Torsade de pointes and T-U wave alternans associated with arsenic poisoning

Arsenic trioxide for acute promyelocytic leukemia in a patient on chronic hemodialysis

Acute promyelocytic leukemia (APL) is a rare acute leukemia generally considered curable with all-trans retinoic acid (ATRA) and arsenic trioxide (ATO). Some patients have co-morbidities that may limit the use of these agents and therefore impact curability. Adverse effects of ATO include life-threatening electrocardiographic abnormalities. ATO and its metabolites are partially excreted in the urine, and it is unclear to what extent ATO pharmacokinetics are impacted by hemodialysis. We present a patient on chronic hemodialysis successfully treated with ATO and ATRA for newly diagnosed APL. Complete molecular remission was achieved after induction and several drug-related toxicities were managed.

Management of QT prolongation induced by anti-cancer drugs: Target therapy and old agents. Different algorithms for different drugs

The side effects of anticancer drugs still play a critical role in survival and quality of life. Although the recent progresses of cancer therapies have significantly improved the prognosis of oncologic patients, side effects of antineoplastic treatments are still responsible for the increased mortality of cancer survivors. Cardiovascular toxicity is the most dangerous adverse effect induced by anticancer therapies. A survey conducted by the National Health and Nutrition Examination, showed that 1807 cancer survivors followed up for seven years: 51% died of cancer and 33% of heart disease (Vejpongsa and Yeh, 2014). Moreover, the risk of cardiotoxicity persists even with the targeted therapy, the newer type of cancer treatment, due to the presence of on-target and off-target effects related to this new class of drugs. The potential cardiovascular toxicity of anticancer agents includes: QT prolongation, arrhythmias, myocardial ischemia, stroke, hypertension (HTN), thromboembolism, left ventricular dysfunction and heart failure (HF). Compared to other cardiovascular disorders, the interest in QT prolongation and its complications is fairly recent. However, oncologists have to deal with it and to evaluate the risk-benefit ratio before starting the treatment or during the same. Electrolyte abnormalities, low levels of serum potassium and several drugs may favour the acquired QT prolongation. Treatment of marked QT prolongation includes cardiac monitoring, caution in the use or suspension of cancer drugs and correction of electrolyte abnormalities (hypokalaemia, hypomagnesaemia, hypocalcaemia). Syndrome of QT prolongation can be associated with potentially fatal cardiac arrhythmias and its treatment consists of intravenous administration of magnesium sulphate and the use of electrical cardioversion.

Calcium homeostasis and endoplasmic reticulum stress are involved in Salvianolic acid B-offered protection against cardiac toxicity of arsenic trioxide

Arsenic trioxide (ATO) is a potent anticancer agent used to treat acute promyelocytic leukemia. However, its cardiotoxicity limits ATO’s widespread clinical use. Previous studies demonstrated that ATO may aggravate Ca²⁺ overload and promote endoplasmic reticulum stress (ERS). Salvianolic acid B (Sal B) is cardioprotective against ATO and enhances ATO’s anticancer activities. The present study assessed whether the Sal B protective effect was related to maintenance of Ca²⁺ homeostasis and inhibition of ER stress. Male BALB/c mice were injected with ATO or ATO+Sal B once a day via the tail vein for 2 weeks. We then detected the effects of Sal B in real time using adult rat ventricular cardiomyocytes in vitro using an IonOptix MyoCam system. Sal B treatment alleviated ATO-induced abnormal cardiac contractions and Ca²⁺ homeostasis imbalance. Sal B increased sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) activity, regulated Ca²⁺ handling protein expression, and decreased expression of ERS proteins. Our results demonstrate that the cardioprotective effect of Sal B correlates with SERCA modulation, maintenance of Ca²⁺ homeostasis, and inhibition of ER stress. These findings suggest Sal B may ameliorate ATO cardiotoxicity during clinical application.

Drug-induced Inhibition and Trafficking Disruption of ion Channels: Pathogenesis of QT Abnormalities and Drug-induced Fatal Arrhythmias

Risk of severe and fatal ventricular arrhythmias, presenting as Torsade de Pointes (TdP), is increased in congenital and acquired forms of long QT syndromes (LQTS). Drug-induced inhibition of K+ currents, IKs, IKr, IK1, and/or Ito, delay repolarization, prolong QT, and increase the risk of TdP. Drug-induced interference with IKr is the most common cause of acquired LQTS/TdP. Multiple drugs bind to KNCH2-hERG-K+ channels affecting IKr, including antiarrythmics, antibiotics, antivirals, azole-antifungals, antimalarials, anticancer, antiemetics, prokinetics, antipsychotics, and antidepressants. Azithromycin has been recently added to this list. In addition to direct channel inhibition, some drugs interfere with the traffic of channels from the endoplasmic reticulum to the cell membrane, decreasing mature channel membrane density; e.g., pentamidine, geldalamicin, arsenic trioxide, digoxin, and probucol. Other drugs, such as ketoconazole, fluoxetine, norfluoxetine, citalopram, escitalopram, donepezil, tamoxifen, endoxifen, atazanavir, and roxitromycin, induce both direct channel inhibition and impaired channel trafficking. Although many drugs prolong the QT interval, TdP is a rare event. The following conditions increase the risk of drug-induced TdP: a) Disease states/electrolyte levels (heart failure, structural cardiac disease, bradycardia, hypokalemia); b) Pharmacogenomic variables (presence of congenital LQTS, subclinical ion-channel mutations, history of or having a relative with history of drug-induced long QT/TdP); c) Pharmacodynamic and kinetic factors (high doses, women, elderly, metabolism inhibitors, combining two or more QT prolonging drugs, drugs that prolong the QT and increase QT dispersion, and drugs with multiple actions on ion channels). Because most of these conditions are preventable, careful evaluation of risk factors and increased knowledge of drug use associated with repolarization abnormalities are strongly recommended.

Cardiovascular disease and arsenic exposure in Inner Mongolia, China: a case control study

BACKGROUND

Millions of people are at risk from the adverse effects of arsenic exposure through drinking water. Increasingly, non-cancer effects such as cardiovascular disease have been associated with drinking water arsenic exposures. However, most studies have been conducted in highly exposed populations and lacked individual measurements.

OBJECTIVE

To evaluate the association between cardiovascular disease and well-water arsenic exposure.

METHODS

We conducted a hospital based case control study in Inner Mongolia, China. Cases and controls were prospectively identified and enrolled from a large hospital in the Hangjin Hou area. Cases were patients diagnosed with cardiovascular disease and controls were patients free from cardiovascular disease, admitted for conditions unrelated to arsenic exposure. Water from the primary water source and toenail samples were collected from each subject and tested for inorganic arsenic.

RESULTS

Arsenic exposures were moderate with mean and median arsenic exposures of 8.9 μg/L and 13.1 μg/L, respectively. A total of 298 cases and 275 controls were enrolled. The adjusted odds ratio (AOR) and corresponding 95% confidence interval (95% CI) for a 10 μg/L increase in water arsenic were 1.19 (95% CI: 1.03, 1.38). Compared to exposures less than 10 μg/L, the AOR for water arsenic exposures above 40 μg/L was 4.05 (95% CI: 1.1-14.99, p = 0.04). Nail arsenic above 1.38 μg/g was also associated with an increased risk of cardiovascular disease.

CONCLUSIONS

By using standardized case definitions and collecting individual measurements of arsenic, this study addressed several limitations of previous studies. The results provide further evidence of the association between cardiovascular disease and arsenic at moderate exposures.

The Influence of Arsenic, Lead, and Mercury on the Development of Cardiovascular Diseases

As a group, cardiovascular disease (CVD) is the leading cause of death worldwide. It killed twice as many people as infectious and parasitic disease and three times as many people as all forms of cancer. There are other crucial risk factors next to the major risk factors identified by the Framingham Heart Study. In the last few years, detailed studies showed the correlation between environmental pollution and the development of CVD. The question, which environmental toxin is particularly harmful, is answered by CERCLA Priority List of Hazardous Substances with the following toxins: arsenic, lead, and mercury. The effect of these potential toxic metals on the development of cardiovascular diseases includes pathomechanisms as the accumulation of free radicals, damage of endothelial nitric oxide synthase, lipid peroxidation, and endocrine influences. This leads to the damage of vascular endothelium, atherosclerosis, high blood pressure, and an increased mortality from cardiovascular diseases. The cardiovascular effects of arsenic, lead, and mercury exposure and its impact on cardiovascular mortality need to be included in the diagnosis and the treatment of CVD.

Heavy metal poisoning: management of intoxication and antidotes

Of the known elements, nearly 80% are either metals or metalloids. The highly reactive nature of most metals result in their forming complexes with other compounds such oxygen, sulfide and chloride. Although this reactivity is the primary means by which they are toxic, many metals, in trace amounts, are vital to normal physiological processes; examples include iron in oxygen transport, manganese and selenium in antioxidant defense and zinc in metabolism. With these essential metals toxicity occurs when concentrations are either too low or too high. For some metals there are no physiological concentrations that are beneficial; as such these metals only have the potential to cause toxicity. This chapter focuses on four of these: arsenic, mercury, lead and thallium.

Association between low-level environmental arsenic exposure and QT interval duration in a general population study

High-level arsenic exposure is consistently associated with QT prolongation, a risk factor for arrhythmia and sudden cardiac death. Arsenic may act on QT by increasing cardiac calcium currents. The authors hypothesized that low-level arsenic exposure would be associated with QT duration and that this effect would be stronger among persons not using calcium channel blockers. They performed a cross-sectional analysis in elderly men from the Normative Aging Study to analyze associations between toenail arsenic and QT and heart rate-corrected QT (QTc) durations and to examine effect modification by calcium channel blocker use, using linear regression and adjusting for potential confounders. Participants were examined in Boston, Massachusetts, between 2000 and 2002 or in 2006. An interquartile range increase in arsenic concentration was associated with a 3.8-millisecond increase in QT (95% confidence interval: 0.82, 6.8) and a 2.5-millisecond increase in QTc (95% confidence interval: 0.11, 4.9). There was no evidence of effect modification by medication use for either QT (P = 0.93) or QTc (P = 0.58). The authors observed positive associations between a biomarker of arsenic exposure and QT duration but found no evidence of effect modification by calcium channel blocker use, possibly because of modest power.

Iatrogenic QT Abnormalities and Fatal Arrhythmias: Mechanisms and Clinical Significance

Severe and occasionally fatal arrhythmias, commonly presenting as Torsade de Pointes [TdP] have been reported with Class III-antiarrhythmics, but also with non-antiarrhythmic drugs. Most cases result from an action on K(+) channels encoded by the HERG gene responsible for the IKr repolarizing current, leading to a long QT and repolarization abnormalities. The hydrophobic central cavity of the HERG-K+ channels, allows a large number of structurally unrelated drugs to bind and cause direct channel inhibition. Some examples are dofetilide, quinidine, sotalol, erythromycin, grepafloxacin, cisapride, dolasetron, thioridazine, haloperidol, droperidol and pimozide. Other drugs achieve channel inhibition indirectly by impairing channel traffic from the endoplasmic reticulum to the cell membrane, decreasing channel membrane density (pentamidine, geldalamicin, arsenic trioxide, digoxin, and probucol). Whereas, ketoconazole, fluoxetine and norfluoxetine induce both direct channel inhibition and impaired channel trafficking. Congenital long QT syndrome, subclinical ion-channel mutations, subjects and relatives of subjects with previous history of drug-induced long QT or TdP, dual drug effects on cardiac repolarization [long QT plus increased QT dispersion], increased transmural dispersion of repolarization and T wave abnormalities, use of high doses, metabolism inhibitors and/or combinations of QT prolonging drugs, hypokalemia, structural cardiac disease, sympathomimetics, bradycardia, women and older age, have been shown to increase the risk for developing drug-induced TdP. Because most of these reactions are preventable, careful evaluation of risk factors and increased knowledge of drugs use associated with repolarization abnormalities is strongly recommended. Future genetic testing and development of practical and simple provocation tests are in route to prevent iatrogenic TdP.

Drug-induced long QT syndrome in women: review of current evidence and remaining gaps

BACKGROUND

Women are at an increased risk of drug-induced long QT syndrome (LQTS). This major cardiac adverse effect may lead to malignant polymorphic ventricular tachycardias, termed torsades de pointes, which may degenerate into ventricular fibrillation and cause sudden death.

OBJECTIVE

This article reviews current evidence and remaining gaps in knowledge about drug-induced LQTS in women.

METHODS

Using the search terms gender, sex, and sex differences in combination with cardiac electrophysiology, long QT syndrome, HERG, membrane transporters, and cytochromes, we conducted a systematic review of the available literature in the PubMed database. Relevant English- and French-language publications (to October 2007) on sex differences in LQTS were identified.

RESULTS

Clinical and experimental studies have reported that gonadal hormones play a role in sex-related differences of QT interval prolongation. Androgens may diminish drug effects on heart repolarization, and estrogens may facilitate arrhythmias. Furthermore, sex-related differences in the density of ion channels may partially explain this phenomenon. However, the magnitude of hormone-dependent differences observed in these studies remains very small compared with the large differences observed in clinical settings. Therefore, many scientists agree that the mechanisms responsible for sex-related differences in the risk of proarrhythmia from drugs remain largely undefined.

CONCLUSIONS

Other factors, such as sex-related modulation of drug disposition in situ, may fill the gaps in our understanding of the sex differences observed in drug-induced LQTS. We suggest that mechanisms such as the modulation of the pharmacokinetics of IKr (rapid component of the delayed rectifier potassium current) blockers, via modulation of intra- and extracellular concentrations, may be of major importance. Sex-specific changes in drug transport and metabolism will result in different plasma and intracellular levels acting along a dose-response effect on IKr block. Consequently, important hormone-dependent factors such as metabolic enzymes and membrane transporters need to be investigated in new basic research studies.

Effect of chronic arsenic exposure from drinking waters on the QT interval and transmural dispersion of repolarization

This study investigated the effects of chronic arsenic exposure on QT- and QTc-interval prolongation, QTc dispersion (QTcd) and transmural dispersion of repolarization (TDR). We compared cardiac parameters from 40 male subjects chronically exposed to arsenic (group A) with those of 40 male subjects not exposed to arsenic (group B). Although subjects in both groups had non-corrected QT intervals within normal limits, subjects in group A had significantly longer QTc and QTcd intervals compared with group B. A total of 70% of group A compared with 10% of group B had QTcd values > 50 ms. The mean TDR value was also significantly higher in group A compared with group B. Although non-corrected QT intervals were within normal limits, those subjects chronically exposed to arsenic had a slight QT prolongation and a higher prevalence of subtle repolarization abnormalities, which might be clinically relevant.

Resveratrol protects against arsenic trioxide-induced cardiotoxicity in vitro and in vivo

BACKGROUND AND PURPOSE

The clinical use of arsenic trioxide (As(2)O(3)), a potent antineoplastic agent, is limited by its severe cardiotoxic effects. QT interval prolongation and apoptosis have been implicated in the cardiotoxicity of As(2)O(3). The present study was designed to evaluate the effects of resveratrol on As(2)O(3)-induced apoptosis and cardiac injury.

EXPERIMENTAL APPROACH

In a mouse model of As(2)O(3)-induced cardiomyopathy in vivo, QT intervals and plasma enzyme activities were measured; cardiac tissues were examined histologically and apoptosis assessed. In H9c2 cardiomyocyte cells, viability, apoptosis, generation of reactive oxygen species (ROS) and cellular calcium levels were measured.

KEY RESULTS

In the mouse model, resveratrol reduced As(2)O(3)-induced QT interval prolongation and cardiomyocyte injury (apoptosis, myofibrillar loss and vacuolization). In addition, increased lactate dehydrogenase activity and decreased activities of glutathione peroxidase, catalase and superoxide dismutase were observed in the plasma of As(2)O(3)-treated mice; these changes were prevented by pretreatment with resveratrol. In As(2)O(3)-treated H9c2 cardiomyocytes, resveratrol significantly increased cardiomyocyte viability and attenuated cell apoptosis as measured by acridine orange/ethidium bromide staining, TdT-mediated dUTP nick end labelling assay and caspase-3 activity. As(2)O(3)-induced generation of ROS and intracellular calcium mobilization in H9c2 cells was also suppressed by pretreatment with resveratrol.

CONCLUSIONS AND IMPLICATIONS

Our results showed that resveratrol significantly attenuated As(2)O(3)-induced QT prolongation, structural abnormalities and oxidative damage in the heart. In H9c2 cardiomyocytes, resveratrol also decreased apoptosis, production of ROS and intracellular calcium mobilization induced by treatment with As(2)O(3). These observations suggested that resveratrol has the potential to protect against cardiotoxicity in As(2)O(3)-exposed patients.

Chronic arsenic exposure and cardiac repolarization abnormalities with QT interval prolongation in a population-based study

BACKGROUND

Chronic arsenic exposure is associated with cardiovascular abnormalities. Prolongation of the QT (time between initial deflection of QRS complex to the end of T wave) interval and profound repolarization changes on electrocardiogram (ECG) have been reported in patients with acute promyelocytic leukemia treated with arsenic trioxide. This acquired form of long QT syndrome can result in life-threatening arrhythmias.

OBJECTIVE

The objective of this study was to assess the cardiac effects of arsenic by investigating QT interval alterations in a human population chronically exposed to arsenic.

METHODS

Residents in Ba Men, Inner Mongolia, have been chronically exposed to arsenic via consumption of water from artesian wells. A total of 313 Ba Men residents with the mean arsenic exposure of 15 years were divided into three arsenic exposure groups: low (< or = 21 microg/L), medium (100-300 microg/L), and high (430-690 microg/L). ECGs were obtained on all study subjects. The normal range for QTc (corrected QT) interval is 0.33-0.44 sec, and QTc > or = 0.45 sec was considered to be prolonged.

RESULTS

The prevalence rates of QT prolongation and water arsenic concentrations showed a dose-dependent relationship (p = 0.001). The prevalence rates of QTc prolongation were 3.9, 11.1, 20.6% for low, medium, and high arsenic exposure, respectively. QTc prolongation was also associated with sex (p < 0.0001) but not age (p = 0.486) or smoking (p = 0.1018). Females were more susceptible to QT prolongation than males.

CONCLUSIONS

We found significant association between chronic arsenic exposure and QT interval prolongation in a human population. QT interval may potentially be useful in the detection of early cardiac arsenic toxicity.

[Early onset of torsades de Pointes and elevated levels of serum troponin I due to acute arsenic poisoning]

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

Two Cases of Acute Promyelocytic Leukemia Complicated by Torsade de Pointes during Arsenic Trioxide Therapy

We describe 2 patients with acute promyelocytic leukemia (APL) in whom torsade de pointes (TdP) developed during treatment with arsenic trioxide. Patient 1 was a 23-year-old woman with second-relapse APL. Ventricular premature beat bigeminy developed on day 27 of treatment, and episodes of TdP developed on day 28. Patient 2 was a 51-year-old woman with second-relapse APL who had cardiomyopathy due to prior anthracycline treatment. TdP developed on day 17 of treatment. Arsenic trioxide is known to cause electrocardiographic abnormalities, such as ventricular tachycardia and prolongation of QT interval. Patient 1 was given fluconazole as a concomitant drug. Patient 2 had cardiomyopathy and hypokalemia. Careful management is needed during arsenic trioxide therapy because this treatment prolongs the QT interval, possibly inducing episodes of TdP.

Arrhythmogenic Effects of Arsenic Trioxide in Patients With Acute Promyelocytic Leukemia and an Electrophysiological Study in Isolated Guinea Pig Papillary Muscles

BACKGROUND

Arsenic trioxide (As(2)O (3)) is a new promising regimen for patients with a relapse of acute promyelocytic leukemia (APL), but causes life-threatening arrhythmias. This study aimed to investigate the incidence and mechanism of arrythmogenesis caused by As(2)O(3).

METHODS AND RESULTS

Standard 12-lead ECGs were monitored throughout As(2)O(3) therapy in 20 APL patients. As(2)O (3) (0.15 mg/kg) significantly prolonged the corrected QT interval (QTc: 445+/-7 to 517+/-17 ms, means+/-SE, p<0.01), and also increased the QTc dispersion and transmural dispersion of repolarization. Non-sustained ventricular tachycardias and torsades de pointes occurred in 4 and 1 patients, respectively. The action potentials and isometric contraction were measured in guinea pig papillary muscles during As(2)O (3) perfusion (350 micromol/L). The action potential duration was prolonged (APD(90): 150+/-11 to 195+/-12 ms at 60 min, p<0.01, n=5) and perfusion of As(2)O(3) in a low K(+) solution with a low stimulation rate augmented the prolongation of APD, and provoked early after-depolarizations and triggered activities. The prolonged exposure to As(2)O(3) induced muscle contracture, aftercontractions, triggered activities and electromechanical alternans. Tetrodotoxin or butylated hydroxytoluene partially prevented the As(2)O(3)-induced prolongation of APD.

CONCLUSIONS

The prolonged QTc and spatial heterogeneity are responsible for the As(2)O(3)-induced ventricular tachyarrhythmias. In addition to prolongation of the APD, cellular Ca(2+) overload and lipid peroxidation might contribute to the electrophysiological abnormalities caused by As(2)O(3).

Arsenic trioxide in the treatment of haematological malignancies

Arsenic trioxide (As(2)O(3)) for leukaemia treatment was described a century ago. Recent resurgence in the use of arsenic trioxide is related to its high efficacy in acute promyelocytic leukaemia (APL). Most arsenic trioxide preparations are intravenous, although an oral formulation is similarly efficacious. Side effects of arsenic trioxide are usually minor, including skin reactions, gastrointestinal upset, and reversible increases in transaminases. During therapy, a leukocytosis occasionally occurs, which may be complicated by fluid accumulation and pulmonary infiltration. Arsenic trioxide causes an asymptomatic QT prolongation in most patients. However, if concomitant cardiopulmonary diseases or electrolyte disturbances are present, more sinister arrhythmias may develop. Therefore, before commencement of arsenic trioxide therapy, a full cardiac assessment and avoidance of drugs that prolong QT interval should be instituted. Arsenic trioxide is partly renally excreted and, therefore, dose adjustment is required when renal function is impaired. In addition to its use in APL, arsenic trioxide is now tested in other malignancies, notably multiple myeloma.

Acute arsenic poisoning in two siblings

We report a case series of acute arsenic poisoning of 2 siblings, a 4-month-old male infant and his 2-year-old sister. Each child ingested solubilized inorganic arsenic from an outdated pesticide that was misidentified as spring water. The 4-month-old child ingested a dose of arsenic that was lethal despite extraordinary attempts at arsenic removal, including chelation therapy, extracorporeal membrane oxygenation, exchange transfusion, and hemodialysis. The 2-year-old fared well with conventional therapy.

Mechanisms of arsenic-induced prolongation of cardiac repolarization

Arsenic trioxide (As(2)O(3)) produces dramatic remissions in patients with relapsed or refractory acute promyelocytic leukemia. Its clinical use is burdened by QT prolongation, torsade de pointes, and sudden cardiac death. In the present study, we analyzed the molecular mechanisms leading to As(2)O(3)-induced abnormalities of cardiac electrophysiology. Using biochemical and electrophysiological methods, we show that long-term exposure to As(2)O(3) increases cardiac calcium currents and reduces surface expression of the cardiac potassium channel human ether-a-go-go-related gene (HERG) at clinically relevant concentrations of 0.1 to 1.5 microM. In ventricular myocytes, As(2)O(3) increases action potential duration measured at 30 and 90% of repolarization. As(2)O(3) interferes with hERG trafficking by inhibition of hERG-chaperone complexes and increases calcium currents by a faster cellular process. We propose that an increase in cardiac calcium current and reduced trafficking of hERG channels to the cell surface cause QT prolongation and torsade de pointes in patients treated with As(2)O(3). Our results suggest that calcium-channel antagonists will be useful in normalizing QT prolongation during As(2)O(3) therapy. As(2)O(3) is the first example of a drug that produces hERG liability by inhibition of ion-channel trafficking. Other drugs that interfere with proteins in the processing pathway of cardiac ion channels may be proarrhythmic for similar reasons.

QT Prolongation and Fatal Arrhythmias: A Review of Clinical Implications and Effects of Drugs

A long QT interval due to prolonged repolarization may be associated with a polymorphic ventricular tachycardia known as torsades de pointes. During marked prolongation of the action potential (long QT) early after depolarizations may occur, which when propagated may trigger an arrhythmia. The duration of QTc interval is the major determinant of the risk of drug-induced torsades. Congenital long QT syndrome, female gender, hypokalemia and use of sympathomimetics increase the risk of torsades, and potentiate the QT prolonging effects of drugs. Antiarrhythmics that block the potassium channel prolong the QT and increase the risk for torsades (amiodarone, sotalol, quinidine, procainamide, ibutilide, disopyramide). Additionally, some macrolide and fluoroquinolone antibiotics, antipsychotic and antidepressant drugs, serotonin agonists of the triptan class, cisapride, dolasetron and others have been reported to be associated with QT prolongation or cases of torsades. Drug-induced effects on the QT interval with the associated possibility of inducing fatal arrhythmias have become a new challenge for the practitioner, the drug development process and the regulatory agencies.

Effect of Arsenic Trioxide on QT Interval in Patients With Advanced Malignancies

Purpose: Arsenic trioxide is an effective treatment for patients with acute promyelocytic leukemia (APL) who have relapsed from or are refractory to all-trans-retinoic acid and anthracycline chemotherapy. Since arsenic can prolong the QT interval and lead to torsade de pointes, a life-threatening ventricular arrhythmia, this retrospective analysis was conducted to determine the degree of QT prolongation in patients treated with arsenic trioxide.

Patients and Methods: Clinical data and serial ECGs from 99 patients with advanced malignancies who received 170 courses of arsenic trioxide in either a phase I or phase II investigational study were reviewed.

Results: Prolonged QT intervals developed in 38 patients (26 patients had intervals ≥ 500 milliseconds). Compared with baseline, the heart rate—corrected (QTc) interval was prolonged by 30 to 60 milliseconds in 36.6% of treatment courses, and by more than 60 milliseconds in 35.4% of patients. The degree of prolongation was higher in men than in women during the first course of therapy, and in patients with hypokalemia. In patients receiving multiple courses, QTc intervals returned to pretreatment levels before the second course, signifying that arsenic trioxide does not permanently prolong the QTc interval. One hypokalemic, arsenic trioxide–treated patient with relapsed APL developed asymptomatic torsade de pointes, which resolved spontaneously and did not recur after electrolyte replacement. There were no sudden or arrhythmia-related deaths.

Conclusion: This analysis shows that arsenic trioxide can prolong the QTc interval. However, with appropriate ECG monitoring and management of electrolytes and concomitant medications, arsenic trioxide can be safely administered in patients with relapsed APL.

Catecholamine-provoked microvoltage T wave alternans in genotyped long QT syndrome

Macrovoltage T wave alternans (TWA) has been described in congenital long QT syndrome (LQTS). Microvoltage T wave alternans (microV-TWA) at low heart rate (HR) is a marker of arrhythmogenic risk in many conditions, but its significance in LQTS has not been established. Twenty-three genotypically heterogeneous patients with LQTS and 16 control subjects were studied at rest and during phenylephrine and dobutamine provocation. Genotyping was established by PCR amplification and DNA sequencing of the three most common LQTS genes; KCNQ1/KVLQT1 (LQT1), KCNH2/HERG (LQT2), and SCN5A (LQT3). microV-TWA was determined using Fast Fourier transform. Precluded by ectopy, microV-TWA could not be assessed in 8 of 23 patients with LQTS. In the remaining 15 patients with LQTS, microV-TWA occurred at lower HR in LQTS than in controls (117 +/- 49 vs 153 +/- 37 beats/min; P < 0.05). Patients with LQTS developed microV-TWA at HR < 150 beats/min more often than controls (10/15 vs 2/16; P = 0.003). However, microV-TWA was not detected in the 3 individuals with a history of out-of-hospital cardiac arrest including a 14-year-old male with an F339del-KVLQT1 mutation (LQT1) who had dobutamine-provoked polymorphic ventricular tachycardia requiring external defibrillation. Catecholamine-provoked microV-TWA occurs at lower HR in patients with LQTS than in healthy people but does not identify high risk subjects.

Direct cardiac effects of As2O3 in rabbits: evidence of reversible chronic toxicity and tissue accumulation of arsenicals after parenteral administration

Although parenteral administration of As(2)O(3) is highly effective in the treatment of acute promyelocytic leukemia, cardiac toxicity has been reported. This study employed Langendorff perfusion to determine the direct effects of As(2)O(3) in the electrophysiological properties of rabbit hearts after acute or chronic As(2)O(3) treatment (0.2 mg/kg/day iv for 30 days). Tissue accumulations of arsenicals and pathological changes as well as the reversibility of chronic As(2)O(3) effects were assessed. We found that cardiac conduction and repolarization were not altered whatsoever after acute As(2)O(3) treatment at clinically relevant (1, 3, and 10 microM) and higher (30 microM) doses. Nevertheless, an extremely high concentration of As(2)O(3) (300 microM) prolonged the corrected QT interval. Subsequent to chronic As(2)O(3) administration and with 30 microM As(2)O(3) via Langendorff perfusion, polymorphic ventricular tachycardia was observed (1/7, 14%). Corrected QT interval was prolonged, while basic cycle length was shortened. Significant accumulation of arsenicals in the cardiac tissue was found, but without any pathological changes. After As(2)O(3) was discontinued for 30 days, the chronic As(2)O(3) -induced electrophysiological changes improved, no ventricular arrhythmia was noted, and the tissue concentration of arsenicals decreased considerably. We therefore conclude that, although no immediate cardiac effects were discemable at clinically relevant doses, an extremely high concentration of As(2)O(3) could prolong ventricular repolarization. Chronic As(2)O(3) treatment resulted in a prolonged ventricular repolarization, in association with arsenicals accumulation and with risk of ventricular tachycardia. These chronic cardiac toxicities and the tissue accumulation of arsenicals were, however, partially reversible after cessation of As(2)O(3).

Electrophysiologic mechanisms of the long QT interval syndromes and torsade de pointes

PURPOSE

To review the current understanding of the mechanisms and treatment of the long QT interval syndromes and torsade de pointes.

DATA SOURCES

Personal databases of the authors and a search of the MEDLINE database from 1966 to 1994.

STUDY SELECTION

Experimental and clinical studies and topical reviews on the electrophysiologic mechanisms and treatment of torsade de pointes were analyzed.

RESULTS

The long QT interval syndromes have been classified into acquired and hereditary forms, both of which are associated with a characteristic type of life-threatening polymorphic ventricular tachycardia called torsade de pointes. The acquired form is caused by various agents and conditions that reduce the magnitude of outward repolarizing K+ currents, enhance inward depolarizing Na+ or Ca2+ currents, or both, thereby triggering the development of early afterdepolarizations that initiate the tachyarrhythmia. The hereditary form appears to result from an abnormal response to adrenergic or sympathetic nervous system stimulation. At least some cases of the hereditary long QT interval syndromes may result from a single gene defect that alters the intracellular regulatory proteins responsible for the modulation of K+ channel function. Treatment of the acquired form is primarily directed at identifying and withdrawing the offending agent, although emergent therapy using maneuvers and agents that favorably modulate transmembrane ion currents can be lifesaving. In torsade de pointes associated with the hereditary long QT interval syndromes, early diagnosis leading to treatments designed to both shorten the QT interval and block the beta-adrenergic-induced instability of the QT interval is essential.

CONCLUSIONS

The long QT interval syndromes and torsade de pointes are potentially life-threatening conditions caused by various agents, conditions, and genetic defects. The mechanisms responsible for these conditions and available treatment options for them are reviewed.

Adenosine induced torsades de pointes in a child with congenital long QT syndrome

Torsades de pointes is a rare arrhythmia characterized by its bradycardia dependence and increased adrenergic discharge, whether it occurs as a congenital anomaly or as an acquired problem resulting from drug intoxication or other conditions. There are no reliable tests to assess the propensity toward torsades de pointes or evaluate the efficacy of treatment in these patients. Adenosine can result in marked slowing of sinus and ventricular rate and leads to increased sympathetic discharge when given intravenously. We induced torsades de pointes in a child with congenital long QT syndrome (Jervell-Lange-Nielsen syndrome) using 200 micrograms/kg IV adenosine bolus. Higher dosage of adenosine (600 micrograms/kg) did not lead to torsades de pointes after beta blockade. Adenosine may induce torsades de pointes in patients with the long QT syndrome and may be used as a test to reproduce the clinical arrhythmia. Whether adenosine proves to be useful for assessing the efficacy of treatment will require extensive investigation in larger series of patients.

Torsades de pointes induced by erythromycin

We describe two patients who develop torsades de pointes in a temporal relationship to the intravenous administration of erythromycin lactobionate in the absence of other drugs or metabolic abnormalities known to cause the arrhythmia. We also review the current literature regarding this topic, including other case histories and the evidence for erythromycin's effect on cardiac tissue. Due to the increasing use of erythromycin in clinical practice, we believe it is important that all physicians be made aware of this potential complication, which was not recognized at our institutions until these patients were seen by one of us (B.G.).