Newer developments in the management of atrial fibrillation

Treatment of Acute Atrial Fibrillation: Ventricular Rate Control and Restoration of Sinus Rhythm

Atrial fibrillation (AF) is a familiar arrhythmia seen in the emergency department and the general population. In the past it was treated in the majority of cases by controlling the ventricular rate, whether the AF is acute or chronic. However, ventricular rate control alone does not address the underlying problem and the patients still remain in AF, cardiac output and symptoms have not been optimally corrected. There is definite risk of thromboembolism. Restoration of sinus rhythm is the only way of resuming the normal conduction physiology of the heart and correcting these problems This article provides a review of the two major principles of rhythm treatment of acute AF: rate control and restoration of sinus rhythm. Transthoracic electrical cardioversion is the mainstay of treatment in haemodynamically unstable AF, whereas in stable AF, there is a choice between rate control and restoration of sinus rhythm, or they can be carried out in conjunction with each other.

Effects of intravenous amiodarone and ibutilide on action potential duration and atrial conduction kinetics in patients with persistent atrial fibrillation

Class III antiarrhythmic drugs have been shown to be effective for termination of atrial fibrillation (AF). The aim of this study was to determine the steady state and non-steady state effects of amiodarone and ibutilide on the atrial monophasic action potential (MAP) duration (MAPD), effective refractory period (ERP), and intra-atrial conduction time (IACT) in human persistent AF.Fourteen patients with persistent AF who underwent internal atrial defibrillation were included in the study. The atrial MAP was recorded at the high right atrium. IACT was measured from the pacing spike to the distal coronary sinus. MAPD and IACT were assessed during the steady state and at the shortest diastolic interval (DI) at a basic cycle length (CL) of 600 msec and after a premature stimulus. Amiodarone did not affect MAPD or the ERP at the basic CL, but it increased MAPD at the shortest DI. Amiodarone increased IACT at both the basic CL and the shortest DI. Ibutilide increased the MAPD and ERP at the basic CL and at the shortest DI. Ibutilide did not affect IACT at the basic CL or the shortest DI.Ibutilide increases atrial MAPD not only in the steady state but also at the shortest DI, but it does not affect IACT in patients with persistent AF. Amiodarone does not affect MAPD or ERP, but it increases IACT in the steady state, and it increases MAPD and IACT at the shortest DI.

Rate-dependent electrophysiologic effects of the class III antiarrhythmic drugs nifekalant, amiodarone, and ibutilide on the atrium in patients with persistent atrial fibrillation

Persistent atrial fibrillation (AF) is characterized by electrical remodeling, ie, marked decreases in the atrial effective refractory period (ERP), ERP rate adaptation, and atrial conduction velocity. Little information is available on the effects of class III antiarrhythmic drugs on the remodeled atrium. We studied the effects of the class III antiarrhythmic drugs nifekalant, ibutilide, and amiodarone on rate-dependent changes in atrial action potential duration in patients with persistent AF. Right atrial (RA) monophasic action potential duration (MAPD) and intra-atrial conduction time (IACT) were measured at pacing cycle lengths (CLs) of 800, 700, 600, 500, 400, 350, 300, and 250 ms before and after administration of nifekalant (0.4 mg/kg + 0.3 mg/kg/hr, iv), amiodarone (5 mg/kg, iv), or ibutilide (0.01 mg/kg, iv) in 31 patients after successful internal cardioversion of chronic AF of > 2 months duration. Nifekalant and ibutilide significantly increased RA MAPD and the ERP at each CL in a reverse rate-dependent manner. Amiodarone did not affect RA MAPD. Nifekalant did not affect IACT, whereas amiodarone increased IACT at each CL in a rate-dependent manner, and ibutilide increased IACT at CLs ≤ 350 ms. The atrial electrophysiologic effects of the class III antiarrhythmic drugs nifekalant, amiodarone, and ibutilide differ, depending on the degree of electrical and structural remodeling and the effects of the drugs on the depolarizing and repolarizing currents.

Pharmacological treatment of atrial fibrillation: a review on prevention of recurrences and control of ventricular response

Atrial fibrillation is the most common sustained arrhythmia, however its treatment remains controversial and problematic. Electrical or pharmacological cardioversion are able to restore sinus rhythm in many patients but maintenance of sinus rhythm requires long term treatment with antiarrrhythmic agents. Today there is major concern regarding the ventricular proarrhythmic effects of antiarrhythmic drugs because they may increase mortality. Even non-cardiac toxicity of these agents must be considered. An alternative strategy based on pharmacological control of ventricular response rate coupled with antithromboembolic prophylaxis can be followed. For rate control digoxin alone has some specific limitations, therefore, use of calcium antagonists (verapamil or diltiazem) or beta-blockers must be considered. At the present time, the relative efficacy and risks of these two alternative strategies in specific patients subgroups remain to be established. Today, non-pharmacological treatments, as atrio-ventricular node ablation are also available. In elderly patients, moreover, advanced age, underlying heart disease, concomitant systemic illnesses and patient compliance to treatments condition our decision making and treatment needs to be individualized. Appropriate knowledge of the advantages, of the limitations and of the costs of every pharmacological or non-pharmacological treatment option is required for deciding in every patient in view of the best risk-benefit and cost-benefit ratio.

Characterization and comparison of Na+, K+ and Ca2+ currents between myocytes from human atrial right appendage and atrial septum

Atrial pacing to reduce paroxysmal atrial fibrillation recurrences is performed in right atrial appendage (RAA) traditionally. However, recent studies indicate that atrial septal (AS) pacing produces better outcomes than the RAA pacing. The underlying mechanisms for this difference remained unclear. One possible explanation for the superiority of AS pacing over RAA pacing is that the two different regions have distinct electrophysiological properties. The study was to explore whether there indeed exist regional differences of electrical activities between RAA and AS, using whole-cell patch clamp techniques. The results showed that RAA cells had longer action potential duration, more negative resting potential and greater amplitude of action potential, whereas AS cells had more rapid depolarizing velocity. The sodium current was significantly smaller in RAA cells, whereas the calcium current was markedly smaller in AS cells. The transient outward K(+) current was similar in both regions. The ultrarapid delayed rectifier K(+) current was greater in RAA than that in AS cells. The inward rectifier K(+) current was similar at potentials more negative to -60 mV in both regions. The results indicate that RAA and AS of patients with rheumatic heart disease possess distinct electrophysiological properties. These differences provided a rational explanation for the different efficacies in treating atrial fibrillation by atrial pacing in RAA and AS regions.

Comparison of potent Kv1.5 potassium channel inhibitors reveals the molecular basis for blocking kinetics and binding mode

In this study, we analysed the inhibitory potency, blocking characteristics and putative binding sites of three structurally distinct Kv1.5 channel inhibitors on cloned human Kv1.5 channels. Obtained IC(50) values for S9947, MSD-D and ICAGEN-4 were 0.7 microM, 0.5 microM, and 1.6 microM, respectively. The Hill-coefficients were close to 1 for S9947 and approximately 2 for MSD-D and ICAGEN-4. All three compounds inhibited Kv1.5 channels preferentially in the open state, with Kv1.5 block displaying positive frequency dependence, but no clear voltage and potassium dependence. In contrast to slow on- and off-rates of apparent binding of MSD-D and ICAGEN-4, S9947 had fast on- and off-rates resulting in faster adaptation to changes in pulse frequency. Utilizing Alanine-scanning and in silico modeling we suggest binding of the compounds to the central cavity with crucial residues Ile508 and Val512 in the S6-segment. Residue Thr480 located at the base of the selectivity filter is important for ICAGEN-4 and S9947 inhibition, but less so for MSD-D binding. Our docking models suggest that the innermost potassium ion in the selectivity filter may form a tertiary complex with oxygens of S9947 and ICAGEN-4 and residue Thr480. This binding component is absent in the MSD-D block. As S9947 and ICAGEN-4 show faster block with proceeding channel openings, formation of this tertiary complex may increasingly stabilise binding of S9947 and ICAGEN-4, thereby explaining open channel block kinetics of these compounds.

Atrial Tachyarrhythmias in Primary and Secondary Prevention ICD Recipients: Clinical and Prognostic Data

BACKGROUND

Atrial fibrillation (AF) is the most common sustained arrhythmia encountered in clinical practice. The natural history of this disturbance and its effect on survival is still not known in patients with implantable cardioverter defibrillators (ICDs).

METHODS AND RESULTS

Several controlled trials for both secondary and primary prevention of sudden death using ICDs have been published in literature, and meta-analysis of them provided useful clinical information on the outcome during the follow-up of this population. AF occurs in about 25% of the patients with secondary prevention indication for ICD implantation. The prevalence of AF in patients with primary prevention indication for ICD implantation is much more difficult to define; it seems to be higher in patients with left ventricular dysfunction due to nonischemic etiology (ranging from 15% to 25%), and is lower in patients with ischemic etiology (about 5-10%). However, data from clinical registries, which are expected to better reflect clinical practice than randomized trials, seem to show a substantial difference as compared to the latter ones. A history of AF episodes in patients with an ICD indication for both primary and secondary prevention is probably associated with a higher risk of death. This is particularly evident in secondary prevention in ICD recipients, while it is still controversial in patients who received an ICD for primary prevention, particularly when patients with nonischemic etiology of their left ventricular dysfunction are considered. In a population of patients implanted with an ICD, there are several other clinical factors (ejection fraction, New York Heart Association functional class, age) that can interfere with the risk of death much more than AF itself.

CONCLUSIONS

Further large-scale registries are needed to further characterize the population receiving ICD implantation, assessing the course of risk of death with regard to clinical variables and to evaluate the degree of acceptance of trials in clinical practice.

The outcome of Direct Current Cardioversion (DCC) for the treatment of Atrial Fibrillation (AF) in a district general hospital in Ireland

BACKGROUND

Direct current cardioversion (DCC) is a method to control persistent AF, to facilitate a reduction in stroke risk. Although this is a frequently performed procedure, there are no available published data regarding its outcome in an Irish setting.

AIMS

To determine the short- and long-term outcome of DCC, factors predicting a successful outcome, and its safety.

METHODS

Data relating to each DCC were collected retrospectively from patient notes over a 6.3 year-period, and subsequently entered into a Microsoft Access database before subsequent statistical analysis.

RESULTS

Forty-five consecutive unselected patients were identified, in which 59 DCCs were performed. Sinus rhythm (SR) was achieved immediately after DCC in 54/59 (91%) patients. There was a significant positive correlation between patient body weight and the energy level required to achieve SR (p=0.0001). No thromboembolic complications were noted. After a mean follow-up time of 12 +/- 13.7months, 30/45 (67%) had maintained SR. After univariate analysis, a number of important factors predictive of maintenance of SR at follow-up were identified.

CONCLUSION

DCC was found to be an effective method for short- and long-term control of AF, without thromboembolic complications, and patients with a favourable long-term outcome after DCC could conceivably be predicted on the basis of a methodical history, careful examination, simple investigations and pharmacological variables.

Effect of IKr blocker nifekalant on atrial action potential duration after successful internal cardioversion of chronic atrial fibrillation

BACKGROUND

Chronic atrial fibrillation (AF) is characterized by a marked decrease in the atrial effective refractory period (ERP) and in the ERP adaptation to rate as well as a decrease in the atrial conduction velocity. Little information is available about the ionic mechanisms underlying AF in humans.

MATERIALS AND METHODS

We studied the effect of IKr blocker nifekalant on the rate-dependent changes in atrial action potential duration in 11 patients after successful internal cardioversion of chronic AF of >2 months duration and in 7 patients without AF. In AF patients, right atrial (RA) monophasic action potential (MAP) was recorded at pacing cycle lengths (CLs) of 800-250 ms before and after administration of nifekalant. In control patients, RAMAP was recorded at CLs of 600 and 350 ms before and after administration of nifekalant.

RESULTS

Nifekalant significantly increased RAMAPD at 90% repolarization (RAMAPD90) at CLs of 800-300 ms in the AF patients. The increase in RAMAPD90 by nifekalant became significantly smaller at shorter CLs (42.5 +/- 12.4 ms at a CL of 600 ms vs 32.8 +/- 14.5 ms at a CL of 350 ms, P < 0.05). Effect of nifekalant on RAPMAPD was attenuated at CL of 600 ms in AF patients in comparison to control patients (increase in RAMAPD in control; 73.0 +/- 36.6 ms vs increase in RAMAPD in AF; 42.5 +/- 12.4 ms, P < 0.05); however, it was similar at a CL of 350 ms between control and AF patients.

CONCLUSIONS

Electrophysiological effects of nifekalant are significantly attenuated in the chronically remodeled human atrium at slower heart rates, but the beneficial effect of RAMAPD prolongation by IKr blocker was well-preserved even at shorter CLs after chronic AF.

Use of beta-blockers in atrial fibrillation

Atrial fibrillation is the most common arrhythmia in the general population and is frequently associated with organic heart disease. beta-adrenoceptor antagonists (b-blockers) are very effective in preventing atrial fibrillation after coronary artery bypass surgery. It has been shown recently that the beta-blocker metoprolol controlled release/extended release (CR/XL) is also effective in maintaining sinus rhythm after conversion of atrial fibrillation. There is concern that class I antiarrhythmic drugs, such as quinidine, disopyramide, and flecainide in particular, may increase mortality. The risk of proarrhythmia associated with beta-blocker treatment is very low. Therefore b-blockers, such as metoprolol CR/XL, may be the first line of treatment to maintain sinus rhythm, especially after myocardial infarction and in patients with chronic heart failure and in those with arterial hypertension. In patients with persistent atrial fibrillation, AV-nodal conduction-slowing drugs, such as calcium channel antagonists and beta-blockers are used to control the ventricular rate during atrial fibrillation. Several studies clearly show that beta-blockers alone, or in combination with digoxin are very effective in controlling the ventricular rate at rest and during exercise. beta-blockers are effective in maintaining sinus rhythm and controlling the ventricular rate during atrial fibrillation. Given these effects and their favorable effects on mortality, beta-blockers should be considered as first-line agents in the management of patients with atrial fibrillation.

Antiarrhythmic drug target choices and screening

Most antiarrhythmic drugs are ion channel blockers, and to date, those tested in large randomized placebo-controlled clinical trials have shown no decrease in mortality outcome. This apparent lack of survival benefit may result from the significant liabilities associated with these agents that offset any long-term benefit. Despite the current success of implantable defibrillators and the future promise of gene therapy, there is still a pressing need for new antiarrhythmic drugs. An improved understanding of cardiac ion channels and novel approaches to target selection and compound screening will provide new opportunities for drug discovery in the near future. Here, we briefly review the multiple mechanisms of arrhythmia, the history of drug failures, and the possibilities that evolving technologies may provide in the search for more efficacious and safer antiarrhythmic drugs.

Current management of symptomatic atrial fibrillation

Atrial fibrillation (AF) is the commonest arrhythmia. It presents in distinct patterns of paroxysmal, persistent and chronic AF, and patient management aims differ according to the pattern. In paroxysmal AF, drug treatment with beta-blockers, class Ic and class III agents reduce the frequency and duration of episodes. In persistent AF (recent onset, non-paroxysmal), early cardioversion with either pharmacological agents or by direct current (DC) cardioversion should be actively considered, in those patients who are suitable. Patients most likely to cardiovert and remain in sinus rhythm include those with duration of AF of <1 year, an acute reversible cause, left atrial diameter <50 mm and good left ventricular function on echocardiography. Recent data show that maintenance of sinus rhythm after successful cardioversion is enhanced by the use of class III drugs including amiodarone and dofetilide. In chronic or permanent AF, management is aimed at controlling the ventricular rate response with combinations of digoxin, beta-blockers and calcium antagonists with atrio-ventricular nodal activity (diltiazem and verapamil). There is some debate about the prognostic significance of AF. Certainly AF is associated with an excess mortality but this is largely accounted for by its association with serious intrinsic heart disease and the thrombo-embolic complications of the arrhythmia. Atrial fibrillation is a common default arrhythmia for the sick heart.

New ideas about atrial fibrillation 50 years on

Atrial fibrillation is a condition in which control of heart rhythm is taken away from the normal sinus node pacemaker by rapid activity in different areas within the upper chambers (atria) of the heart. This results in rapid and irregular atrial activity and, instead of contracting, the atria only quiver. It is the most common cardiac rhythm disturbance and contributes substantially to cardiac morbidity and mortality. For over 50 years, the prevailing model of atrial fibrillation involved multiple simultaneous re-entrant waves, but in light of new discoveries this hypothesis is now undergoing re-evaluation.

Effects of angiotensin-converting enzyme inhibition on the development of the atrial fibrillation substrate in dogs with ventricular tachypacing-induced congestive heart failure

BACKGROUND

Atrial structural remodeling creates a substrate for atrial fibrillation (AF), but the underlying signal transduction mechanisms are unknown. This study assessed the effects of ACE inhibition on arrhythmogenic atrial remodeling and associated mitogen-activated protein kinase (MAPK) changes in a dog model of congestive heart failure (CHF).

METHODS AND RESULTS

Dogs were subjected to various durations of ventricular tachypacing (VTP, 220 to 240 bpm) in the presence or absence of oral enalapril 2 mg. kg(-1). d(-1). VTP for 5 weeks induced CHF, local atrial conduction slowing, and interstitial fibrosis and prolonged atrial burst pacing-induced AF. Atrial angiotensin II concentrations and MAPK expression were increased by tachypacing, with substantial changes in phosphorylated forms of c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and p38-kinase. Enalapril significantly reduced tachypacing-induced changes in atrial angiotensin II concentrations and ERK expression. Enalapril also attenuated the effects of CHF on atrial conduction (conduction heterogeneity index reduced from 3.1+/-0.4 to 1.9+/-0.2 ms/mm, P<0.05), atrial fibrosis (from 11.9+/-1.1% to 7.5+/-0.4%, P<0.01), and mean AF duration (from 651+/-164 to 218+/-75 seconds, P<0.05). Vasodilator therapy of a separate group of VTP dogs with hydralazine and isosorbide mononitrate did not alter CHF-induced fibrosis or AF promotion.

CONCLUSIONS

CHF-induced increases in angiotensin II content and MAPK activation contribute to arrhythmogenic atrial structural remodeling. ACE inhibition interferes with signal transduction leading to the AF substrate in CHF and may represent a useful new component to AF therapy.

Electrophysiologic characteristics of paroxysmal and chronic atrial fibrillation in human right atrium

OBJECTIVES

The aim of the study was to analyze the electrophysiologic characteristics of paroxysmal (PAF) and chronic (CAF) atrial fibrillation (AF) in the human right atrium (RA).

BACKGROUND

Differences that exist between PAF and CAF and the mechanisms of self-sustenance of these arrhythmias are incompletely understood.

METHODS

A total of 53 patients with PAF (25 patients, mean age 59 +/- 6.1 years, 3 women) and CAF (28 patients, mean age 59 +/- 13 years, 7 women) underwent multisite mapping of the RA during ongoing AF using a 64-electrode basket catheter. Quantitative evaluation and three-dimensional activation patterns were performed using a computerized system.

RESULTS

Patients with PAF, as compared with patients with CAF, had significantly longer AF cycle length, shorter time intervals with type III AF throughout the RA and a smaller number of endocardial breakthroughs (mean 51 +/- 19 vs. 104 +/- 40, p < 0.001). The majority of endocardial breakthrough points (88% in PAF patients and 98% in CAF patients) were located in the septal region and coincided anatomically with major interatrial connection routes. Coexistence of re-entrant and apparently focal activation determined maintenance of AF in the RA in PAF, whereas random re-entry was documented more frequently in patients with CAF. In patients with CAF, the duration of arrhythmia (in years) correlated strongly with the percentage of time during which type III AF was observed in the lateral wall of the RA (r = 0.71).

CONCLUSIONS

Clinical PAF and CAF, as recorded in the RA, have, at least quantitatively, distinct electrophysiologic features and different mechanisms of maintenance.

Role of transesophageal echocardiography-guided cardioversion of patients with atrial fibrillation

Electrical cardioversion of patients with atrial fibrillation (AF) is frequently performed to relieve symptoms and improve cardiac performance. Patients undergoing cardioversion are treated conventionally with therapeutic anticoagulation for three weeks before and four weeks after cardioversion to decrease the risk of thromboembolism. A transesophageal echocardiography (TEE)-guided strategy has been proposed as an alternative that may lower stroke and bleeding events. Patients without atrial cavity thrombus or atrial appendage thrombus by TEE are cardioverted on achievement of therapeutic anticoagulation, whereas cardioversion is delayed in higher risk patients with thrombus. The aim of this review is to discuss the issues and controversies associated with the management of patients with AF undergoing cardioversion. We provide an overview of the TEE-guided and conventional anticoagulation strategies in light of the recently completed Assessment of Cardioversion Using Transesophageal Echocardiography (ACUTE) clinical trial. The two management strategies comparably lower the patient's embolic risk when the guidelines are properly followed. The TEE-guided strategy with shorter term anticoagulation may lower the incidence of bleeding complications and safely expedite early cardioversion. The inherent advantages and disadvantages of both strategies are presented. The TEE-guided approach with short-term anticoagulation is considered to be a safe and clinically effective alternative to the conventional approach, and it is advocated in patients in whom earlier cardioversion would be clinically beneficial.

Atrial fibrillation: rate control versus maintenance of sinus rhythm

Atrial fibrillation is a common tachyarrhythmia encountered in clinical practice. Management has become increasingly complex as the therapeutic options have multiplied. Two basic strategies are available: rhythm control with or without pharmacologic manipulation, and rate control with anticoagulation. To date, no randomized controlled trial that compares the two strategies has been completed, although the Atrial Fibrillation Follow-Up Investigation of Rhythm Management (AFFIRM) trial is underway. This review outlines the rationale for each of the two basic treatment strategies, providing an overview of the advantages and disadvantages of each. Included are clinical criteria used in selecting the appropriate treatment plan.

Exercise tolerance and quality of life in elderly patients with chronic atrial fibrillation

BACKGROUND

Atrial fibrillation is the most common arrhythmia affecting the elderly. Although the risk of cardioembolic stroke is well defined, the effects of chronic atrial fibrillation on exercise tolerance and quality of life have been less well quantified.

METHODS

We compared a group of 52 elderly patients with chronic atrial fibrillation to a group of 48 control patients in sinus rhythm. Each patient underwent an interview that incorporated the Short Form-36 Health Survey (SF-36) to quantify individual perceptions on quality of life. In addition each person underwent physiologic testing that included a Modified Bruce Protocol exercise tolerance test, 24-hour ambulatory monitor test, and an echocardiogram.

RESULTS

Both groups were elderly, 77 vs 76 years of age (P=0.35). The two groups had similar ejection fractions, 55.4% vs 58.4% (P=0.10). The atrial fibrillation patients demonstrated a higher level of comorbidity based on the Charlson Comorbidity Index, 2.46 vs 1.57 (P=0.03). On formal exercise testing there was no statistical difference in exercise duration between the two groups 9.0 vs 10.1 minutes (P=0.24). Similarly the Physical Summary Score (PCS) and the Mental Summary Score (MCS) of the SF-36 quality of life survey did not demonstrate a statistical difference between the two groups. PCS: 43.0 vs 45.9 (P=0.24);

MCS

52.5 vs 55.7 (P=0.07).

CONCLUSIONS

Despite a higher level of comorbidity, elderly, ambulatory patients with chronic atrial fibrillation demonstrate similar exercise tolerance and report similar quality of life to a group of age-matched control patients in sinus rhythm. There is a cohort of patients in chronic atrial fibrillation in whom a strategy of rate control and anticoagulation may be appropriate.

Low dose amiodarone and sotalol in the treatment of recurrent, symptomatic atrial fibrillation: a comparative, placebo controlled study

OBJECTIVE

To assess and compare the safety and efficacy of amiodarone and sotalol in the treatment of patients with recurrent symptomatic atrial fibrillation.

DESIGN

Prospective, randomised, single blind, placebo controlled study.

SETTING

Tertiary cardiac referral centre.

PATIENTS

186 consecutive patients (97 men, 89 women; mean (SD) age, 63 (10) years) with recurrent, symptomatic atrial fibrillation.

INTERVENTIONS

65 patients were randomised to amiodarone, 61 to sotalol, and 60 to placebo. Patients receiving amiodarone were maintained at a dose of 200 mg/day after a 30 day loading phase. The sotalol dose was 160-480 mg daily, as tolerated.

MAIN OUTCOME MEASURES

Recurrence of atrial fibrillation or side effects.

RESULTS

In the amiodarone group, 31 of the 65 patients developed atrial fibrillation after an average of six months, while 15 (11 in sinus rhythm and four in atrial fibrillation) experienced significant side effects after an average of 16 months. In the sotalol group, relapse to atrial fibrillation occurred in 47 of the 61 patients after an average of eight months; three experienced side effects during the titration phase. In the placebo group, 53 of the 60 patients developed atrial fibrillation after an average of four months (p < 0.001 for amiodarone and sotalol v placebo; p < 0.001 for amiodarone v sotalol).

CONCLUSIONS

Both amiodarone and sotalol can be used for the maintenance of normal sinus rhythm in patients with symptomatic atrial fibrillation. Amiodarone is more effective but causes more side effects.

Amiodarone as a first-choice drug for restoring sinus rhythm in patients with atrial fibrillation: a randomized, controlled study

STUDY OBJECTIVES

To investigate the efficacy and safety of amiodarone administered as the drug of first choice in the conversion of atrial fibrillation, regardless of its duration.

DESIGN

: Prospective, randomized, controlled clinical study.

SETTING

: Tertiary cardiac referral center.

PATIENTS

Two-hundred eight consecutive patients (102 men; mean [+/- SD] age, 65 +/- 10 years) with atrial fibrillation.

INTERVENTIONS

One-hundred eight patients received amiodarone, and 100 patients received placebo treatment. Patients randomized to amiodarone received 300 mg IV for 1 h, and then 20 mg/kg for 24 h. They were also given 600 mg/d orally, divided into three doses, for 1 week, and thereafter 400 mg/d for 3 weeks. Patients randomized to placebo treatment received an identical amount of saline solution IV over 24 h, and oral placebo treatment for 1 month.

MEASUREMENTS AND RESULTS

Baseline clinical characteristics were similar in the two groups. Conversion to sinus rhythm was achieved in 87 of 108 patients (80.05%) who received amiodarone, and in 40 of 100 patients (40%) in the placebo group (p < 0.0001). Statistical analysis showed that the duration of the arrhythmia and the size of the left atrium affected both the likelihood of conversion to sinus rhythm and the time to conversion in both groups. No side effects requiring discontinuation of treatment were observed in either group.

CONCLUSIONS

Amiodarone appears to be safe and effective in the termination of atrial fibrillation. However, extreme cases with a large left atrium and long-lasting arrhythmia need long-term therapy.

Determination of refractory periods and conduction velocity during atrial fibrillation using atrial capture in dogs: direct assessment of the wavelength and its modulation by a sodium channel blocker, pilsicainide

OBJECTIVES

The purposes of this study were to measure the atrial refractory period and the conduction velocity (CV) during atrial fibrillation (AF) and to explore the antiarrhythmic mechanism of a sodium channel blocker, pilsicainide, during AF.

BACKGROUND

Sodium channel blockers not only decrease the CV, but also prolong the atrial refractory period, particularly during rapid excitation. Because these effects on the wavelength are counteractive and rate dependent, it is critical to measure these parameters during AF.

METHODS

In eight dogs, after AF was induced under vagal stimulation, a single extra-stimulus was repeatedly introduced from the left atrium and its capture was statistically determined for each coupling interval. The local CV was also measured during constant capture of the fibrillating atrium by rapid pacing. The same procedure was repeated after pilsicainide administration.

RESULTS

Pilsicainide significantly increased the mode of AF intervals from 81 +/- 10 to 107 +/- 16 ms (p < 0.01). While the CV was decreased from 0.9 +/- 0.1 to 0.7 +/- 0.1 m/s (p < 0.02), the effective refractory period during AF was increased from 69 +/- 11 ms to 99 +/- 17 ms (p < 0.01). As a result, the wavelength was significantly increased by pilsicainide from 6.6 +/- 0.9 to 7.6 +/- 1.2 cm (p < 0.05).

CONCLUSIONS

During AF, whereas the sodium channel blocker pilsicainide decreases CV, it lengthens the wavelength by increasing the refractory period, an action that is likely to contribute to the drug's ability to terminate the arrhythmia. The direct measurement of refractoriness and CV during AF may provide new insights into the determinations of the arrhythmia and antiarrhythmic drug action.

Pharmacological management of atrial fibrillation: an update

Therapy of atrial fibrillation remains difficult in many patients. There is increasing awareness that antiarrhythmic drug therapy instituted to maintain sinus rhythm after successful cardioversion of atrial fibrillation may pose a substantial risk to the patient. Therefore, results of prospective randomized trials are needed to allow a more evidence-based approach to the treatment of this common arrhythmia. Two recently published studies have shown superiority of amiodarone over conventional antiarrhythmic drugs in maintaining sinus rhythm. The largest such study published today, the Canadian Trial in Atrial Fibrillation (CTAF), has randomized 403 patients to amiodarone or to sotalol or propafenone. At the end of the observation period, amiodarone-treated patients were significantly more likely to remain in sinus rhythm than conventionally treated patients. A number of new antiarrhythmic drugs, mainly class III substances, are currently developed for the treatment of atrial fibrillation or atrial flutter. Ibutilide has recently been released for intravenous administration, attempting pharmacological cardioversion of atrial fibrillation/atrial flutter. It has been evaluated in a number of prospective trials, which showed a higher conversion rate in patients with atrial flutter. Dofetilide is another new compound developed mainly for maintenance of sinus rhythm after restoration of sinus rhythm. It has been evaluated in two prospective, randomized, placebo-controlled trials; moreover, analysis of the DIAMOND trials showed effectiveness of dofetilide in maintaining sinus rhythm in patients with depressed left ventricular function without increased mortality when compared with placebo. Finally, several ongoing studies compare the therapeutic strategy of controlling ventricular rate in atrial fibrillation compared with the strategy of maintaining sinus rhythm. These trials will help to optimize therapy in atrial fibrillation, the most commonly encountered arrhythmia.

The T-type Ca(2+) channel blocker mibefradil prevents the development of a substrate for atrial fibrillation by tachycardia-induced atrial remodeling in dogs

BACKGROUND

Ca(2+) overload is believed to play a role in tachycardia-induced atrial electrophysiological remodeling. L-type Ca(2+) channel blockers attenuate effective refractory period (ERP) changes caused by 24 hours of atrial tachycardia but may not substantially alter atrial fibrillation (AF) inducibility. This study assessed the effects of the T-type Ca(2+) channel blocker mibefradil on tachycardia-induced atrial remodeling.

METHODS AND RESULTS

Dogs subjected to rapid atrial pacing (400 bpm) for 7 days were treated with mibefradil (100 mg/d, n=8) or matching placebo (n=10) in blinded fashion. Radiofrequency ablation of atrioventricular conduction and ventricular pacing were used to control ventricular rate. Placebo dogs showed significant decreases in atrial ERP (76+/-5 ms at a cycle length of 300 ms) and increases in ERP heterogeneity (27.7+/-2.4%), AF duration (414+/-232 seconds), and AF inducibility by single extrastimuli (41+/-10% of sites) compared with 10 unpaced control dogs (ERP 114+/-3 ms, ERP heterogeneity 13.8+/-0.9%, AF duration 7+/-3 seconds, AF inducibility 1.9+/-1.0% of sites). The changes caused by atrial tachycardia were strongly attenuated in mibefradil dogs, with ERPs averaging 102+/-7 ms, ERP heterogeneity 18.8+/-1.4%, AF duration 3+/-1 seconds, and AF inducibility 9.6+/-4.0% of sites. Among mibefradil-treated dogs, ERP, AF duration, and inducibility correlated with plasma drug concentration. Acute mibefradil administration did not alter ERP or AF.

CONCLUSIONS

Mibefradil, a drug with strong T-type Ca(2+) channel blocking properties, prevents AF-promoting electrophysiological remodeling by atrial tachycardia. These findings have important potential implications for the mechanisms of tachycardia-induced atrial remodeling and demonstrate the feasibility of preventing electrical remodeling caused by several days of atrial tachycardia.

Evolution, mechanisms, and classification of antiarrhythmic drugs: focus on class III actions

Since the use of cinchona bark to treat heart palpitations in the 1700s, antiarrhythmic drug therapy has developed with the discovery of new compounds and the identification of ionic, cellular, and tissue mechanisms of action. Classifications have been developed that organize the large amount of information available about antiarrhythmic drugs around groups of compounds with common mechanisms of action. Despite important and well-recognized limitations, antiarrhythmic drug classification is still widely used. In particularly broad use is the system developed by Singh and Vaughan Williams in the early 1970s and subsequently modified by Singh and Hauswirth and by Harrison. This classification divides drug actions into class I for sodium-channel blockade (with subclasses IA, IB and IC), class II for adrenergic antagonism, class III for action-potential prolongation, and class IV for calcium-channel blockade. The development of class I drugs was curtailed when studies showed that potent sodium-channel blockers (particularly IC agents) can increase mortality in patients with active coronary artery disease. The emphasis in drug development shifted to class III agents, but their use has been limited by the risk of ventricular tachyarrhythmia induction associated with QT prolongation. Current research focuses on the development of new class III drugs that may have improved safety by virtue of greater selectivity of action at faster rates (like those of arrhythmia) or for atrial tissue. Alternative approaches include the modification of existing molecules (like amiodarone) to maintain positive properties while removing undesirable ones, and treatments that target development of the arrhythmia substrate instead of the final electrical product.

Promotion of atrial fibrillation by heart failure in dogs: atrial remodeling of a different sort

BACKGROUND

Studies of atrial fibrillation (AF) due to atrial tachycardia have provided insights into the remodeling mechanisms by which "AF begets AF" but have not elucidated the substrate that initially supports AF before remodeling occurs. We studied the effects of congestive heart failure (CHF), an entity strongly associated with clinical AF, on atrial electrophysiology in the dog and compared the results with those in dogs subjected to rapid atrial pacing (RAP; 400 bpm) with a controlled ventricular rate (AV block plus ventricular pacemaker at 80 bpm).

METHODS AND RESULTS

CHF induced by 5 weeks of rapid ventricular pacing (220 to 240 bpm) increased the duration of AF induced by burst pacing (from 8+/-4 seconds in control dogs to 535+/-82 seconds; P<0.01), similar to the effect of 1 week of RAP (713+/-300 seconds). In contrast to RAP, CHF did not alter atrial refractory period, refractoriness heterogeneity, or conduction velocity at a cycle length of 360 ms; however, CHF dogs had a substantial increase in the heterogeneity of conduction during atrial pacing (heterogeneity index in CHF dogs, 2. 76+/-0.16 versus 1.46+/-0.10 for control and 1.51+/-0.06 for RAP dogs; P<0.01) owing to discrete regions of slow conduction. Histological examination revealed extensive interstitial fibrosis (connective tissue occupying 12.8+/-1.9% of the cross-sectional area) in CHF dogs compared with control (0.8+/-0.3%) and RAP (0. 9+/-0.2%) dogs.

CONCLUSIONS

Experimental CHF strongly promotes the induction of sustained AF by causing interstitial fibrosis that interferes with local conduction. The substrates of AF in CHF are very different from those of atrial tachycardia-related AF, with important potential implications for understanding, treating, and preventing AF related to CHF.

Electrophysiological mechanisms by which hypothyroidism delays repolarization in guinea pig hearts

Thyroid hormone is known to exert important effects on cardiac repolarization, but the underlying mechanisms are poorly understood. We investigated the electrophysiological mechanisms of differences in repolarization between control guinea pigs and hypothyroid animals (thyroidectomy plus 5-propyl-2-thiouracil). Hypothyroidism significantly prolonged the rate-corrected Q-T interval in vivo and action potential duration (APD) of isolated ventricular myocytes. Whole cell voltage-clamp studies showed no change in current density or kinetics of L-type Ca(2+) current, inward rectifier K(+) current, or Na(+) current in hypothyroid hearts. Dofetilide-resistant current (I(Ks)) step current densities were smaller by approximately 65%, and tail current densities were reduced by 80% in myocytes from hypothyroid animals compared with controls. The ratio of delayed rectifier step current at +50 mV to tail current at -40 mV was significantly larger in hypothyroid cells for test pulses from 60- to 4,200-ms duration, reflecting a smaller I(Ks). Dofetilide-sensitive current (I(Kr)) densities were not significantly changed. I(Ks) half-activation voltage shifted to more positive voltages in hypothyroidism (29.5 +/- 2.2 vs. 21.3 +/- 2.7 mV in control, P < 0.01), whereas I(Kr) voltage dependence was unchanged. We conclude that hypothyroidism delays repolarization in the guinea pig ventricle by decreasing I(Ks), a novel and potentially important mechanism for thyroid regulation of cardiac electrophysiology.

Molecular mechanisms underlying ionic remodeling in a dog model of atrial fibrillation

The rapid atrial rate during atrial fibrillation (AF) decreases the ionic current density of transient outward K+ current, L-type Ca2+ current, and Na+ current, thereby altering cardiac electrophysiology and promoting arrhythmia maintenance. To assess possible underlying changes in cardiac gene expression, we applied competitive reverse transcriptase-polymerase chain reaction to quantify mRNA concentrations in dogs subjected to 7 (group P7 dogs) or 42 (group P42 dogs) days of atrial pacing at 400 bpm and in sham controls. Rapid pacing reduced mRNA concentrations of Kv4.3 (putative gene encoding transient outward K+ current; by 60% in P7 and 74% in P42 dogs; P<0.01 and P<0.001, respectively, versus shams), the alpha1c subunit of L-type Ca2+ channels (by 57% in P7 and 72% in P42 dogs; P<0.01 versus shams for each) and the alpha subunit of cardiac Na+ channels (by 18% in P7 and 42% in P42; P=NS and P<0.01, respectively, versus shams) genes. The observed changes in ion channel mRNA concentrations paralleled previously measured changes in corresponding atrial ionic current densities. Atrial tachycardia did not affect mRNA concentrations of genes encoding delayed or Kir2.1 inward rectifier K+ currents (of which the densities are unchanged by atrial tachycardia) or of the Na+,Ca2+ exchanger. Western blot techniques were used to quantify protein expression for Kv4.3 and Na+ channel alpha subunits, which were decreased by 72% and 47%, respectively, in P42 dogs (P<0.001 versus control for each), in a manner quantitatively similar to measured changes in mRNA and currents, whereas Na+,Ca2+ exchanger protein concentration was unchanged. We conclude that chronic atrial tachycardia alters atrial ion channel gene expression, thereby altering ionic currents in a fashion that promotes the occurrence of AF. These observations provide a potential molecular basis for the self-perpetuating nature of AF.

Amiodarone versus propafenone for conversion of chronic atrial fibrillation: results of a randomized, controlled study

OBJECTIVES

The purpose of this study was to investigate the efficacy and safety of amiodarone and propafenone in the conversion of chronic atrial fibrillation in a prospective, randomized, placebo-controlled study.

BACKGROUND

The effectiveness of amiodarone and propafenone in the treatment of patients with chronic atrial fibrillation has not been adequately studied.

METHODS

One hundred one patients (48 men, mean age 64 +/- 9 years) with atrial fibrillation lasting >3 weeks participated in the study. Thirty-four patients received amiodarone (300 mg intravenously over 1 h, followed by 20 mg/kg over the next 24 h plus 600 mg orally, in three doses, for 1 week, then 400 mg/day orally, for three weeks), 32 received propafenone (2 mg/kg intravenously over 15 min, followed by 10 mg/kg over 24 h and then 450 mg/day orally, for one month) and the remaining 35 served as control subjects. All patients received digoxin and anticoagulant treatment as indicated (International Normalized Ratio 2 to 3).

RESULTS

Conversion to sinus rhythm was achieved in 16 (47.05%) patients who received amiodarone, in 13 (40.62%) who received propafenone and in none of the control subjects (p < 0.001 for both groups vs. control subjects). Those who converted had smaller atria than those who did not and atrial fibrillation of shorter duration in both the amiodarone and propafenone groups. Treatment was discontinued in one patient of the propafenone group because of significant QRS widening.

CONCLUSIONS

Amiodarone and propafenone appear to be safe and equally effective in the termination of chronic atrial fibrillation. Left atrial diameter and arrhythmia duration are independent predictors of conversion.

Optimal management with Class I and Class III antiarrhythmic drugs should be done in the outpatient setting: protagonist

It has been suggested that patients be admitted for the initiation of Class I and Class III antiarrhythmic drugs to avoid serious proarrhythmic consequences. The most clinically significant proarrhythmic response to Class IC agents is likely due to an interaction with acute ischemia, and hospitalization for initiation of drug therapy has little predictive or preventive value. Amiodarone has a low risk of proarrhythmia, and any proarrhythmic reactions are generally delayed. Class IA and Class III antiarrhythmic drugs cause acquired long QT syndrome arrhythmias, which can occur soon after initiation of therapy; however, only about half of the arrhythmic events occur within 3 days of initiation of therapy. It could be argued that all patients should be hospitalized to begin Class IA or Class III drugs; however, this approach has a low yield and is extremely expensive. An alternative is to use Class IA and Class III drugs for patients at low risk of torsades de pointes (e.g., males without heart failure, ventricular tachyarrhythmias, or active coronary disease), in whom hospitalization for drug initiation is not warranted. Higher risk patients are probably better treated with other agents, such as Class IC drugs or amiodarone for women without organic heart disease and amiodarone for patients with heart failure, a history of ventricular tachycardia, or active coronary disease. When a Class IA or Class III drug is required for patient with an increased risk of torsades de pointes, hospital admission for drug initiation may be indicated.

Efficacy of amiodarone for the termination of persistent atrial fibrillation

The efficacy and safety of amiodarone in the conversion of persistent atrial fibrillation (AF) were investigated in a prospective, randomized, controlled study. Of 67 consecutive patients (32 men, mean age 64+/-9 years) with AF lasting >48 hours, 33 received amiodarone and 34 received placebo. Baseline clinical characteristics were similar in the 2 groups. Patients randomized to amiodarone received 300 mg intravenously for 1 hour and then 20 mg/kg for 24 hours. They were also given 600 mg/day orally, divided into 3 doses, for 1 week and thereafter 400 mg/day for 3 weeks. Patients randomized to placebo received an identical amount of saline IV over 24 hours and then oral placebo for 1 month. Conversion to sinus rhythm was achieved in 16 of the 33 patients (48.5%) who received amiodarone and in none of the 34 patients in the placebo group (p <0.001). None of the patients converted to sinus rhythm within the first 3 days. Those who converted had smaller atria than those who did not (diameter 41.9+/-7.2 vs 50.4+/-5.7 mm, p <0.001). Sex, age, baseline heart rate, left ventricular ejection fraction, and the duration of AF did not differ significantly between patients who converted and those who did not. No side effects requiring discontinuation of treatment were observed in either group. Amiodarone, administered both intravenously and orally, appears to be safe and effective in the termination of persistent AF. Left atrial diameter is the sole independent predictor of conversion.

Effects of oral repetitive loading of disopyramide on acute-onset atrial fibrillation with concurrent monitoring of serum drug concentration

We investigated the efficacy and safety of oral repetitive loading of disopyramide, for the termination of acute-onset (i.e., therapy started within 2 days after the onset of palpitations) atrial fibrillation (AF) in 96 consecutive patients, with concurrent monitoring of the serum concentration of this agent in fifteen of the patients. Outpatients with AF verified by standard electrocardiogram (ECG) were hospitalized and received disopyramide (200 mg) every 4-6 h, with a maximal dose of 800 mg daily, until the termination of AF under ECG monitoring was obtained. Conversion to sinus rhythm occurred within the first day of treatment in 88 patients (92%), on the second day of treatment in six patients (6%), and on the third and fifth days of treatment in the remaining two patients. No major adverse effects, such as hypotension, congestive heart failure, proarrythmic events or systemic embolism were noted. The serum levels of disopyramide evaluated in fifteen of the enrolled patients were found to be maintained within the therapeutic range throughout the treatment period. In spite of the absence of any placebo-controlled group in this study, these findings suggest that repetitive oral loading of disopyramide (200 mg) with an interval of 4-6 h is effective and safe for the termination of acute-onset AF under a stable therapeutic serum drug concentration, hence offering the possibility of self-medication for patients with episodic AF.

Spontaneous conversion and maintenance of sinus rhythm by amiodarone in patients with heart failure and atrial fibrillation: observations from the veterans affairs congestive heart failure survival trial of antiarrhythmic therapy (CHF-STAT). The Department of Veterans Affairs CHF-STAT Investigators

BACKGROUND

In a multicenter, double-blind, placebo-controlled study, the long-term effects of amiodarone on morbidity and mortality in patients with congestive heart failure (CHF) and atrial fibrillation (AF) were evaluated during a 4-year period.

METHODS AND RESULTS

Of 667 patients with CHF, 103 (15%) had AF at baseline. Of these, 51 were randomized to amiodarone and 52 to placebo. The group with sinus rhythm and the group in AF were comparable except for a higher proportion of AF in patients with nonischemic versus ischemic cardiomyopathy (41% versus 27%, P<0.005). The mean ventricular response (VR) during AF over 24 hours was reduced by amiodarone at 2 weeks (20%, P=0.001), at 6 months (18%, P=0.001), and at 12 months (16%, P=0.006). Maximal VR was reduced 22% (P=0.001) at 2 weeks, 19% (P=0.001) at 6 months, and 14% (P=0.001) at 12 months. Sixteen of 51 patients on amiodarone and 4 of 52 on placebo converted to sinus rhythm during the study (chi2=9.23, P=0.002). During follow-up, 11 of 268 patients in sinus rhythm on amiodarone at baseline and 22 of the 263 in sinus rhythm on placebo developed AF; the difference was significant (chi2=12.88, P=0.005). Analysis of total mortality during follow-up showed a significantly lower mortality rate (P=0. 04) in patients in AF at baseline who subsequently converted to sinus rhythm on amiodarone than in those who did not convert to sinus rhythm on the drug.

CONCLUSIONS

In patients with CHF, amiodarone has a significant potential to spontaneously convert patients in AF to sinus rhythm, with patients who convert having a lower mortality rate than those who do not. The drug prevented the development of new-onset AF and significantly reduced the VR in those with persistent AF.

Importance of refractoriness heterogeneity in the enhanced vulnerability to atrial fibrillation induction caused by tachycardia-induced atrial electrical remodeling

BACKGROUND

Rapid atrial activation causes electrical remodeling that promotes the occurrence and the maintenance of atrial fibrillation (AF). Although remodeling has been shown to alter electrophysiological variables, the spatial uniformity of these changes is unknown.

METHODS AND RESULTS

Dogs subjected to rapid atrial pacing (400 bpm) for 24 hours (n=12) were compared with sham-operated dogs (instrumented but not paced, n=12). Epicardial mapping (240 bipolar electrodes) and extrastimulation at a large number of sites (mean+/-SEM, 66+/-4 per dog) were used to evaluate atrial activation and the heterogeneity of the effective refractory period (ERP), respectively. Rapid pacing increased both the percentage of sites at which AF could be induced by single premature stimuli (from 2.6+/-0.9% to 11.8+/-2.8%, P=0.007) and AF duration (from 39+/-28 to 146+/-49 seconds, P=0.03). Atrial tachycardia decreased atrial ERP (from 120+/-4 to 103+/-2 ms, P=0.003), increased the coefficient of variation of ERP (from 14.9+/-0.9% to 20.7+/-0.9%, P<0.0001), and accelerated conduction velocity (from 91+/-2 to 108+/-3 cm/s, P=0.0004), with no change in the wavelength. The increase in ERP heterogeneity was due both to interregional differences in the extent of ERP remodeling and to increased intersite variability within regions. Stepwise multilinear regression indicated that ERP heterogeneity was an independent determinant of the inducibility (P<0.0001) and duration (P<0.0001) of AF, whereas ERP per se and wavelength were not significant determinants. Combined mapping of AF induction and atrial ERP showed that premature extrastimuli induced AF at sites with short ERP by causing local conduction slowing and/or block in adjacent zones with longer ERP values.

CONCLUSIONS

Atrial tachycardia causes nonuniform remodeling of atrial refractoriness that plays an important role in increasing atrial vulnerability to AF induction and the duration of induced AF.

Ultrarapid delayed rectifier current inactivation in human atrial myocytes: properties and consequences

The ultrarapid delayed rectifier current (IK,ur) plays a significant role in human atrial repolarization and is generally believed to show little rate dependence because of slow and partial inactivation. This study was designed to evaluate in detail the properties and consequences of IK,ur inactivation in isolated human atrial myocytes. IK,ur inactivated with a biexponential time course and a half-inactivation voltage of -7.5 +/- 0.6 mV (mean +/- SE), with complete inactivation during 50-s pulses to voltages positive to +10 mV (37 degreesC). Recovery from inactivation proceeded slowly, with time constants of 0.42 +/- 0.06 and 7.9 +/- 0.9 s at -80 mV (37 degreesC). Substantial frequency dependence was observed at 37 degreesC over a clinically relevant range of frequencies. Inactivation was faster and occurred at more positive voltages at 37 degreesC compared with room temperature. The voltage and time dependencies of Kv1.5 inactivation were studied in Xenopus oocytes to avoid overlapping currents and strongly resembled those of IK,ur in native myocytes. We conclude that, while IK,ur inactivation is slow, it is extensive, and slow recovery from inactivation confers important frequency dependence with significant consequences for understanding the role of IK,ur in human atrial repolarization.

Intravenous propafenone versus intravenous amiodarone in the management of atrial fibrillation of recent onset: a placebo-controlled study

The efficacy and safety of intravenous propafenone, amiodarone, or placebo were compared in the treatment of atrial fibrillation (AF) of recent onset (duration < or = 48 hours).

METHODS

143 patients (77 men, mean age 63 +/- 12 years) were studied, of whom 46 received propafenone (2 mg/kg over 15 minutes followed by 10 mg/kg over the next 24 hours), 48 received amiodarone (300 mg intravenously over 1 hour, followed by 20 mg/kg over the next 24 hours, plus 1,800 mg/day orally, in 3 divided doses), and 49 received placebo (the equivalent amount of saline i.v. over 24 hours). Digoxin was administered to all patients who had not previously received it.

RESULTS

Conversion to normal sinus rhythm occurred in 36 of 46 patients (78.2%) receiving propafenone, in 40 of 48 patients (83.3%) receiving amiodarone, and in 27 of the 49 (55.10%) controls (P < 0.02, drug vs placebo, between drugs NS). The mean time to conversion was 2 +/- 3 hours for propafenone, 7 +/- 5 hours for amiodarone, and 13 +/- 9 for placebo (P < 0.05). Patients who converted had smaller atria than those who did not (diameter: 42.7 +/- 5 vs 47.2 +/- 7 mm, P < 0.001 for all). Treatment was discontinued in one patient in the amiodarone group because of an allergic reaction and in two patients in the propafenone group because of excessive QRS widening. No side effects were observed in the placebo group.

CONCLUSIONS

Both drugs tested intravenously were equally effective and safe for the rapid conversion of recent-onset atrial fibrillation to sinus rhythm. However, propafenone offered the advantage of more rapid conversion than amiodarone.

The peri-operative management of atrial fibrillation

Atrial fibrillation is a common arrhythmia frequently seen in surgical patients. The onset of new atrial fibrillation during the peri-operative period is less common. There are many possible precipitating factors, although volatile agents themselves may have an antifibrillatory action. The management of atrial fibrillation includes removal of any precipitating factors and treatment of the arrhythmia itself. Immediate management of acute-onset atrial fibrillation is usually direct current cardioversion. Alternatively, anti-arrhythmic drugs can be used to achieve cardioversion. In patients with rapid, chronic atrial fibrillation or those refractory to cardioversion, priority is given to control of the ventricular rate. Thrombo-embolism is a significant risk if atrial fibrillation is paroxysmal or persists for more than 48 h.

Low-dose amiodarone versus sotalol for suppression of recurrent symptomatic atrial fibrillation

To compare the safety and efficacy of amiodarone and sotalol in the treatment of patients with recurrent symptomatic atrial fibrillation (AF), 70 patients were entered into a randomized, double-blind study. Of these, 35 received amiodarone and 35 sotalol. There were no significant differences in baseline clinical characteristics between groups. Patients with ejection fraction < 40% or clinically significant heart disease were excluded. Patients randomized to amiodarone began with 800 to 1,600 mg/day for 7 to 14 days orally. After the initial loading phase, the drug dose was tapered to maintenance levels over 7 to 12 days; thereafter, therapy was generally maintained at a dosage of 200 mg/day. The sotalol dosage was 80 to 360 mg twice daily, as tolerated. Follow-up clinical evaluations were conducted at 1, 2, 4, 6, 9, and 12 months. The proportion of patients remaining in sinus rhythm on each agent was calculated for the 2 groups using the Kaplan-Meier method. Ten of the 35 patients who were taking amiodarone developed AF during the 12-month observation period, compared with 21 of the 35 who were taking sotalol (p = 0.008). No significant effect of sex, age, left atrial size, or type of AF could be detected that increased the risk of development of AF. We conclude that both amiodarone and sotalol can be used for the maintenance of normal sinus rhythm in patients with recurrent symptomatic AF but that amiodarone is the more effective of the 2 drugs for this purpose.

Update on Atrial Fibrillation: Restoration of Sinus Rhythm or Ventricular Rate Control?

In patients with persistent atrial fibrillation, two therapeutic alternatives exist, namely restoration and maintenance of sinus rhythm versus ventricular rate control combined with anticoagulation. Currently, the selection of the best therapeutic strategy in an individual patient relies for the most part on clinical judgement and personal experience. At present, there are no prospective scientific data to support the superiority of one treatment over the other with respect to overall survival or quality of life. This review summarizes the present knowledge on this important clinical problem with particular emphasis on issues such as efficacy of antiarrhythmic drugs to prevent recurrent atrial fibrillation, proarrhythmic hazards of these compounds, or efficacy and safety of anticoagulation in nonrheumatic atrial fibrillation. These data serve as the basis of ongoing clinical trials prospectively comparing the merits and demerits of the two therapeutic strategies in the most common arrhythmia encountered in clinical practice.

Acute treatment of atrial fibrillation

Atrial fibrillation (AFib) is a common clinical entity, responsible for significant morbidity and mortality, but it also accounts for a large percentage of healthcare dollar expenditures. Efforts to treat this arrhythmia in the past have focused on subacute antithrombotic therapy and eventually use of antiarrhythmic drugs for maintenance of sinus rhythm. However, there has been a growing interest in the concept of acute electrical and pharmacologic conversion. This treatment strategy has a number of benefits, including immediate alleviation of patient symptoms, avoidance of antithrombotic therapy, and prevention of electrophysiologic remodeling, which is thought to contribute to the perpetuation of the arrhythmia. There is also increasing evidence that this is a cost-effective strategy in that it may obviate admission to the hospital and the cost of long-term therapy. This article represents a summary of the treatments that may be used acutely to control the ventricular response to AFib, prevent thromboembolic events, and provide for acute conversion either pharmacologically or electrically. It includes information on modalities that are currently available and those that are under active development. We anticipate that an active, acute treatment approach to AFib and atrial flutter will become the therapeutic norm in the next few years, especially as the benefits of these interventions are demonstrated in clinical trials.

Rhythm management in atrial fibrillation--with a primary emphasis on pharmacological therapy: Part 1

Atrial fibrillation (AF) is the most common, sustained, symptomatic tachyarrhythmia that clinicians are called upon to manage. Management strategies include ventricular rate control coupled with anticoagulation, versus restoration and maintenance of sinus rhythm. Rate control may be achieved pharmacologically, with agents that impair AV nodal conduction directly and/or by increasing parasympathetic/sympathetic balance, or by modifying or ablating the AV nodal region anatomically. Rhythm control may be achieved by electrical or pharmacological conversion followed by maintenance of sinus rhythm by pharmacological (or occasionally ablative) therapies. This article will present current approaches to rate and rhythm control issues in AF. Part 1, the current manuscript, details approaches to rate control and includes a drug selection algorithmic conclusion. It also introduces the subject of the pursuit of sinus rhythm. Parts 2 and 3, to be published in subsequent editions of PACE, will deal with therapeutic measures to restore and maintain sinus rhythm.

Factors influencing long term persistence of sinus rhythm after a first electrical cardioversion for atrial fibrillation

It is conventionally thought that electrical cardioversion in patients with atrial fibrillation (AF) of longstanding duration or with a large left atrial diameter, only seldom results in long term success. Recurrence is common, although antiarrhythmic drugs often effectively decrease the number and duration of recurrent AF episodes. We analysed clinical, functional and pharmacological variables which could possibly influence the long term outcome after a first electrical cardioversion for AF in a retrospective study on 85 patients. Univariate and multivariate analysis was used to identify factors predicting maintenance of sinus rhythm at 100 days, and absence of recurrence during the entire follow-up. In univariate analysis, the only significant predictor for maintenance of sinus rhythm at 100 days was the duration of the preceding AF episode. Multivariate analysis with persistence of sinus rhythm at 100 days as endpoint confirmed this as a prognostic factor (p < 0.03), but sotalol treatment also contributed to maintenance of sinus rhythm (p < 0.05). When considering the entire observation period, class III antiarrhythmic drugs, i.e. sotalol and amiodarone, were useful in preventing recurrence (p < 0.01 and < 0.02). High age (above 75 years) was a predictor of recurrence. In conclusion, class III antiarrhythmic drugs, the duration of atrial fibrillation and high age were the most important determinants of long term outcome, while echocardiographic parameters and the presence of heart disease played no role.