The long QT syndromes: genetic basis and clinical implications

An LQT mutant minK alters KvLQT1 trafficking

Cardiac I(Ks), the slowly activated delayed-rectifier K(+) current, is produced by the protein complex composed of alpha- and beta-subunits: KvLQT1 and minK. Mutations of genes encoding KvLQT1 and minK are responsible for the hereditary long QT syndrome (loci LQT1 and LQT5, respectively). MinK-L51H fails to traffic to the cell surface, thereby failing to produce effective I(Ks). We examined the effects that minK-L51H and an endoplasmic reticulum (ER)-targeted minK (minK-ER) exerted over the electrophysiology and biosynthesis of coexpressed KvLQT1. Both minK-L51H and minK-ER were sequestered primarily in the ER as confirmed by lack of plasma membrane expression. Glycosylation and immunofluorescence patterns of minK-L51H were qualitatively different for minK-ER, suggesting differences in trafficking. Cotransfection with the minK mutants resulted in reduced surface expression of KvLQT1 as assayed by whole cell voltage clamp and immunofluorescence. MinK-L51H reduced current amplitude by 91% compared with wild-type (WT) minK/KvLQT1, and the residual current was identical to KvLQT1 without minK. The phenotype of minK-L51H on I(Ks) was not dominant because coexpressed WT minK rescued the current and surface expression. Collectively, our data suggest that ER quality control prevents minK-L51H/KvLQT1 complexes from trafficking to the plasma membrane, resulting in decreased I(Ks). This is the first demonstration that a minK LQT mutation is capable of conferring trafficking defects onto its associated alpha-subunit.

Sevoflurane Inhibition of the Slowly Activating Delayed Rectifier K+ Current in Guinea Pig Ventricular Cells

Single ventricular cells were enzymatically isolated from guinea pig hearts and the effects of sevoflurane on the delayed rectifier K(+) current were investigated by the patch clamp method. The rapidly (I(Kr)) and slowly activating delayed rectifier K(+) current (I(Ks)) were isolated using chromanol 293B, a selective blocker for I(Ks) or E4031 (N-[4-[[1-[2-(6-methyl-2-pyridinyl)ethyl]-4-piperidinyl]carbonyl]phenyl]methanesulfonamide dihydrochloride), a blocker for I(Kr). Sevoflurane and halothane decreased I(Ks) in a concentration-dependent manner with an IC(50) value of 0.38 mM for sevoflurane and 1.05 mM for halothane. I(Ks) inhibition was characterized by suppression of maximum conductance with little effect on activation kinetics. Inhibition occurred immediately after anesthetic application and recovered upon wash-out. In contrast to the marked inhibition of I(Ks), I(Kr) was hardly affected by sevoflurane. Under the current clamp, sevoflurane prolonged the action potential duration in a reversible manner and this effect was more marked when I(Kr) was inhibited by E4031. The results suggest that sevoflurane inhibits I(Ks), and not I(Kr), in a concentration-dependent manner at clinically relevant concentrations. The resulting prolongation of ventricular repolarization may partly account for the clinical observation of excessive QT prolongation by these anesthetics.

A new oral therapy for long QT syndrome

OBJECTIVES

We sought to determine whether oral potassium supplementation safely increases serum K(+) and results in sustained improvement of repolarization parameters in long QT syndrome type 2 (LQT2) subjects.

BACKGROUND

Mutations in HERG (LQT2), the gene encoding the rapid delayed rectifier K(+) current I(Kr), account for a significant proportion of congenital long QT syndrome (LQTS). The magnitude of I(Kr) is paradoxically increased by an increase in extracellular K(+). We tested the hypothesis that long-term oral potassium supplementation results in a mild, sustainable increase in serum K(+) that improves repolarization abnormalities in subjects with LQT2.

METHODS

After an initial evaluation consisting of electrocardiography, electrolytes, blood urea nitrogen, and creatinine, escalating doses of potassium chloride (KCl) and spironolactone were administered to eight subjects with six distinct HERG mutations. Medications were continued for four weeks, at which time, the final evaluation was undertaken. Beta-adrenergic blocking therapy was maintained.

RESULTS

The subjects ranged in age from 11 to 52 years. The average daily KCl and spironolactone dose was 3.3 +/- 1.5 mEq/kg and 3.5 +/- 1.2 mg/kg, respectively, and this regimen resulted in an increase in serum K(+) from 4.0 +/- 0.3 to 5.2 +/- 0.3 mEq/l. There were no serious complications associated with therapy. The increase in serum K(+) resulted in a decrease in the corrected QT interval from 526 +/- 94 to 423 +/- 36 ms (mean +/- SD; lead V(2)). Both QT dispersion and T-wave morphology improved in most subjects.

CONCLUSIONS

Long-term oral potassium administration increases serum K(+) in patients with LQT2. This can be achieved safely and results in improvement in repolarization. Further studies are warranted to determine whether this will reduce the incidence of life-threatening events in LQTS patients.

Structure of the HERG K+ channel S5P extracellular linker: role of an amphipathic alpha-helix in C-type inactivation

The HERG K+ channel has very unusual kinetic behavior that includes slow activation but rapid inactivation. These features are critical for normal cardiac repolarization as well as in preventing lethal ventricular arrhythmias. Mutagenesis studies have shown that the extracellular peptide linker joining the fifth transmembrane domain to the pore helix is critical for rapid inactivation of the HERG K+ channel. This peptide linker is also considerably longer in HERG K+ channels, 40 amino acids, than in most other voltage-gated K+ channels. In this study we show that a synthetic 42-residue peptide corresponding to this linker region of the HERG K+ channel does not have defined structural elements in aqueous solution; however, it displays two well defined helical regions when in the presence of SDS micelles. The helices correspond to Trp585-Ile593 and Gly604-Tyr611 of the channel. The Trp585-Ile593 helix has distinct hydrophilic and hydrophobic surfaces. The Gly604-Tyr611 helix corresponds to an N-terminal extension of the pore helix. Electrophysiological studies of HERG currents following application of exogenous S5P peptides show that the amphipathic helix in the S5P linker interacts with the pore region of the channel in a voltage-dependent manner.

Nicotine induces a long QT phenotype in Kcnq1-deficient mouse hearts

We have previously shown that targeted disruption of the mouse Kcnq1 gene produces a long QT phenotype in vivo that requires extracardiac factors for manifestation (Casimiro et al., 2001). In the present study, we explore the hypothesis that autonomic neuroeffector transmission represents the "extra cardiac" stimulus that induces a long QT phenotype in mouse hearts lacking Kcnq1. Using the isolated perfused (Langendorff) mouse heart preparation, we challenged wild-type (Kcnq1+/+) and mutant (Kcnq1-/-) mouse hearts with nicotine, an autonomic stimulant. ECGs were recorded continuously, and QT intervals were compared at baseline and peak nicotine-induced heart rates. No significant differences in QT or any other ECG parameters were observed in Kcnq1+/+ versus Kcnq1-/- hearts at baseline. In the presence of nicotine, however, the JT, QT, and rate-corrected QT (QTc) intervals were significantly prolonged in Kcnq1-/- hearts relative to Kcnq1+/+ hearts (e.g., QTc = 92 +/- 11 ms versus 66 +/- 2 ms, respectively, p < 0.01). Similar findings were obtained when the hearts were challenged with either epinephrine or isoproterenol (0.1 microM each), thereby suggesting that sympathetic stimulation drives the long QT phenotype in Kcnq1-deficient hearts. This idea is supported by in vivo ECG data obtained from unrestrained conscious mice using radiotelemetry recording techniques. Again, no significant ECG differences were observed in Kcnq1-/- versus Kcnq1+/+ mice at baseline, but handling/injection stress led to significant QTc increases in Kcnq1-/- mice relative to wild-type controls (11 +/- 3 versus -1 +/- 1%, respectively, p < 0.05). These data suggest that sympathetic stimulation induces a long QT phenotype in Kcnq1-deficient mouse hearts.

Ventricular repolarization components on the electrocardiogram: cellular basis and clinical significance

Ventricular repolarization components on the surface electrocardiogram (ECG) include J (Osborn) waves, ST-segments, and T- and U-waves, which dynamically change in morphology under various pathophysiologic conditions and play an important role in the development of ventricular arrhythmias. Our primary objective in this review is to identify the ionic and cellular basis for ventricular repolarization components on the body surface ECG under normal and pathologic conditions, including a discussion of their clinical significance. A specific attempt to combine typical clinical ECG tracings with transmembrane electrical recordings is made to illustrate their logical linkage. A transmural voltage gradient during initial ventricular repolarization, which results from the presence of a prominent transient outward K(+) current (I(to))-mediated action potential (AP) notch in the epicardium, but not endocardium, manifests as a J-wave on the ECG. The J-wave is associated with the early repolarization syndrome and Brugada syndrome. ST-segment elevation, as seen in Brugada syndrome and acute myocardial ischemia, cannot be fully explained by using the classic concept of an "injury current" that flows from injured to uninjured myocardium. Rather, ST-segment elevation may be largely secondary to a loss of the AP dome in the epicardium, but not endocardium. The T-wave is a symbol of transmural dispersion of repolarization. The R-on-T phenomenon (an extrasystole originating on the T-wave of a preceding ventricular beat) is probably due to transmural propagation of phase 2 re-entry or phase 2 early after depolarization that could potentially initiate polymorphic ventricular tachycardia or fibrillation.

Action potential changes associated with a slowed inactivation of cardiac voltage-gated sodium channels by KB130015

1. We have studied the acute cardiac electrophysiological effects of KB130015 (KB), a drug structurally related to amiodarone. Membrane currents and action potentials were measured at room temperature or at 37 degrees C during whole-cell patch-clamp recording in ventricular myocytes. Action potentials were also measured at 37 degrees C in multicellular ventricular preparations. 2. The effects of KB were compared with those of anemone toxin II (ATX-II). Both KB and ATX-II slowed the inactivation of the voltage-gated Na(+) current (I(Na)). While KB shifted the steady-state voltage-dependent inactivation to more negative potentials, ATX-II shifted it to more positive potentials. In addition, while inactivation proceeded to completion with KB, a noninactivating current was induced by ATX-II. 3. KB had no effect on I(K1) but decreased I(Ca-L) The drug also did not change I(to) in mouse myocytes. 4. The action potential duration (APD) in pig myocytes or multicellular preparations was not prolonged but often shortened by KB, while marked APD prolongation was obtained with ATX-II. Short APDs in mouse were markedly prolonged by KB, which frequently induced early afterdepolarizations. 5. A computer simulation confirmed that long action potentials with high plateau are relatively less sensitive to a mere slowing of I(Na) inactivation, not associated with a persisting, noninactivating current. In contrast, simulated short action potentials with marked phase-1 repolarization were markedly modified by slowing I(Na) inactivation. 6 It is suggested that a prolongation of short action potentials by drugs or mutations that only slow I(Na) inactivation does not necessarily imply identical changes in other species or in different myocardial regions.

Drug-induced Prolonged Repolarisation (Acquired Long QT Syndrome) Arrhythmias

Long QT Syndrome is a genetically determined disease of protein structures in the heart called ionic channels that control the flow of ions such as sodium, potassium and calcium, which produce the electrical activity of heart, depolarisation and repolarisation. Measurement of the QT interval on the electrocardiogram (ECG) can be quite difficult. Treatment of TdP due to ALQTS entails withdrawal of any precipitating agent, administration of MgSO(4) and potassium supplements. Correction of bradycardia is very important and temporary pacing may be necessary. If an antiarrhythmic agent is required after all the above, then lignocaine can be used.

Protein kinase C is necessary for recovery from the thyrotropin-releasing hormone-induced r-ERG current reduction in GH3 rat anterior pituitary cells

The biochemical cascade linking activation of phospholipase C-coupled thyrotropin-releasing hormone (TRH) receptors to rat ERG (r-ERG) channel modulation was studied in situ using perforated-patch clamped adenohypophysial GH3 cells and pharmacological inhibitors. To check the recent suggestion that Rho kinase is involved in the TRH-induced r-ERG current suppression, the hormonal effects were studied in cells pretreated with the Rho kinase inhibitors Y-27632 and HA-1077. The TRH-induced r-ERG inhibition was not significantly modified in the presence of the inhibitors. Surprisingly, the hormonal effects became irreversible in the presence of HA-1077 but not in the presence of the more potent Rho kinase inhibitor Y-27632. Further experiments indicated that the effect of HA-1077 correlated with its ability to inhibit protein kinase C (PKC). The hormonal effects also became irreversible in cells in which PKC activity was selectively impaired with GF109203X, Gö6976 or long-term incubation with phorbol esters. Furthermore, the reversal of the effects of TRH, but not its ability to suppress r-ERG currents, was blocked if diacylglycerol generation was prevented by blocking phospholipase C activity with U-73122. Our results suggest that a pathway involving an as yet unidentified protein kinase is the main cause of r-ERG inhibition in perforated-patch clamped GH3 cells. Furthermore, they demonstrate that although not necessary to trigger the ERG current reductions induced by TRH, an intracellular signal cascade involving phosphatidylinositol-4,5-bisphosphate hydrolysis by phospholipase C, activation of an alpha/betaII conventional PKC and one or more dephosphorylation steps catalysed by protein phosphatase 2A, mediates recovery of ERG currents following TRH withdrawal.

Long QT syndrome caused by noncardiac drugs

Numerous medications not intended for cardiac use (including antibiotics, histamine blockers, and antipsychotic medications) incidentally block potassium channels in myocardial cells, prolong the QT interval, and may trigger malignant arrhythmias. Although the odds for a given patient for developing arrhythmias are small, the number of patients receiving such drugs is enormous. Most patients developing proarrhythmia have additional risk factors that could be easily identified from their medical history. The list of risk factors includes female gender, organic heart disease, hypokalemia, and a history of long QT or drug-induced arrhythmias. Patients without risk factors are at very low risk. For these patients, it is neither practical nor necessary to record an electrocardiogram before therapy is initiated and the most important preventive measure is to avoid concurrent administration of 2 or more drugs that prolong the QT interval or administration of a medication that impairs the metabolism of a QT-prolonging drug. We performed a computerized literature search using the key words "long QT," "torsade," "drug-adverse effects," and "drug-ventricular arrhythmias," searching for published reports of drug-induced torsade de pointes. The references in each of these reports also were reviewed to identify additional publications. In addition, we reviewed the published reviews and the Internet sites dealing with drug-induced arrhythmias. All the original articles quoted in these reviews and Web sites were examined critically.

High Throughput Ion-Channel Pharmacology: Planar-Array-Based Voltage Clamp

Technological advances often drive major breakthroughs in biology. Examples include PCR, automated DNA sequencing, confocal/single photon microscopy, AFM, and voltage/patch-clamp methods. The patch-clamp method, first described nearly 30 years ago, was a major technical achievement that permitted voltage-clamp analysis (membrane potential control) of ion channels in most cells and revealed a role for channels in unimagined areas. Because of the high information content, voltage clamp is the best way to study ion-channel function; however, throughput is too low for drug screening. Here we describe a novel breakthrough planar-array-based HT patch-clamp technology developed by Essen Instruments capable of voltage-clamping thousands of cells per day. This technology provides greater than two orders of magnitude increase in throughput compared with the traditional voltage-clamp techniques. We have applied this method to study the hERG K(+) channel and to determine the pharmacological profile of QT prolonging drugs.

Deferoxamine promotes survival and prevents electrocardiographic abnormalities in the gerbil model of iron-overload cardiomyopathy

We investigated the time course of electrocardiographic (ECG) changes in the Mongolian gerbil model of iron overload and the effects of the iron chelator deferoxamine (DFO) on these changes. Iron overload was produced with weekly subcutaneous injections of low doses (200 mg/kg/wk) or high doses (800 mg/kg/wk) of iron-dextran. DFO was administered subcutaneously at a dose of 200 mg/kg/day to high-dose animals. Our results show that (1) survival of iron-overloaded gerbils is dose-dependent, with median survival times of 68 and 14 weeks for low- and high-dose animals, respectively; (2) both low and high doses produce prolongation of the PR interval and bradycardia in early stages and prolongation of the QT interval, premature ventricular contractions, variable degrees of atrioventricular block, changes in the ST segment, and T-wave inversion at later stages coinciding with the development of heart failure; (3) DFO prevented death during 20 weeks of high-dose iron-dextran; (4) DFO prevented ECG changes, although delayed prolongation of PR intervals and QRS complexes occurred; and (5) despite marked prolongation of survival and prevention of ECG changes, DFO had modest effects on total cardiac iron content. We speculate that DFO chelates a small iron pool located within the cytoplasm of iron-overloaded cardiomyocytes.

Genetic modifiers of cardiac arrhythmias

Rhythmic contraction of a four-chambered mammalian heart is a highly coordinated process, requiring a functional conduction system. Both acquired and inherited forms of arrhythmia can be life threatening, and are major causes of mortality and morbidity in developed nations. Knowledge derived from human genetics and from studies of mouse genetic models has led to the discovery of multiple molecular defects responsible for arrhythmogenesis, including mutations in ion channels, cytoplasmic ion-channel-interacting proteins, gap-junction proteins, transcription factors and, most recently, a kinase subunit. However, phenotypic expression of a given mutation does not always appear to be uniform in human patients, implying a contribution from environmental factors and/or the presence of other genetic modifiers. Accumulating evidence suggests that 'multiple hits' affecting the interaction and integrity of multiple pathways might be responsible for many forms of arrhythmia.

Long-term outcome in patients with Marfan syndrome: is aortic dissection the only cause of sudden death?

OBJECTIVES

We sought to assess outcomes in a series of young patients with Marfan syndrome and to define the prevalence of ventricular arrhythmias in this patient population.

BACKGROUND

While sudden death is a well-recognized outcome in Marfan syndrome, ventricular arrhythmias are not well described.

METHODS

Patients were followed with echocardiography, electrocardiography, and ambulatory electrocardiography. The prevalence and associated factors for ventricular dysrhythmias were defined.

RESULTS

Seventy patients with Marfan syndrome diagnosed at birth to 52 years were followed for a period of up to 24 years. All patients had cardiovascular involvement and were started on medical therapy. No patient died from aortic dissection, while 4% died from arrhythmias. Ventricular arrhythmias were present in 21% and were associated with increased left ventricular size, mitral valve prolapse, and abnormalities of repolarization.

CONCLUSIONS

Cardiac complications are rare in young patients with Marfan syndrome receiving medical therapy and close clinical follow-up. Sudden death still occurs, and appears more common in patients with a dilated left ventricle. Left ventricular dilation may predispose to alterations of repolarization and fatal ventricular arrhythmias.

Ca2+ entry-dependent inactivation of L-type Ca current: a novel formulation for cardiac action potential models

Cardiac L-type Ca current (I(Ca,L)) is controlled not only by voltage but also by Ca(2+)-dependent mechanisms. Precise implementation of I(Ca,L) in cardiac action potential models therefore requires thorough understanding of intracellular Ca(2+) dynamics, which is not yet available. Here, we present a novel formulation of I(Ca,L) for action potential models that does not explicitly require the knowledge of local intracellular Ca(2+) concentration ([Ca(2+)](i)). In this model, whereas I(Ca,L) is obtained as the product of voltage-dependent gating parameters (d and f), Ca(2+)-dependent inactivation parameters (f(Ca): f(Ca-entry) and f(Ca-SR)), and Goldman-Hodgkin-Katz current equation as in previous studies, f(Ca) is not a instantaneous function of [Ca(2+)](i) but is determined by two terms: onset of inactivation proportional to the influx of Ca(2+) and time-dependent recovery (dissociation). We evaluated the new I(Ca,L) subsystem in the framework of the standard cardiac action potential model. The new formulation produced a similar temporal profile of I(Ca,L) as the standard, but with different gating mechanisms. Ca(2+)-dependent inactivation gradually proceeded throughout the plateau phase, replacing the voltage-dependent inactivation parameter in the LRd model. In typical computations, f declined to approximately 0.7 and f(Ca-entry) to approximately 0.1, whereas deactivation caused fading of I(Ca,L) during final repolarization. These results support experimental findings that Ca(2+) entering through I(Ca,L) is essential for inactivation. After responses to standard voltage-clamp protocols were examined, the new model was applied to analyze the behavior of I(Ca,L) when action potential was prolonged by several maneuvers. Our study provides a basis for theoretical analysis of I(Ca,L) during action potentials, including the cases encountered in long QT syndromes.

Long QT syndrome: first and fatal events provoked by hemodialysis

Long QT syndrome (LQTS) involves both congenital and acquired predispositions toward the characteristic torsades de pointes (TP) ventricular arrhythmia. Congenital long QT syndrome generally manifests with TP, syncope, or sudden death early in life. This is a documented case of previously undiagnosed congenital LQTS in a 48-year-old woman where the first and fatal episodes of TP were provoked by hemodialysis.

Antipsychotic drugs and QT interval prolongation

The QTc prolongation by antipsychotic drugs is of major concern, especially in light of the data indicating an increased risk of sudden death in psychiatric patients taking these drugs. Sudden death in psychiatric patients could be partially attributed to drug-induced torsades de pointes and for this reason careful evaluation of QTc prolonging properties of antipsychotic drugs is needed. Antipsychotic drugs prolong QT interval usually by blocking the potassium IKr current. Improved understanding of ion channel structure and kinetics and its role in repolarization has tremendous impact on understanding of the mechanisms of drug-induced QT prolongation and torsades de pointes. Proarrhythmia caused by a QT-prolonging drug occurs infrequently, and usually multiple factors need to operate to precipitate such an event including a combination of two or more drugs affecting the same pathway, hypokalemia, and possibly genetic predisposition. Currently prescribed antipsychotics might cause QT prolongation ranging from 4-6 ms for haloperidol and olanzapine to 35 ms for thioridazine. The response of a patient to a drug is very individual and therefore an individualized system of drug administration and monitoring needs to be developed which takes into account baseline QTc duration and its changes after a drug was introduced. A systematic approach while stratifying psychiatric patients as those with short QTc (QTc < or = 0.41 sec), borderline QTc (QTC = 0.42-0.44 sec), and prolonged QTc (0.45 sec) is being proposed to improve the safety of administering antipsychotic drugs and to decrease the risk of drug-related sudden death in psychiatric patients.

Drug-induced long QT in isolated rabbit Purkinje fibers: importance of action potential duration, triangulation and early afterdepolarizations

In the present study, we investigated three drug-induced long-QT syndromes in isolated rabbit Purkinje fibers in order to identify the relationship of action potential duration (APD), triangulation of action potentials (APD(90)-APD(40)) and early afterdepolarizations. Isolated rabbit Purkinje fibers were superperfused in Tyrode solution with solvent, indapamide (1 x 10 (-4) M, an I(ks) blocker mimicking long QT1), dofetilide (1 x 10 (-9), 1 x 10 (-8) or 1 x 10 (-7) M, an I(kr) blocker mimicking long QT2) or anthopleurin (1 x 10 (-8) M, an inhibitor of the inactivation of the I(Na(+)) current mimicking long QT3) (n=8 per group) for 25 min, and stimulated at 1 Hz for 20 min and at 0.2 Hz for another 5 min. Indapamide did not change APD and triangulation or elicit early afterdepolarizations even in the presence of beta-adrenergic stimulation with isoproterenol. Dofetilide concentration-dependently prolonged APD(90), increased triangulation and elicited early afterdepolarizations. Anthopleurin markedly increased APD(90) as well as triangulation and elicited early afterdepolarizations. The induction of early afterdepolarizations by dofetilide and anthopleurin was associated with a prolongation of APD(90) or an increase in triangulation, but not with a change in APD(40). Moreover, the degree of the increase in the triangulation was larger than that of APD(90) in long QT2 (dofetilide-induced) and long QT3 (anthopleurin-induced) models in isolated rabbit Purkinje fibers. Our present study indicates that rabbit Purkinje fibers can be used as long QT2 (dofetilide-mimicking) and LQT3 (anthopleurin-mimicking) syndrome models, and confirms that drug-induced long QT1 (indapamide-mimicking) is absent. Our present study also shows the relationship between a prolongation of APD(90) or increase in triangulation and the induction of early afterdepolarizations with dofetilide (I(kr) blocker) and anthopleurin (I(Na) modulator) in isolated rabbit Purkinje fibers.

Safety of non-antiarrhythmic drugs that prolong the QT interval or induce torsade de pointes: an overview

The long and growing list of non-antiarrhythmic drugs associated with prolongation of the QT interval of the electrocardiogram has generated concern not only for regulatory interventions leading to drug withdrawal, but also for the unjustified view that QT prolongation is usually an intrinsic effect of a whole therapeutic class [e.g. histamine H(1) receptor antagonists (antihistamines)], whereas, in many cases, it is displayed only by some compounds within a given class of non-antiarrhythmic drugs because of an effect on cardiac repolarisation. We provide an overview of the different classes of non-antiarrhythmic drugs reported to prolong the QT interval (e.g. antihistamines, antipsychotics, antidepressants and macrolides) and discusses the clinical relevance of the QT prolonging effect. Drug-induced torsade de pointes are sometimes considered idiosyncratic, totally unpredictable adverse drug reactions, whereas a number of risk factors for their occurrence is now recognised. Widespread knowledge of these risk factors and implementation of a comprehensive list of QT prolonging drugs becomes an important issue. Risk factors include congenital long QT syndrome, clinically significant bradycardia or heart disease, electrolyte imbalance (especially hypokalaemia, hypomagnesaemia, hypocalcaemia), impaired hepatic/renal function, concomitant treatment with other drugs with known potential for pharmacokinetic/pharmacodynamic interactions (e.g. azole antifungals, macrolide antibacterials and class I or III antiarrhythmic agents). This review provides insight into the strategies that should be followed during a drug development program when a drug is suspected to affect the QT interval. The factors limiting the predictive value of preclinical and clinical studies are also outlined. The sensitivity of preclinical tests (i.e. their ability to label as positive those drugs with a real risk of inducing QT pronglation in humans) is sufficiently good, but their specificity (i.e. their ability to label as negative those drugs carrying no risk) is not well established. Verapamil is a notable example of a false positive: it blocks human ether-a-go-go-related (HERG) K(+) channels, but is reported to have little potential to trigger torsade de pointes. Although inhibition of HERG K(+) channels has been proposed as a primary test for screening purposes, it is important to remember that several ion currents are involved in the generation of the cardiac potential and that metabolites must be specifically tested in this in vitro test. At the present state of knowledge, no preclinical model has an absolute predictive value or can be considered as a gold standard. Therefore, the use of several models facilitates decision making and is recommended by most experts in the field.

Prolongation of cardiac repolarization by arsenic trioxide

Arsenic trioxide (As(2)O(3); ATO) has recently been found to be very effective for relapsed acute promyelocytic leukemia. Several articles reported prolongation of QT interval or ventricular arrhythmias in patients receiving ATO. However, the QT-prolonging effect has not been confirmed and the direct membrane effect of ATO has never been studied. In the present investigation, using conventional action potential recording technique, we found that ATO dose dependently prolonged action potential duration (APD) in guinea pig papillary muscle with a slow pacing frequency. Parenteral administration of ATO prolonged QT interval and APD in guinea pig hearts. Intravenous infusion of clinically relevant doses of ATO prolonged QT interval and APD dose dependently. These studies suggest that ATO has a direct effect on cardiac repolarization. Patients who are receiving ATO should avoid concomitant administration of other QT-prolonging agents or conditions in favor of delaying cardiac repolarization.

Enhancement of closed-state inactivation in long QT syndrome sodium channel mutation DeltaKPQ

DeltaKPQ, a three amino acid [lysine (K), proline (P), glutamine (Q)] deletion mutation of the human cardiac Na channel (hH1), which is one cause of long QT syndrome (LQT3), has impaired inactivation resulting in a late sodium current. To better understand inactivation in DeltaKPQ, we applied a site-3 toxin anthopleurin A, which has been shown to inhibit inactivation from the open state with little or no effect on inactivation from the closed state(s) in wild-type hH1. In contrast to the effect of site-3 toxins on wild-type hH1, inactivation from closed state(s) in toxin-modified DeltaKPQ demonstrated a large negative shift in the Na channel availability curve of nearly -14 mV. Recovery from inactivation showed that toxin-modified DeltaKPQ channels recovered slightly faster than those in control, whereas development of inactivation at potentials negative to -80 mV showed that inactivation developed much more rapidly in toxin-modified DeltaKPQ channels compared with control. An explanation for our results is that closed-state inactivation in toxin-modified DeltaKPQ is enhanced by the mutated inactivation lid being positioned "closer" to its receptor resulting in an increased rate of association between the inactivation lid and its receptor.

Increasing I(Ks) corrects abnormal repolarization in rabbit models of acquired LQT2 and ventricular hypertrophy

Excessive action potential (AP) prolongation and early afterdepolarizations (EAD) are triggers of malignant ventricular arrhythmias. A slowly activating delayed rectifier K+ current (I(Ks)) is important for repolarization of ventricular AP. We examined the effects of I(Ks) activation by a new benzodiazepine (L3) on the AP of control, dofetilide-treated, and hypertrophied rabbit ventricular myocytes. In both control and hypertrophied myocytes, L3 activated I(Ks) via a negative shift in the voltage dependence of activation and a slowing of deactivation. L3 had no effect on L-type Ca(2+) current or other cardiac K+ currents tested. L3 shortened AP of control, dofetilide-treated, and hypertrophied myocytes more at 0.5 than 2 Hz. Selective activation of I(Ks) by L3 attenuates prolonged AP and eliminated EAD induced by rapidly activating delayed rectifier K+ current inhibition in control myocytes at 0.5 Hz and spontaneous EAD in hypertrophied myocytes at 0.2 Hz. Pharmacological activation of I(Ks) is a promising new strategy to suppress arrhythmias resulting from excessive AP prolongation in patients with certain forms of long QT syndrome or cardiac hypertrophy and failure.

14-3-3 amplifies and prolongs adrenergic stimulation of HERG K+ channel activity

Acute stress provokes lethal cardiac arrhythmias in the hereditary long QT syndrome. Here we provide a novel molecular mechanism linking beta-adrenergic signaling and altered human ether-a-go-go related gene (HERG) channel activity. Stress stimulates beta-adrenergic receptors, leading to cAMP elevations that can regulate HERG K+ channels both directly and via phosphorylation by cAMP-dependent protein kinase (PKA). We show that HERG associates with 14-3-3epsilon to potentiate cAMP/PKA effects upon HERG. The binding of 14-3-3 occurs simultaneously at the N- and C-termini of the HERG channel. 14-3-3 accelerates and enhances HERG activation, an effect that requires PKA phosphorylation of HERG and dimerization of 14-3-3. The interaction also stabilizes the lifetime of the PKA-phosphorylated state of the channel by shielding the phosphates from cellular phosphatases. The net result is a prolongation of the effect of adrenergic stimulation upon HERG activity. Thus, 14-3-3 interactions with HERG may provide a unique mechanism for plasticity in the control of membrane excitability and cardiac rhythm.

Effects of glucose-induced insulin secretion on ventricular repolarization in patients with congenital long QT syndrome

To assess the role of insulin in ventricular repolarization in patients with congenital long QT syndrome (LQTS), an oral glucose tolerance (OGT) test was performed in 11 patients with LQTS and in 11 control cases without QT prolongation. Plasma glucose, potassium level and the immunoreactive insulin concentration (IRI) were measured, and the QT interval and T wave morphology on 12-lead ECG were analyzed during fasting and after glucose load. The LQTS group had a higher incidence of changes in T wave morphology, such as biphasic, bifid or notched T wave, after glucose load than the control group (11 of 11 patients [100%] vs 0 of 11 [0%]; p<0.00001). The T wave changes returned to baseline at 180 min after glucose load in 7 patients. The maximal QT interval and QT dispersion increased significantly and returned to baseline level in response to IRI after glucose load in LQTS, whereas the QT interval was unaffected in the control group. After glucose load, ventricular arrhythmias and T wave alternans were observed in 3 and 1 patients with LQTS, respectively, but none in the control group. The findings suggest that glucose-induced insulin secretion plays a role in inducing abnormalities and inhomogeneity of ventricular repolarization in patients with LQTS.

Molecular mechanisms underlying the long QT syndrome

Recent studies of the molecular basis of the long QT syndrome (LQTS) have advanced our understanding of the mechanisms responsible for the abnormal prolongation of ventricular repolarization and revealed associations between LQTS and other primary electrical diseases of the heart such as Brugada syndrome. The role of DNA single nucleotide polymorphisms in acquired LQTS and differences between the Romano-Ward and Jervell-Lange-Nielsen forms of congenital LQTS are gradually coming into focus. In this brief review, our goal is to summarize the molecular mechanisms proposed to underlie the susceptibility to arrhythmias in LQTS and discuss the direction of current and future research.

Causes of death in autism

The objective of this study was to determine which causes of death are more frequent in persons with autism, and by how much, compared with the general population. Subjects were 13,111 ambulatory Californians with autism, followed between 1983 and 1997. The units of study were person-years, each linked to the subject's age, sex, and cause of death (if any) for the specific year. Observed numbers of cause-specific deaths were compared with numbers expected according to general population mortality rates. Standardized mortality rates (SMRs) were computed for each mental retardation level. Elevated death rates were observed for several causes, including seizures and accidents such as suffocation and drowning; elevated mortality due to respiratory disease was observed among persons with severe mental retardation. Overall, excess mortality was especially marked for persons with severe mental retardation, but life expectancy is reduced even for persons who are fully ambulatory and who have only mild mental retardation.

Should all implantable cardioverter defibrillators for ventricular arrhythmias be dual-chamber devices?

The advantages of a dual-chamber implantable cardioverter defibrillator (ICD) over a single-chamber ICD include physiologic pacing capability, atrial electrogram storage, enhanced arrhythmia discrimination algorithms, and a potential to treat atrial arrhythmia by pacing or defibrillation. Current evidence supports the supposition that dual-chamber ICDs are definitely indicated in patients who have a concomitant indication for physiologic pacing, such as bradycardia or bradycardia-dependent ventricular tachyarrhythmias. Refined dual-chamber arrhythmia discrimination algorithms and enhanced atrial therapies are probably required for patients with frequent supraventricular arrhythmias. Furthermore, in patients with systolic heart failure, low ejection fraction, and intraventricular conduction delay, triple-chamber ICDs with biventricular pacing may improve their functional status and prevent sudden arrhythmic death. Careful patient selection is required to optimize the cost-effectiveness of these sophisticated technologies.

Ventricular hypertrophy amplifies transmural repolarization dispersion and induces early afterdepolarization

The effects of left ventricular hypertrophy (LVH) on the generation of phase 2 early afterdepolarization (EAD) and transmural dispersion of repolarization (TDR) were assessed using arterially perfused rabbit ventricular wedge preparations. Transmembrane action potentials from epicardium, subendocardium, and endocardium were simultaneously recorded together with a transmural ECG. Transmural action potential duration (APD) was also mapped. LVH (renovascular hypertension model) produced significant prolongation in ventricular APD and QT interval. Preferential APD prolongation in subendocardium and endocardium was associated with a marked increase in TDR. Phase 2 EADs were generated from subendocardium or endocardium in all LVH rabbits (15 of 15) in the absence of APD prolonging agents at basic cycle lengths of 2,000-4,000 ms. Phase 2 EAD could produce "R on T" extrasystoles, initiating polymorphic ventricular tachycardia (VT). This study provides the first direct evidence from intracellular recordings that phase 2 EAD could be generated from rabbit intact hypertrophied LV wall in the absence of APD prolonging agents, resulting in R on T extrasystoles capable of initiating polymorphic VT under enhanced TDR.

De novo mutation in the SCN5A gene associated with early onset of sudden infant death

BACKGROUND

Congenital long QT syndrome (LQTS), a cardiac ion channel disease, is an important cause of sudden cardiac death. Prolongation of the QT interval has recently been associated with sudden infant death syndrome, which is the leading cause of death among infants between 1 week and 1 year of age. Available data suggest that early onset of congenital LQTS may contribute to premature sudden cardiac death in otherwise healthy infants.

METHODS AND RESULTS

In an infant who died suddenly at the age of 9 weeks, we performed mutation screening in all known LQTS genes. In the surface ECG soon after birth, a prolonged QTc interval (600 ms(1/2)) and polymorphic ventricular tachyarrhythmias were documented. Mutational analysis identified a missense mutation (Ala1330Pro) in the cardiac sodium channel gene SCN5A, which was absent in both parents. Subsequent genetic testing confirmed paternity, thus suggesting a de novo origin. Voltage-clamp recordings of recombinant A1330P mutant channel expressed in HEK-293 cells showed a positive shift in voltage dependence of inactivation, a slowing of the time course of inactivation, and a faster recovery from inactivation.

CONCLUSIONS

In this study, we report a de novo mutation in the sodium channel gene SCN5A, which is associated with sudden infant death. The altered functional characteristics of the mutant channel was different from previously reported LQTS3 mutants and caused a delay in final repolarization. Even in families without a history of LQTS, de novo mutations in cardiac ion channel genes may lead to sudden cardiac death in very young infants.

Loss of the potassium channel beta-subunit gene, KCNAB2, is associated with epilepsy in patients with 1p36 deletion syndrome

PURPOSE

Clinical features associated with chromosome 1p36 deletion include characteristic craniofacial abnormalities, mental retardation, and epilepsy. The presence and severity of specific phenotypic features are likely to be correlated with loss of a distinct complement of genes in each patient. We hypothesize that hemizygous deletion of one, or a few, critical gene(s) controlling neuronal excitability is associated with the epilepsy phenotype. Because ion channels are important determinants of seizure susceptibility and the voltage-gated K(+) channel beta-subunit gene, KCNAB2, has been localized to 1p36, we propose that deletion of this gene may be associated with the epilepsy phenotype.

METHODS

Twenty-four patients were evaluated by fluorescence in situ hybridization with a probe containing KCNAB2. Clinical details were obtained by neurologic examination and EEG.

RESULTS

Nine patients are deleted for the KCNAB2 locus, and eight (89%) of these have epilepsy or epileptiform activity on EEG. The majority of patients have a severe seizure phenotype, including infantile spasms. In contrast, of those not deleted for KCNAB2, only 27% have chronic seizures, and none had infantile spasms.

CONCLUSIONS

Lack of the beta subunit would be predicted to reduce K(+) channel-mediated membrane repolarization and increase neuronal excitability, suggesting a possible relation between loss of this gene and the development of seizures. Because some patients with seizures were not deleted for KCNAB2, there may be additional genes within 1p36 that contribute to epilepsy in this syndrome. Hemizygosity of this gene in a majority of monosomy 1p36 syndrome patients with epilepsy suggests that haploinsufficiency for KCNAB2 is a significant risk factor for epilepsy.

Characterization of mice with a combined suppression of I(to) and I(K,slow)

Cardiac-specific expression of a truncated Kv1.1 polypeptide (Kv1DN) attenuates the slow inactivating outward K(+) current (I(K,slow)), increases action potential duration (APD) and Q-T intervals, and induces spontaneous ventricular arrhythmias. Expression of the pore mutant of Kv4.2 (Kv4DN) eliminates the fast component of the transient outward current (I(to)) and prolongs APDs and Q-T intervals markedly; however, no arrhythmias are seen in Kv4DN mice, suggesting that APD and Q-T prolongation are not per se proarrhythmic. To test this hypothesis, the Kv1DN and Kv4DN lines were crossbred to produce animals (Kv1/Kv4DN) expressing both transgenes in an identical genetic background. Whole cell voltage-clamp recordings from left ventricular apex cells confirmed that in Kv1/Kv4DN left ventricular apex cells, both components (fast and slow) of I(to) and the 4-aminopyridine-sensitive component of I(K,slow) are eliminated, resulting in marked APD prolongation compared with wild-type, Kv1DN, or Kv4DN cells. Telemetric electrocardiogram monitoring (n = 10 mice/group) revealed a significant prolongation of Q-Tc and P-R intervals in Kv1/Kv4DN animals compared with Kv1DN or Kv4DN animals. Spontaneous arrhythmias were observed mainly in Kv1DN mice. Thus the attenuation of fast I(to) in addition to I(K,slow) in Kv1/Kv4DN mice causes significant prolongation of APD and Q-T intervals and attenuation of spontaneous arrhythmias.

Evaluation and treatment of syncope in infants

Syncope in the infant and newborn occurs as a loss of consciousness due to a variety of etiologies. Because syncope at this age may be a harbinger of sudden infant death, the symptom provokes anxiety and challenges clinicians to identify those babies with an increased risk for life threatening events. Recently introduced diagnostic tests and advances in molecular biology offer promising potential, but the population at risk remains unknown. Controversy surrounds: many potential risk factors; the value of home monitoring; and appropriate preventive and therapeutic strategies. This article reviews the differential diagnosis of syncope in children less than 18 months of age, with particular attention to those diagnoses and problems specific to the evaluation and treatment in this age group. Recommendations are presented for an efficient evaluation, which must include a careful history, complete physical examination and thorough investigation of the family history and home environment. In addition, specific diagnostic tests and a practical approach to treatment are suggested.

Irritable bowel syndrome: new agents targeting serotonin receptor subtypes

Although the past few years have seen an exponential growth of compounds of potential interest for the treatment of functional gastrointestinal (GI) tract disorders, the gap that still exists between basic and clinical research is easily noticed if one considers the relative paucity of drugs that have received marketing authorisation for the treatment of irritable bowel syndrome (IBS). Traditional efficacy outcomes in drug development for IBS include the ability of the compound to affect GI tract motility (i.e. to exert a prokinetic or an antispasmodic effect), which is thought to be of importance if a motor disorder is the underlying pathophysiological mechanism. More recently, altered visceral sensitivity to a distending stimulus has been suggested to be a key pathophysiological feature, at least in some patients, and has become a target for therapeutic interventions. However, there is now growing consensus that the primary outcome measure in the treatment of functional disorders are those that reflect overall control of the patient's symptoms (pain, diarrhoea, constipation) in everyday situations such as the clinical global improvement scales. Although, in general, guidelines on the design of treatment trials for functional GI tract disorders advise against subcategorisation of patients according to the main symptom (because of symptom instability), subcategorisation indeed makes sense especially in IBS (constipation- or diarrhoea-predominant). Compounds with a specific indication for each subpopulation of patients are now emerging. The rationale for investigations on serotonin (5-hydroxytryptamine; 5-HT) receptor ligands in IBS rests mainly on the fact that serotonin, which may be released by enterochromaffin-like cells in the GI tract as well as from other sources, has a number of well documented motor effects on the GI tract and can produce hyperalgesia in several experimental models. Serotonin receptors belonging to the 5-HT3 and 5-HT4 subtype are the most extensively studied in gastroenterology, although hitherto 'orphan' receptor subtypes, such as the 5-HT7 and the 5-HT(1B/D) receptors, are now emerging. Among 5-HT3 receptor antagonists, alosetron was recently approved for the treatment of diarrhoea-predominant IBS and is an example of a compound that, at least theoretically, may act at multiple levels: by inhibiting visceral sensitivity, by increasing compliance, and by inhibiting excitatory 5-HT3 receptors located on both ascending and descending neuronal pathways involved in peristalsis. For this reason, 5-HT3 receptor antagonists may slow transit, hence the specific indication of alosetron in diarrhoea-predominant IBS. However, alosetron has been recently withdrawn by the manufacturer because of safety concerns. Hypomotility remains an attractive therapeutic target in IBS and the new generation of prokinetics includes several partial agonists at the 5-HT4 receptor, such as tegaserod (HTF-919) and prucalopride (R0-93877). In addition, preliminary evidence suggests that 5-HT4 receptors may also be involved in the modulation of visceral sensitivity. Second-generation 5-HT4 receptor agonists seem to be devoid of the QT-prolonging effects observed in some clinical circumstances with cisapride and may be more active at the colonic level. Piboserod (SB-207266A) is a 5-HT4 receptor antagonist under development for the treatment of diarrhoea-predominant IBS. Finally, interest in 5-HT7 and 5-HT(1B/D) receptor subtypes stems from the observation that the former receptors mediate smooth muscle relaxation (at least in the human colon), whereas sumatriptan (a 5-HT(1B/D) receptor agonist) can affect GI tract motility and visceral sensitivity.

Phase 2 early afterdepolarization as a trigger of polymorphic ventricular tachycardia in acquired long-QT syndrome : direct evidence from intracellular recordings in the intact left ventricular wall

BACKGROUND

This study examined the role of phase 2 early afterdepolarization (EAD) in producing a trigger to initiate torsade de pointes (TdP) with QT prolongation induced by dl-sotalol and azimilide. The contribution of transmural dispersion of repolarization (TDR) to transmural propagation of EAD and the maintenance of TdP was also evaluated.

METHODS AND RESULTS

Transmembrane action potentials from epicardium, midmyocardium, and endocardium were recorded simultaneously, together with a transmural ECG, in arterially perfused canine and rabbit left ventricular preparations. dl-Sotalol preferentially prolonged action potential duration (APD) in M cells dose-dependently (1 to 100 micromol/L), leading to QT prolongation and an increase in TDR. Azimilide, however, significantly prolonged APD and QT interval at concentrations from 0.1 to 10 micromol/L but shortened them at 30 micromol/L. Unlike dl-sotalol, azimilide (>3 micromol/L) increased epicardial APD markedly, causing a diminished TDR. Although both dl-sotalol and azimilide rarely induced EADs in canine left ventricles, they produced frequent EADs in rabbits, in which more pronounced QT prolongation was seen. An increase in TDR by dl-sotalol facilitated transmural propagation of EADs that initiated multiple episodes of spontaneous TdP in 3 of 6 rabbit left ventricles. Of note, although azimilide (3 to 10 micromol/L) increased APD more than dl-sotalol, its EADs often failed to propagate transmurally, probably because of a diminished TDR.

CONCLUSIONS

This study provides the first direct evidence from intracellular action potential recordings that phase 2 EAD can be generated from intact ventricular wall and produce a trigger to initiate the onset of TdP under QT prolongation.

[Congenital long QT syndrome]

Long QT syndrome (LQTS) is a clinically and genetically heterogenous syndrome characterized by a lengthening of the QT interval on the surface ECG and a propensity to severe ventricular arrhythmias such as torsades de pointes and ventricular fibrillation, leading eventually to syncope and sudden death. This rare syndrome with a mendelian inheritance occurs in subjects with otherwise normal cardiac morphological examination. The potentially severe prognosis justifies a presymptomatic diagnosis. The genetic nature of the disease has been confirmed with the identification of at least six loci and five genes. This syndrome is a perfect illustration of an adrenergic-induced ventricular arrhythmia. The first-line treatment is a beta-blocking agent for all symptomatic patients. In addition, a number of drugs known to lengthen ventricular repolarization must be prohibited. In case of suspicion of LQTS, all family members should be tested both clinically with a surface ECG and genetically in order to diagnose presymptomatic patients.

HERG K+ channels: friend and foe

The K+ channel encoded by the human ether-à-go-go related gene (HERG) is one of many ion channels that are crucial for normal action potential repolarization in cardiac myocytes. HERG encodes the pore-forming subunit of the rapid component of the delayed rectifier K+ channel, I(K(Vr)). HERG K+ channels are of considerable pharmaceutical interest as possible therapeutic targets for anti-arrhythmic agents and as the molecular target responsible for the cardiac toxicity of a wide range of pharmaceutical agents. Recent studies of the molecular basis of the promiscuity of HERG K+ channel drug binding has not only started to shed light on this tricky pharmaceutical problem but has also provided further insights into the structure and function of HERG K+ channels.

Advances in cardiac electrophysiology and pacing

Significant advances have been made in the management of cardiac arrhythmias. New technology has enhanced the ability to understand and treat a variety of tachycardias. Excitement and caution surround ablative approaches for atrial fibrillation. The role of ICDs and class III antiarrhythmic drugs in the management of patients at risk for sudden cardiac death has been clarified. A new indication for cardiac pacing is evolving as a supplemental treatment for patients with refractory congestive heart failure. These and other advances provide numerous exciting options for management of cardiac patients.

Mutations of the cardiac ryanodine receptor (RyR2) gene in familial polymorphic ventricular tachycardia

BACKGROUND

Familial polymorphic ventricular tachycardia is an autosomal-dominant, inherited disease with a relatively early onset and a mortality rate of approximately 30% by the age of 30 years. Phenotypically, it is characterized by salvoes of bidirectional and polymorphic ventricular tachycardias in response to vigorous exercise, with no structural evidence of myocardial disease. We previously mapped the causative gene to chromosome 1q42-q43. In the present study, we demonstrate that patients with familial polymorphic ventricular tachycardia have missense mutations in the cardiac sarcoplasmic reticulum calcium release channel (ryanodine receptor type 2 [RyR2]).

METHODS AND RESULTS

In 3 large families studied, 3 different RyR2 mutations (P2328S, Q4201R, V4653F) were detected and shown to fully cosegregate with the characteristic arrhythmic phenotype. These mutations were absent in the nonaffected family members and in 100 healthy controls. In addition to identifying 3 causative mutations, we identified a number of single nucleotide polymorphisms that span the genomic structure of RyR2 and will be useful for candidate-based association studies for other arrhythmic disorders.

CONCLUSIONS

Our data illustrate that mutations of the RyR2 gene cause at least one variety of inherited polymorphic tachycardia. These findings define a new entity of disorders of myocardial calcium signaling.

Etiology and management of sustained ventricular tachycardia

Ventricular tachyarrhythmias secondary to a variety of underlying cardiovascular problems pose a therapeutic challenge to the clinician. The initial presentation may be as sudden cardiac death, which underlies its public health problem. The underlying conditions predisposing to this arrhythmia include ischemic heart disease, dilated cardiomyopathy, hypertrophic cardiomyopathy, arrhythmiogenic right ventricle dysplasia and certain postoperative states including corrective surgery for tetralogy of Fallot and valve replacement. Other causes include prolonged QT syndrome, idiopathic right and left ventricle tachycardia and bundle branch re-entry tachycardia. Ischaemic heart disease is the most common cause of ventricular tachycardia and therapy has evolved considerably over the past two decades. The development of and refinements in the implantable cardioverter-defibrillator (ICD) have introduced a new dimension in therapeutic options and markedly improved survival in these patients. Insights in the dichotomy between arrhythmia suppression and total mortality have reoriented drug therapy with a decrease in the use of sodium channel blockers. beta-blockers have emerged as antiarrhythmic drugs in their own right and their synergistic effects with amiodarone have strengthened the antiarrhythmic drug arm. The role of these drugs in patients with hemodynamically stable ventricular tachycardia, especially in relatively preserved ventricles needs to be explored. Catheter ablation techniques have provided curative therapy in patients with idiopathic and bundle branch reentry tachycardia. Further advances in radiofrequency ablation, including use of newer mapping techniques, promise a greater role for ablation of ischemic ventricular tachycardia in the future. A hybrid approach consisting of drugs, catheter ablation and/ or ICD may provide effective therapeutic approach in some situations. Further innovations and technologic developments promise a further reorientation in therapy towards identification and treatment of the underlying arrhythmogenic substrate.