Intravenous amiodarone for acute heart rate control in the critically ill patient with atrial tachyarrhythmias

Amiodarone-induced acute lung toxicity in an ICU setting

Amiodarone is a highly effective antiarrhythmic drug, albeit notorious for its serious pulmonary toxicity. The incidence of amiodarone-induced pulmonary toxicity (APT) appears to be 1% per year (1). We report a case of very acute APT in a man suffering from postoperative atrial fibrillation.

Acute ventricular rate control in atrial fibrillation and atrial flutter

Atrioventricular node blocking agents including beta-adrenergic blockers, non-dihydropyridine calcium channel blockers and digoxin are usually effective in controlling ventricular rate in atrial fibrillation and flutter. Intravenous beta-blockers and non-dihydropyridine calcium channel blockers are equally effective in rapidly controlling the ventricular rate. The addition of digoxin to the regimen causes a favorable outcome but digoxin as a single agent is generally less effective in slowing the ventricular rate in acute setting. Clonidine, magnesium, and amiodarone have also been used for acute ventricular rate control in atrial fibrillation. Limited data suggest that combination regimens provide better ventricular rate control than any agent alone. The agent of first choice is usually individualized depending upon the clinical situation. Beta-blockers are preferable in patients with myocardial ischemia, myocardial infarction and hyperthyroidism and in post-operative state, but should be avoided in patients with bronchial asthma and chronic obstructive pulmonary disease where non-dihydropyridine calcium channel blockers are preferred. Beta-blockers are preferred drugs used for acute ventricular rate control in atrial fibrillation during pregnancy. In atrial fibrillation with Wolff-Parkinson-White syndrome, beta-blockers, calcium channel blockers and digoxin should be avoided, as these drugs are selective atrioventricular node blockers without slowing conduction through the accessory pathway, which can lead to increased transmission of impulses preferentially through the accessory pathway and precipitate ventricular fibrillation. The drug of choice for atrial fibrillation in pre-excitation syndrome is procainamide but propafenone, flecainide and disopyramide have also been used. When clinical condition is unstable or patient is hemodynamically compromised, immediate electrical cardioversion is the treatment of choice, as the best measure to control ventricular rate is by conversion to sinus rhythm. Factors precipitating rapid ventricular rate should be treated as well.

High-dosage continuous amiodarone therapy to treat new-onset supraventricular tachyarrhythmias in surgical intensive care patients: an observational study

BACKGROUND

New-onset supraventricular tachyarrhythmias (SVTA) are a complication contributing significantly to morbidity and mortality in surgical intensive care unit (SICU) patients. Although only few data on efficiency can be found in the literature, class III antiarrhythmics have become popular in the treatment of SVTA in critically ill patients.

SETTING

12-bed general and surgical ICU in a university teaching hospital.

DESIGN

Observational, retrospective study.

PATIENTS

131 SICU patients with SVTA (narrow-complex non-sinus tachyarrhythmias with heart rates > or = 100 bpm).

INTERVENTION

High-dosage amiodarone infusion according to an institutional protocol.

MEASUREMENTS

Hemodynamic data, acid-base status, and single organ functions were obtained in all patients before amiodarone infusion and at 12, 24, and 48 hours afterwards. Patients were divided into responders and nonresponders. Amiodarone infusion (mean dosage 24 h: 1625+/-528 mg; 48 h: 2708+/-895 mg) restored sinus rhythm in 54% of study patients within 12 h, in 64% within 24 h, and in 75% within 48 h. Heart rate, central venous pressure, and milrinone requirements significantly decreased in all patients; this was accompanied by a significant increase in stroke-volume index and mean arterial pressure. Serum concentrations of creatinine and bilirubin increased in all patients.

CONCLUSION

High-dosage continuous amiodarone infusion during a period of 48 hours resulted in restoration of SR in 75% of SICU patients with new-onset SVTA and moderate to severe multiple-organ dysfunction syndrome. A significant improvement in cardiocirculatory function was more pronounced in responders but could be demonstrated irrespective of restoration of sinus rhythm in all patients. Apart from a possibly amiodarone-mediated increase in concentrations of creatinine and bilirubin, no major drug-related adverse effects occurred during the observation period.

Biochemistry and biology of mammalian DNA methyltransferases

DNA methylation is a stable but not irreversible epigenetic signal that silences gene expression. It has a variety of important functions in mammals, including control of gene expression, cellular differentiation and development, preservation of chromosomal integrity, parental imprinting and X-chromosome inactivation. In addition, it has been implicated in brain function and the development of the immune system. Somatic alterations in genomic methylation patterns contribute to the etiology of human cancers and ageing. It is tightly interwoven with the modification of histone tails and other epigenetic signals. Here we review our current understanding of the molecular enzymology of the mammalian DNA methyltransferases Dnmt1, Dnmt3a, Dnmt3b and Dnmt2 and the roles of the enzymes in the above-mentioned biological processes.

Ventricular rate control during atrial fibrillation and AV node modifications: past, present, and future

Atrial fibrillation (AF) is the most common arrhythmia. Currently there are two broad strategic treatment options for AF: rhythm control and rate control. For rhythm control, the treatment is directed toward restoring and maintaining the sinus rhythm. For rate control, the intention is to slow ventricular rate while allowing AF to continue. In both cases anticoagulation therapy is recommended. The results of currently available clinical trials demonstrated clearly that rate control is not inferior to rhythm control. Thus, rate control is an acceptable primary therapy for many AF patients. The rate control can be achieved essentially by depressing or modifying the filtering properties of the atrioventricular (AV) node. This can be attained by medications that depress the impulse transmission within the AV node, by anatomic modification of the AV communications, as well as by autonomic manipulations that produce AV node negative dromotropic effect. We are reviewing current clinical and newer experimental modalities aimed at enhancing the lifesaving function of this remarkable nodal structure.

A perspective on rate control in the treatment of atrial fibrillation

Until recently, the standard approach to therapy of atrial fibrillation (AF) in most cases was restoration and maintenance of sinus rhythm (rhythm control). Although difficult to accomplish, and associated with potential serious adverse effects of antiarrhythmic agents, this therapeutic approach was influenced by the belief that rhythm control was associated with better survival, fewer symptoms, better exercise tolerance, lower risk of stroke, better quality of life, and absence of need for long-term anticoagulation. However, four clinical trials comparing rate control with rhythm control have failed to demonstrate these advantages, indicating that rate control should be considered a legitimate primary therapeutic option, particularly in patients at risk for stroke. Pursuit of rate or rhythm control should be decided on a case-by-case basis.

Clinical review: clinical management of atrial fibrillation - rate control versus rhythm control

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia in the critically ill and is associated with adverse outcomes. Although there are plausible benefits from conversion and maintenance of sinus rhythm (the so-called 'rhythm-control' strategy), recent randomized trials have failed to demonstrate the superiority of this approach over the rate-control strategy. Regardless of approach, continuous therapeutic anticoagulation is crucial for stroke prevention. This review addresses the findings of these studies and their implications for clinical management of patients with atrial fibrillation.

Atrial Fibrillation in Heart Failure:

AF in Heart Failure. Atrial fibrillation and congestive heart failure are commonly occurring cardiac disorders that often exist concomitantly. The prognostic significance of the presence or absence of atrial fibrillation, as an independent risk factor, in patients with heart failure remains controversial. Antiarrhythmic drugs with good hemodynamic profiles and neutral effects on survival are preferred treatments for converting atrial fibrillation and maintaining sinus rhythm. Other standard therapies for congestive heart failure, such as angiotensin-converting enzyme inhibitors, angiotensin receptor blockers, and beta-blockers also have a role in the treatment of these coexisting disease states. The article presents an overview of atrial fibrillation in patients with heart failure and reviews the prevalence, prognostic significance, and efficacy of various antiarrhythmic agents for the conversion and maintenance of sinus rhythm.

Rate or rhythm control in persistent atrial fibrillation?

Atrial fibrillation (AF) is the most common sustained tachyarrhythmia encountered in clinical practice, with the majority of patients aged > 65 years. With an increasingly ageing population, the burden of AF in society continues to rise. One of the principal controversies in AF management is whether to control the ventricular rate and accept the underlying rhythm, or to attempt to achieve sinus rhythm. Until recently there were no clinical trial data directly comparing a rate versus rhythm strategy, and most physicians have opted for rhythm control, based on its theoretical benefits. We present an up-to-date evidence-based overview of the relative merits of rate versus rhythm control in AF, including data from five recent randomized trials. We draw conclusions from these studies and present evidence-based guidance on when to adopt which approach in routine clinical practice.

Rate control in atrial fibrillation: choice of treatment and assessment of efficacy

The clinical relevance and high social costs of atrial fibrillation have boosted interest in rate control as a cost-effective alternative to long-term maintenance of sinus rhythm (i.e. rhythm control). Prospective studies show that rate control (coupled with thromboembolic prophylaxis) is a valuable treatment option for all forms of atrial fibrillation. The rationale for rate control is that high ventricular rates, frequently found in atrial fibrillation, lead to haemodynamic impairment, consisting of a variable combination of loss of atrial kick, irregularity in ventricular response and inappropriately rapid ventricular rate, depending on the type of underlying heart disease. Long-term persistence of tachycardia at a high ventricular rate can lead to various degrees of ventricular dysfunction and even to tachycardiomyopathy-related heart failure. Identification of this reversible and often concealed form of left ventricular dysfunction can permit effective management by rate (or rhythm) control. Although acute rate control (to reduce ventricular rate within hours) is still often based on digoxin administration, for patients without left ventricular dysfunction, calcium channel antagonists or beta-adrenoceptor antagonists (beta-blockers) are generally more appropriate and effective. In chronic atrial fibrillation, long-term rate control (to reduce morbidity/mortality and improve quality of life) must be adapted to patients' individual characteristics to grant control during daily activities, including exercise. According to current guidelines, the clinical target of rate control should be a ventricular rate below 80-90 bpm at rest. However, in many patients, assessment of the appropriateness of different drugs should include exercise testing and 24h-Holter monitoring, for which specific guidelines are needed. In practice, rate control is considered a valid alternative to rhythm control. Recent prospective trials (e.g. the Pharmacological Intervention in Atrial Fibrillation [PIAF] and the Atrial Fibrillation Follow-up Investigation of Rhythm Management [AFFIRM] trials) have shown that in selected patients, rate control provides similar benefits, more economically, in terms of quality of life and long-term mortality. The choice of a rate control medication (digoxin, beta-blockers, calcium channel antagonists or possibly amiodarone) or a non-pharmacological approach (mainly atrioventricular node ablation coupled with pacing) must currently be based on clinical assessment, which includes assessing the presence of underlying heart disease and haemodynamic impairment. Definite guidelines are required for each different subset of patients. Rate control is particularly tricky in patients with heart failure, for whom non-pharmacological options can also be considered. The preferred pharmacological options are beta-blockers for stabilised heart failure and digoxin for unstabilised forms.

Arrhythmias in the intensive care patient

PURPOSE OF REVIEW

Atrial fibrillation, atrial flutter, AV-nodal reentry tachycardia with rapid ventricular response, atrial ectopic tachycardia, and preexcitation syndromes combined with atrial fibrillation or ventricular tachyarrhythmias are typical arrhythmias in intensive care patients. Most frequently, the diagnosis of the underlying arrhythmia is possible from the physical examination, the response to maneuvers or drugs, and the 12-lead surface electrocardiogram. In all patients with unstable hemodynamics, immediate DC-cardioversion is indicated. Conversion of atrial fibrillation to sinus rhythm is possible using antiarrhythmic drugs. Amiodarone has a conversion rate in atrial fibrillation of up to 80%. However, caution in the use of short-term administration of intravenous amiodarone in critically ill patients with recent-onset atrial fibrillation is absolutely necessary, and the duration of therapy should not exceed 24 to 48 hours. Ibutilide represents a relatively new class III antiarrhythmic agent that has been reported to have conversion rates of 50% to 70%; it seems that ibutilide is even successful when intravenous amiodarone failed to convert atrial fibrillation.

RECENT FINDINGS

Newer studies compared the outcome of patients with atrial fibrillation and rhythm- or rate-control. Data from these studies (AFFIRM, RACE) clearly showed that rhythm control is not superior to rate control for the prevention of death and morbidity from cardiovascular causes. Therefore, rate-control may be an appropriate therapy in patients with recurrent atrial fibrillation after DC-cardioversion. Acute therapy of atrial flutter in intensive care patients depends on the clinical presentation. Atrial flutter can most often be successfully cardioverted to sinus rhythm with energies less than 50 joules. Ibutilide trials showed efficacy rates of 38-76% for conversion of atrial flutter to sinus rhythm compared with conversion rates of 5-13% when intravenous flecainide, propafenone, or verapamil was administered. In addition, a high dose (2 mg) of ibutilide was more effective than sotalol (1.5 mg/kg) in conversion of atrial flutter to sinus rhythm (70% versus 19%).

SUMMARY

There is general agreement that bystander first aid, defibrillation, and advanced life support is essential for neurologic outcome in patients after cardiac arrest due to ventricular tachyarrhythmias. The best survival rate from cardiac arrest can be achieved only when (1) recognition of early warning signs, (2) activation of the emergency medical services system, (3) basic cardiopulmonary resuscitation, (4) defibrillation, (5) management of the airway and ventilation, and (6) intravenous administration of medications occurs as rapidly as possible. Public access defibrillation, which places automatic external defibrillators in the hands of trained laypersons, seems to be an ideal approach in the treatment of ventricular fibrillation. The use of automatic external defibrillators by basic life support ambulance providers or first responder in early defibrillation programs has been associated with a significant increase in survival rates. Drugs such as lidocaine, procainamide, sotalol, amiodarone, or magnesium were recommended for treatment of ventricular tachyarrhythmias in intensive care patients. Amiodarone is a highly efficacious antiarrhythmic agent for many cardiac arrhythmias, ranging from atrial fibrillation to malignant ventricular tachyarrhythmias, and seems to be superior to other antiarrhythmic agents.

Emergency management of atrial fibrillation

Atrial fibrillation is the most common cardiac arrhythmia managed by emergency and acute general physicians. There is increasing evidence that selected patients with acute atrial fibrillation can be safely managed in the emergency department without the need for hospital admission. Meanwhile, there is significant variation in the current emergency management of acute atrial fibrillation. This review discusses evidence based emergency management of atrial fibrillation. The principles of emergency management of acute atrial fibrillation and the subset of patients who may not need hospital admission are reviewed. Finally, the need for evidence based guidelines before emergency department based clinical pathways for the management of acute atrial fibrillation becomes routine clinical practice is highlighted.

Pharmacologic and nonpharmacologic options to maintain sinus rhythm: guideline-based and new approaches

Atrial fibrillation is a common arrhythmia in patients with heart failure and is responsible for substantial morbidity and mortality. Restoration and preservation of sinus rhythm, therefore, has a premium. Of the numerous treatment options available, many must be avoided because of their potential for adverse effects or because of limited proof of efficacy in defined populations. Published guidelines provide help by synthesizing clinical trial data into a recommended approach. This article summarizes current information regarding the best methods applicable to patients with left ventricular dysfunction for rate control, sinus rhythm restoration and maintenance, and stroke prevention. New and evolving therapies and how they might fit into the evolving treatment paradigm are also briefly reviewed.

Atrial fibrillation in the elderly: facts and management

Although atrial fibrillation is not widely known by the general public, in developed countries it is the most common arrhythmia. The incidence increases markedly with advancing age. Thus, with the growing proportion of elderly individuals, atrial fibrillation will come to represent a significant medical and socioeconomic problem. The consequences of atrial fibrillation have the greatest impact. The risk of thromboembolism is well known; other outcomes of atrial fibrillation are less well recognised, such as its relationship with dementia, depression and death. Such consequences are responsible for diminished quality of life and considerable economic cost. Atrial fibrillation is characterised by rapid and disorganised atrial activity, with a frequency between 300 and 600 beats/minute. The ventricles react irregularly, and may contract rapidly or slowly depending on the health of the conduction system. Clinical symptoms are varied, including palpitations, syncope, dizziness or embolic events. Atrial fibrillation may be paroxysmal, persistent or chronic, and a number of attacks are asymptomatic. Suspicion or confirmation of atrial fibrillation necessitates investigation and, as far as possible, appropriate treatment of underlying causes such as hypertension, diabetes mellitus, hypoxia, hyperthyroidism and congestive heart failure. In the evaluation of atrial fibrillation, cardiac exploration is invaluable, including electrocardiogram (ECG) and echocardiography, with the aim of detecting cardiac abnormalities and directing management. In elderly patients (arbitrarily defined as aged >75 years), the management of atrial fibrillation varies; it requires an individual approach, which largely depends on comorbid conditions, underlying cardiac disease, and patient and physician preferences. This management is essentially based on pharmacological treatment, but there are also nonpharmacological options. Two alternatives are possible: restoration and maintenance of sinus rhythm, or control of ventricular rate, leaving the atria in arrhythmia. Pharmacological options include antiarrhythmic drugs, such as class III agents, beta-blockers and class IC agents. These drugs have some adverse effects, and careful monitoring is necessary. The nonpharmacological approach to atrial fibrillation includes external or internal direct-current cardioversion and new methods, such as catheter ablation of specific foci, an evolving science that has been shown to be successful in a very select group of atrial fibrillation patients. Another serious challenge in the management of chronic atrial fibrillation in older individuals is the prevention of stroke, its primary outcome, by choosing an appropriate antithrombotic treatment (aspirin or warfarin). Several risk-stratification schemes have been validated and may be helpful to determine the best antithrombotic choice in individual patients.

Prehospital management of acute tachyarrhythmias

Arrhythmias are commonly encountered by emergency medical services (EMS) personnel. The potential seriousness of acute symptomatic arrhythmias necessitates thorough up-to-date training of EMS personnel. The three most common acute tachyarrhythmias, not linked to cardiac arrest, that are observed outside the hospital are paroxysmal supraventricular tachycardia (PSVT), atrial fibrillation with rapid ventricular response (RAF), and perfusing ventricular tachycardia (VT). Ideally, these tachyarrhythmias should be operationally defined in a manner that simplifies, particularly for EMS providers, their diagnosis and treatment. The authors recommend referring to these rhythms as regular narrow-complex tachycardia (presumed PSVT), irregularly irregular narrow-complex tachycardia (presumed RAF), or regular wide-complex tachycardia (presumed VT or aberrantly conducted PSVT). Although the value of treatments such as cardioversion is widely understood, the benefit from others, such as lidocaine, is unclear. Current preferences, recommendations, and concerns regarding the treatment of most arrhythmias outside the hospital reflect the dichotomy that sometimes exists between available evidence and actual practice.

Amiodarone: an emergency medicine perspective

Amiodarone is a highly efficacious antiarrhythmic agent for many cardiac arrhythmias, ranging from atrial fibrillation to malignant ventricular rhythm disturbances. Significant interest has developed in recent years with the publication of randomized controlled trials supporting the efficacy of amiodarone over placebo and lignocaine for improving survival to hospital in patients with shock-resistant ventricular fibrillation. Amiodarone has complex pharmacological and pharmacokinetic properties. It has significant long-term adverse effects, but short-term administration of intravenous amiodarone is generally well tolerated. This article will explore issues related to the clinical use of amiodarone from an emergency medicine perspective.

Atrial fibrillation: beyond irregularly irregular: the basis for acute and chronic treatment

Today atrial fibrillation is the most prevalent sustained arrhythmia encountered in clinical practice; it places a heavy burden on the healthcare system. The purpose of this article is to explore the principles underlying the treatment of both acute and chronic atrial fibrillation.

Prevention of and medical therapy for atrial arrhythmias in heart failure

A large proportion of heart failure patients suffer from atrial arrhythmias, prime amongst them being atrial fibrillation (AF). Ventricular dysfunction and the syndrome of heart failure can also be a concomitant pathology in up to 50% of patients with AF. However this association is more than just due to shared risk factors, research from animal and human studies suggest a causal relationship between AF and heart failure. There are numerous reports of tachycardia-induced heart failure where uncontrolled ventricular rate in AF results in heart failure, which is reversible with cardioversion to sinus rhythm or ventricular rate control. However the relationship extends beyond tachycardia-induced cardiomyopathy. Optimal treatment of AF may delay progressive ventricular dysfunction and the onset of heart failure whilst improved management of heart failure can prevent AF or improve ventricular rate control. Prevention and treatment of atrial arrhythmias, and in particular atrial fibrillation, is therefore an important aspect of the management of patients with heart failure. This review describes the incidence and possible predictors of AF and other atrial arrhythmias in patients with heart failure and discusses the feasibility of primary prevention. The evidence for the management of atrial fibrillation in heart failure is systematically reviewed and the strategies of rate versus rhythm control discussed in light of the prevailing evidence.

Effect of low-dose amiodarone on atrial fibrillation or flutter in Japanese patients with heart failure

The efficacy and safety of amiodarone in the management of atrial fibrillation (AF) or flutter in 108 Japanese patients with heart failure was retrospectively examined. Thirty-four (41%) of the 82 patients who were in sinus rhythm after 1 month of amiodarone administration had their first recurrence, 70% of cases occurring within 1 year of initiation. The cumulative rates of maintenance of sinus rhythm were 0.68, 0.55, and 0.47 at 1, 3, and 5 years, respectively. Amiodarone was more effective in maintaining sinus rhythm in patients with paroxysmal AF or flutter than in those with the persistent form (p<0.05). The cumulative rates for cases that remained in permanent AF were 0.04, 0.11, and 0.14 at 1, 3, and 5 years, respectively. Apart from suppressing AF, the mean heart rate during Holter monitoring was significantly decreased with amiodarone therapy in cases of permanent AF. Adverse effects requiring the discontinuation of amiodarone therapy occurred in 16% of patients. Low-dose amiodarone therapy may prevent AF or flutter in Japanese patients with heart failure.

Advanced life support drugs: do they really work?

Basic life support and rapid defibrillation for ventricular fibrillation or pulseless ventricular tachycardia are the only two interventions that have been shown unequivocally to improve survival after cardiac arrest. Several drugs are advocated to treat cardiac arrest, but despite very encouraging animal data, no drug has been reliably proven to increase survival to hospital discharge after cardiac arrest. This review focuses on recent experimental and clinical data concerning the use of vasopressin, amiodarone, magnesium, and fibrinolytics during advanced life support (ALS). Animal data indicate that, in comparison with epinephrine (adrenaline), vasopressin produces better vital organ blood flow during cardiopulmonary resuscitation (CPR). These apparent advantages have yet to be converted into improved survival in large-scale trials of cardiac arrest in humans. Data from two prospective, randomized trials suggest that amiodarone may improve short-term survival after out-of-hospital ventricular fibrillation cardiac arrest. On the basis of anecdotal data, magnesium is recommended therapy for torsades de pointes and for shock-resistant ventricular fibrillation associated with hypomagnesemia. In the past, CPR has been a contraindication to giving fibrinolytics, but several studies have demonstrated the relative safety of fibrinolysis during and after CPR. Fibrinolytics are likely to be beneficial when cardiac arrest is associated with plaque rupture and fresh coronary thrombus or massive pulmonary embolism. Fibrinolysis may also improve cerebral microcirculatory perfusion once a spontaneous circulation has been restored. A planned, prospective, randomized trial may help to define the role of fibrinolysis during out-of-hospital CPR.

Pharmacologic conversion of atrial fibrillation: a systematic review of available evidence

This report reviews the efficacy of currently available antiarrhythmic agents for conversion of atrial fibrilation (AF) to normal sinus rhythm (NSR). A systematic search of literature in the English language was done on computerized databases, such as MEDLINE, EMBASE, and Current Contents, in reference lists, by manual searching, and in contact with expert informants. Published studies involving humans that described the use of antiarrhythmic therapy for conversion of AF to NSR were considered and only studies that examined the use of agents currently available in the United States were included. Studies exclusively describing antiarrhythmic therapy for conversion of postsurgical AF were excluded. The methodology and results of each trial were assessed and attempts were made to acquire additional information from investigators when needed. Assessment of methodological quality was incorporated into a levels-of-evidence scheme. Eighty-eight trials were included, of which 34 (39%) included a placebo group (level I data). We found in recent-onset AF of less than 7 days, intravenous (i.v.) procainamide, high-dose i.v. or high-dose combination i.v. and oral amiodarone, oral quinidine, oral flecainide, oral propafenone, and high-dose oral amiodarone are more effective than placebo for converting AF to NSR. In recent-onset AF of less than 90 days, i.v. ibutilide is more effective than placebo and i.v. procainamide. In chronic AF, oral dofetilide converts AF to NSR within 72 hours, and oral propafenone and amiodarone are effective after 30 days of therapy. We conclude than for conversion of recent-onset AF of less than 7 days, procainamide may be considered a preferred i.v. agent and propafenone a preferred oral agent. For conversion of recent-onset AF of longer duration (less than 90 days), i.v. ibutilide may be considered a preferred agent. For patients with chronic AF and left ventricular dysfunction, direct current cardioversion is the preferred conversion method. Larger, well-designed randomized controlled trials with clinically important endpoints in specific populations of AF patients are needed.

Atrial Flutter

Atrial flutter (AFl) is an arrhythmia resulting from reentry in a macroreentrant circuit, most commonly in the right atrium. Typical AFl uses the narrow isthmus of right atrial tissue between the tricuspid valve annulus and the inferior vena cava orifice as part of the macroreentrant circuit. The treatment of AFl is directed toward achieving the following four goals. 1) In the presence of AFl, adequate rate control is required, which can be achieved in most but not all patients by oral or intravenous digoxin, calcium channel blockers, or beta-blockers, alone or in combination. 2) Anticoagulation with warfarin should be considered in patients with recurrent AFl, especially those over 70 years of age, and those with a history of atrial fibrillation, stroke, or structural heart disease. 3) Conversion to sinus rhythm can be achieved in up to 70% of patients with intravenous ibutilide, but this should be reserved for patients with either normal hearts or only mild left ventricular dysfunction. Direct-current cardioversion is nearly 100% effective and is ideal for patients with left ventricular dysfunction. 4) Long-term maintenance of sinus rhythm may be achieved in up to 50% to 60% of patients by using antiarrhythmic drugs, including sotalol, amiodarone, dofetilide, propafenone, and flecainide, but with the potential for causing significant proarrhythmia and side effects. Radiofrequency catheter ablation may cure over 90% of patients with type 1 AFl (using the tricuspid valve to inferior vena cava isthmus), and from 70% to 90% of patients with atypical AFl. Newer mapping techniques, such as electroanatomic mapping, are likely to further reduce procedure time and improve success rates.

Amiodarone versus diltiazem for rate control in critically ill patients with atrial tachyarrhythmias

OBJECTIVE

To compare the rate-lowering effect of diltiazem and two amiodarone regimens in critically ill patients with recent-onset atrial tachyarrhythmias.

DESIGN

Prospective, randomized, controlled study.

SETTING

Medical cardiologic intensive care unit in a university hospital.

PATIENTS

Sixty critically ill patients (Acute Physiology and Chronic Health Evaluation [APACHE] III score 70 +/- 30, age 67 +/- 10 yrs).

INTERVENTIONS

Patients with atrial fibrillation (n = 57), atrial flutter (n = 2), or atrial tachycardia (n = 1, and a heart rate consistently >120 beats/min over 30 mins were randomly assigned to one of three intravenous treatment regimens. Group 1 received diltiazem in a 25-mg bolus followed by a continuous infusion of 20 mg/hr for 24 hrs, group 2 received amiodarone in a 300-mg bolus, and group 3 received amiodarone in a 300-mg bolus followed by 45 mg/hr for 24 hrs.

MEASUREMENTS AND MAIN RESULTS

The primary study end point was a >30% rate reduction within 4 hrs. The secondary study end point was a heart rate <120 beats/min (a patient was considered to have uncontrolled tachycardia if heart rate was >120 beats/min 4 hrs after study drug). The primary study end point was achieved in 14/20 (70%), 11/20 (55%), and 15/20 (75%) of patients in groups 1, 2, and 3, respectively (chi2 = 1.95, p =.38). Uncontrolled tachycardia was more frequently observed in group 2 (0/20, 9/29 [55%], and 1/20 [5%] of patients in groups 1, 2, and 3, respectively; chi2 = 17, p =.00016). In patients achieving tachycardia control, diltiazem showed a significantly better rate reduction (p =.0001 group 1 vs. group 3, p =.0001 over time; p =.0001 group 1 vs. group 2, p =.001 over time) when compared with the amiodarone groups. Premature drug discontinuation due to hypotension was required significantly more often in group 1 (6/20 [30%], 0/20, and 1/20 [5%] for groups 1, 2, and 3, respectively; chi2 = 10, p =.01).

CONCLUSION

Sufficient rate control can be achieved in critically ill patients with atrial tachyarrhythmias using either diltiazem or amiodarone. Although diltiazem allowed for significantly better 24-hr heart rate control, this effect was offset by a significantly higher incidence of hypotension requiring discontinuation of the drug. Amiodarone may be an alternative in patients with severe hemodynamic compromise.

Intravenous antiarrhythmic agents

Intravenous antiarrhythmic drugs can be used as diagnostic tools; for example, adenosine can be used to reveal the underlying rhythm in narrow QRS tachycardia. Newer class III antiarrhythmic agents, like ibutilide and dofetilide, are effective at the conversion of acute atrial fibrillation; however, electrical cardioversion is still the most effective method for restoration of sinus rhythm in persistent atrial fibrillation. Lidocaine and bretylium in the treatment and prevention of ventricular tachyarrhythmia are de-emphasized because of inefficacy, safety concerns (lidocaine), or shortage of drug (bretylium). Procainamide is effective for stable ventricular tachycardia, and amiodarone is effective in the treatment of shock-refractory ventricular fibrillation. Adrenergic blockade is likely important in the management of tachyarrhythmias, particularly in electrical storm, but more data will be necessary to establish its role.

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.

Management and prevention of atrial fibrillation after cardiovascular surgery

Atrial arrhythmias occur frequently after cardiac surgery. This article discusses the incidence of postoperative atrial arrhythmia as well as its prognosis, potential mechanisms of pathogenesis, and management. Prophylactic therapy for postoperative atrial arrhythmia is recommended because of the frequency of occurrence and the ease with which therapies can often be implemented. Treatments with pharmacologic and nonpharmacologic modalities are described. Management strategies for atrial arrhythmias that occur postoperatively, including pharmacologic and nonpharmacologic measures as well as anticoagulation recommendations, are discussed.

Cost-effective management of acute atrial fibrillation: role of rate control, spontaneous conversion, medical and direct current cardioversion, transesophageal echocardiography, and antiembolic therapy

Management strategies for the acute treatment of atrial fibrillation (AF) include: (1) the use of intravenous drugs for rate control, (2) drug termination, or (3) direct current (DC) cardioversion. Delays in cardioversion can promote atrial remodeling and add thromboembolic risk. Rate control awaiting spontaneous or pharmacologic conversion may be a cost-effective strategy in patients presenting with recent onset of symptoms. Early DC cardioversion can be cost-effective and minimize antiembolic therapy issues in the acute setting. In patients presenting with AF of unknown or >48 hours' duration, rate control and therapeutic warfarin for 3-4 weeks followed by medical or DC cardioversion is standard practice. However, delays in conversion promote atrial remodeling that makes restoration of sinus rhythm more difficult and increases the likelihood of postcardioversion AF recurrence. Transesophageal echocardiography can identify patients at low risk for a cardioversion-related embolic event and allows cardioversion to be performed earlier, thereby minimizing atrial remodeling.

Ventricular rate control during atrial fibrillation by cardiac parasympathetic nerve stimulation: a transvenous approach

OBJECTIVES

To identify intravascular sites for continuous, stable parasympathetic stimulation (PS) in order to control the ventricular rate during atrial fibrillation (AF).

BACKGROUND

Ventricular rate control during AF in patients with congestive heart failure is a significant clinical problem because many drugs that slow the ventricular rate may depress ventricular function and cause hypotension. Parasympathetic stimulation can exert negative dromotropic effects without significantly affecting the ventricles.

METHODS

In 22 dogs, PS was performed using rectangular stimuli (0.05 ms duration, 20 Hz) delivered through a catheter with an expandable electrode-basket at its end. The catheter was positioned either in the superior vena cava (SVC, n = 6), coronary sinus (CS, n = 10) or right pulmonary artery (RPA, n = 6). The basket was then expanded to obtain long-term catheter stability. Atrial fibrillation was induced and maintained by rapid atrial pacing.

RESULTS

Nonfluoroscopic (SVC) and fluoroscopic (CS/RPA) identification of effective intravascular PS sites was achieved within 3 to 10 min. The ventricular rate slowing effect during AF started and ceased immediately after on-offset of PS, respectively, and could be maintained over 20 h. In the SVC, at least a 50% increase of ventricular rate (R-R) intervals occurred at 22 +/- 11 V (331 +/- 139 ms to 653 +/- 286 ms, p < 0.001), in the CS at 16 +/- 10 V (312 +/- 102 ms vs. 561 +/- 172 ms, p < 0.001) and in the RPA at 18 +/- 7 V (307 +/- 62 ms to 681 +/- 151 ms, p < 0.001). Parasympathetic stimulation did not change ventricular refractory periods.

CONCLUSIONS

Intravascular PS results in a significant ventricular rate slowing during AF in dogs. This may be beneficial in patients with AF and rapid ventricular response since many drugs that decrease atrioventricular conduction have negative inotropic effects which could worsen concomitant congestive heart failure.

Intravenous antiarrhythmic therapy in the acute control of in-hospital destabilizing ventricular tachycardia and fibrillation

Ventricular tachycardia, which causes hemodynamic instability, and ventricular fibrillation do not occur frequently in any hospital. However, they usually occur in patients who have severe underlying cardiovascular disease such as myocardial ischemia/infarction or congestive heart failure, and they are associated with high mortality. Most of those deaths are due to an intractable arrhythmia, not suppressible with even the most potent antiarrhythmic drugs. Fortunately, during the last few years, our ability to suppress highly lethal ventricular arrhythmia has been enhanced by the approval of intravenous amiodarone. When used in appropriate patient populations, intravenous amiodarone has been successful in suppressing the most malignant arrhythmia, thus permitting aggressive and successful treatment of severe underlying cardiac conditions. This article reviews data on the use of parenteral antiarrhythmic drugs for the control of ventricular arrhythmia in patients in hospital, and will attempt to provide some guidance as to how these antiarrhythmic drugs may be used in specific patient populations to maximize their efficacy and safety. We will also make recommendations on the sequence of therapy for specific arrhythmias to optimize the chances of patient survival.

Pharmacotherapy of atrial fibrillation

Atrial fibrillation (AF) remains a widespread health problem and the drugs available for its treatment suffer from several drawbacks, including potentially lethal proarrhythmia, serious non-cardiac toxicity and limited efficacy. The evidence for efficacy of currently available anti-arrhythmic agents for sinus rhythm restoration and maintenance is reviewed, with emphasis on randomised trials when available. The current approach to thromboembolism prophylaxis in AF is summarised.

Intravenous Amiodarone in the Management of Atrial Fibrillation

BACKGROUND: Although approved only for therapy of life-threatening ventricular tachyarrhythmias, intravenous amiodarone is also being used for the treatment of atrial fibrillation (AF), generally in the intensive care unit setting and most often after cardiac surgery. When used for AF, dosing regimens and clinical experience have varied. METHODS AND RESULTS: This article summarizes representative reports in hopes of clarifying the role of intravenous amiodarone for practitioners who prescribe it for the management of AF. The most immediate and most predictable response is reduction of the ventricular rate, which generally is noted after the first 300-400 mg. Restoration of sinus rhythm (cardioversion) may occur, but the precise incidence in a placebo-controlled, blinded study has not been determined. When present, it often takes 24 hours, and a total dose of 1,000 mg or more. Least certain is the efficacy of the drug in preventing the appearance (when used prophylactically) or reappearance of AF. CONCLUSIONS: More data are required with regard to patient characterization, electrical system status, and dosing regimen to better characterize intravenous amiodarone for this role.