Carbon monoxide-releasing molecules inhibit the cystic fibrosis transmembrane conductance regulator Cl- channel.

The gasotransmitter carbon monoxide (CO) regulates fluid and electrolyte movements across epithelial tissues. However, its action on anion channels is incompletely understood. Here, we investigate the direct action of CO on the cystic fibrosis transmembrane conductance regulator (CFTR) by applying CO-releasing molecules (CO-RMs) to the intracellular side of excised inside-out membrane patches from cells heterologously expressing wild-type human CFTR. Addition of increasing concentrations of tricarbonyldichlororuthenium(II) dimer (CORM-2) (1-300 µM) inhibited CFTR channel activity, whereas the control RuCl3 (100 µM) was without effect. CORM-2 predominantly inhibited CFTR by decreasing the frequency of channel openings and, hence, open probability (Po). But, it also reduced current flow through open channels with very fast kinetics, particularly at elevated concentrations. By contrast, the chemically distinct CO-releasing molecule CORM-3 inhibited CFTR by decreasing Po without altering current flow through open channels. Neither depolarizing the membrane voltage nor raising the ATP concentration on the intracellular side of the membrane affected CFTR inhibition by CORM-2. Interestingly, CFTR inhibition by CORM-2, but not by CFTRinh-172, was prevented by prior enhancement of channel activity by the clinically approved CFTR potentiator ivacaftor. Similarly, when added after CORM-2, ivacaftor completely relieved CFTR inhibition. In conclusion, CORM-2 has complex effects on wild-type human CFTR consistent with allosteric inhibition and open-channel blockade. Inhibition of CFTR by CO-releasing molecules suggests that CO regulates CFTR activity and that the gasotransmitter has tissue-specific effects on epithelial ion transport. The action of ivacaftor on CFTR Cl- channels inhibited by CO potentially expands the drug's clinical utility.

Error recovery by dialysis technicians.

Experts are believed to make fewer errors than novices. Researchers in other domains have shown that experts not only make less errors, they also detect and recover from these errors better than non-experts. To investigate this phenomenon among dialysis technicians working in hemodialysis, we evaluated the ability of dialysis technicians to detect and recover from healthcare errors. Two clinical cases with embedded errors were created by an expert nephrology nurse. Twenty-four dialysis technician subjects read the cases aloud and then answered a set of related questions. Subjects' error detection and recovery responses were scored against the clinical cases. We found that there was no significant difference between the ability of expert and non-expert dialysis technicians to detect errors. However, expert dialysis technicians recovered from significantly more healthcare errors than less experienced non-expert dialysis technicians. This has implications for training dialysis technicians in better error detection and recovery strategies.

Carbon monoxide: an emerging regulator of ion channels.

Carbon monoxide is rapidly emerging as an important cellular messenger, regulating a wide range of physiological processes. Crucial to its role in both physiology and disease is its ability differentially to regulate several classes of ion channels, including examples from calcium-activated K(+) (BK(Ca)), voltage-activated K(+) (K(v)) and Ca(2+) channel (L-type) families, ligand-gated P2X receptors (P2X2 and P2X4), tandem P domain K(+) channels (TREK1) and the epithelial Na(+) channel (ENaC). The mechanisms by which CO regulates these ion channels are still unclear and remain somewhat controversial. However, available structure-function studies suggest that a limited range of amino acid residues confer CO sensitivity, either directly or indirectly, to particular ion channels and that cellular redox state appears to be important to the final integrated response. Whatever the molecular mechanism by which CO regulates ion channels, endogenous production of this gasotransmitter has physiologically important roles and is currently being explored as a potential therapeutic.

Alveolar epithelial CNGA1 channels mediate cGMP-stimulated, amiloride-insensitive, lung liquid absorption.

Impairment of lung liquid absorption can lead to severe respiratory symptoms, such as those observed in pulmonary oedema. In the adult lung, liquid absorption is driven by cation transport through two pathways: a well-established amiloride-sensitive Na(+) channel (ENaC) and, more controversially, an amiloride-insensitive channel that may belong to the cyclic nucleotide-gated (CNG) channel family. Here, we show robust CNGA1 (but not CNGA2 or CNGA3) channel expression principally in rat alveolar type I cells; CNGA3 was expressed in ciliated airway epithelial cells. Using a rat in situ lung liquid clearance assay, CNG channel activation with 1 mM 8Br-cGMP resulted in an approximate 1.8-fold stimulation of lung liquid absorption. There was no stimulation by 8Br-cGMP when applied in the presence of either 100 µM L: -cis-diltiazem or 100 nM pseudechetoxin (PsTx), a specific inhibitor of CNGA1 channels. Channel specificity of PsTx and amiloride was confirmed by patch clamp experiments showing that CNGA1 channels in HEK 293 cells were not inhibited by 100 µM amiloride and that recombinant αßγ-ENaC were not inhibited by 100 nM PsTx. Importantly, 8Br-cGMP stimulated lung liquid absorption in situ, even in the presence of 50 µM amiloride. Furthermore, neither L: -cis-diltiazem nor PsTx affected the ß(2)-adrenoceptor agonist-stimulated lung liquid absorption, but, as expected, amiloride completely ablated it. Thus, transport through alveolar CNGA1 channels, located in type I cells, underlies the amiloride-insensitive component of lung liquid reabsorption. Furthermore, our in situ data highlight the potential of CNGA1 as a novel therapeutic target for the treatment of diseases characterised by lung liquid overload.

The carbon monoxide donor, CORM-2, is an antagonist of ATP-gated, human P2X4 receptors.

Carbon monoxide (CO) is produced endogenously by heme oxygenase (HO) enzymes. HO-1 is highly expressed in many inflammatory disease states, where it is broadly protective. The protective effects of HO-1 expression can be largely mimicked by the exogenous application of CO and CO-releasing molecules (CORMs). Despite a dearth of pharmacological tools for their study, molecular methodologies have identified P2X4 receptors as a potential anti-nociceptive drug target. P2X4 receptors are up-regulated in animal models of inflammatory pain, and their knock-down reduces pain behaviours. In these same animal models, HO-1 expression is anti-nociceptive, and we therefore investigated whether P2X4 was a target for CO and tricarbonyldichlororuthenium (II) dimer (CORM-2). Using conventional whole-cell and perforated-patch recordings of heterologously expressed human P2X4 receptors, we demonstrate that CORM-2, but not CO gas, is an inhibitor of these channels. We also investigated the role of soluble guanylate cyclase and mitochondria-derived reactive oxygen species using pharmacological inhibitors but found that they were largely unable to affect the ability of CORM-2 to inhibit P2X4 currents. A control breakdown product of CORM-2 was also without effect on P2X4. These results suggest that P2X4 receptors are not a molecular target of endogenous CO production and are, therefore, unlikely to be mediating the anti-nociceptive effects of HO-1 expression in inflammatory pain models. However, these results show that CORM-2 is an effective antagonist at human P2X4 receptors and represents a useful pharmacological tool for the study of these receptors given the current dearth of antagonists.

An exon 5-less splice variant of the extracellular calcium-sensing receptor rescues absence of the full-length receptor in the developing mouse lung.

The authors have recently demonstrated that, in the developing mouse lung, fetal plasma Ca(2+) suppresses branching morphogenesis and cell proliferation while promoting fluid secretion via activation of the extracellular Ca(2+)-sensing receptor (CaSR). The aim of the current study was to further elucidate the role of Ca(2+) in lung development by studying the effects of extracellular Ca(2+) on fetal lung development in mice lacking the CaSR. These mice were produced by exon 5 deletion in the CaSR gene. Since such a maneuver has been known to induce the expression of an exon 5-less splice variant of the CaSR in some tissues, the molecular and functional expression of this splice variant in the developing mouse lung was also investigated. Whereas there was a mild in vivo phenotype observed in these mice, in vitro sensitivity of Casr(-/-) lung explants to specific activators of the CaSR was unaffected. These results imply that compensatory expression of an exon 5-less splice variant rescues CaSR function in this mouse model and therefore a lung-specific, complete CaSR knockout model must be developed to fully appreciate the role for this receptor in lung development and the contribution of its ablation to postnatal respiratory disease.

Purinergic signaling in the pulmonary neuroepithelial body microenvironment unraveled by live cell imaging.

Pulmonary neuroepithelial bodies (NEBs) are densely innervated groups of complex sensory airway receptors involved in the regulation of breathing. Together with their surrounding Clara-like cells, they exhibit stem cell potential through their capacity to regenerate depopulated areas of the epithelium following lung injury. We have employed confocal live cell imaging microscopy and novel electrophysiological techniques in a new ex vivo lung slice model to unravel potential purinergic signaling pathways within the NEB microenvironment. Quinacrine histochemistry indicated high amounts of vesicular ATP in NEB cells. Using a "reporter-patching" method adapted to create a uniquely sensitive and selective biosensor for the direct detection of ATP release from NEBs ex vivo, we demonstrated quantal ATP release from NEBs following their depolarization. Enhancing enzymatic extracellular ATP hydrolysis or inhibiting P2 receptors confirmed the central role of ATP in paracrine interactions between NEB cells and Clara-like cells. Combined calcium imaging, pharmacology, and immunohistochemistry showed that ligand-binding to functional P2Y(2) receptors underpins the activation of Clara-like cells. Hence, NEB cells communicate with their cellular neighbors in the NEB microenvironment by releasing ATP, which rapidly evokes purinergic activation of surrounding Clara-like cells. Besides ATP acting on the P2X(3) receptor expressing vagal sensory nerve terminals between NEB cells, local paracrine purinergic signaling within this potential stem cell niche may be important to both normal airway function, airway epithelial regeneration after injury, and/or the pathogenesis of small cell lung carcinomas.

Analytical study of gyrophase, pitch angle, and normal speed of particles leaving an ideal magnetohydrodynamic discontinuity surface.

Particle populations that have velocity distributions with only a small spread of gyrophase angles are commonly observed in the vicinity of magnetohydrodynamic (MHD) discontinuity surfaces such as collisionless shocks. Previous theoretical particle trajectory studies have concentrated on ion behavior at an ideal planar Earth's bow shock and have either assumed that a gyrotropic incident initial velocity distribution is reflected at the surface or instead focused on unique fixed initial gyrophase and pitch angle values specified by the generation mechanism assumed for the particle. In this analytical study of trajectories of particles departing an ideal planar MHD surface we demonstrate that a particle's initial gyrophase and pitch angle determine completely whether it will escape the surface or return to it, regardless of its initial energy. We identify the region in initial gyrophase-pitch angle space which leads to trajectories that return to the surface of the discontinuity. The speed normal to the surface of a returning particle, which can affect its ability to traverse the discontinuity, is shown to increase or decrease compared to its initial value according only to the orientation of its guiding-center motion in the frame of reference in which the discontinuity is at rest and the incoming plasma flow is aligned with the constant magnetic field. The dependence of our results on the direction of the upstream magnetic field is illustrated. Our general analytical results are discussed in the context of observations at the Earth's bow shock.

Novel regulatory aspects of the extracellular Ca2+-sensing receptor, CaR.

The capacity to sense and adapt to changes in environmental cues is of paramount importance for every living organism. From yeast to man, cells must be able to match cellular activities to growth environment and nutrient availability. Key to this process is the development of membrane-bound systems that can detect modifications in the extracellular environment and to translate these into biological responses. Evidence gathered over the last 15 years has demonstrated that many of these cell surface "sensors" belong to the G protein-coupled receptor superfamily. Crucial to our understanding of nutrient sensing in mammalian species has been the identification of the extracellular Ca(2+)/cation-sensing receptor, CaR. CaR was the first ion-sensing molecule identified in man and genetic studies in humans have revealed the importance of the CaR in mineral ion metabolism. Latter, it has become apparent that the CaR also plays an important role outside the Ca(2+) homeostatic system, as an integrator of multiple environmental signals for the regulation of many vital cellular processes, from cell-to-cell communication to secretion and cell survival/cell death. Recently, novel aspects of receptor function reveal an unexpected role for the CaR in the regulation of growth and development in utero.

Regulation of mouse lung development by the extracellular calcium-sensing receptor, CaR.

Postnatal lung function is critically dependent upon optimal embryonic lung development. As the free ionized plasma calcium concentration ([Ca(2+)](o)) of the fetus is higher than that of the adult, the process of lung development occurs in a hypercalcaemic environment. In the adult, [Ca(2+)](o) is monitored by the G-protein coupled, extracellular calcium-sensing receptor (CaR), but neither its ontogeny nor its potential role in lung development are known. Here, we demonstrate that CaR is expressed in the mouse lung epithelium, and that its expression is developmentally regulated, with a peak of expression at embryonic day 12.5 (E12.5) and a subsequent decrease by E18, after which the receptor is absent. Experiments carried out using the lung explant culture model in vitro show that lung branching morphogenesis is sensitive to [Ca(2+)](o), being maximal at physiological adult [Ca(2+)](o) (i.e. 1.0-1.3 mM) and lowest at the higher, fetal (i.e. 1.7 mM) [Ca(2+)](o). Administration of the specific CaR positive allosteric modulator, the calcimimetic R-568, mimics the suppressive effects of high [Ca(2+)](o) on branching morphogenesis while both phospholipase C and PI3 kinase inhibition reverse these effects. CaR activation suppresses cell proliferation while it enhances intracellular calcium signalling, lung distension and fluid secretion. Conditions which are restrictive either to branching or to secretion can be rescued by manipulating [Ca(2+)](o) in the culture medium. In conclusion, fetal Ca(2+)(o), acting through a developmentally regulated CaR, is an important extrinsic factor that modulates the intrinsic lung developmental programme. Our observations support a novel role for the CaR in preventing hyperplastic lung disease in utero.

Azimilide for the treatment of atrial fibrillation, atrial flutter, and paroxysmal supraventricular tachycardia: results of a randomized trial and insights on the concordance of symptoms and recurrent arrhythmias.

INTRODUCTION: Azimilide hydrochloride is an investigational antiarrhythmic medication that had shown evidence of efficacy in prolonging the time to recurrence of atrial fibrillation (AF) or atrial flutter (AFL) and paroxysmal supraventricular tachycardia (PSVT). This study was designed to confirm efficacy of 125 mg daily azimilide. METHODS AND RESULTS: The primary endpoint was ECG-documented recurrence of AF, AFL, or PSVT, followed for a maximum of 180 days. Four hundred eighty-two patients were enrolled in the United States and Canada (422 with AF or AFL and 60 with PSVT). The primary efficacy analysis included 402 patients with AF-AFL and 56 patients with PSVT. There was no significant difference in the time to first recurrence of symptomatic supraventricular arrhythmia in the AF-AFL stratum (median of 38 days for azimilide versus 27 days for placebo; hazard ratio [HR] of 1.14, P = 0.29). Similarly, there was no difference in time to recurrence in the PSVT stratum (>180 days for azimilide versus 135 days for placebo; HR = 1.28, P = 0.55). There were three deaths in the azimilide group and one in the placebo group. Four patients had nonsustained ventricular tachycardia (one torsades de pointes), all in the azimilide group. Asymptomatic recurrence was frequent in the AF-AFL group (8% with azimilide and 11% with placebo), but was absent in the PSVT group. False recurrence was common in both groups. CONCLUSION: Azimilide 125 mg daily was not associated with significant prolongation of the time to recurrent symptomatic supraventricular arrhythmias. There was substantial discordance between symptoms and recurrence.

Antiarrhythmic efficacy of azimilide in patients with atrial fibrillation. Maintenance of sinus rhythm after conversion to sinus rhythm.

BACKGROUND: Azimilide dihydrochloride (azimilide) is an investigational antiarrhythmic drug that has been tested in patients with a variety of arrhythmias. In patients with atrial fibrillation, it has shown excellent efficacy in some previous trials and minimal efficacy in others. METHODS: Patients who had symptomatic atrial fibrillation for > 48 hours but < 6 months were eligible for this multicenter, randomized, placebo-controlled clinical trial. Patients were admitted to a hospital and randomly assigned to receive either azimilide 125 mg or a matched placebo twice daily for 3 days and then once daily. Patients who were in sinus rhythm spontaneously or had sinus rhythm restored by electric cardioversion on day 4 were discharged from the hospital. Recurrence of atrial fibrillation was documented by electrocardiogram. In the primary efficacy analysis, time to recurrence in the 2 treatment groups was compared with the log-rank test in the subgroup of patients with structural heart disease. Safety was assessed as deaths, adverse events, and serious adverse events. RESULTS: A total of 446 patients were randomized in the study; 314 were in the subgroup with structural heart disease. The median time to arrhythmia recurrence in both treatment groups with structural heart disease was 13 days, and the difference between treatments was not significant (P = .4596, n = 314). The relative risk for recurrence (placebo:azimilide) was 1.104 (95% CI 0.849-1.436). There was 1 death in the placebo group and 3 in the azimilide group. CONCLUSIONS: Azimilide did not demonstrate clinically important or statistically significant efficacy in reducing the risk for arrhythmia recurrence in patients with structural heart disease who were in atrial fibrillation and converted to sinus rhythm.

Efficacy of azimilide for the maintenance of sinus rhythm in patients with paroxysmal atrial fibrillation in the presence and absence of structural heart disease.

Azimilide hydrochloride (azimilide), an investigational antiarrhythmic drug, has shown variable efficacy in preventing atrial fibrillation (AF). This study was designed to assess its efficacy in maintaining sinus rhythm in patients with paroxysmal AF and heart disease. Patients with symptomatic paroxysmal AF were screened for 1 month by transtelephonic monitoring. After recording 1 episode of AF in the screening period, they were randomized to receive azimilide 125 mg or placebo once daily. Patients were stratified by the presence or absence of congestive heart failure or coronary heart disease (CHF/CHD). A maximum of 220 patients without CHF/CHD were randomized, with the remainder having CHF/CHD. Patients with CHF/CHD were monitored for 3 days during loading. The primary efficacy analysis was the time to the first symptomatic recurrence of AF in the CHF/CHD group. Secondary analyses were the time to the first recurrence in the entire population and the time to the first recurrence in those with significant structural heart disease. The median time to recurrence of AF in the CHF/CHD group was 10 days in the 2 treatment arms. Nonsignificant trends were seen toward efficacy of azimilide in the CHF/CHD group (hazard ratio 1.28, 95% confidence interval 0.97 to 1.70, p=0.087), structural heart disease group (hazard ratio 1.22, 95% confidence interval 0.96 to 1.56, p=0.11), and overall group (hazard ratio 1.22, 95% confidence interval 1.00 to 1.49, p=0.053). No patient died. In conclusion, azimilide showed a nonsignificant trend toward efficacy in maintaining sinus rhythm in patients with AF.

Indicators of activity-friendly communities: an evidence-based consensus process.

BACKGROUND: Regular physical activity, even at modest intensities, is associated with many health benefits. Most Americans, however, do not engage in the recommended levels. As practitioners seek ways to increase population rates of physical activity, interventions and advocacy efforts are being targeted to the community level. Yet, advocates, community leaders, and researchers lack the tools needed to assess local barriers to and opportunities for more active, healthy lifestyles. Investigators used a systematic review process to identify key indicators of activity-friendly communities that can assess and improve opportunities for regular physical activity. METHODS: Investigators conducted a comprehensive literature review of both peer-reviewed literature and fugitive information (e.g., reports and websites) to generate an initial list of indicators for review (n=230). The review included a three-tiered, modified Delphi consensus-development process that incorporated input of international, national, state, and local researchers and practitioners from academic institutions, federal and state government agencies, nonprofit organizations, and funding agencies in public health, transportation, urban planning, parks and recreation, and public policy. RESULTS: Ten promising indicators of activity-friendly communities were identified: land use environment, access to exercise facilities, transportation environment, aesthetics, travel patterns, social environment, land use economics, transportation economics, institutional and organizational policies, and promotion. CONCLUSIONS: Collaborative, multidisciplinary approaches are underway to test, refine, and expand this initial list of indicators and to develop measures that communities, community leaders, and policymakers can use to design more activity-friendly community environments.

The extracellular calcium-sensing receptor regulates human fetal lung development via CFTR.

Optimal fetal lung growth requires anion-driven fluid secretion into the lumen of the developing organ. The fetus is hypercalcemic compared to the mother and here we show that in the developing human lung this hypercalcaemia acts on the extracellular calcium-sensing receptor, CaSR, to promote fluid-driven lung expansion through activation of the cystic fibrosis transmembrane conductance regulator, CFTR. Several chloride channels including TMEM16, bestrophin, CFTR, CLCN2 and CLCA1, are also expressed in the developing human fetal lung at gestational stages when CaSR expression is maximal. Measurements of Cl(-)-driven fluid secretion in organ explant cultures show that pharmacological CaSR activation by calcimimetics stimulates lung fluid secretion through CFTR, an effect which in humans, but not mice, was also mimicked by fetal hypercalcemic conditions, demonstrating that the physiological relevance of such a mechanism appears to be species-specific. Calcimimetics promote CFTR opening by activating adenylate cyclase and we show that Ca(2+)-stimulated type I adenylate cyclase is expressed in the developing human lung. Together, these observations suggest that physiological fetal hypercalcemia, acting on the CaSR, promotes human fetal lung development via cAMP-dependent opening of CFTR. Disturbances in this process would be expected to permanently impact lung structure and might predispose to certain postnatal respiratory diseases.

Asymptomatic or "silent" atrial fibrillation: frequency in untreated patients and patients receiving azimilide.

BACKGROUND: Asymptomatic, or "silent" atrial fibrillation could increase the risk of stroke. Little is known about the frequency of asymptomatic atrial fibrillation in patients who also have symptomatic atrial fibrillation; similarly, little is known about the effect of antiarrhythmic drug therapy on asymptomatic atrial fibrillation. METHODS AND RESULTS: Patients in sinus rhythm with a history of symptomatic atrial fibrillation or atrial flutter received placebo or azimilide (35 to 125 mg) once daily for 6 or 9 months in 4 similar double-blind trials. The end point was the first recurrence of a symptomatic ECG-documented supraventricular arrhythmia. Routine transtelephonic electrocardiograms, in the absence of symptoms, were recorded for 30 seconds every 2 weeks until patients completed follow-up or documented a symptomatic supraventricular arrhythmia. Of the 1380 patients, 489 received placebo. Among these patients receiving placebo, 303 transmitted at least one routine ECG while asymptomatic. Asymptomatic atrial fibrillation was recorded in 50 (17%) within 6 months and before recurrence of symptomatic supraventricular arrhythmia. In the 3 trials evaluating azimilide in therapeutic doses (100 and 125 mg), asymptomatic atrial fibrillation occurred in 49 of 382 (13%) receiving azimilide and 43 of 233 (18%) receiving placebo. Although drug effect on time to first asymptomatic event was not statistically significant (hazard ratio, 0.70; P=0.09), there was a 40% reduction in asymptomatic atrial fibrillation on azimilide compared with placebo (P=0.03) when repeated observations were considered. CONCLUSIONS: Asymptomatic atrial fibrillation is common in untreated patients with a history of symptomatic atrial fibrillation (and is likely underestimated by this analysis). Azimilide may reduce the occurrence of this silent arrhythmia.

Antiarrhythmic effects of azimilide in paroxysmal supraventricular tachycardia: efficacy and dose-response.

BACKGROUND: Azimilide is a novel classification III antiarrhythmic agent that blocks both I(Kr)and I(Ks)and shows evidence of efficacy in patients with atrial fibrillation or flutter. Its effect on paroxysmal supraventricular tachycardia (PSVT) has not been reported. METHODS AND RESULTS: One hundred ninety-three patients with symptomatic PSVT were enrolled in 4 double-blind, randomized, placebo-controlled clinical trials with almost identical trial design (supraventricular arrhythmia-1 [SVA-1], SVA-2, SVA-3, and SVA-4), performed as a separate stratum of studies that also included a stratum of patients with atrial fibrillation or flutter. Patients received oral azimilide (100 mg in SVA-1 and SVA-3, 35 or 75 mg in SVA-2, and 125 mg in SVA-4) or matching placebo twice daily for 3 days (loading period), followed by once-daily dosing (maintenance period). The primary outcome variable was the first recording of a symptomatic supraventricular arrhythmia (either PSVT, atrial fibrillation, or atrial flutter) recorded on a transtelephonic electrocardiographic event recorder. The duration of study was 270 days in SVA-1 and SVA-2 and 180 days in SVA-3 and SVA-4. Combined analysis results of the PSVT stratum from the 4 studies showed a dose-response relationship in prolongation of time to recurrence (P =.02). In the combined 100-mg daily dose, the hazard ratio (placebo:azimilide) was 2.35 (P =.023). The hazard ratio for the 125-mg daily dose measured 1.28 (P = not significant). However, the time to recurrence was prolonged when the patients receiving 100 and 125 mg daily were combined and compared with placebo (P =.02). There were no deaths and 1 case of torsades de pointes. CONCLUSION: These trial results suggest a significant dose-related suppression of PSVT with azimilide, with a low risk of serious adverse events.

Symptoms at the time of arrhythmia recurrence in patients receiving azimilide for control of atrial fibrillation or flutter: results from randomized trials.

BACKGROUND: Azimilide is a new antiarrhythmic agent being developed for the management for atrial fibrillation and flutter (AF). Four randomized, placebo-controlled, double-blind trials have been performed that investigated the effect of azimilide on time to first recurrence of symptomatic AF. This paper examines the data collected during those studies regarding the symptoms reported by patients at the time of AF recurrence METHODS: At the time that patients reported their first documented symptomatic recurrence of arrhythmia, they were systematically asked whether or not they were experiencing any of the following 6 symptoms: palpitation, fatigue, chest pain, shortness of breath, dizziness, or sweating. Patients were required to answer yes or no. A symptom score was created varying from 0 to 6, in increasing order of number of symptoms reported. This was compared for patients receiving either of 2 doses of azimilide or placebo. The relationship between the number of symptoms, heart rate at time of arrhythmia recurrence and treatment was analyzed. RESULTS: In 2 separate studies, azimilide at a dose of 125 mg/day significantly reduced the number of symptoms at the time of arrhythmia recurrence compared to placebo. On the other hand, in 2 studies, the dose of 100 mg/day did not significantly reduce symptom burden. The individual symptoms significantly reduced by azimilide125 mg/day were fatigue, shortness of breath, chest pain and dizziness. Palpitations and sweating were not significantly reduced. Modeling of heart rate at the time of arrhythmia recurrence, symptoms and treatment indicated that a small reduction in heart rate with azimilide accounted for only a small part of the symptom reduction. There was another effect of azimilide: an average reduction of 0.38 symptoms (P <.01) that was independent of heart rate. CONCLUSION: Azimilide (125 mg/day) reduces the number of symptoms reported at the time of AF recurrence.

Effects of azimilide on heart rate and ECG conduction intervals during sinus rhythm in patients with a history of atrial fibrillation.

The purpose of this study was to assess the effect of azimilide, a Class III antiarrhythmic drug, on ECG conduction intervals recorded during sinus rhythm in patients with a history of symptomatic atrial fibrillation or atrial flutter. In Phase I clinical pharmacology studies, azimilide was associated with prolongation of the QT and QTc intervals on electrocardiograms recorded during sinus rhythm in normal subjects, but the effect of azimilide on the target population of patients with atrial fibrillation has not been reported in detail previously. Patients with a history of atrial fibrillation, atrial flutter, or both were randomly assigned to receive placebo or azimilide twice daily for 3 days and then qd thereafter. Azimilide doses of 50 mg, 100 mg, or 125 mg were tested. The RR, PR, QRS, QT, QTc(Bazett), and QTc(Fridericia) intervals were measured from electrocardiograms recorded at baseline and on Day 4 of test therapy. Increasing azimilide doses were associated with significant increases in the RR, QT, QTc(Bazett), and QTc(Fridericia) compared with changes in the placebo group based on the F-test for differences among treatment groups and the test for a dose response. In the azimilide 125 mg dose group, the mean change in RR was significantlygreater than the mean change in the placebo group (+61.4 ms in the azimilide 125 mg group vs. -14.1 ms in the placebo group). The mean change in QT was significantly greater in the azimilide 125 mg group than the mean change in the placebo group (+44.2 ms in the azimilide 125 mg group vs. -1.0 ms in the placebo group). The mean change in QTc using both correction methods was significantly greater in the azimilide 125 mggroup than the mean change in the respective placebo group: QTc(Bazett) +31.6 ms in the azimilide 125 mg group versus +2.1 ms in the placebo group and QTc(Fridericia) +35.8 in the azimilide 125 mg group versus +1.0 ms in the placebo group. It was concluded that in patients with a history of atrial fibrillation or flutter, azimilide was associated with statistically significant increases in RR, QT, QTc(Bazett), and QTc(Fridericia) when patients were in sinus rhythm.