated primarily due to ectopic excitation propagating around the unidirectional conduction block in the M cell region. This suggests an electrophysiological mechanism for the anti- and proarrhythmic effects of the class III drugs: the relative safety of amiodarone in comparison to d-sotalol can be explained by relatively low transmural APD dispersion, and hence, a narrow vulnerable window and low probability of re-entry in the tissue.

Sustained ventricular tachycardia as a marker of inadequate myocardial perfusion during the acute phase of myocardial infarction

BACKGROUND

Sustained ventricular tachycardia (VT) complicating the acute phase of myocardial infarction (AMI) is a quite rare event but with short-term unfavorable prognosis. The clinical characteristics as well as the therapeutic implications have not yet been well defined.

HYPOTHESIS

This paper attempts to prove that VT may be considered a marker of inadequate myocardial perfusion after thrombolysis.

METHODS

To assess the clinic-electroangiographic characteristics and prognosis of patients with VT occurring within the first 4 days of an AMI, a case-control study was carried out in 23 patients from a total of 1,100 patients (1.9%) hospitalized with AMI between March 1993 and July 1997. These patients were compared with a control group of 131 patients hospitalized consecutively. A statistical analysis was made using the chi-square test, t-test, and logistic regression.

RESULTS

There were no differences among groups with regard to age, gender, and area of necrosis. Average time for the onset of VT was 26 h (range 0-92 h). Sixteen patients underwent coronary angiography: 4 patients had left main coronary artery disease, 2 had single-vessel disease, 8 had lesions in two vessels, and 2 had triple-vessel disease. Univariate analysis showed that patients with VT had a higher incidence of creatine phosphokinase (CPK)-MB peak > 300 UI/l (61 vs. 30%; p<0.001), more frequent occurrence of previous AMI (48 vs. 17%; p<0.001), and acute intraventricular conduction disorders (26 vs. 4%; p<0.001). Furthermore, these patients suffered ischemia previous to VT more frequently (65 vs. 11%; p<0.0001), and had a greater mortality rate than that in the control group (35 vs. 4%; p<0.0001). In the multivariant analysis, the variables related to the occurrence of VT were CPK-MB peak > 300 IU/l (OR 5.9; 95% CI 1.6-21), acute intraventricular conduction disorders (OR 9.02; 95% CI 1.7-48), and ischemia immediately prior to VT (odds ratio [OR] 19.64; 95% confidence interval [CI] 5.3-73).

CONCLUSIONS

Ventricular tachycardia may be considered a marker of inadequate myocardial perfusion after thrombolysis; therefore, a more aggressive revascularization treatment in these patients would be advisable. The profile of patients with AMI, hospitalized in the coronary care unit, who will likely suffer from VT is previous AMI, CPK-MB peak > 300, acute intraventricular conduction disorders, Killip > I, and ischemia previous to VT.

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.

Cumulative Experience of Azimilide-Associated Torsades de Pointes Ventricular Tachycardia in the 19 Clinical Studies Comprising the Azimilide Database

OBJECTIVES

The purpose of this study was to assess the incidence, temporal characteristics, and risk factors associated with azimilide-associated torsades de pointes (TdP) ventricular tachycardia.

BACKGROUND

Azimilide dihydrochloride is a class III antiarrhythmic drug possessing Ikr and Iks channel-blocking properties.

METHODS

Oral azimilide (75 to 125 mg/day) was taken by 5,375 patients in 19 clinical trials conducted at 775 international centers. Of 3,964 patients in double-blind studies, 1,427 had a history of atrial fibrillation or other supraventricular arrhythmia, 510 had an implantable cardioverter-defibrillator, and 2,027 were post-myocardial infarction patients with a left ventricular ejection fraction < or =35%.

RESULTS

The TdP occurred in 56 patients assigned to azimilide, was dose-related, and tended to occur earlier with an azimilide-loading regimen. Forty-three percent of TdP patients had a QT interval corrected by Bazett's formula, for heart rate, (QTc) > or =500 ms at the time of or before the TdP occurrence. Significant risk factors using logistic regression were increasing age, female gender, diuretic use, and lack of aspirin use.

CONCLUSIONS

Azimilide-associated TdP has characteristics and risk factors similar to other Ikr blockers. However, there is a distinctive temporal profile. The TdP events are not concentrated in the first week. The azimilide-associated TdP rate is 1% (95% confidence interval 0.78 to 1.35) and is not increased in patients with low left ventricular ejection fraction, even in women.

Polymorphic ventricular tachycardia in the coronary care unit

OBJECTIVE

To describe the clinical experience of patients with polymorphic ventricular tachycardia (PMVT) in a hospital setting.

METHODS

A 2-year prospective, observational study of patients with symptomatic and asymptomatic PMVT admitted to the coronary care unit of a community medical center. Electrocardiograms were reviewed for a pattern diagnostic of PMVT, and the QTc interval of the baseline ECG was determined. Etiologic factors, management, and clinical outcomes were also analyzed.

RESULTS

The study included 27 patients (13 men) with a mean age of 66.6 +/- 10 years. Fourteen patients had a prolonged QTc interval >or=520 ms (group A), and 10 patients had a normal QTc interval <or=440 ms (group B). Acute hypokalemia (n = 7) in the setting of underlying heart disease was the principal cause of the acquired QT syndrome; other causally related factors included severe bradycardia and the proarrhythmic effect of drugs. Acute myocardial infarction (n = 6) was the principal cause of PMVT associated with a normal QTc interval; other causal factors included right ventricular cardiomyopathy and the proarrhythmic effect of electrical cardioversion. Eight patients (group C) had brief runs of asymptomatic nonsustained PMVT, which recurred in 5 patients as symptomatic sustained PMVT despite appropriate treatment. Cardiac arrest (63%) requiring emergency defibrillation was the predominant clinical presentation irrespective of the QT interval. Four patients (15%) died, but only 2 owing to refractory PMVT/VF.

CONCLUSION

PMVT with or without QTc prolongation is a sporadic tachyarrhythmia that has frequent malignant potential for cardiac arrest. Successful management mandates emergency defibrillation for cardiac arrest and other appropriate measures for suppression of PMVT. The prognosis of PMVT is improved when the cause is correctly identified and promptly treated.

Assessing the proarrhythmic potential of drugs: current status of models and surrogate parameters of torsades de pointes arrhythmias

Torsades de pointes (TdP) is a potentially lethal cardiac arrhythmia that can occur as an unwanted adverse effect of various pharmacological therapies. Before a drug is approved for marketing, its effects on cardiac repolarisation are examined clinically and experimentally. This paper expresses the opinion that effects on repolarisation duration cannot directly be translated to risk of proarrhythmia. Current safety assessments of drugs only involve repolarisation assays, however the proarrhythmic profile can only be determined in the predisposed model. The availability of these proarrhythmic animal models is emphasised in the present paper. It is feasible for the pharmaceutical industry to establish one or more of these proarrhythmic animal models and large benefits are potentially available if pharmaceutical industries and patient-care authorities embraced these models. Furthermore, suggested surrogate parameters possessing predictive power of TdP arrhythmia are reviewed. As these parameters are not developed to finalisation, any meaningful study of the proarrhythmic potential of a new drug will include evaluation in an integrated model of TdP arrhythmia.

Use of preclinical assays to predict risk of drug-induced torsades de pointes

Numerous medications, including drugs prescribed for noncardiac indications, can induce electrophysiologic changes that trigger the rare, malignant polymorphic ventricular tachyarrhythmia known as torsades de pointes (TdP). Although the exact relationship between electrophysiologic events and the development of TdP is not defined, prolongation of the QT interval and inhibition of the rapidly activating potassium current I(Kr) by drugs may be associated with an increased risk of TdP. The ability of a drug to reduce I(Kr) and prolong the QT interval often is considered to predict the likelihood that the drug will cause TdP in humans. However, these surrogate measures of the drug-induced risk of causing TdP, and therefore of drug safety, now are recognized to be imperfect predictors of drug safety. New preclinical models should be used to assess drug risk, including preparations, conditions, and measurements used by basic research scientists to produce ventricular polymorphic arrhythmias in the laboratory. In this review, we discuss the task of assessing the arrhythmogenic potential of a drug. Assays of drug effect to induce early afterdepolarizations and ectopic beats and/or to increase the dispersion of ventricular repolarization when "repolarization reserve" is reduced appear to be the best predictors of the drug-induced risk of TdP. Current experimental models and protocols, especially those using conditions wherein the net repolarizing current is reduced, can detect the potential for a drug to induce TdP, even when the potential is extremely low.

Refining detection of drug-induced proarrhythmia: QT interval and TRIaD

QT interval prolongation is so frequently associated with torsades de pointes (TdP) that it has come to be recognized as a surrogate marker of this unique tachyarrhythmia. However, not only does TdP not always follow QT interval prolongation, but TdP can occur even in the absence of a prolonged QT interval. Worse still, even shortening of the QT interval may be associated with serious arrhythmias (particularly ventricular tachycardia [VT] and ventricular fibrillation [VF]). It appears increasingly probable that the distinction between various ventricular tachyarrhythmias may be arbitrary, and drug-induced TdP, polymorphic VT, VT, catecholaminergic polymorphic VT, and VF may represent discrete entities within a spectrum of drug-induced proarrhythmia. Although they are differentiated by the coupling interval and the duration of QT interval, they appear to share a common substrate: a set of disturbances of repolarization characterized by Triangulation, Reverse use dependency, electrical Instability of the action potential, and Dispersion (TRIaD). It is becoming increasingly evident that augmentation of TRIaD, rather than changes in the duration of QT interval, provides the proarrhythmic substrate. In contrast, when not associated with an increase of TRIaD, QT interval prolongation can be an antiarrhythmic property. Electrophysiologically, augmentation of TRIaD can be explained by inhibition of hERG (human ether-a-go-go related gene) channel. Because drug-induced disturbances in repolarization commonly result from inhibition of hERG channels or I(Kr), hERG blockade and the resulting prolongation of QT interval are important properties of a drug to be studied. However, these need only be a concern if associated with TRIaD. More significantly, TRIaD so often precedes prolongation of action potential duration or QT interval and ventricular tachyarrhythmias that it should be considered a marker of proarrhythmia until proven otherwise, even in the absence of QT interval prolongation. Detecting drug-induced augmentation of TRIaD may offer an additional, more sensitive, and accurate indicator of the broader proarrhythmic potential of a drug than may QT interval prolongation alone.

Drug-induced QT dispersion: does it predict the risk of torsade de pointes?

Drug-induced delay in ventricular repolarization and proarrhythmias have attracted considerable regulatory attention. The measure of delayed ventricular repolarization most frequently used clinically is the ability of the new chemical entity (NCE) to prolong the QTc interval on surface electrocardiogram. Before they can be approved, new chemical entities with systemic bioavailability require characterization for their potential to prolong the QTc interval. Inevitably, QTc interval prolongation has come to be recognized as a surrogate marker of the risk of torsade de pointes (TdP)--a unique form of potentially fatal polymorphic ventricular tachycardia. Although it is the best and the simplest clinical measure that is available at present, QTc interval is not a reliable surrogate of TdP. Intramyocardial dispersion of repolarization appears to play a more important role both in electrical stability of the ventricles and in arrhythmogenesis. The potential importance of myocardial dispersion of refractoriness in arrhythmogenesis has led to a number of attempts to assess it from the surface electrocardiogram. This review summarizes the evidence for and against the predictive value of one of these attempts-measurement of the so-called QT dispersion. Although the concept of QT dispersion is the best known and most widely investigated, it has also proved to be the least successful in predicting the risks of drug-induced TdP.

Torsade de pointes: the clinical considerations

Torsade de pointes is a form of polymorphic ventricular tachycardia occurring in a setting of prolonged QT interval on surface electrocardiogram. Congenital causes of prolonged QT interval occur in individuals with genetic mutations in genes that control expression of potassium and sodium channels and acquired causes are numerous, predominantly drugs causing prolonged QT interval by blockade of potassium channels. Among the drugs, antiarrhythmic agents most notably quinidine, sotalol, dofetilide and ibutilide have the potential to induce the fatal torsade de pointes. Many non-antiarrhythmic drugs can also cause torsade de pointes. Although it is important to distinguish between the congenital and the acquired forms of long QT syndrome as the later can often be reversed by correction of the underlying disorder or discontinuation of the offending drug, both forms are not mutually exclusive. Clinical considerations and management of torsade de pointes are described.

Psychotropic drugs, cardiac arrhythmia, and sudden death

A variety of drugs targeted towards the central nervous system are associated with cardiac side effects, some of which are linked with reports of arrhythmia and sudden death. Some psychotropic drugs, particularly tricyclic antidepressants (TCAs) and antipsychotic agents, are correlated with iatrogenic prolongation of the QT interval of the electrocardiogram (ECG). In turn, this is associated with the arrhythmia (TdP). This review discusses the association between psychotropic agents, arrhythmia and sudden death and, focusing on TCAs and antipsychotics, considers their range of cellular actions on the heart; potentially pro-arrhythmic interactions between psychotropic and other medications are also considered. At the cellular level TCAs, such as imipramine and amitriptyline, and antipsychotics, such as thioridazine, are associated with inhibition of potassium channels encoded by In many cases this cellular action correlates with ECG changes and a risk of TdP. However, not all psychotropic agents that inhibit HERG at the cellular level are associated equally with QT prolongation in patients, and the potential for QT prolongation is not always equally correlated with TdP. Differences in risk between classes of psychotropic drugs, and between individual drugs within a class, may result from additional cellular effects of particular agents, which may influence the consequent effects of inhibition of repolarizing potassium current.

[The efficacy of scheduled cardioversion in atrial fibrillation. Comparison of two schemes of treatment: electrical versus pharmacological cardioversion]

INTRODUCTION AND OBJECTIVES

Atrial fibrillation is an arrhythmia with high morbidity and mortality. Restoring sinus rhythm is one of the principle objectives in its management. The present study aimed to assess the efficacy of scheduled cardioversion on atrial fibrillation by comparing two different therapeutic approaches: electrical vs. pharmacological cardioversion.

PATIENTS AND METHOD

Two hundred thirty patients with atrial fibrillation of more than 48 hours duration and requiring sinus rhythm restoration were included. One hundred forty-four patients underwent external electrical cardioversion and 86 patients received quinidine. We analyzed the rate of success, duration of hospital stay, complications and clinical and echocardiographic variable that might predict success.

RESULTS

Sinus rhythm was restored in 181 of 230 patients (79%). The rate of success was 77% (111/144 patients) in the electrical group and 81% (70 of 86 patients) in the pharmacological group (ns). In 13 pharmacological group patients for whom the first attempt failed attempt, a second attempt with electrical cardioversion was made and was successful in 8 patients (61%). No embolic complication was recorded and only two electrical disturbances were seen. Only atrial fibrillation lasting less than 8 weeks was associated with a higher success rate (p < 0.01).

CONCLUSIONS

Scheduled cardioversion in atrial fibrillation is an effective technique with a high success rate and a very low rate of complication. Electrical cardioversion and pharmacological cardioversion with quinidine are similarly effective, although the latter involves a longer hospital stay.

Clinical and therapeutic aspects of congenital and acquired long QT syndrome

The long QT syndrome is characterized by prolongation of the corrected QT (QTc) interval on the surface electrocardiogram. It is associated with precipitation of a polymorphic ventricular tachycardia, torsade de pointes, which may cause sudden death. The syndrome is a disorder of cardiac repolarization caused by the alterations in the transmembrane potassium and sodium currents. Six genetic loci for the congenital forms of the syndrome have been identified; sporadic cases occur because of spontaneous mutations. Acquired causes of the long QT syndrome include drugs, electrolyte imbalance, toxins, marked bradycardia, subarachnoid hemorrhage, stroke, myocardial ischemia, protein-sparing fasting, autonomic neuropathy, and human immunodeficiency virus disease. Clinical symptoms are the result of the precipitation of torsade de pointes and range from such minor symptoms as dizziness to syncope and sudden death. Short-term treatment is aimed at preventing the recurrences of torsade de pointes and includes intravenous magnesium and potassium administration, temporary cardiac pacing, and correction of electrolyte imbalance; rarely, intravenous isoproterenol is indicated. Long-term management includes use of beta-blockers, permanent pacemaker placement, and cardioverter-defibrillator implantation. Asymptomatic patients are treated if under the age of 40 years at the time of diagnosis.

The effect of intravenous haloperidol on QT interval dispersion in critically ill patients: comparison with QT interval prolongation for assessment of risk of Torsades de Pointes

The objective of this study was to determine the effect of intravenous haloperidol on QT interval dispersion in critically ill patients and to compare increases in QT interval dispersion and QTc intervals in patients who developed haloperidol-induced Torsades de Pointes versus those in patients who did not. This was a case-controlled study of 30 critically ill patients who received intravenous haloperidol for delusional agitation. Cases were patients (n = 6) who developed Torsades de Pointes during haloperidol therapy. Controls were patients (n = 24) who did not experience haloperidol-induced Torsades dePointes. QTc intervals were measured and QT interval dispersion was calculated. Haloperidol prolonged QTc interval compared to pretreatment values in Torsades de Pointes patients (606 +/- 61 ms vs. 501 +/- 44 ms, p = 0.007) by a greater magnitude than in patients who did not experience Torsades de Pointes (507 +/- 60 ms vs. 466 +/- 44, p = 0.01). Twelve-lead analysis revealed that QT interval dispersion increased in patients who experienced Torsades de Pointes (from 63 +/- 11 to 95 +/- 22 ms, p = 0.03) but not in those who did not (62 +/- 18 vs. 60 +/- 26 ms, p = 0.66). Analysis of precordial leads only showed no significant haloperidol-associated increases in QTinterval dispersion in eithergroup. The odds of developing haloperidol-induced Torsades de Pointes were highest in patients with QTc interval > 521 ms during haloperidol therapy(odds ratio = 12.1). It was concluded that intravenous haloperidol prolongs QTc intervals in critically ill patients. The degree of prolongation is greater in patients who experience Torsades de Pointes. QT interval dispersion may be increased in patients who develop haloperidol-induced Torsades de Pointes compared with those who do not. However, these effects are dependent on the method of measurement (12 leads vs. precordial leads). In addition, the odds of haloperidol-induced Torsades de Pointes are higherin patients with QTc intervalprolongation compared with increased QT interval dispersion. Therefore, QTc interval determination remains preferable to QT interval dispersion as a means assessment of risk for haloperidol-induced Torsades de Pointes.

Torsades de pointes associated with chlorpromazine: case report and review of associated ventricular arrhythmias

PURPOSE

To present a case of chlorpromazine-associated torsades de pointes, review established cases of ventricular arrhythmias associated with chlorpromazine, and describe the proarrhythmic characteristics of this drug.

DATA SOURCES

Articles identified through a search of MEDLINE and IDIS from January 1966-November 2000 and thorough review of the article bibliographies. Patient cases also were identified from a search of the Food and Drug Administration's Adverse Event Reporting System database (November 1997-March 2001). Cases involving intentional overdoses of chlorpromazine were excluded.

RESULTS

In addition to the case reported herein, 12 cases of documented, chlorpromazine-associated ventricular arrhythmias were identified; five had characteristic features of torsades de pointes. Chlorpromazine delayed repolarization and produced electrocardiographic abnormalities; although, whether chlorpromazine induced torsades de pointes through a mechanism of early afterdepolarizations is unclear. Similar to other instances of drug-induced torsades de pointes, concurrent factors such as electrolyte deficiencies may place the patient at increased risk for arrhythmia.

CONCLUSIONS

Chlorpromazine can delay repolarization and produce electrocardiographic abnormalities. These can result infrequently in ventricular arrhythmias and torsades de pointes, particularly in patients with confounding factors.

Pause-dependent polymorphic ventricular tachycardia during long-term treatment with dofetilide: a placebo-controlled, implantable cardioverter-defibrillator-based evaluation

OBJECTIVES

To compare the incidence of pause-dependent polymorphic ventricular tachycardia (PVT) in patients with implantable cardioverter-defibrillators (ICDs) randomly assigned to the QT-prolonging antiarrhythmic dofetilide or placebo.

BACKGROUND

Drug-related torsade de pointes (TdP) is usually recognized within days of initiating therapy, but its incidence during long-term therapy is unknown.

METHODS

We assessed the frequency of TdP and ICD electrograms compatible with TdP in a multicenter study that randomized ICD patients to placebo (n = 87) or dofetilide (n = 87). As reported elsewhere, the number of patients with a primary trial end point (ICD intervention for VT or ventricular fibrillation) was similar in the two groups. For this analysis, a qualifying event was TdP (on electrocardiogram) or an intracardiac electrogram showing pause-dependent PVT.

RESULTS

A total of 620 electrograms obtained in 131 patients were analyzed blindly by prospectively defined criteria for episodes of pause-dependent polymorphic VT. These were identified in 15/87 (17%) patients receiving dofetilide and 5/87 (6%) patients on placebo (p < 0.05). Five of these episodes were early (<3 days), all of which were TdP on dofetilide. There were 15 late events, 10 on dofetilide and five on placebo (p = 0.29). The median time to a late event was 22 days (range 6 to 107 days) for dofetilide and 99 days (range 34 to 207 days) for placebo.

CONCLUSIONS

Pause-dependent PVT was more common among patients receiving dofetilide, although total VT incidence was similar in the two groups. These data suggest that in ICD patients either long-term dofetilide therapy is associated with an increased risk of TdP or the drug alters VT morphology.

Polymorphic ventricular tachycardia, long Q-T syndrome, and torsades de pointes

PMVT is an uncommon arrhythmia with multiple causes. Classification and management are based on the Q-T interval. Torsades de pointes denotes PMVT in the setting of a prolonged Q-T interval and usually is iatrogenic in origin, although congenital LQTS is being recognized more frequently. Therapy of PMVT focuses on the establishment of hemodynamic stability, the removal or correction of precipitants, and the acute and long-term inhibition of subsequent episodes. Evaluation of these patients should include a thorough history and physical examination and an assessment for underlying heart disease and known [figure: see text] eliciting factors. Long-term management must be tailored to the individual and the underlying cause and should be conducted by an experienced cardiac electrophysiologist.

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.

Increased QT variability in patients with panic disorder and depression

This study investigated beat-to-beat QT variability in patients with panic disorder and depression, and normal control subjects using an automated algorithm to compute QT intervals. An increase in QT variability appears to be associated with symptomatic patients with dilated cardiomyopathy and also with an increased risk for sudden death. QT(vm) (QT variability normalized for mean QT interval) and QT(vi) (a log ratio of QT variance normalized for mean QT over heart rate variability normalized for mean heart rate) were significantly higher in patients with panic disorder and depression in supine as well as standing postures (P=0.002 and 0.0001 for QT(vm) and QT(vi), respectively). In another analysis, QT(vi) was significantly higher in patients with panic disorder compared to control subjects in supine as well as standing postures during spontaneous breathing as well as 12, 15 and 20 per minute breathing (P=0.005). These findings are important especially in view of the recent reports of increased risk for cardiovascular mortality and sudden death in patients with anxiety and depression and the utility of QT(vi) as a noninvasive measure of temporal repolarization lability.

Prevalence, therapeutic response, and outcome of ventricular tachycardia in the out-of-hospital setting: a comparison of monomorphic ventricular tachycardia, polymorphic ventricular tachycardia, and torsades de pointes

OBJECTIVE

To investigate out-of-hospital ventricular tachycardia (VT) cardiac arrest patients, comparing the prevalences and outcomes of the following VT subtypes among this population: monomorphic VT (MVT), polymorphic VT (PVT), and torsades de pointes (TdP, PVT with a prolonged QT interval).

METHODS

This was a retrospective review from a fire department-based paramedic system of nontraumatic VT cardiac arrest patients (January 1991 to December 1994) with a supraventricular perfusing rhythm (SVPR) at some time during out-of-hospital care, with a measurable QT interval. QT interval was measured from an SVPR, and corrected QT interval (QTc) was calculated and considered prolonged if > 0.45 sec. VT was classified as polymorphic or monomorphic. TdP was defined as PVT with a prolonged QT interval.

RESULTS

196 patients were identified; six were excluded due to incomplete medical records, leaving 190 who met inclusion criteria and were used for data analysis. 117 (62%) patients had MVT, while 73 (38%) patients had PVT; of the 73 patients with PVT, 37 (51%) had normal QTc (non-TdP PVT) and 36 (49%) had prolonged QTc (TdP PVT). 97 (51%) patients had prolonged QTc (PQTc). Regardless of VT type (i.e., MVT vs PVT), 97 (51%) patients had prolonged QTc, with a mean QTc of 0.476+/-0.15 seconds prearrest and 0.464+/-12 seconds postarrest. Patients with PQTc were not more likely to have PVT (70 [37%] vs 76 [40%]; p = 0.705). No significant difference with respect to paramedic-witnessed arrests in each VT morphology group and each QT group was found. The overall hospital discharge rate was 28.4%. Regardless of VT type, patients had similar rates of out-of-hospital return of spontaneous circulation (ROSC) and hospital discharge; patients with PQTc were less likely to be discharged from the hospital (19.6% vs 37.6%; p = 0.01). 27.8% of TdP and 26.8% of non-TdP patients were discharged (p = 0.912).

CONCLUSIONS

In this population of out-of-hospital VT arrest patients, MVT is the most common form of VT encountered; PVT and the subtype TdP are also seen in this population with approximately equal frequencies. All three rhythm types demonstrate similar responses to standard Advanced Cardiac Life Support therapy with equal rates of out-of-hospital ROSC and hospital discharge. PQTc may be a marker of poor clinical outcome in patients with out-of-hospital VT arrest.

Evaluation of the acute electrophysiologic effects of intravenous dronedarone, an amiodarone-like agent, with special emphasis on ventricular repolarization and acquired torsade de pointes arrhythmias

In the anesthetized dog with complete chronic AV block (CAVB), we evaluated and compared the acute electrophysiologic effects of dronedarone i.v. (Dron, 2 times 2.5 mg/kg/10 min) and amiodarone i.v. (Amio, 2 times 5 mg/kg/10 min). This canine model with a high sensitivity for acquired torsade de pointes (TdP) provides an ideal substrate to evaluate ventricular repolarization abnormalities. Six ECG leads and two endocardial monophasic action potential (MAP) recordings in the left and right ventricle (LV and RV) were simultaneously recorded to measure QT time, action-potential duration (APD), interventricular dispersion (deltaAPD = LV(APD) - RV(APD)), early afterdepolarizations (EADs), ectopic beats (EBs), and TdP. Measurements were made at the spontaneous idioventricular rhythm (IVR) and 1,000-ms steady-state pacing. To investigate its short-term, antiarrhythmic properties, Dron was given after almokalant (0.12 mg/kg)-induced TdP. Furthermore, in another set of experiments, oral Dron (20 mg/kg, b.i.d) was given for 3 weeks to conscious CAVB dogs. Dron, i.v., shortened ventricular repolarization (QT, 435 +/- 60 to 360 +/- 55; LV(APD) 395 +/- 75 to 335 +/- 60 ms; p < 0.05), whereas IVR and ventricular effective refractory period (VERP, 225 +/- 30 to 230 +/- 30 ms) remained similar. Therefore the VERP/QT ratio increased (0.55 +/- 0.04 to 0.61 +/- 0.03; p < 0.05). Similar results were obtained with Amio, i.v.. Almokalant-induced TdP was characterized by an increased repolarization duration, deltaAPD, and EADs. Dron, i.v., suppressed the EADs, EBs, and TdP by a reduction and homogenization of repolarization (LV(APD), 505 +/- 110 to 455 +/- 80 ms, and deltaAPD, 110 +/- 55 to 65 +/- 40 ms). Long-term oral Dron increased the PP interval, CL-IVR, and QT(c) time. In contrast to oral treatment, Dron i.v. shortens ventricular repolarization parameters, resulting in suppression of EAD-dependent acquired TdP. The increased VERP/QT ratio after Dron i.v. may indicate an important second antiarrhythmic property.