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

Diastolic Dysfunction and Atrial Fibrillation: Recognition, Interplay, and Management

Diastolic dysfunction occurs when the left ventricle loses its ability to relax normally, impairing ventricular filling during diastole. This most commonly occurs as a pathological sequela of left ventricular hypertrophy and remodeling due to chronic hypertension and/or age-related sclerotic changes of the aortic valve. This can subsequently deteriorate to diastolic heart failure or heart failure with preserved ejection fraction. There is a substantive interplay between atrial fibrillation and diastolic dysfunction, as atrial fibrillation can cause, exacerbate, or be a direct result of diastolic dysfunction and vice versa. In this review, we first independently define diastolic heart failure and atrial fibrillation while discussing the diagnostic guidelines, which encompass various modalities such as medical history, electrocardiography, echocardiography, and laboratory tests. We subsequently examine their interplay and pathophysiological links drawing on recent evidence in the literature. Finally, we discuss management approaches, including pharmacological interventions targeting rate and rhythm control, diuretics, and addressing comorbidities.

Mortality and ventricular arrhythmias in patients on d,l-sotalol for rhythm control of atrial fibrillation: A nationwide cohort study

BACKGROUND

Use of d,l-sotalol for rhythm control in patients with atrial fibrillation (AF) has raised safety concerns. Previous randomized studies are few and not designed for mortality outcome.

OBJECTIVE

The purpose of this study was to compare the incidences of mortality and ventricular arrhythmias in AF patients treated with d,l-sotalol for rhythm control vs matched control patients treated with cardioselective beta-blockers.

METHODS

This population-based cohort study included AF patients from the Swedish National Patient Registry (2006-2017) who underwent rhythm control after a second cardioversion. Incidence rates (IRs) and adjusted hazard ratios (aHRs) for mortality and a composite endpoint of cardiac arrest/death and ventricular arrhythmias were calculated for the overall cohort and a 1:1 propensity score matched cohort of d,l-sotalol vs beta-blocker treatment.

RESULTS

Among patient treated with d,l-sotalol (n = 4987) and beta-blocker (n = 27,078) (mean follow-up 458 days), all-cause mortality was lower in patients treated with d,l-sotalol: IR 1.21; 95% confidence interval 0.95-1.52 vs 2.42 (2.26-2.60) deaths per 100 patient-years; aHR 0.66 (0.52-0.83). The difference in mortality persisted in the propensity score matched comparison (n = 4953 in each group): aHR 0.63 (0.48-0.86). No differences were observed in the composite outcome: IR in propensity cohorts 2.13 (1.78-2.52) vs 2.07 (1.73-2.53) events per 100 years; aHR 1.01 (0.78-1.29).

CONCLUSION

There was no excess mortality with d,l-sotalol compared with cardioselective beta-blockers in patients undergoing rhythm control treatment for AF after a second cardioversion. Our results indicate that the risk associated with d,l-sotalol treatment for AF can be mitigated by careful patient selection and strict adherence to follow-up protocols.

Outpatient Initiation of Sotalol in Patients with Atrial Fibrillation: Utility of Cardiac Implantable Electronic Devices for Therapy Monitoring

Background

Antiarrhythmic drugs are often used in the management of patients with atrial fibrillation (AF). Sotalol is conventionally initiated in the inpatient setting for monitoring efficacy and adverse effects, including QTc interval prolongation and torsades de pointes (TdP) proarrhythmia.

Objective

We aimed to evaluate the efficacy and safety of outpatient initiation of sotalol for the treatment of AF in a select group of patients with cardiac implantable electronic devices (CIEDs): permanent pacemakers (PPMs), implantable cardioverter defibrillators (ICDs), and implantable loop recorders (ILRs) capable of continuous rhythm monitoring remotely.

Methods

We conducted our clinical study in a real-world practice setting with longitudinal follow-up of the study cohort. We included adult patients with symptomatic paroxysmal and persistent AF eligible for sotalol for rhythm control strategy and who had CIEDs in our study. Patients with a known contraindication to sotalol were excluded. After making a shared management decision with patients, sotalol was initiated as an outpatient, with regular clinical encounters with patients to assess the efficacy and safety of treatment, and monitoring cardiac rhythm and QTc intervals with CIEDs utilizing their remote monitoring platforms.

Results

The study cohort comprised 105 patients; 38 (36%) females, mean age ± standard deviation (SD) 73.9 ± 10.36 years, and with a CHA₂DS₂-VASc score of 3.26 ± 1.37 and left ventricular ejection fraction of 60.16 ± 9.10%. Twenty-six (24.8%) patients were implanted with PPMs, 10 (9.5%) with dual-chamber ICDs, and 69 (65.7%) with ILRs. Over a follow-up period of 23 ± 15 months, sotalol was continued at a steady median dose of 80 mg twice daily, 105 ± 42 mg (mean ± SD) in 77 (73%) patients who maintained sinus rhythm, and discontinued in 28 (27%) patients because of inefficacy or development of adverse effects. No adverse effects relating to QTc prolongation and TdP or mortality were observed during the study period.

Conclusions

Effective and safe outpatient initiation and maintenance of sotalol therapy is possible in select patients who have CIEDs for continuous remote monitoring and surveillance capabilities.

[Perioperative Atrial Fibrillation]

New atrial fibrillation is a risk factor for increased morbidity and mortality in the perioperative phase. The prevalence and incidence of atrial fibrillation depend on age, previous illnesses and the intercurrent diagnoses in the perioperative phase. Pathomechanisms for both permanent and acute forms of atrial fibrillation relate to electrophysiological, histopathological and other pathophysiological abnormalities. In the perioperative phase, decompensated heart failure, systemic inflammation, sepsis and cardiac surgery are risk factors for conversion to atrial fibrillation and/or rapid transition. The consequences of newly occurring and/or rapidly transferred atrial fibrillation are cardiac instability due to a drop in blood pressure or cardiac output volume or coronary underperfusion due to tachycardia and the risk of thromboembolism. Associated with this is a significantly increased long-term mortality risk in the elderly if atrial fibrillation occurs again in the perioperative phase. The diagnosis of atrial fibrillation is made in the monitor or 12-channel electrocardiogram. Echocardiography and the adenosine test can be included in the differential diagnosis in cases of doubt. Important current guidelines for the treatment of atrial fibrillation are the ESC (atrial fibrillation) and the ERC (Advanced Cardiac Life Support) guidelines. The conversion into the sinus rhythm can be done electrically or medicinally. It is indicated in cases of acute instability or symptomatic atrial fibrillation despite frequency control after cardiac thrombi have been excluded by echocardiography. A step-by-step concept for thromboembolism prophylaxis from initial parenteral and secondary oral therapy must take place up to four weeks after conversion to sinus rhythm or permanently in the case of permanent atrial fibrillation. The individual indication for thromboembolism prophylaxis results from the CHA2-DS2-VASc score.

QT Dispersion and Drug-Induced Torsade de Pointes

Background

Amiodarone causes less drug-induced torsade de pointes (TdP) compared to other class III antiarrhythmics. Two theories proposed for this finding include that amiodarone has less repolarization heterogeneity, and/or decreases early after depolarization (EADs). Corrected QT (QTc) dispersion as measured on a surface electrocardiogram (ECG) represents spatial heterogeneity of ventricular repolarization.

Objective

The purpose of this study was to analyze the difference in QT dispersion between amiodarone and other class III antiarrhythmics and to determine the etiology of TdP.

Methods

This was a retrospective, observational study at Montefiore Medical Center between January 2005 and January 2015. Inclusion criteria were adults >18 years on amiodarone, dofetilide, or sotalol with prolonged QT interval on 12-lead ECG. ECGs were reviewed by three blinded observers. QTc was calculated using the Bazett and Framingham formulas. QTc dispersion was calculated by subtracting the shortest from the longest QTc. Analysis of variance (ANOVA) was applied for comparison between antiarrhythmic groups with Bonferroni correction for multiple comparisons.

Results

A total of 447 ECGs were reviewed and 77 ECGs met inclusion criteria. The average QT dispersion for amiodarone, dofetilide, and sotalol was 0.050, 0.037, and 0.034, respectively (p=0.006) and the average QTc dispersion by Bazett was 0.053, 0.038, and 0.037 (p=0.008) and by Framingham was 0.049, 0.036, and 0.035 (p=0.009), respectively.

Conclusion

Our results show that given the increase in QT dispersion seen with amiodarone, heterogeneous ventricular repolarization as measured by QTc dispersion likely does not account for the lower incidence of drug-induced TdP seen with amiodarone. The ability of amiodarone to decrease EADs via sodium-channel blockade is more likely the explanation for its lower incidence of drug-induced TdP.

Frontal plane QRS-T angle in the monitoring of intravenous amiodarone infusion for pharmacological cardioversion of acute atrial fibrillation

WHAT IS KNOWN AND OBJECTIVE

Intravenous amiodarone infusion is effective and widely used treatment for pharmacological cardioversion of recent-onset atrial fibrillation (Af). Although amiodarone may trigger various alterations in cardiac electrophysiology and electrocardiography (ECG), the impact of amiodarone treatment on frontal plane QRS-T angle remains unclear. Frontal plane QRS-T angle is the angle between the depolarization and repolarization axes and indicates instability in the cardiac cellular electrophysiology. Therefore, the present study aimed to investigate whether intravenous amiodarone infusion has effect on frontal plane QRS-T angle in patients with acute Af.

METHODS

A total of 179 patients with acute-onset Af who underwent pharmacological cardioversion with intravenous amiodarone infusion were included into the study. Patients with successful and failed pharmacological cardioversion were compared regarding pre- and post-treatment frontal plane QRS-T angle.

RESULTS AND DISCUSSION

At the end of the amiodarone infusion, sinus rhythm was restored in 112 (62.6%) patients, whereas Af was persisted in 67 (37.4%) patients. Despite the similar frontal plane QRS-T angle at baseline (59.6°±21.73°vs.60.4°±25.67°, p = 0.822), patients with failed pharmacological cardioversion had significantly higher post-treatment frontal plane QRS-T angle compared to patients with successful pharmacological cardioversion (68.8°±21.71°vs.58.6°±25.15° p < 0.001). Furthermore, multivariate analysis demonstrated that post-treatment increased frontal plane QRS-T angle was found to be an independent predictor of failure of pharmacological cardioversion with amiodarone infusion (OR:1.233, 95% CI:1.147-1.919, p = 0.024).

WHAT IS NEW AND CONCLUSION

Amiodarone may significantly affect the frontal plane QRS-T angle. As a parameter that can be easily calculated from automated ECG recordings, frontal plane QRS-T angle may be useful in the monitoring of intravenous amiodarone treatment.

Dynamics of Pivoting Electrical Waves in a Cardiac Tissue Model

Through a detailed mathematical analysis we seek to advance our understanding of how cardiac tissue conductances govern pivoting (spiral, scroll, rotor, functional reentry) wave dynamics. This is an important problem in cardiology since pivoting waves likely underlie most reentrant tachycardias. The problem is complex, and to advance our methods of analysis we introduce two new tools: a ray tracing method and a moving-interface model. When used in combination with an ionic model, they permit us to elucidate the role played by tissue conductances on pivoting wave dynamics. Specifically we simulate traveling electrical waves with an ionic model that can reproduce the characteristics of plane and pivoting waves in small patches of cardiac tissue. Then ray tracing is applied to the simulated pivoting waves in a manner to expose their real displacement. In this exercise we find loci with special characteristics, as well as zones where a part of a pivoting wave quickly transitions from a regenerative to a non-regenerative propagation mode. The loci themselves and the monitoring of the ionic model state variables in this zone permit to elucidate several aspects of pivoting wave dynamics. We then formulate the moving-interface model based on the information gathered with the above-mentioned analysis. Equipped with a velocity profile v(s), s: distance along of the pivoting wave contour and the steady- state action potential duration (APD) of a plane wave during entrainment, APDss(T), at period T, this simple model can predict: shape, orbit of revolution, rotation period, whether a pivoting wave will break up or not, and whether the tissue will admit pivoting waves or not. Because v(s) and APDss(T) are linked to the ionic model, dynamical analysis with the moving-interface model conveys information on the role played by tissue conductances on pivoting wave dynamics. The analysis conducted here enables us to better understand previous results on the termination of pivoting waves. We surmise the method put forth here could become a means to discover how to alter tissue conductances in a manner to terminate pivoting waves at the origin of reentrant tachycardias.

Amiodarone-induced Hyponatremia: A Case Report and a Review of the Literature

Amiodarone is a widely used medication for controlling various types of cardiac arrhythmias. Nonetheless, it carries several known adverse effects that may preclude its use or necessitate discontinuation. Hyponatremia resulting from amiodarone is rarely reported, and its incidence is unknown. We present a case of severe hyponatremia secondary to amiodarone therapy and a review of the literature.

Cardiac microphysiological devices with flexible thin-film sensors for higher-throughput drug screening

Microphysiological systems and organs-on-chips promise to accelerate biomedical and pharmaceutical research by providing accurate in vitro replicas of human tissue. Aside from addressing the physiological accuracy of the model tissues, there is a pressing need for improving the throughput of these platforms. To do so, scalable data acquisition strategies must be introduced. To this end, we here present an instrumented 24-well plate platform for higher-throughput studies of engineered human stem cell-derived cardiac muscle tissues that recapitulate the laminar structure of the native ventricle. In each well of the platform, an embedded flexible strain gauge provides continuous and non-invasive readout of the contractile stress and beat rate of an engineered cardiac tissue. The sensors are based on micro-cracked titanium-gold thin films, which ensure that the sensors are highly compliant and robust. We demonstrate the value of the platform for toxicology and drug-testing purposes by performing 12 complete dose-response studies of cardiac and cardiotoxic drugs. Additionally, we showcase the ability to couple the cardiac tissues with endothelial barriers. In these studies, which mimic the passage of drugs through the blood vessels to the musculature of the heart, we regulate the temporal onset of cardiac drug responses by modulating endothelial barrier permeability in vitro.

Analysis of 24-h Rhythm in Ventricular Repolarization Identifies QT Diurnality As a Novel Clinical Parameter Associated with Previous Ventricular Arrhythmias in Heart Failure Patients

Introduction: Cardiac repolarization abnormalities are among the major causes of ventricular arrhythmias and sudden cardiac death. In humans, cardiac repolarization duration has a 24-h rhythm. Animal studies show that this rhythm is regulated by 24-h rhythms in ion channel function and that disruption of this rhythm leads to ventricular arrhythmias. We hypothesized that 24-h rhythms in QT duration can be used as a predictor for sudden cardiac death and are associated with ventricular arrhythmias. Secondly, we assessed a possible mechanistic explanation by studying the putative role of hERG channel dysfunction.

Materials and Methods: In 2 retrospective studies, measures of the 24-h variation in the QT and QTc intervals (QT and QTc diurnality, QTd and QTcd, respectively) have been derived from Holter analyses and compared between groups: 1) 39 post-infarct patients with systolic heart failure (CHF: EF < 35%), of which 14 with, and 25 without a history of ventricular arrhythmias and 2) five patients with proven (LQTS2) and 16 with potential (Sotalol-induced) hERG channel dysfunction vs. 22 controls.

Results: QTd was two-fold higher in CHF patients with a history of ventricular arrhythmias (38 ± 15 ms) compared to CHF patients without VT (16 ± 9 ms, p = 0.001). QTd was significantly increased in LQT2 patients (43 ± 24 ms) or those treated with Sotalol (30 ± 10 ms) compared to controls (21 ± 8 ms, p < 0.05 for both).

Discussion: QT diurnality presents a novel clinical parameter of repolarization that can be derived from Holter registrations and may be useful for identification of patients at risk for ventricular arrhythmias.

Gene therapy to restore electrophysiological function in heart failure

INTRODUCTION

Heart failure (HF) is a major public health epidemic and a leading cause of morbidity and mortality in the industrialized world. Existing treatments for patients with HF are often associated with pro-arrhythmic activity and risk of sudden cardiac death. Therefore, development of novel, effective and safe therapeutic options for HF patients is a critical area of unmet need.

AREAS COVERED

In this article, we review recent advances in the emerging field of cardiac gene therapy for the treatment of tachy- and bradyarrhythmias in HF. We provide an overview of gene-based approaches that modulate myocardial conduction, repolarization, calcium cycling and adrenergic signaling to restore heart rate and rhythm.

EXPERT OPINION

We highlight major advantages of gene therapy for arrhythmias, including the ability to selectively target specific cell populations and to limit the therapeutic effect to the region that requires modification. We illustrate how advances in our fundamental understanding of the molecular origins of arrhythmogenic disorders are allowing investigators to use targeted gene-based approaches to successfully correct abnormal excitability in the atria, ventricles and conduction system. Translation of various gene therapy approaches to humans may revolutionize our ability to combat lethal arrhythmias in HF patients.

Gene therapies for arrhythmias in heart failure

In this article, we review recent advances in our understanding of arrhythmia mechanisms in the failing heart. We focus on changes in repolarization, conduction, and intracellular calcium cycling because of their importance to the vast majority of clinical arrhythmias in heart failure. We highlight recent efforts to combat arrhythmias using gene-based approaches that target ion channel, gap junction, and calcium cycling proteins. We further discuss the advantages and limitations associated with individual approaches.

QTc compared to JTc for monitoring drug-induced repolarization changes in the setting of ventricular pacing

BACKGROUND

QT prolongation is a risk factor for proarrhythmia when beginning antiarrhythmic drug therapy (AAD). However, there are no data regarding monitoring repolarization changes during a ventricular paced (VP) rhythm.

OBJECTIVE

The purpose of this study was to compare serial changes in corrected QT and JT intervals, during native conduction (NC) and VP rhythms when initiating Class III AADs.

METHODS

Twenty-two patients (73% men; mean age 65 ± 11 years) with an implantable device and with <10% VP were monitored during AAD initiation (16 sotalol, 6 dofetilide). QTc and JTc were measured from ECGs obtained during NC and VP at baseline (pre-AAD) and then after each AAD dose.

RESULTS

During AAD loading, mean QTc increased significantly during NC (431 ± 28 ms to 463 ± 33 ms, P = .002) but not with VP (520 ± 48 ms to 538 ± 45 ms, P = .07). Mean percent increase in peak QTc during NC was significantly greater than during VP (12% vs 7%, P = .003). In contrast, peak JTc during AAD loading was not significantly different between NC and VP (P = .67).

CONCLUSION

When initiating AAD, the change in QTc during VP does not correlate with the change in QTc during NC; thus, the VP QTc is inadequate for monitoring repolarization changes. However, VP JTc correlates well with JTc during NC. When initiating Class III AADs in patients with VP rhythms, the JTc, and not the QTc, interval is the useful marker for assessing repolarization.

Effects of bilastine on T-wave morphology and the QTc interval: a randomized, double-blind, placebo-controlled, thorough QTc study

BACKGROUND AND OBJECTIVES

The International Conference of Harmonisation (ICH) E14 guideline for thorough QT studies requires assessing the propensity of new non-antiarrhythmic drugs to affect cardiac repolarization. The present study investigates whether a composite ECG measure of T-wave morphology (Morphology Combination Score [MCS]) can be used together with the heart rate corrected QT interval (QTc) in a fully ICH E14-compliant thorough QT study to exclude clinically relevant repolarization effects of bilastine, a novel antihistamine.

METHODS

Thirty participants in this crossover study were randomly assigned to receive placebo, moxifloxacin 400 mg, bilastine at therapeutic and supratherapeutic doses (20 and 100 mg) and bilastine 20 mg co-administered with ketoconazole 400 mg. Resting ECGs recorded at 12 nominal time points before and after treatments were used to determine Fridericia corrected QTc (QTcF) and MCS from the T-wave characteristics: asymmetry, flatness and notching.

RESULTS

There were no effects of bilastine monotherapy (20 and 100 mg) on MCS or QTcF at those study times where the bilastine plasma concentrations were highest. MCS changes for bilastine monotherapy did not exceed the normal intrasubject variance of T-wave shapes for triplicate ECG recordings. Maximum QTcF prolongation for bilastine monotherapy was 5 ms or less: 3.8 ms (90% CI 0.3, 7.3 ms) for bilastine 20 mg and 5.0 ms (90% CI 2.0, 8.0 ms) for bilastine 100 mg. There were no indications of bilastine inducing larger repolarization effects on T-wave morphology as compared with the QTcF interval, as evidenced by the similarity of z-score equivalents for placebo-corrected changes in MCS and QTcF values.

CONCLUSION

This study shows that bilastine, at therapeutic and supratherapeutic dosages, does not induce any effects on T-wave morphology or QTcF. These results confirm the absence of an effect for bilastine on cardiac repolarization.

Comparison of electrophysiological and antiarrhythmic effects of vernakalant, ranolazine, and sotalol in canine pulmonary vein sleeve preparations

BACKGROUND

Vernakalant (VER) is a relatively atrial-selective antiarrhythmic drug capable of blocking potassium and sodium currents in a frequency- and voltage-dependent manner. Ranolazine (RAN) is a sodium-channel blocker shown to exert antiarrhythmic effects in pulmonary vein (PV) sleeves. dl-Sotalol (SOT) is a β-blocker commonly used in the rhythm-control treatment of atrial fibrillation. This study evaluated the electrophysiological and antiarrhythmic effects of VER, RAN, and SOT in canine PV sleeve preparations in a blinded fashion.

METHODS

Transmembrane action potentials were recorded from canine superfused PV sleeve preparations exposed to VER (n = 6), RAN (n = 6), and SOT (n = 6). Delayed afterdepolarizations were induced in the presence of isoproterenol and high-calcium concentrations by periods of rapid pacing.

RESULTS

In PV sleeves, VER, RAN, and SOT (3-30 μM) produced small (10-15 ms) increases in action potential duration. The effective refractory period, diastolic threshold of excitation, and the shortest S(1)-S(1) cycle length permitting 1:1 activation were significantly increased by VER and RAN in a rate- and concentration-dependent manner. VER and RAN significantly reduced V(max) in a concentration- and rate-dependent manner. SOT did not significantly affect the effective refractory period, V(max), diastolic threshold of excitation, or the shortest S(1)-S(1) cycle length permitting 1:1 activation. All 3 agents (3-30 μM) suppressed delayed afterdepolarization-mediated triggered activity induced by isoproterenol and high calcium.

CONCLUSIONS

In canine PV sleeves, the effects of VER and RAN were similar and largely characterized by concentration- and rate-dependent depression of sodium-channel-mediated parameters, which were largely unaffected by SOT. All 3 agents demonstrated an ability to effectively suppress delayed afterdepolarization-induced triggers of atrial arrhythmia.

Torsades de pointes following concurrent amiodarone and levofloxacin therapy

A case of torsades de pointes is reported following administration of amiodarone concurrent with the fluoroquinolone levofloxacin. Prolongation of the QTc interval has occurred with the fluoroquinolone class of antibiotics. The incidence of torsades has been considered rare with amiodarone. Caution is warranted when these two agents are administered concurrently.

Genetic suppression of atrial fibrillation using a dominant-negative ether-a-go-go-related gene mutant

BACKGROUND

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia. Gene therapy-dependent modulation of atrial electrophysiology may provide a more specific alternative to pharmacological and ablative treatment strategies.

OBJECTIVE

We hypothesized that genetic inactivation of atrial repolarizing ether-a-go-go-related gene (ERG) K(+) currents using a dominant-negative mutant would provide rhythm control in AF.

METHODS

Ten domestic swine underwent pacemaker implantation and were subjected to atrial burst pacing to induce persistent AF. Animals were then randomized to receive either AdCERG-G627S to suppress ERG/I(Kr) currents or green fluorescent protein (AdGFP) as control. Adenoviruses were applied using a novel hybrid technique combining atrial virus injection and epicardial electroporation to increase transgene expression.

RESULTS

In pigs treated with AdCERG-G627S, the onset of persistent AF was prevented (n = 2) or significantly delayed compared with AdGFP controls (12 ± 2.1 vs. 6.2 ± 1.3 days; P < .001) during 14-day follow-up. Effective refractory periods were prolonged in the AdCERG-G627S group compared with AdGFP animals (221.5 ± 4.7 ms vs. 197.0 ± 4.7 ms; P < .006). Impairment of left ventricular ejection fraction (LVEF) during AF was prevented by AdCERG-G627S application (LVEF(CERG-G627S) = 62.1% ± 4.0% vs. LVEF(GFP) = 30.3% ± 9.1%; P < .001).

CONCLUSION

Inhibition of ERG function using atrial AdCERG-G627S gene transfer suppresses or delays the onset of persistent AF by prolongation of atrial refractoriness in a porcine model. Targeted gene therapy represents an alternative to pharmacological or ablative treatment of AF.

Covariate analysis of QTc and T-wave morphology: new possibilities in the evaluation of drugs that affect cardiac repolarization

This study adds the dimension of a T-wave morphology composite score (MCS) to the QTc interval-based evaluation of drugs that affect cardiac repolarization. Electrocardiographic recordings from 62 subjects on placebo and 400 mg moxifloxacin were compared with those from 21 subjects on 160 and 320 mg D,L-sotalol. T-wave morphology changes, as assessed by DeltaMCS, are larger after 320 mg D,L-sotalol than after 160 mg D,L-sotalol; and the changes associated with 160 mg D,L-sotalol are, in turn, larger than those associated with moxifloxacin and placebo. Covariate analyses of DeltaQTc and DeltaMCS showed that changes in T-wave morphology are a significant effect of D,L-sotalol. By contrast, moxifloxacin was found to have no significant effect on T-wave morphology (DeltaMCS) at any given change in QTc. This study offers new insights into the repolarization behavior of a drug associated with low cardiac risk vs. one associated with a high risk and describes the added benefits of a T-wave MCS as a covariate to the assessment of the QTc interval.

The effect of sertindole on QTD and TPTE

OBJECTIVE

Recent research suggests that other surrogate markers than QTc, including QTc dispersion and Tpeak-Tend, may better correlate with cardiac arrhythmia risk. While sertindole significantly prolongs the QTc interval, the effects on other markers of arrhythmia risk, such as QTc dispersion and Tpeak-Tend are unknown.

METHOD

Digital 12-lead ECG was recorded at baseline and at steady-state in 37 patients switched to sertindole. ECG was analysed for Fridericia-corrected QT duration (QTcF), QT dispersion and Tpeak-Tend.

RESULTS

From a baseline QTcF of 407 +/- 22 ms, mean QTcF prolongation during sertindole treatment was 20 +/- 23 ms, P < 0.01. No effect on QTc dispersion was found (-1 +/- 11 ms; P = 0.41). No increased duration of the Tpeak-Tend interval from baseline was found (+7 +/- 21 ms; P = 0.05).

CONCLUSION

These findings might be related to the absence of confirmed Torsade de Pointes (TdP) cases related to sertindole exposure, despite sertindole's QTc prolonging effects.

Beneficial Electrophysiological Effects of Trimetazidine in Patients With Postischemic Chronic Heart Failure

The aim of the study was to assess whether trimetazidine (TMZ) could affect dispersion of atrial depolarization and ventricular repolarization. Corrected QT interval (QTc), QTc dispersion (QTc-d), Tpeak—Tend, and Tpeak—Tend dispersion (Tpeak—Tend-d) were measured in 30 patients with chronic heart failure (CHF) before and 6 months after randomization to conventional therapy plus TMZ (17 patients) or conventional therapy alone (13 patients). After 6 months, QTc was significantly reduced in both groups, whereas QT-peak was increased only in control group. Tpeak—Tend-d decreased (from 63.53 ± 24.73 to 42.35 ± 21.07 milliseconds, P = .006) only in TMZ group. When subgrouped according to CHF etiology, only ischemic patients on TMZ showed Tpeak—Tend-d reduction (65.00 ± 27.14 vs 36.67 ± 11.55 milliseconds, P = .001 in ischemic patients; 60.00 ± 20.00 vs 56.00 ± 33.86 milliseconds, P = NS, in nonischemic). These electrophysiological properties indicate an undiscovered mechanism of action of TMZ, which could be useful in conditions at risk of major arrhythmias.

Thyrotoxicosis-induced ventricular arrhythmias

BACKGROUND

Cardiac arrhythmias associated with thyrotoxicosis tend to be supraventricular in nature with atrial fibrillation being the most common. Ventricular arrhythmias are rarely associated with thyrotoxicosis and are considered to be secondary to intrinsic cardiac disease.

SUMMARY

We present three patients with thyrotoxicosis and stable coronary disease in whom the primary cardiac rhythm disturbance was ventricular tachycardia. In all of these patients, the ventricular arrhythmias terminated with achievement of a euthyroid state. We hypothesize that the thyrotoxic state contributed to the etiology of, or lowered the threshold for the ventricular arrhythmias.

CONCLUSION

Prompt attention to the management of thyrotoxicosis in patients with a history of significant heart disease is warranted in order to avoid potentially fatal arrhythmias.

The additive effects of the active component of grapefruit juice (naringenin) and antiarrhythmic drugs on HERG inhibition

BACKGROUND

Grapefruit juice causes significant QT prolongation in healthy volunteers and naringenin has been identified as the most potent human ether-a-go-go-related gene (HERG) channel blocker among several dietary flavonoids. The interaction between naringenin and I(Kr)-blocking antiarrhythmic drugs has not been studied. We evaluated the effect of combining naringenin with I(Kr)-inhibiting antiarrhythmic drugs on cardiac I(Kr).

METHODS AND RESULTS

I(Kr) current was studied by using HERG expressed in Xenopus oocytes, and the two-electrode voltage clamp technique was employed. Antiarrhythmic drugs (azimilide, amiodarone, dofetilide and quinidine) were tested. Experiments were performed at room temperature. Naringenin blocked HERG current dose dependently with an IC(50) of 173.3 +/- 3.1 microM. Naringenin 100 microM alone inhibited HERG current by 31 +/- 6%, and this inhibitory effect was increased with coadministration of 1 or 10 microM antiarrhythmic drugs. When 100 microM naringenin was added to antiarrhythmic drugs, greater HERG inhibition was demonstrated, compared to the current inhibition caused by antiarrhythmic drugs alone. Addition of naringenin significantly increased current inhibition (p < 0.05).

CONCLUSIONS

There is an additive inhibitory effect on HERG current when naringenin is combined with I(Kr)-blocking antiarrhythmic drugs. This additive HERG inhibition could pose an increased risk of arrhythmias by increasing repolarization delay and possible repolarization heterogeneity.

Risk factors and predictors of Torsade de pointes ventricular tachycardia in patients with left ventricular systolic dysfunction receiving Dofetilide

The purpose of this study was to identify risk factors of Torsade de pointes (TdP) ventricular tachycardia in patients medicated with a class III antiarrhythmic drug (dofetilide) and left ventricular systolic dysfunction with heart failure (HF) or recent myocardial infarction (MI). The 2 Danish Investigations of Arrhythmia and Mortality on Dofetilide (DIAMOND) studies enrolled patients with HF (DIAMOND-HF) or MI (DIAMOND-MI) and left ventricular systolic dysfunction. The present analysis includes only patients treated solely with dofetilide. The incidence of TdP was 2.1% (32 of 1,511). Twenty-five of the incidences occurred in the DIAMOND-HF study and 7 cases in the DIAMOND-MI study (p = 0.0015). TdP was more frequent in women than in men (47% vs 28%, p = 0.02). Risk factors for developing TdP were female gender (odds ratio 2.2, 95% confidence interval [CI] 1.0 to 5.0), MI within 8 weeks (odds ratio 0.3, 95% CI 0.1 to 0.7), being in New York Heart Association class III or IV (odds ratio 3.2, 95% CI 1.2 to 8.6), and baseline QTc duration (odds ratio 1.14, 95% CI 1.00 to 1.30) per 10 ms. Women with chronic HF, QTc duration >400 ms. and New York Heart Association class III or IV had a risk of TdP of 10%, whereas no TdP episodes were observed in patients with QTc duration <400 ms. In conclusion, severity of HF, female gender, and QTc duration make it possible to identify patients with a high risk of early TdP when treated with dofetilide. Patients with recent MI less often had TdP compared with patients with chronic HF.

Idiopathic cardiac electrical storm

Cardiac electrical storm has been described as three or more distinct episodes of ventricular fibrillation or hemodynamically destabilizing ventricular tachycardia in a 24-h period, typically requiring treatment with electrical cardioversion or defibrillation. We report the case of a 45-year-old man who presented to the Emergency Department with idiopathic cardiac electrical storm, ultimately requiring defibrillation over 30 times in the Emergency Department and infusion of multiple antidysrhythmic agents for dysrhythmia control. Treatment of cardiac electrical storm entails immediate resuscitative therapy during the hemodynamically destabilizing episode (including cardioversion/defibrillation and the timely administration of antidysrhythmic agents), concurrent identification and correction of any factors that are potentially contributing to the acute dysrhythmia (i.e., electrolyte disturbances, myocardial ischemia), and ultimately, institution of long-term preventive therapy (such as an implantable cardioverter defibrillator) to quell recurrence. Amiodarone and beta-adrenergic blockers seem to be the agents of greatest clinical benefit to patients with cardiac electrical storm. Despite its potentially devastating nature, the majority of patients with cardiac electrical storm may have favorable clinical outcomes if the dysrhythmias are treated swiftly and aggressively.

Weighing the QT intervals with the slope or the amplitude of the T wave

OBJECTIVE

The reproducibility of QT interval measurements is low, even for the mean QT interval based on the standard ECG. In this study we analyzed whether the reproducibility of the mean weighed QT interval was better than the simple mean QT interval. The weighing was based on the amplitude of the T wave or the slope of the steepest tangent on the terminal part of the T wave.

MATERIAL AND METHODS

12-lead ECGs of 130 postmyocardial infarction patients were obtained. The QT intervals were measured by the tangent-method on two occasions by the same observer Mismatch QT intervals were defined as QT intervals that were measured at only one occasion. Sixteen ECGs were rejected. The data were split into 34 and 80 ECGs for optimization and validation of the weighing, respectively. The weighed QT dispersion was calculated as the weighed mean of the three longest minus the weighed mean of the three shortest QT intervals.

RESULTS

Weighing with the slope increased the reproducibility by 41% (P = 3 10(-6)), but weighing with the amplitude reduced it by 20% (P = 0.02). However, if measurements with errors above 75 ms were rejected, weighing with the slope or the amplitude increased the reproducibility with 26% and 20% (P = 0.02), respectively. Weighing did not change the reproducibility of the weighed QT dispersion.

CONCLUSION

Weighing with the slope improved the reproducibility of the mean weighed QT interval. However, if measurements with errors above 75 ms were rejected, weighing with the amplitude also increased the reproducibility. Weighing did not change the reproducibility of the weighed QT dispersion. Weighing is particularly efficient at reducing the negative impact of mismatch QT intervals on the reproducibility.

The prognostic accuracy of different QT interval measures

BACKGROUND

The QT intervals accuracy for predicting arrhythmic death varies between studies, possibly due to differences in the selection of the lead used for measurement of the QT interval. The purpose of this study was to analyze the prognostic accuracy of all known ways to select the lead.

METHODS AND RESULTS

Three institutions that used different methods for measuring QT intervals provided their QT databases. They included more than 3500 twelve-lead surface ECGs. The data represented low- and high-risk patients of the normal population (survivors vs dead from cardiovascular causes), acute myocardial infarction (survivors versus death from all causes) and remote myocardial infarction (with vs without a history of ventricular arrhythmia). The prognostic accuracy was defined as the area under the Receiver Operator Curve (ROC-area). The most accurate standard leads were I and aVL and the least accurate was AVR. The most accurate precordial lead was V4. The prognostic accuracy of the longest QT interval was higher than for any standard lead. The prognostic accuracy of the mean of the three longest QT intervals was equal to or slightly lower than for the longest QT interval.

CONCLUSIONS

The highest prognostic accuracy is obtained with the longest QT interval. The accuracies of the lead selection methods are so different that it can explain a substantial part of the differences between otherwise similar studies in the literature. We recommend the use of the mean value of the three longest QT intervals.

Pharmacogenetic issues in thorough QT trials

Drug-induced QT prolongation (DI-LQT), through its associated arrhythmias, is a leading cause of drugs being withdrawn from the market. As a consequence, the US FDA and other regulatory agencies are mandating that all new drugs go through a so-called 'Thorough QT' (TQT) study to evaluate the potential for 'QT liability', specifically the potential for a drug to cause a discernible increase in the QT interval. Several genetic factors that modulate the risk of DI-LQT have been discovered. These are genes responsible for the congenital long QT syndrome, drug metabolism genes (mainly CYP2D6 and CYP3A4), and genes in other regulatory pathways. Here, we briefly review the links between genetic variants and drug-induced QT risk, and propose approaches to consider for using pharmacogenetics in planning and analyzing TQT studies.

The Effect of High Extracellular Potassium on IKr Inhibition by Anti-Arrhythmic Agents

BACKGROUND

Hyperkalemia is a potentially life-threatening disorder frequently occurring in hospitalized patients. The ischemic myocardium releases potassium into the extracellular space which can cause regional hyperkalemia. These changes may modify the effects of anti-arrhythmic drugs acting on the rapid component of the delayed rectifier potassium current (IKr). We evaluated the influence of increased extracellular potassium concentration [K(+)](e) on IKr inhibition by amiodarone, azimilide, dofetilide, quinidine and sotalol.

METHODS AND RESULTS

Experiments were performed at room temperature. IKr current was studied by using HERG gene expressed in Xenopus oocytes as a model of cardiac IKr. Two-electrode voltage clamp technique was employed. The recording bath solutions contained either 5 or 10 mmol/l KCl. Amiodarone, azimilide, dofetilide, quinidine and sotalol all produced a dose-dependent inhibition of HERG current. At 5 mmol/l [K(+)](e), the IC(50) was 37.0 +/- 12.5 microM for amiodarone, 5.8 +/- 0.4 microM for azimilide, 1.5 +/- 0. 2 microM for dofetilide, 9.1 +/- 1.5 microM for quinidine, and 5.1 +/- 0.8 mM for sotalol. Raising the extracellular potassium to 10 mmol/l, HERG block by azimilide, dofetilide, quinidine and sotalol was significantly decreased, while the block by amiodarone was unchanged. The differences in the percentage current block produced by 3 microM drugs at 5 and 10 mmol/l [K(+)](e) were: -0.9% for amiodarone, 13.8% for quinidine, 20.5% for azimilide, and 16.2% for dofetilide. The differences in percentage block between 5 and 10 mmol/l [K(+)](e) by sotalol 10 and 30 mM were 7.1 and 5.6%. At 10 mmol/l [K(+)](e), the IC(50) was increased for azimilide, dofetilide, quinidine and sotalol but not for amiodarone; the IC(50) was 24.7 +/- 7.4 microM for amiodarone, 29.3 +/- 3.9 microM for azimilide, 2.7 +/- 0.2 microM for dofetilide, 27.6 +/- 4.0 microM for quinidine, and 7.2 +/- 1.7 mM for sotalol.

CONCLUSION

Inhibition of IKr by azimilide, quinidine, dofetilide and sotalol was diminished by increasing [K(+)](e), while the inhibition by amiodarone was unchanged at normal and high [K(+)](e). The differential effects of azimilide, dofetilide, quinidine and sotalol at normal and high [K(+)](e) could be pro-arrhythmic by favoring re-entry arrhythmias. These results further support the unique electrophysiological effect of amiodarone.

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

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

Pro-arrhythmic effects of amiodarone and concomitant rate-control medication

AIMS

Amiodarone is one of the most efficient and safe antiarrhythmic drugs in the treatment of atrial fibrillation (AF). Although pro-arrhythmic effects of amiodarone therapy are rare, the aim of the present study was to identify clinical constellations which may lead to amiodarone-associated pro-arrhythmia.

METHODS AND RESULTS

Sixty-three consecutive patients (pts) (49 males; 64+/-10.3 years; 35 with coronary heart disease, 17 with lone AF) were retrospectively included in this study. All received an oral (92.1%) or i.v. (7.9%) loading dose of amiodarone for the treatment of AF. Cardiac diseases, concomitant medical treatment, and incidence of pro-arrhythmic effects were analysed. Three pts (4.8% of the total population) developed a clinical relevant, polymorphic ventricular tachyarrhythmia, 3-48 h after initiation of amiodarone loading. Coronary heart disease was present in all of these pts, and in two of them left ventricular ejection fraction was severely reduced. The mean QTc in these pts was only slightly prolonged; mean heart rate was significantly decreased compared with the total study population (61.0+/-7.5 vs. 74.5+/-24.1 bpm; P < or = 0.05). In all pts with pro-arrhythmia, amiodarone (two pts i.v., one patient oral) was initiated during concomitant beta-blocker/digitalis therapy. Twenty-five per cent of the patients receiving this 'triple' therapy developed ventricular arrhythmia.

CONCLUSION

The present study implies that initiation of amiodarone therapy in pts with structural heart disease and AF that are concomitantly treated with beta-blockers and digitalis may have an increased risk of amiodarone-associated pro-arrhythmia.

"Torsade de Pointes" in Patients with Structural Heart Disease and Atrial Fibrillation Treated with Amiodarone, beta-Blockers, and Digitalis

Amiodarone is one of the most efficient and safe antiarrhythmic drugs in the treatment of atrial fibrillation (AF). Yet, though rare, proarrhythmic effects remain a clinical problem. We present three cases of amiodarone-associated "Torsade de pointes" tachycardia (Tdp) in patients treated concomitantly with heart rate controlling medication for AF. Amiodarone loading therapy was started for the treatment of tachyarrhythmic AF in all the three patients. All presented with a history of coronary heart disease, resulting in a severely reduced left ventricular ejection fraction in two patients. One received oral amiodarone loading, in the others, amiodarone was administered intravenously because of hemodynamically relevant AF episodes. Amiodarone therapy was combined with a heart rate controlling medication including a beta-blocking agent and digitalis in all the cases. All the subjects suffered from clinically relevant Tdp in the early run after initiation of amiodarone loading (max. 48 hours). The mean QTc in all patients before induction of Tdp was prolonged. The present case reports imply that amiodarone in combination with beta-blocker/digitalis therapy may be associated with an elevated proarrhythmic risk in selected patients with structural heart disease and AF.

Sustained torsade de pointes occurring early during oral sotalol therapy for atrial fibrillation recurrence prophylaxis in a patient without heart disease

This report describes a 64 year-old female patient admitted to our department for recurrent and symptomatic episodes of atrial fibrillation. Antiarrhythmic therapy with sotalol at 240 mg/day was started, and after 48 h the patient experienced several episodes of sustained torsade de pointes, dramatic marked QT interval prolongation and negative T wave, in absence of overt cardiac disease, renal failure, electrolyte abnormalities or baseline QT interval prolongation. This case emphasizes the importance of hospitalization at the starting of sotalol therapy, especially in female patients, even in absence of predisposing factors for drug-induced tachyarrhythmias.

The influence of extracellular acidosis on the effect of IKr blockers

BACKGROUND

Myocardial infarction causes the acidification of the cellular environment and the resultant acidosis maybe arrhythmogenic. The effect of acidosis on the action of antiarrhythmic drugs, an important issue in the antiarrhythmic drug therapy after myocardial infarction, remains to be studied.

METHODS

To evaluate the effect of acidosis on rectifier potassium current (Ikr) blockers, the human ether-a-go-go-related gene (HERG), which encodes IKr, was expressed in Xenopus laevis oocytes. The two electrodes voltage clamp technique was used and the experiments were performed at room temperature.

RESULTS

Quinidine (10 microM) inhibited HERG tail current by 37% +/- 5% at pH7.4. The block decreased to 5% +/- 2% with extracellular pH at 6.2. Dofetilide (0.3 microM) inhibited HERG tail current by 34% +/- 3% and 1% +/- 2% at extracellular pH 7.4 and 6.2, respectively. Azimilide (10 microM) inhibited HERG tail current by 59% +/- 3% and 17% +/- 3% at extracellular pH 7.4 and 6.2. There were significant differences in the HERG inhibition by quinidine, dofetilide, and azimilide between pH 7.4 and pH 6.2 (P < .01). The drug concentration blocking 50% of current (IC50) was 5.8 +/- 0.3 microM for azimilide, 9.9 +/- 1.0 microM for quinidine, and 0.5 +/- 0.02 microM for dofetilide at pH 7.4. When extracellular pH was decreased from 7.4 to 6.2, the IC50 increased to 95.5 +/- 11.3 microM for azimilide, 203.2 +/- 15.7 microM for quinidine, and 12.6 +/- 1.2 microM for dofetilide. Unlike quinidine, dofetilide, and azimilide, there was no significant difference in the percentage of current block by amiodarone between pH 6.2 and 7.4. For amiodarone, the IC50 was 38.3 +/- 8.5 microM at pH 7.4 and 27.3 +/- 1.6 microM at pH 6.2.

CONCLUSION

Our data show that the Ikr blocking effect of azimilide, dofetilide, and quinidine was attenuated at acid pH, whereas this was not the case for amiodarone. These observations may explain the efficacy of amiodarone in reducing arrhythmic death in patients after a myocardial infarction compared with other IKr blockers.

Electrophysiologic properties and antiarrhythmic actions of a novel antianginal agent

Ranolazine is a novel antianginal agent capable of producing anti-ischemic effects at plasma concentrations of 2 to 6 microM without a significant reduction of heart rate or blood pressure. This review summarizes the electrophysiologic properties of ranolazine. Ranolazine significantly blocks I(Kr) (IC(50) = 12 microM), late I(Na), late I(Ca), peak I(Ca), I(Na-Ca) (IC(50) = 5.9, 50, 296, and 91 microM, respectively) and I(Ks) (17% at 30 microM), but causes little or no inhibition of I(to) or I(K1). In left ventricular tissue and wedge preparations, ranolazine produces a concentration-dependent prolongation of action potential duration (APD) in epicardium, but abbreviation of APD of M cells, leading to either no change or a reduction in transmural dispersion of repolarization (TDR). The result is a modest prolongation of the QT interval. Prolongation of APD and QT by ranolazine is fundamentally different from that of other drugs that block I(Kr) and induce torsade de pointes in that APD prolongation is rate-independent (ie, does not display reverse rate-dependent prolongation of APD) and is not associated with early after depolarizations, triggered activity, increased spatial dispersion of repolarization, or polymorphic ventricular tachycardia. Torsade de pointes arrhythmias were not observed spontaneously nor could they be induced with programmed electrical stimulation in the presence of ranolazine at concentrations as high as 100 microM. Indeed, ranolazine was found to possess significant antiarrhythmic activity, acting to suppress the arrhythmogenic effects of other QT-prolonging drugs. Ranolazine produces ion channel effects similar to those observed after chronic exposure to amiodarone (reduced late I(Na), I(Kr), I(Ks), and I(Ca)). Ranolazine's actions to reduce TDR and suppress early after depolarization suggest that in addition to its anti-anginal actions, the drug possesses antiarrhythmic activity.

The new selective IKs?blocking agent HMR 1556 restores sinus rhythm and prevents heart failure in pigs with persistent atrial fibrillation

BACKGROUND

Antiarrhythmic drugs for treatment of atrial fibrillation in patients with heart failure are limited by proarrhythmia and low efficacy. Experimental studies indicate that the pure I(Ks) blocking agents chromanol 293b and HMR 1556 prolong repolarization more markedly at fast than at slow heart rates and during beta-adrenergic stimulation. These properties may overcome some of the above quoted limitations.

METHODS AND RESULTS

Ten domestic swine underwent pacemaker implantation (PM) and atrial burst pacing to induce persistent AF. Four days after onset of persistent AF, pigs were randomized to HMR 1556 (30 mg/kg, p.o., 10 days) or placebo. All animals receiving HMR 1556 converted to SR (5.2 +/- 1.9 days), whereas placebo pigs remained in AF. Pigs treated with placebo developed high ventricular rates (297 +/- 5 bpm) and severe heart failure, whereas pigs treated with HMR 1556 remained hemodynamically stable. Left ventricular ejection fraction on the day of euthanization was significantly lower in the placebo compared to the HMR 1556 group (30 +/- 4% vs. 69 +/- 5%, p < 0.005). Similar results were seen with epinephrine levels (placebo 1563 +/- 193 pmol/l vs. HMR 613 +/-196 pmol/l, p < 0.05). Right atrial monophasic action potentials were significantly longer in the HMR 1556 compared to the placebo group (230 +/- 7 ms vs. 174 +/- 13 ms, p < 0.05).

CONCLUSIONS

The new I(Ks) blocker HMR 1556 efficiently and safely restores SR and prevents CHF in a model of persistent AF. Restoration of SR is most likely linked to a marked prolongation of atrial repolarization even at high heart rates.

Pharmacological cardioversion of atrial fibrillation: current management and treatment options

Atrial fibrillation (AF) is the most common form of arrhythmia, carrying high social costs. It is usually first seen by general practitioners or in emergency departments. Despite the availability of consensus guidelines, considerable variations exist in treatment practice, especially outside specialised cardiological settings. Cardioversion to sinus rhythm aims to: (i) restore the atrial contribution to ventricular filling/output; (ii) regularise ventricular rate; and (iii) interrupt atrial remodelling. Cardioversion always requires careful assessment of potential proarrhythmic and thromboembolic risks, and this translates into the need to personalise treatment decisions. Among the many clinical variables that affect strategy selection, time from onset is crucial. In selected patients, pharmacological cardioversion of recent-onset AF can be a safely used, feasible and effective approach, even in internal medicine and emergency departments. In most cases of recent-onset AF, pharmacological cardioversion provides an important--and probably more cost effective--alternative to electrical cardioversion, which can then be employed as a second-line therapy for nonresponders. Class IC agents (flecainide or propafenone), which can be safely used in hospitalised patients with recent-onset AF without left ventricular dysfunction, can provide rapid conversion to sinus rhythm after either intravenous administration or oral loading. Although intravenous amiodarone requires longer conversion times, it is still the standard treatment for patients with heart failure. Ibutilide also provides good conversion rates and could be used for AF patients with left ventricular dysfunction (were it not for high costs). For long-lasting AF most pharmacological treatments have only limited efficacy and electrical cardioversion remains the gold standard in this setting. However, a widely used strategy involves pretreatment with amiodarone in the weeks before planned electrical cardioversion: this provides optimal prophylaxis and can sometimes even restore sinus rhythm. Dofetilide may also be capable of restoring sinus rhythm in up to 25-30% of patients and can be used in patients with heart failure. The potential risk of proarrhythmia increases the need for careful therapeutic decision making and management of pharmacological cardioversion. The results of recent trials (AFFIRM [Atrial Fibrillation Follow-up Investigation of Rhythm Management] and RACE [Rate Control versus Electrical Cardioversion for Persistent Atrial Fibrillation]) on rate versus rhythm control strategies in the long term have led to a generalised shift in interest towards rate control. Although carefully designed studies are required to better define the role of pharmacological rhythm control in specific AF settings, this alternative option remains a recommendable strategy for many patients, especially those in acute care.

Arrhythmogenic mechanisms of QT prolonging drugs: is QT prolongation really the problem?

Torsade de Pointes (TdP) is an atypical ventricular arrhythmias associated with the acquired and congenital forms of the long QT syndrome. The substrate for the arrhythmia develops as a consequence of the amplification of electrical heterogeneities intrinsic to the ventricular myocardium. These heterogeneities exist because of differences in the time course of repolarization of the three predominant cell types that make up the ventricular myocardium, giving rise to transmural voltage gradients and a dispersion of repolarization responsible for the inscription of the electrocardiographic T wave. A wide variety of drugs are capable of reducing net repolarizing current and thus amplifying the intrinsic spatial dispersion of repolarization, so as to create the substrate for the development of re-entry. The result is a prolongation of the QT interval, abnormal T waves, and development of polymorphic re-entrant ventricular tachycardia displaying characteristics of TdP. Recent studies demonstrate that prolongation of the QT interval is not the sole determinant of the potential of a drug to cause TdP; agents that do not increase transmural dispersion of repolarization have little or no potential to induce the arrhythmia despite their ability to prolong the QT interval. Moreover, drugs such as sodium pentobarbital, which reduce transmural dispersion of repolarization, can diminish the likelihood of TdP, despite their ability to prolong the QT interval.

Antiarrhythmic Properties of a Prior Oral Loading of Amiodarone in In Vivo Canine Coronary Ligation/Reperfusion-Induced Arrhythmia Model: Comparison With Other Class III Antiarrhythmic Drugs

Amiodarone, which is generally classified as class III antiarrhythmic drug in the Vaughan Williams classification, is widely used for the treatments of refractory arrhythmias. However, we previously reported that intravenous infusion of amiodarone (6.67 mg/kg per hour) did not suppress arrhythmias induced by coronary ligation/reperfusion in dogs. In this study, we examined effects of a prior oral loading of amiodarone on arrhythmias induced by coronary ligation/reperfusion. Sixteen female beagle dogs (8.5 - 12.5 kg) were divided into two groups; one group was given amiodarone (40 mg/kg, orally, n = 8), and the other was given empty gelatin capsules (n = 8) 2 h before the operation. Dogs were anesthetized with pentobarbital and artificially ventilated. The left chest was opened, and the left anterior descending coronary artery was ligated for 30 min and then reperfused. The mean plasma concentration of amiodarone was over 1.3 mug/ml. Although the prior oral loading of amiodarone did not change the QT interval, amiodarone suppressed the number of ectopic beats during coronary ligation and the incidence of ventricular fibrillation during coronary ligation and reperfusion periods (P<0.05 vs control group). In conclusion, a prior oral loading of amiodarone suppressed arrhythmias induced by coronary ligation/reperfusion with a dose that did not prolong the QT interval. This antiarrhythmic property of amiodarone is different from those of the other class III drugs in that antiarrhythmic effects were accompanied by QT prolongation in our all previous studies.

QT prolongation with antimicrobial agents: understanding the significance

Cardiac toxicity has been relatively uncommon within the antimicrobial class of drugs, but well described for antiarrhythmic agents and certain antihistamines. Macrolides, pentamidine and certain antimalarials were traditionally known to cause QT-interval prolongation, and now azole antifungals, fluoroquinolones and ketolides can be added to the list. Over time, advances in preclinical testing methods for QT-interval prolongation and a better understanding of its sequelae, most notably torsades de pointes (TdP), have occurred. This, combined with the fact that five drugs have been removed from the market over the last several years, in part because of QT-interval prolongation-related toxicity, has elevated the urgency surrounding early detection and characterisation methods for evaluating non-antiarrhythmic drug classes. With technological advances and accumulating literature regarding QT prolongation, it is currently difficult or overwhelming for the practising clinician to interpret these data for purposes of formulary review or for individual patient treatment decisions. Certain patients are susceptible to the effects of QT-prolonging drugs. For example, co-variates such as gender, age, electrolyte derangements, structural heart disease, end organ impairment and, perhaps most important, genetic predisposition, underlie most if not all cases of TdP. Between and within classes of drugs there are important differences that contribute to delayed repolarisation (e.g. intrinsic potency to inhibit certain cardiac ion currents or channels, and pharmacokinetics). To this end, a risk stratification scheme may be useful to rank and compare the potential for cardiotoxicity of each drug. It appears that in most published cases of antimicrobial-associated TdP, multiple risk factors are present. Macrolides in general are associated with a greater potential than other antimicrobials for causing TdP from both a pharmacodynamic and pharmacokinetic perspective. The azole antifungal agents also can be viewed as drugs that must be weighed carefully before use since they also have both pharmacodynamic and pharmacokinetic characteristics that may trigger TdP. The fluoroquinolones appear less likely to be associated with TdP from a pharmacokinetic perspective since they do not rely on cytochrome P450 (CYP) metabolism nor do they inhibit CYP enzyme isoforms, with the exception of grepafloxacin and ciprofloxacin. Nonetheless, patient selection must be carefully made for all of these drugs. For clinicians, certain responsibilities are assumed when prescribing antimicrobial therapy: (i) appropriate use to minimise resistance; and (ii) appropriate patient and drug selection to minimise adverse event potential. Incorporating information learned regarding QT interval-related adverse effects into the drug selection process may serve to minimise collateral iatrogenic toxicity.