Comparative efficacy of intravenous ibutilide versus procainamide for enhancing termination of atrial flutter by atrial overdrive pacing

Variations in duration and composition of the excitable gap around the tricuspid annulus during typical atrial flutter

BACKGROUND

Differences in the duration of the excitable gap along the reentry circuit during typical atrial flutter are poorly known.

AIM

To prospectively evaluate and compare the duration and composition of the excitable gap during typical counterclockwise atrial flutter in different parts of the circuit all around the tricuspid annulus.

METHODS

The excitable gap was determined by introducing a premature stimulus at various sites around the tricuspid annulus during typical counterclockwise atrial flutter in 34 patients. Excitable gap was calculated as the difference between the longest resetting coupling interval and the effective atrial refractory period.

RESULTS

The duration of the excitable gap, the effective atrial refractory period and the resetting coupling interval differed significantly along the tricuspid annulus. Duration of excitable gap was significantly longer at the low lateral right atrium (79±22 ms) than at the cavotricuspid isthmus (66±23 ms; P=0.002). The effective atrial refractory period was significantly longer at the cavotricuspid isthmus (160±26 ms) than at the high lateral right atrium (149±29 ms; P=0.004). Other locations, such as coronary sinus ostium, right atrial septum and atrial roof displayed intermediate values.

CONCLUSION

The duration of the excitable gap differed significantly along the tricuspid annulus, with a larger excitable gap at the lateral right atrium and a shorter excitable gap at the cavotricuspid isthmus, because of longer refractory periods at the isthmus.

Alternans amplification following a two-stimulus protocol in a one-dimensional cardiac ionic model of reentry: from annihilation to double-wave quasiperiodic reentry

Electrical pacing is a common procedure in both experimental and clinical settings to study and/or annihilate anatomical reentry. A previous study [Comtois and Vinet, Chaos 12, 903 (2002)] has described new ways to terminate reentry in a one-dimensional loop model by a protocol consisting of only two stimulations. Annihilation of the reentrant activity was much more likely with these new scenarios than through a unidirectional block. This paper investigates the sensitivity of these scenarios of annihilation to the length of the pathway. It shows that double-pulse stimulation can stop the reentry if the circuit is shorter than a limiting length. Beyond this upper limit, stimulation rather yields sustained double-wave reentry. The same dynamical mechanism, labeled alternans amplification, is found to be responsible for these two types of post-stimulus dynamics.

Ibutilide – recent molecular insights and accumulating evidence for use in atrial flutter and fibrillation

Ibutilide is a 'pure' class III antiarrhythmic drug, used intravenously against atrial flutter and fibrillation. At a cellular level it exerts two main actions: induction of a persistent Na+ current sensitive to dihydropyridine Ca2+ channel blockers and potent inhibition of the cardiac rapid delayed rectifier K+ current, by binding within the channel pore cavity upon channel gating. Ibutilide has been shown to terminate atrial flutter and fibrillation in animal studies, with some risk of ventricular pro-arrhythmia. Experimental models of hypertrophy/heart failure show altered sensitivity to ibutilide, with increased dispersion of repolarisation and incidence of pro-arrhythmia. Patient trials show that ibutilide is effective at terminating atrial arrhythmias when given alone, and that it can increase effectiveness and reduce energy requirements of electrical cardioversion. The risk to patients of polymorphic ventricular tachycardia necessitates careful patient selection and monitoring during and after treatment. An ibutilide analogue, trecetilide, requires further investigation but may offer a less readily metabolised and pro-arrhythmic alternative to ibutilide.

Analysis of the surface electrocardiogram for monitoring and predicting antiarrhythmic drug effects in atrial fibrillation

Specific antiarrhythmic therapy with class I and III drugs for atrial fibrillation (AF) conversion and prevention of its recurrence is frequently utilized in clinical practice. Besides being only moderate effective, the utilization of antiarrhythmic drugs may be associated with serious side effects. In the clinical setting it is difficult to directly evaluate the effects of antiarrhythmic drugs on the individual patient's atrial electrophysiology, thereby predicting their efficacy in restoring and maintaining sinus rhythm. Analysis of the surface electrocardiogram in terms of P-wave signal averaged ECG during sinus rhythm and spectral characterization of fibrillatory waves during AF for evaluation of atrial antiarrhythmic drug effects is a new field of investigation. Both techniques provide reproducible parameters for characterizing atrial electrical abnormalities and seem to contain prognostic information regarding antiarrhythmic drug efficacy. Further research is needed which elucidates the most challenging clinical questions in AF management whom to place on antiarrhythmic drug treatment and what antiarrhythmic drug to prescribe. Analysis of the surface ECG might have the potential to answer these questions.

Effect of chronic amiodarone therapy on excitable gap during typical human atrial flutter

INTRODUCTION

Class I antiarrhythmic drugs increase duration of the excitable gap (EG) during typical atrial flutter whereas intravenous class III drugs decrease the EG. The effect of chronic oral amiodarone therapy on the EG is unknown.

METHODS AND RESULTS

EG was prospectively determined by introducing a premature stimulus and analyzing the response pattern during typical atrial flutter in 30 patients without antiarrhythmic drugs and in 20 patients under chronic oral amiodarone therapy. EG was calculated by the difference between the longest coupling interval leading to resetting and the effective atrial refractory period (EARP). A fully EG was defined by the portion of EG where the response curve of the return cycles was flat. A partially EG was defined by the portion of EG where the return cycle increases while coupling interval decreases. A resetting response curve was constructed by plotting the duration of the return cycle against the value of the coupling interval. Cycle length (CL; 222 +/- 17 vs 267 +/- 20 msec, P < 0.0001), EARP (128 +/- 16 vs 152 +/- 18 msec, P < 0.0001), and EG (54 +/- 19 vs 70 +/- 21 msec, P = 0.01) were significantly longer in patients taking amiodarone than in controls. Compared to CL, the relative part of the EARP (57 +/- 7 vs 57 +/- 6%, P = 0.96) and EG (24 +/- 7 vs 26 +/- 8%, P = 0.41) were comparable in both groups. The fully EG was larger in patients under chronic amiodarone therapy than in controls (39 +/- 21 vs 26 +/- 20 msec, P = 0.03). Neither duration of the partially EG (28 +/- 15 vs 31 +/- 15 msec, P = 0.42) nor slope of the ascending portion of the resetting response curve (1.15 +/- 0.5 vs 1.13 +/- 0.4 msec/msec, P = 0.71) differed between the two groups.

CONCLUSION

EG in patients under chronic amiodarone therapy is significantly larger than in controls, mainly because of a longer fully EG. This observation may be explained by opposite effects on conduction velocity and refractoriness.

Antiarrhythmic drug therapy of atrial fibrillation

In the post-AFFIRM era, treatment of AF has become the treatment of symptoms. In some patients, this will be simple rate control, but there remain a significant cohort of patients in whom rate control alone does not give acceptable symptom relief. In this group, antiarrhythmic therapy still has a role, and the AFFIRM trial indicates that this therapeutic strategy is without significant deleterious effect on mortality. The choice of antiarrhythmic agent must be individualized according to underlying cardiac pathologies and comorbidities, however. Most recently, the introduction of dofetilide has widened the therapeutic options in patients with severe heart disease, and the Canadian Trial of Atrial Fibrillation indicated the superior efficacy of amiodarone at low doses. The release/ development of newer Class III antiarrhythmic agents may offer hope for the benefits of amiodarone without the serious adverse effects with long-term therapy.

Use of global atrial fibrillation organization to optimize the success of burst pace termination

OBJECTIVES

The purpose of this study was to determine if burst atrial pacing would have an effect on terminating atrial fibrillation.

BACKGROUND

We hypothesized that frequency domain analysis of a filtered wide bipolar atrial electrogram describes the global organization of atrial fibrillation (AF) and should vary over time. Timing burst pacing to periods of high organization of AF should promote regional atrial conduction block and terminate AF.

METHODS

Nine dogs were conditioned with rapid atrial pacing for 48 h. Electrogram recordings were made from a wide right atrium (RA) to left atrium (LA) bipole and digitally filtered. A fast-Fourier transform was performed every 0.5 s on a sliding 2-s window, and the organization index (OI) was calculated as a ratio of the area of the first four harmonic peaks to the total power of the spectrum. Organization indexes >0.5 indicated more organized AF activity. Right atrium and LA burst pacing (burst) (cycle length 50 ms, 9.9 ms, 9.9 mA, 1 to 4 s) was performed through decapolar catheters. Burst was either random or synchronized to OI >0.5.

RESULTS

Burst termination was attempted 1,814 times (889 OI sync, 925 random) and succeeded in seven of nine dogs. Burst had an overall success rate of 11.1% versus 6.3% for random (p < 0.0003). Biatrial pacing had the highest efficacy for terminating AF, with a success rate of 16.5% for OI sync versus 8.2% for random (p < 0.0001).

CONCLUSIONS

Timing the delivery of the burst pace when the OI is >0.5 increases the efficacy of burst pace termination of AF. Biatrial pacing is more effective than either RA or LA pacing alone.

Resetting and annihilation of reentrant activity in a model of a one-dimensional loop of ventricular tissue

Resetting and annihilation of reentrant activity by a single stimulus pulse (S1) or a pair (S1-S2) of coupled pulses are studied in a model of one-dimensional loop of cardiac tissue using a Beeler-Reuter-type ionic model. Different modes of reentry termination are described. The classical mode of termination by unidirectional block, in which a stimulus produces only a retrograde front that collides with the activation front of the reentry, can be obtained for both S1 and S1-S2 applied over a small vulnerable window. We demonstrate that another scenario of termination-that we term collision block-can also be induced by the S1-S2 protocol. This scenario is obtained over a much wider range of S1-S2 coupling intervals than the one leading to a unidirectional block. In the collision block, S1 produces a retrograde front, colliding with the activation front of the pre-existing reentry, and an antegrade front propagating in the same direction as the initial reentry. Then, S2 also produces an antegrade and a retrograde front. However, the propagation of these fronts in the spatial profile of repolarization left by S1 leads to a termination of the reentrant activity. More complex behaviors also occur in which the antegrade fronts produced by S1 and S2 both persist for several turns, displaying a growing alternation in action potential duration ("alternans amplification") that may lead to the termination of the reentrant activity. The hypothesis that both collision block and alternans amplification depend on the interaction between the action potential duration restitution curve and the recovery curve of conduction velocity is supported by the fact that the dynamical behaviors were reproduced using an integro-delay equation based on these two properties. We thus describe two new mechanisms (collision block and alternans amplification) whereby electrical stimulation can terminate reentrant activity. (c) 2002 American Institute of Physics.

Electrophysiological response of the right atrium to ibutilide during typical atrial flutter

BACKGROUND

The efficacy of ibutilide in conversion of atrial fibrillation and flutter (AFL) has been demonstrated. However, its electrophysiological effects on human atria have not been fully studied.

METHODS AND RESULTS

Twelve patients with typical AFL were studied. Electrograms were recorded from the anterolateral right atrium, His bundle position, and coronary sinus. During AFL, we measured the conduction time, CTi, through the isthmus between the tricuspid annulus and eustachian ridge and the conduction time, CTni, through the remainder of the right atrium. Resetting response curves and atrial effective refractory periods were determined with single extrastimuli delivered in the tricuspid annulus-eustachian ridge isthmus. After infusion of ibutilide (2 mg over 15 minutes), AFL cycle length (CL) increased from 260+/-30 to 295+/-39 ms (P<0.0003) because of an increase in either CTi, CTni, or both. Effective refractory periods increased from 149+/-16 to 208+/-26 ms (P<0.001). AFL CL variability increased, with a rightward shift of the resetting response curves and loss of full excitability. In 8 patients, AFL was terminated by atrial overdrive pacing after ibutilide at CLs equal to or longer than those that were not effective at baseline, which was caused by orthodromic block in the tricuspid annulus-eustachian ridge isthmus or was associated with development of transient rapid rhythms around newly formed sites of intra-atrial conduction block.

CONCLUSIONS

Ibutilide causes prolongation of AFL CL and increased CL variability by abolishment of a fully excitable gap. Ibutilide may facilitate pace termination of AFL by development of new short-lived reentry around functional blocks.

"Pills and pulses": hybrid therapy for atrial fibrillation

Nonpharmacologic techniques are being increasingly applied to the treatment of atrial fibrillation (AF). None of these techniques (other than maze surgery) begins to approach 100% efficacy for long-term elimination of arrhythmia. This review examines the evidence for "hybrid" therapy, using combinations of drug and nonpharmacologic treatments. The immediate success rate of electrical cardioversion can be increased with amiodarone or ibutilide, and a number of drugs reduce the risk of AF recurrence. Preventing or reversing electrical atrial remodeling is an attractive strategy for maintenance of sinus rhythm. However, the available evidence (relating to the use of verapamil) is limited and conflicting. Ablation of the cavotricuspid isthmus is effective when antiarrhythmic drugs given for AF give rise to typical flutter. Isthmus and other right atrial linear lesions are poor as a sole therapy for AF, but better when drugs are added. Better still is the combination of left atrial linear lesions with drugs. In patients with AF recurrence following focal ablation/pulmonary vein isolation procedures, drugs are an alternative to extensive linear ablation. Some studies indicate that pacing to prevent AF may be effective, but rarely without continued antiarrhythmic drug therapy. This may represent a specific effect or simply improved drug tolerance. Drugs also might assist pacemaker therapy by increasing the proportion of atrial arrhythmias that are highly organized and thus amenable to antitachycardia pacing. This and other forms of hybrid therapy will remain the subject of conjecture in the absence of controlled clinical trials, which are urgently needed.

Suppression of atrial tachyarrhythmias by pacing

INTRODUCTION

Treatment of atrial tachyarrhythmias (ATs) remains difficult in many patients. Accordingly, new therapeutic approaches for AT suppression are evaluated. Atrial pacing may prevent ATs by modifying the electrophysiologic conditions required for sustained ATs.

METHODS AND RESULTS

New pacing algorithms for prevention of AT are aimed at permanent overdrive suppression of arrhythmic activity, reduction of dispersion of atrial refractoriness produced by short-long cycles, more aggressive overdrive pacing after spontaneous sinus conversion to prevent early reinitiation of ATs, and prevention of inadequate rate decay in patients with vagally induced ATs. AT prevention may be achieved by dedicated atrial pacing sites, e.g., pacing at the insertion of Bachmann's bundle or biatrial pacing, which compensates for interatrial conduction delay. Preexciting regions of critical conduction delay, pacing at the triangle of Koch or coronary sinus os, and dual-site right atrial pacing have shown antiarrhythmic effects. Atrial preventive pacing and pharmacologic treatment may work synergistically in the concept of hybrid therapy. To prevent atrial electrical remodeling, early termination of AT seems desirable. This may be achieved by implanted devices that automatically detect ATs and provide atrial antitachycardia pacing for organized ATs. Initial studies showed that regular AT can automatically be terminated in approximately 50% of treated episodes.

CONCLUSION

Pacing for prevention of AT and termination of organized AT episodes may become important steps within the concept of hybrid therapy of AT. However, their clinical efficacy and optimal patient selection remain to be evaluated in prospective, well-designed clinical trials.

Efficacy of pacing therapies for treating atrial tachyarrhythmias in patients with ventricular arrhythmias receiving a dual-chamber implantable cardioverter defibrillator

BACKGROUND

Although overdrive pacing for treating atrial flutter is well established, the efficacy of device-based atrial pacing for treating spontaneous atrial tachyarrhythmias in patients with implantable cardioverter defibrillators (ICD) is unknown. This study evaluated the efficacy of novel pacing therapies for treating atrial tachyarrhythmias in patients receiving a dual-chamber ICD to treat ventricular tachyarrhythmias.

METHODS AND RESULTS

A Jewel AF ICD was implanted in 537 patients with ventricular arrhythmia who were followed for 11.4+/-8.2 months (74% had a documented history of atrial tachyarrhythmias). The device discriminated atrial tachycardia (AT) from atrial fibrillation (AF) on the basis of cycle length and regularity, and it used 3 different methods of overdrive atrial pacing (Ramp, Burst+, and 50-Hz burst) to treat AT episodes and one method (50-Hz burst) to treat AF episodes. Pacing successfully terminated 59% of 1500 spontaneous AT episodes in 127 patients and 30% of 880 AF episodes in 101 patients (P<0.001). With AT and AF episodes combined, pacing efficacy was 48%. Pacing efficacy was significantly reduced at AT cycle lengths </=220 ms and AF cycle lengths </=160 ms (P<0.01) The median time from pacing to AT/AF termination was 1.1 minute for the pacing successes and 96 minutes for the failures (P<0.001).

CONCLUSIONS

Atrial pacing terminated 48% of AT/AF episodes in patients with a history of ventricular arrhythmias. Pacing efficacy was greater for device-classified AT than AF. Pacing efficacy was significantly influenced by tachycardia cycle length. Successful pacing significantly reduces the time required for AT/AF termination.

Prevalence, characteristics and clinical implications of regular atrial tachyarrhythmias in patients with atrial fibrillation: insights from a study using a new implantable device

OBJECTIVES

This study prospectively analyzed atrial tachyarrhythmia (AT) organization and antitachycardia pacing (ATP) success in patients with an implanted device for AT therapy.

BACKGROUND

In patients with atrial fibrillation (AF), the incidence of regular, slow ATs amendable by ATP is unknown.

METHODS

Forty patients with previously documented AT (70% with AF) received a new pacemaker with atrial electrogram (AEG) storage and atrial ATP capabilities for standard pacing indications. The AEGs acquired during the first month (study phase 1) were classified into high (type I), intermediate (type II) and low (type III) degrees of organization. Atrial ATP was then activated, and treated AT episodes were retrieved three and six months after implantation (study phase 2).

RESULTS

Of 824 AEGs retrieved before ATP activation (study phase 1), 351 (43%) were classified as type 1, 47% as type II and 10% as type III. Episodes of AT starting as type I (35%) and type II or III (65%) maintained their type over 1 min in 73%. All patients with an exclusive history of AF also showed type I AEGs. In 361 subsequently treated AT episodes (study phase 2), ATP was successful in 62% of type I and 34% of type II episodes, but not in type III (p < 0.0001).

CONCLUSIONS

The majority of patients with a history of AF show not only disorganized but also highly organized AT episodes, which can be successfully terminated by ATP.

What niche will newer class III antiarrhythmic drugs occupy?

The decline in the use of sodium channel blockers has led to an expanding use of b-blockers and complex class III agents such as sotalol and amiodarone for controlling cardiac arrhythmias. Success with these agents in the context of their side effects has spurred the development of compounds with simpler ion channel-blocking properties with less complex adverse reactions. The resulting so-called pure class III agents were found to have antifibrillatory effects in atrial fibrillation (AF) and flutter, as well as in ventricular tachyarrhythmias. Pure class III compounds are effective in inducing acute chemical conversion of AF, in preventing paroxysmal AF, and in maintaining sinus rhythm in patients with persistent AF restored to sinus rhythm. Examples of such compounds are dofetilide, which selectively blocks IKr, and ibutilide, available only as an intravenous agent, which blocks the IKr and augments the inactivated Na+ current in atrial myocytes. Dofetilide and ibutilide have been introduced into clinical practice. Azimilide is the first of the class III agents that blocks both components (IKr and IKs) of the delayed rectifier current, which may confer certain electrophysiologic advantages. The potential therapeutic niche of ibutilide, dofetilide, and azimilide in the control of cardiac arrhythmias forms the basis of this review.

Frequency-dependent electrophysiological effect of ibutilide on human atrium and ventricle

Most of the class III antiarrhythmic agents developed in recent years blocks the rapid component of delayed rectifier potassium current (IKr). IKr blocker shows reverse use-dependency and also may cause torsades de pointes at slower heart rate. Ibutilide fumarate, a novel class III antiarrhythmic agent, increases window Na(+) current at the action potential plateau phase. We studied the rate-dependent effect of ibutilide on the electrophysiological parameters of human atrium and ventricle. Franz catheter and a pacing catheter were placed closely in the high right atrium and right ventricular apex to record monophasic action potentials (MAP) during pacing at cycle length (PCL) of 600 ms and 350 ms in eight patients who underwent electrophysiological study. MAP duration of right atrium (RA-MAPD) and right ventricle (RV-MAPD), effective refractory period of RA and RV (RA-ERP and RV-ERP), intra-atrial conduction time (IACT) and intra-ventricular conduction time (IVCT) were measured before and after intravenous administration of ibutilide (0.01 mg/kg up to 1mg). A conduction time from RA pacing spike to distal coronary sinus potential was used to measure IACT, while QRS duration of surface ECG during RV pacing was used to measure IVCT. Ibutilide prolonged RA-MAPD by 60 ms at PCL 600 ms and by 53 ms at PCL 350 ms; RV-MAPD by 48 ms at PCL 600 ms and by 55 ms at PCL 350 ms. Ibutilide did not affected RA and RV-ERP/MAPD ratio, IACT, and IVCT. Ibutilide prolongs MAPD and ERP of human atrium and ventricle without reverse use-dependency.

Cardiac surgery: postoperative arrhythmias

Arrhythmias are common after surgery, particularly after cardiac surgery. Atrial fibrillation is the most common arrhythmia encountered postoperatively, although ventricular arrhythmias and conduction disturbances can also occur. Older age is the most consistent predictor of postoperative atrial arrhythmias. beta-adrenergic blockers, amiodarone, and sotalol are the most effective at preventing postoperative atrial fibrillation. Sustained ventricular arrhythmias in the recovery period after cardiac surgery warrant aggressive therapy, usually with an implantable cardioverter-defibrillator in the absence of reversible causes. Postoperative, nonsustained ventricular tachycardia in the setting of left ventricular dysfunction and ischemic coronary disease also usually warrants risk stratification and possible treatment, often with electrophysiologic testing and implantation of an implantable cardioverter-defibrillator, if sustained ventricular arrhythmias are induced. Transient bradyarrhythmias may be managed with temporary pacing wires placed at surgery, but significant and persistent atrioventricular block or sinus node dysfunction can occur and indicate a need for permanent pacing.

The Management of Atrial Fibrillation in the ICU

Atrial tachyarrhythmias are the most frequent arrhythmias occurring in ICU patients, being particularly common in patients with cardiovascular and respiratory failure. Unlike ambulatory patients in whom atrial fibrillation/flutter (AF) is likely to be short lived, in the critically ill these arrhythmias are unlikely to resolve until the underlying disease process has improved. Urgent cardioversion is indicated for hemodynamic instability. Treatment in hemodynamically stable patients includes correction of treatable precipitating factors, control of the ventricular response rate, conversion to sinus rhythm, and prophylaxis against thromboembolic events in those patients who remain in AF. Diltiazem is the preferred agent for rate control, while procainamide and amiodarone are generally considered to be the antiarrhythmic agents of choice.

Predictors of conversion to sinus rhythm using ibutilide for atrial fibrillation or flutter

To determine what factors can predict conversion to sinus rhythm, we retrospectively studied 201 consecutive patients who received ibutilide for treatment of atrial fibrillation or flutter. On multivariate analysis, the following factors were significantly associated with conversion: recent onset of arrhythmia, an underlying atrial flutter rhythm, lack of a history of congestive heart failure, and lack of concomitant digoxin therapy.

Ibutilide: an antiarrhythmic agent for the treatment of atrial fibrillation or flutter

OBJECTIVE

To discuss the clinical pharmacology of the antiarrhythmic drug ibutilide in patients with atrial fibrillation (AF) or atrial flutter (AFl).

DATA SOURCES

A MEDLINE search (January 1983-December 1997) was used to identify pertinent English-language articles on ibutilide. Key search terms included ibutilide, AF, AFl, cardioversion, and sinus rhythm. The MEDLINE search was supplemented by references included in the bibliographies of comprehensive review articles and studies.

STUDY SELECTION

Studies and review articles describing the chemistry, pharmacology, and pharmacokinetics of ibutilide were selected. All abstracts and published clinical trials evaluating the efficacy and safety were reviewed.

DATA EXTRACTION

Pertinent information on the pharmacology and mechanism of action of ibutilide was summarized. Data were extracted from the clinical trials describing trial design, patient population, interventions, methods of evaluation, outcomes, and statistical significance.

DATA SYNTHESIS

Ibutilide is a Vaughan-Williams class III antiarrhythmic agent approved for intravenous use for the rapid termination of recent-onset AF or AFl. The drug is extensively metabolized by the liver, has a volume of distribution of 11-15 L/kg, is 40% protein bound, and has an elimination half-life of 6 hours (range 2-12). Data from two placebo-controlled trials demonstrated the efficacy of ibutilide for converting AF or AFl of short duration (< or = 90 d) to normal sinus rhythm. A third placebo-controlled trial demonstrated efficacy in patients who developed AF or AFl following cardiac surgery. Comparative trials with procainamide and sotalol have shown at least similar and perhaps superior efficacy with ibutilide. There are no comparative trials with other antiarrhythmic drugs or with direct current cardioversion (DCC). In 586 clinical trial patients receiving ibutilide, the most significant adverse effect was the development of torsade de pointes in 25 patients (4.3%) including 10 cases (1.7%) in which the rhythm was sustained. All cases of torsade de pointes were terminated electrically and none resulted in death or severe morbidity. No prospective cost-effectiveness studies are available; however, results from two decision models suggest that ibutilide may have advantages over other drugs and first-line electrical cardioversion.

CONCLUSIONS

Ibutilide appears to be an effective alternative method for rapid conversion of recent-onset AF or AFl. The drug may be particularly useful in patients who have undergone recent cardiac surgery or those who are not ideal candidates for DCC. Although studies suggest that the risk of proarrhythmia and in particular torsade de pointes is relatively low, caution is advised until additional experience is gained in clinical practice.

Effects of procainamide on the excitable gap composition in common human atrial flutter

The composition of the excitable gap (EG) in common atrial flutter (AF1) was determined before and during infusion of procainamide (PA) in 9 patients (6 men and 3 women; age 70 +/- 7 years). The EG was determined by introducing a premature stimulus after every 20th AF1 complex detected using a quadripolar electrode catheter placed just above the tricuspid valve. Diastole was scanned in 2- to 4-ms decrements to the atrial effective refractory period (ERP). The relationship between the coupling interval and the return cycle length (CL) determined a reset-response curve (RRC), which described the EG. PA (15 mg/kg) was administered during AF1 over 30 minutes and RRC was repeated at maximum AF1 CL. PA prolonged AF1 CL from 227 +/- 29 to 296 +/- 62 ms (P < 0.01) but did not terminate AF1. ERP during AF1 prolonged from 169 +/- 24 to 219 +/- 41 ms (P < 0.01). Control EG was 57 +/- 16 ms or 25% +/- 6% of AF1 CL and on PA EG was 77 +/- 30 ms (P = 0.01), which was still 26% +/- 7% of the CL. Without drug, RRC was mixed in eight cases demonstrating an EG composed of fully excitable tissue (10 +/- 4 ms or 19% +/- 10% of the EG) and partially refractory tissue (48 +/- 18 ms). PA did not change the duration of the fully excitable region (13 +/- 10 ms or 19% +/- 15% of EG). Peak PA plasma concentration was 47 +/- 20 mumol/L. PA prolonged AF1 CL, ERP, and EG duration but did not change the proportion of AF1 CL occupied by the EG. The persistance of fully excitable tissue at the head of the wavefront in the presence of PA may largely explain its inefficacy in the acute termination of common AF1.

Treatment strategies for atrial fibrillation

Atrial fibrillation is the most common arrhythmia observed in clinical practice, occurring in 0.4% of the general population and in up to 4% of people greater than 60 years old. It is often associated with other cardiovascular disorders, such as hypertension, coronary artery disease, or cardiomyopathy. Critical evaluation and management of patients with atrial fibrillation requires knowledge of etiology, prognosis, and treatment options of this arrhythmia. On initial presentation, emergency electrical cardioversion should be performed if the patient is hemodynamically unstable. If the patient is stable, initial rate control is recommended, using atrioventricular nodal blocking agents. Further treatment mainly depends upon the duration of the episode. Patients who are in atrial fibrillation <48 hours can be safely cardioverted. Patients who are in atrial fibrillation for >48 hours are commonly anticoagulated for 3 to 4 weeks before and after cardioversion because of the risk of thromboembolism formation in the left atrial appendage. An alternate strategy, which is especially attractive when immediate cardioversion is desired, is transesophageal echocardiography to exclude left atrial thrombus followed by prompt cardioversion. After cardioversion, sinus rhythm can be maintained with class I and III drugs, such as flecainide and propafenone or amiodarone and sotalol. New treatment options, such as atrial defibrillation, atrioventricular junctional ablation, or modification of atrial pacing to prevent atrial fibrillation, are currently under investigation. Although atrial fibrillation is so common in clinical practice, it still remains difficult to treat. Conversion and maintenance to sinus rhythm with antiarrhythmic drug therapy has not shown any improvement in mortality, and some patients may benefit more from ventricular rate control. This review article discusses different treatment strategies for patients with atrial fibrillation.

Ibutilide. A review of its pharmacological properties and clinical potential in the acute management of atrial flutter and fibrillation

Ibutilide is the first 'pure' class III antiarrhythmic drug to become available. Its predominant action is prolongation of the myocardial action potential duration. This appears to be achieved by a unique ionic mechanism of action that involves activation of a late inward sodium current and possibly blockade of the rapidly activating component of the cardiac delayed rectifier potassium current. Intravenous ibutilide 0.01 to 0.025 mg/kg or 1 to 2 mg successfully converted atrial flutter or fibrillation to sinus rhythm in 33 to 49% of patients in 2 placebo-controlled trials involving 439 patients with sustained arrhythmia. In a third trial in 300 patients who developed atrial flutter or fibrillation after cardiac surgery, ibutilide 2 mg successfully converted the arrhythmia in 57% of patients. The mean times to conversion were < or = 30 minutes in these trials. In 3 comparative trials, ibutilide was significantly more effective than racemic sotalol or procainamide in terminating atrial flutter or fibrillation. The pretreatment duration of the arrhythmia is an important predictor of the success of ibutilide treatment; the greatest conversion rates are achieved when the arrhythmia is of recent onset (i.e. < or = 30 days' duration). Ibutilide is more effective in terminating atrial flutter than atrial fibrillation. Adverse events associated with ibutilide are predominantly cardiovascular. Sustained polymorphic ventricular tachycardia developed in 1.7%, and non-sustained polymorphic ventricular tachycardia in 2.7%, of 586 patients treated with ibutilide in clinical trials. However, no proarrhythmia-related deaths have been reported with the use of ibutilide. The drug has minimal haemodynamic effects and is associated with few noncardiovascular adverse events. Thus, ibutilide is a useful agent for the pharmacological cardioversion of recent-onset atrial fibrillation or flutter, provided that adequate steps are taken to monitor for proarrhythmic events. The drug causes few noncardiovascular adverse events and has minimal haemodynamic effects. Furthermore, it appears to be more effective than procainamide (especially in patients with atrial flutter) and racemic sotalol.

Efficacy of ibutilide for termination of atrial fibrillation and flutter

The clinical utility of ibutilide fumarate (Corvert) for the acute conversion of atrial tachyarrhythmias to normal sinus rhythm has been demonstrated in several randomized, placebo-controlled clinical trials. The efficacy of intravenous ibutilide for rapid conversion of atrial flutter is in the range of 50-70%, whereas its efficacy for conversion of atrial fibrillation is 30-50%. Approximately 80% of atrial tachyarrhythmias that terminate do so within 30 minutes from the initiation of the intravenous infusion. Ibutilide is more effective than either intravenous procainamide or intravenous sotalol for conversion of atrial fibrillation and atrial flutter to sinus rhythm. Age, presence of structural heart disease, gender and concomitant medication do not appear to influence the efficacy of ibutilide; however, shorter duration of atrial fibrillation is a strong predictor of successful termination. Plasma concentration of ibutilide and QTc interval prolongation are not directly correlated with the success rate for conversion of atrial tachyarrhythmias. Ibutilide's greater efficacy compared with other antiarrhythmic drugs may be related to its ability to cause greater prolongation of atrial monophasic action potential duration relative to atrial cycle length. Termination of atrial flutter with ibutilide was preceded by increased atrial cycle length variability. Ibutilide rapidly and effectively converts atrial fibrillation and atrial flutter to sinus rhythm when administered as a 1-mg total dose followed by a second 1-mg dose. It should be used in conjunction with continuous electrocardiographic monitoring for at least 4 hours after the termination of the infusion, or until the QTc interval returns to baseline. Hypokalemia and hypomagnesemia should be corrected before the start of the infusion. An external cardiac defibrillator, intravenous magnesium, and an external transcutaneous cardiac pacemaker should be readily available for immediate use in the event that palymorphic ventricular tachyarrhythmias occur. Ibutilide is a new intravenous agent that safely and rapidly converts atrial fibrillation and atrial flutter to sinus rhythm.