Ventricular rate control in chronic atrial fibrillation during daily activity and programmed exercise: a crossover open-label study of five drug regimens

Atrial Fibrillation: The New Epidemic of the Ageing World

The prevalence of atrial fibrillation (AF) increases with age. As the population ages, the burden of AF increases. AF is associated with an increased incidence of mortality, stroke, and coronary events compared to sinus rhythm. AF with a rapid ventricular rate may cause a tachycardia-related cardiomyopathy. Immediate direct-current (DC) cardioversion should be performed in patients with AF and acute myocardial infarction, chest pain due to myocardial ischemia, hypotension, severe heart failure, or syncope. Intravenous beta blockers, diltiazem, or verapamil may be administered to reduce immediately a very rapid ventricular rate in AF. An oral beta blocker, verapamil, or diltiazem should be used in persons with AF if a fast ventricular rate occurs at rest or during exercise despite digoxin. Amiodarone may be used in selected patients with symptomatic life-threatening AF refractory to other drugs. Digoxin should not be used to treat patients with paroxysmal AF. Nondrug therapies should be performed in patients with symptomatic AF in whom a rapid ventricular rate cannot be slowed by drugs. Paroxysmal AF associated with the tachycardia-bradycardia syndrome should be treated with a permanent pacemaker in combination with drugs. A permanent pacemaker should be implanted in patients with AF and symptoms such as dizziness or syncope associated with ventricular pauses greater than 3 seconds which are not drug-induced. Elective DC cardioversion has a higher success rate and a lower incidence of cardiac adverse effects than does medical cardioversion in converting AF to sinus rhythm. Unless transesophageal echocardiography has shown no thrombus in the left atrial appendage before cardioversion, oral warfarin should be given for 3 weeks before elective DC or drug cardioversion of AF and continued for at least 4 weeks after maintenance of sinus rhythm. Many cardiologists prefer, especially in elderly patients , ventricular rate control plus warfarin rather than maintaining sinus rhythm with antiarrhythmic drugs. Patients with chronic or paroxysmal AF at high risk for stroke should be treated with long-term warfarin to achieve an International Normalized Ratio of 2.0 to 3.0. Patients with AF at low risk for stroke or with contraindications to warfarin should be treated with aspirin 325 mg daily.

Comparison of beta blocker and digoxin alone and in combination for management of patients with atrial fibrillation and heart failure

In patients with atrial fibrillation (AF) and heart failure (HF), beta blockers and digoxin reduce the ventricular rate, but controversy exists concerning how these drugs affect prognosis in this setting. This study compared the effects of beta blocker and digoxin on mortality in patients with both AF and HF. In a single-center institution, patients with AF and HF seen between January 2000 and January 2004 were identified and followed until September 2007. Of 1,269 consecutive patients with both AF and HF, 260 were treated with a beta blocker alone, 189 with beta blocker plus digoxin, 402 with digoxin alone, and 418 without beta blocker or digoxin (control group). During a follow-up of 881+/-859 days, 247 patients died. Compared with the control group, treatment with beta blocker was associated with a decreased mortality (relative risk=0.58, 95% confidence interval 0.40 to 0.85, p=0.005 for beta blocker alone and 0.59, 95% confidence interval 0.40 to 0.87, p=0.008 for beta blocker plus digoxin). By contrast, treatment with digoxin alone was not associated with a better survival (relative risk=0.97, 95% confidence interval 0.73 to 1.30, p=NS). Results remained significant after adjustment for potential confounders and similar when we considered, separately, HF with permanent or nonpermanent AF, presence or absence of coronary disease, and patients with decreased or preserved systolic function. In conclusion, in unselected patients with AF and HF, treatments with beta blocker alone or with beta blocker plus digoxin are associated with a similar decrease in the risk of death. Digoxin alone is associated with a worse survival chance, similar to that of patients without any rate control treatment.

Heart rate control in patients with atrial fibrillation referred for exercise testing

Clinical practice guidelines for patients with atrial fibrillation (AF) recommended a heart rate (HR) of 60 to 80 beats/min at rest and 90 to 115 at moderate exercise. The degree to which HR control at rest and with exercise in patients with AF complies with these recommendations is unknown. HR at rest and at peak exercise was retrospectively examined in 1,097 consecutive patients with AF referred for exercise myocardial perfusion imaging. In a subgroup of 195 patients, HR was also measured at an intermediate "moderate" level. Median HR at rest was 80 beats/min, at the upper end of the recommended range of 60 to 80. Only patients administered a beta blocker (BB; 31%) had lower (p <0.001) median HRs at rest. Median HR at moderate exercise was 128 beats/min, higher than the range of 90 to 115 recommended by the guidelines. Only patients administered a BB had significantly reduced HRs (p <0.003) at moderate exercise. Median peak exercise HR was 147 beats/min. Forty-five percent of patients exceeded their age-predicted maximal HR. Patients administered BBs were significantly less likely (p <0.01) to exceed their age-predicted maximal HR. In conclusion, in patients with AF, HR control at rest and during exercise often did not comply with guideline recommendations. Regimens including a BB were more effective in achieving HR control.

[Pharmaceutical treatment of atrial fibrillation]

Atrial fibrillation is one of the most common long-lasting arrhythmias of the heart. It leads to an increase in morbidity and a substantial reduction in quality of life in most patients. Therefore, an early and adequate therapy strategy and prevention of comorbidities of atrial fibrillation are demanding. There is no controversy about the pharmaceutical treatment as the first choice and gold standard in atrial fibrillation patients. As there is no evidence that frequency control is superior to rhythm control or vice versa, therapy strategies should depend on the clinical status and comorbidities of the individual patient. However, adequate anticoagulation for prevention of thromboembolism should be performed in every patient, even after conversion of atrial fibrillation into sinus rhythm.

Management of atrial fibrillation in patients with heart failure

BACKGROUND

There is a well-documented relationship and a complex interaction between atrial fibrillation (AF) and heart failure. The coexistence of these 2 clinical entities renders their management even more challenging.

METHODS AND RESULTS

We searched current literature to review the management of AF in patients with heart failure. The cornerstones of AF treatment are rate control, cardioversion, and maintenance of sinus rhythm (SR), and prevention of thromboembolism. The issue of rhythm versus rate control remains unresolved. Nonpharmacologic therapies such as radiofrequency catheter ablation of the atrioventricular node with permanent pacemaker implantation, curative catheter ablation of AF, and cardiac resynchronization therapy are emerging and may alter the management of these patients.

CONCLUSION

Treatment of atrial fibrillation in the setting of heart failure encompasses a variety of approaches including drugs, devices, and ablation. Larger randomized trials are required to clarify the management of such patients.

Atrial fibrillation and congestive heart failure

Atrial fibrillation (AF) and congestive heart failure (CHF) are common cardiac conditions that frequently coexist. There is a complex interplay between the two conditions, with each increasing the morbidity and mortality associated with the other. The management of AF in patients with CHF requires special care because of the increased risk of antiarrhythmic drug therapy in the group. This report reviews current treatment options and assesses the role of the newer therapies of biventricular pacing for CHF and radiofrequency ablation for AF. It also discusses results of the AF-CHF study, which were reported in November 2007.

Who, when and how to rate control for atrial fibrillation

PURPOSE OF REVIEW

The aim of this review is to provide a perspective on rate control in atrial fibrillation, in the era after the large randomized trials comparing rate and rhythm control. This review emphasizes the indications for rate control, the optimal heart rate and the different treatment modalities.

RECENT FINDINGS

Large studies have shown that rate control is not inferior to rhythm control with regard to cardiovascular morbidity and mortality. Rate control may now be instituted earlier during the course of the disease, even as first-choice therapy in some patients, particularly those with hypertension and underlying heart diseases, and those who are not (severely) symptomatic. The goals of rate-control therapy are to reduce symptoms, improve quality of life, minimize the development of heart failure, and prevent thromboembolic complications. An important negative aspect of rate-control therapy is the side effects of drugs. The optimal heart rate during atrial fibrillation has not yet been carefully investigated. Several approaches to control rate during atrial fibrillation are available, including pharmacological rate control and atrioventricular nodal ablation with pacemaker implantation.

SUMMARY

Understanding the indications for rate control, treatment goals and options will gain the largest benefit for the individual patient with atrial fibrillation.

Persistent atrial fibrillation worsens heart rate variability, activity and heart rate, as shown by a continuous monitoring by implantable biventricular pacemakers in heart failure patients

BACKGROUND

Atrial fibrillation (AF) induces loss of atrial contribution, heart rate irregularity, and fast ventricular rate.

OBJECTIVES

The objectives of the study were to accurately measure AF incidence and to investigate the mutual temporal patterns of AF and heart failure (HF) in patients indicated to cardiac resynchronization therapy.

METHODS

Four hundred ten consecutive patients (70% male, age 69 +/- 11) with advanced HF (NYHA = 3.0 +/- 0.6), low ejection fraction (EF = 27 +/- 9%), and ventricular conduction delay (QRS = 165 +/- 29 ms) received a biventricular pacemaker. Enrolled patients were divided into two groups: G1 = 249 patients with no AF history, G2 = 161 patients with history of paroxysmal/persistent AF.

RESULTS

In a median follow-up of 13 months, AF episodes longer than 5 minutes occurred in 105 of 249 (42.2%) G1 patients and 76 of 161 (47.2%) G2 patients, while AF episodes longer than one day occurred in 14 of 249 (5.6%) G1 patients and in 36 of 161 (22.4%) G2 patients. Device diagnostics monitored daily values of patient activity, night heart rate (NHR), and heart rate variability (HRV). Comparing 30-day periods before AF onset and during persistent AF, significant (P < 0.0001) changes were observed in patient activity, which decreased from 221 +/- 13 to 162 +/- 12 minutes, and in NHR, which increased from 68 +/- 3 to 94 +/- 7 bpm. HRV significantly decreased (from 75 +/- 5 ms before AF onset to 60 +/- 6 ms after AF termination). NHR during AF was significantly (P < 0.01) and inversely correlated (R(2)= 0.73) with activity, with a significant lower activity associated with NHR >or= 88 bpm.

CONCLUSION

AF is frequent in HF patients. Persistent AF is associated with statistically significant decrease in patient activity and HRV and NHR increase.

Atrial fibrillation: insights from clinical trials and novel treatment options

Atrial fibrillation (AF) is the most common encountered sustained arrhythmia in clinical practice. The last decade the result of large 'rate' versus 'rhythm' control trials have been published that have changed the current day practise of AF treatment. It has become clear that rate control is at least equally effective as a rhythm control strategy in ameliorating morbidity as well as mortality. Moreover, in each individual patient the risk of thromboembolic events should be assessed and antithrombotic treatment be initiated. There have also been great advances in understanding the mechanisms of AF. Experimental studies showed that as a result of electrical and structural remodelling of the atria, 'AF begets AF'. Pharmacological prevention of atrial electrical remodelling has been troublesome, but it seems that blockers of the renin angiotensin system, and perhaps statins, may reduce atrial structural remodelling by preventing atrial fibrosis. Clinical studies demonstrated that the pulmonary veins exhibit foci that can act as initiator and perpetuator of the arrhythmia. Isolation of the pulmonary veins using radiofrequency catheter ablation usually abolishes AF. The most promising advances in the pharmacological treatment of AF include atrial specific antiarrhythmic drugs and direct thrombin inhibitors. In the present review we will describe the results of recent experimental studies, discuss the latest clinical trials, and we will focus on novel treatment modalities.

Rate control in permanent atrial fibrillation

Guidelines on the use of digoxin are inconsistent with evidence from randomised trials

Surgery in older people: an update

In the past two decades, the rate of surgery in older people has increased more rapidly than the rate of aging of the population, so both a larger proportion and a greater number of older people are now undergoing surgery. This may partly reflect a cultural change in surgery and anaesthesia with respect to a greater willingness to undertake elective procedures in older people, although there remain areas where they have less access to surgery than do younger patients. For instance, older people are less likely to undergo operative procedures after a cancer diagnosis. Furthermore, in those who do have surgery, resection rate (i.e. curative therapy) is lower than in younger people with equivalent tumour stages, and even more so in older patients with COPD, cardiovascular disease or diabetes. This article explores the complex relationship between age and surgical outcome, provides an evidence-based overview of risk assessment and common postoperative problems in older people, and summarizes good practice points (at times necessarily pragmatic) for clinical management of the older surgical patient. There has been a substantial expansion in the literature examining risks, outcomes and interventions in older surgical patients since the previous review article of this subject published in this journal. Although we do not cover anaesthesia in older people, the review of that topic remains relevant. The American Society of Anaesthesiologists' Classification of Risk which illustrates that risk is disease- rather than age- based, is shown in Table 1. Most publications examine elective rather than emergency surgery in older people (with the exception of hip fracture), and this is reflected in the content of the paper.

Resynchronization therapy in the context of atrial fibrillation: Benefits and limitations

Atrial fibrillation (AF) and heart failure often coexist and are believed to directly predispose to each other. Cardiac resynchronization does not prevent or increase the induction of AF. However, new onset of AF does not seem to diminish the beneficial effects of CRT on symptoms, cardiac function and, more importantly, all-cause mortality if appropriate ventricular rate control by beta-blockers and digoxin is being achieved. While a pharmacological approach to control ventricular rate may be sufficient in most patients with paroxysmal AF or AF of shorter duration in those with permanent AF ablation strategies may be necessary. Observational studies and one randomized trial indicate a potential benefit of CRT in heart failure patients with chronic AF; particularly, biventricular pacing was superior compared to conventional right-univentricular stimulation. However, recent results suggest that even relatively high percentage biventricular capture may be inadequate, and that the benefits of CRT may only be extended to chronic AF patients with previous AV junctional ablation. Well designed and powered clinical trials are required before pacemaker dependency is created in large numbers of heart failure patients.

Pharmacologic Therapies for Atrial Fibrillation

Pharmacologic therapy for atrial fibrillation may be used for acute cardioversion or ventricular rate control or for long-term therapy to maintain sinus rhythm or control ventricular rates in atrial fibrillation. Therapies must be tailored to elderly patients, with particular attention to structural heart disease, bradycardia, hypotension, and other comorbidities, including renal or hepatic insufficiency. Such considerations may dictate the use or avoidance of certain agents. Other important considerations for elderly patients include challenges associated with anticoagulation and maintaining therapeutic international normalized levels without risk of bleeding. When considering pharmacologic agents for elderly patients, it is also valuable to take into account socioeconomic issues, such as access to medications, adherence to complicated dosing schedules, and availability of appropriate clinical follow-up to assess therapeutic efficacy and adverse reactions to various agents. A carefully constructed therapeutic regimen can provide effective symptom control and atrial fibrillation management for elderly patients.

Effect of Cardiac Resynchronization on the Incidence of Atrial Fibrillation in Patients With Severe Heart Failure

Background— Atrial fibrillation/flutter (AF) and heart failure often coexist; however, the effect of cardiac resynchronization therapy (CRT) on the incidence of AF and on the outcome of patients with new-onset AF remains undefined.

Methods and Results— In the CArdiac REsynchronisation in Heart Failure (CARE-HF) trial, 813 patients with moderate or severe heart failure were randomly assigned to pharmacological therapy alone or with the addition of CRT. The incidence of AF was assessed by adverse event reporting and by ECGs during follow-up, and the impact of new-onset AF on the outcome and efficacy of CRT was evaluated. By the end of the study (mean duration of follow-up 29.4 months), AF had been documented in 66 patients in the CRT group compared with 58 who received medical therapy only (16.1% versus 14.4%; hazard ratio 1.05; 95% confidence interval, 0.73 to 1.50; P =0.79). There was no difference in the time until first onset of AF between groups. Mortality was higher in patients who developed AF, but AF was not a predictor in the multivariable model (hazard ratio 1.17; 95% confidence interval, 0.82 to 1.67; P =0.37). In patients with new-onset AF, CRT significantly reduced the risk for all-cause mortality and all other predefined end points and improved ejection fraction and symptoms (no interaction between AF and CRT; all P >0.2).

Conclusions— Although CRT did not reduce the incidence of AF, CRT improved the outcome regardless of whether AF developed.

Drug therapy for atrial fibrillation

Although the maintenance of sinus rhythm would be the ideal scenario for patients with atrial fibrillation (AF), recent randomised trials have questioned the value of this approach. A careful interpretation of their results showed the limited efficacy of currently available antiarrhythmic drugs in maintaining sinus rhythm, as well as their potentially serious side effects. Therefore, it is imperative to develop safer and more effective drugs for AF. Based on our improved understanding of the pathophysiology of AF and the mechanism of action of antiarrhythmic drugs, significant efforts are being made to develop new antiarrhythmic agents that would prevent electrophysiological remodelling, would be selective for the atria and, therefore, would not prolong ventricular repolarisation, thus lacking any proarrhythmic effect.

Cost-effectiveness of radiofrequency catheter ablation for atrial fibrillation

OBJECTIVES

We sought to compare the cost-effectiveness of left atrial catheter ablation (LACA), amiodarone, and rate control therapy in the management of atrial fibrillation (AF).

BACKGROUND

Left atrial catheter ablation has been performed to eliminate AF, but its cost-effectiveness is unknown.

METHODS

We developed a decision-analytic model to evaluate the cost-effectiveness of LACA in 55- and 65-year-old cohorts with AF at moderate and low stroke risk. Costs, health utilities, and transition probabilities were derived from published literature and Medicare data. We performed primary threshold analyses to determine the minimum level of LACA efficacy and stroke risk reduction needed to make LACA cost-effective at 50,000 dollars and 100,000 dollars per quality-adjusted life-year (QALY) thresholds.

RESULTS

In 65-year-old subjects with AF at moderate stroke risk, relative reduction in stroke risk with an 80% LACA efficacy rate for sinus rhythm restoration would need to be > or =42% and > or =11% to yield incremental cost-effectiveness ratios (ICERs) <50,000 dollars and 100,000 dollars per QALY, respectively. Higher and lower LACA efficacy rates would require correspondingly lower and higher stroke risk reduction for equivalent ICER thresholds. In the 55-year-old moderate stroke risk cohort, lower LACA efficacy rates or stroke risk reduction would be needed for the same ICER thresholds. In patients at low stroke risk, LACA was unlikely to be cost-effective.

CONCLUSIONS

The use of LACA may be cost-effective in patients with AF at moderate risk for stroke, but it is not cost-effective in low-risk patients. Our threshold analyses may provide a framework for the design of future clinical trials by providing effect size estimates for LACA efficacy needed.

The safety of digoxin as a pharmacological treatment of atrial fibrillation

Digoxin has traditionally been the drug of choice for ventricular rate control in patients with chronic atrial fibrillation (AF), with or without heart failure (HF) with systolic dysfunction. In patients with permanent AF, digoxin monotherapy is ineffective to control ventricular rate during exercise, but the combination of digoxin with a beta-blocker or a non-dihydropyridine calcium channel antagonist can control heart rate both at rest and during exercise. Only a few randomised, controlled studies have evaluated the adverse effects of digoxin in patients with AF in a systematic way and side effects requiring drug withdrawal have rarely been reported. When reported, the most frequent adverse effects were cardiac arrhythmias (ventricular arrhythmias, AV block of varying degrees and sinus pauses). This evidence suggested that, in contrast to other antiarrhythmic drugs, digoxin is a safe drug in patients with AF. However, this safety profile can be erroneous due to the short follow-up of the studies and patient selection. Because patients with HF have been excluded in most studies, the safety profile of digoxin in this population has not been directly addressed. Early recognition that an arrhythmia is related to digoxin intoxication as well as recognition of concomitant medications or medical conditions that may directly alter the pharmacokinetic profile of digoxin, or indirectly alter its cardiac effects by pharmacodynamic interactions remain essential for safe and effective use of digoxin in patients with AF.

Short-term Exercise Training in Patients With Chronic Atrial Fibrillation

PURPOSE

A randomized study was conducted to determine whether short-term exercise training in patients with chronic atrial fibrillation (AF) might improve exercise capacity and quality of life (QOL), and influence atrioventricular conduction.

METHODS

Atrial fibrillation patients (age 64 +/- 7 years) were randomized to exercise training (n = 15) or a 2-month control period (n = 15) followed by the training program. Twenty-four training sessions consisted of aerobic exercise and muscle strengthening. A cycle ergometer test and a 15-minute resting high-frequency spectral electrocardiogram analysis were performed and a QOL questionnaire (SF-36) was completed before and after training. Because there were no changes after 2 months in the control group, pooled data for all patients are presented before and after training.

RESULTS

Cumulated work at Borg scale 17 increased by 41% +/- 36%. Heart rate at rest and after 10 minutes of exercise decreased from 75 +/- 14 to 68 +/- 14 bpm and 145 +/- 19 to 137 +/- 21 bpm, respectively. HF increased from 81 +/- 17 to 91 +/- 22 milliseconds. Four of the 8 scales and 1 of the 2 summary scales of the Short-Form-36 improved. P <.05 for all results.

CONCLUSIONS

Exercise capacity, heart rate variability, and QOL improved after 2 months of exercise training in patients with chronic AF. Heart rates at rest and during exercise decreased.

Rate Control and Quality of Life in Patients With Permanent Atrial Fibrillation The Quality Of Life and Atrial Fibrillation (QOLAF) Study

BACKGROUND

The present study aimed to determine whether quality of life (QOL) in permanent atrial fibrillation (AF) patients would be improved by monotherapy with beta-blocker (BB) or calcium antagonist (CAA) as compared with digitalis.

METHODS AND RESULTS

Twenty-nine patients with permanent AF under digitalis were randomized into BB (bisoprolol, atenolol or metoprolol) or CAA (verapamil) monotherapy treatment group. Twenty-five were men and the mean age was 67+/-8 years. After the assigned monotherapy, 12 patients received the other monotherapy in a cross-over fashion. Under each treatment, efficacy of rate control was determined by Holter electrocardiogram (ECG), treadmill testing and QOL questionnaire (Short Form-36 (SF-36) and Quality of Life of Atrial Fibrillation (AFQLQ)), and compared with the baseline digitalis treatment. CAA significantly increased mean and minimum heart rate (HR) in Holter ECG as compared with digitalis, whereas BB increased only minimum HR. Exercise duration in treadmill testing was significantly prolonged by CAA treatment, although it only tended to be prolonged by BB treatment. CAA but not BB improved role function-physical score of SF-36, and frequency and severity of symptoms of AFQLQ.

CONCLUSION

These results indicate that CAA is preferable to digitalis when monotherapy is selected for short-term improvement of QOL and exercise tolerance in patients with permanent AF.

Digitalis in heart failure! Still applicable?

In patients with heart failure and atrial fibrillation cardiac glycosides, generally in combination with beta-blockers, are indicated to control ventricular rate. In systolic heart failure and sinus rhythm, however, the use of digitalis continues to be debated. There are special concerns that cardiac glycosides might lead to an increased mortality rate in women. Retrospective analyses, however, do not indicate any sex-based differences in the effectiveness of cardiac glycosides. Beneficial effects of cardiac glycosides in heart failure seem to be related to the attenuation of sympathetic activation and neurohumoral alterations, which is already obtained at low digoxin serum concentrations, while high serum levels are associated with increased mortality. Therefore, in patients with sinus rhythm who remain symptomatic under an optimized therapy with ACE inhibitors, beta-blockers and diuretics in addition to digitalis should be considered regardless of the gender. However, target serum digoxin concentrations should be low in a range of 0.5 to 0.8 ng/ml.

Atrial fibrillation in dogs with and without structural or functional cardiac disease: A retrospective study of 109 cases

OBJECTIVES

To determine if the heart rate and survival of dogs with atrial fibrillation (AF) varied amongst those: (1) without structural and functional disease (Group NoDz), (2) with structural or functional disease without pulmonary edema or ascites (Group DzNoF), and (3) with structural or functional disease with pulmonary edema or ascites (Group DzF).

ANIMALS, MATERIALS AND METHODS

The records of 109 dogs from the Veterinary Teaching Hospital of the University of Montreal (n=30) and the Cornell University Hospital for Animals (n=79) were examined.

RESULTS

Large and giant breed dogs were most commonly affected (95.5%) with the Irish Wolfhound, Mastiff, Newfoundland, and Rottweiler overrepresented (P<0.01) in Group NoDz and the Irish Wolfhound, Boxer, English Sheepdog, Great Dane and Doberman Pincher overrepresented (P<0.01) in Groups DzNoF and DzF. Males (73.4%) were more commonly affected (P<0.001). Heart rate (mean+/-SD) on presentation was different amongst the 3 groups of dogs (P<0.001) (Group NoDz: 120+/-8.0bpm, Group DzNoF: 155+/-7.6bpm, and Group DzF: 203+/-6.2bpm). Kaplan-Meier survival analysis revealed a longer survival for dogs in Group NoDz (P=0.006) and large and giant breeds (P=0.02). Initial heart rate could not be separated from diseased group as an independent determinant of survival.

CONCLUSIONS

Results suggest that dogs with AF and no demonstrable cardiac disease have a slower presenting heart rate and greater survival than dogs with structural disease with and without heart failure.

Selection of drugs in pursuit of rate control strategy

Atrial fibrillation is the most common sustained arrhythmia. Based on multiple large randomized trials, rate control therapy has been shown to be safe and effective and is gaining greater acceptance as a frontline alternative to drugs to maintain sinus rhythm. Adequate rate control can be achieved by atrioventricular nodal blocking agents both in the acute and chronic settings. In refractory patients, other methods such as atrioventricular node ablation can be used to control rate.

Rate versus rhythm control in the management of patients with atrial fibrillation

The management of patients with atrial fibrillation involves three main areas: anticoagulation, rate control and rhythm control. Importantly, these are not mutually exclusive of each other. Anticoagulation is necessary for patients who are at a high risk of stroke; for example, those who are older than 75 years, or those who have hypertension, severe left ventricular dysfunction, previous cerebrovascular events, or diabetes. It is now clear that patients who are at a high risk of stroke require long-term anticoagulation with warfarin regardless of whether a rate-control or rhythm-control strategy is chosen. One possible exception might be patients who are apparently cured with catheter ablation. Several published trials comparing rate-control and rhythm-control strategies for the treatment of patients with atrial fibrillation have shown no difference in mortality between these approaches. The patients enrolled in these studies were typically over 65 years of age. Data comparing rate and rhythm strategies in patients who are younger than 60 years of age are limited. For more elderly patients, it seems reasonable to consider rate control as a primary treatment option and to reserve rhythm control for those who do not respond to rate control. For younger patients, we prefer to start with a rhythm-control approach and to reserve rate-control approaches for patients in whom antiarrhythmic drugs, ablation, or both, do not ameliorate the symptoms.

Rate versus rhythm control strategies for AF

The safest long-term management strategy for elderly patients with persistent or recurrent episodes of atrial fibrillation (AF) is careful rate control with medications in conjunction with appropriate oral warfarin anticoagulation. Atrioventricular junctional ablation, with pacemaker implantation, may be necessary in patients who cannot have their rate controlled adequately, or have marked fluctuations in rate with standard medical therapies. Maintenance of sinus rhythm with repeat cardioversions, antiarrhythmic medications, device therapy, or atrial ablation approaches are appropriate to consider for younger patients and those elderly patients who suffer from substantial symptoms shown to be related directly to AF.

Rate Control vs Rhythm Control Strategies in Atrial Fibrillation

Rhythm management for atrial fibrillation is a subject of intense interest. In this review, the two main strategies for rhythm management in atrial fibrillation, the "heart rate control" strategy and the "heart rhythm control" strategy, are discussed under several headings. Some of the basic issues surrounding heart rate control and heart rhythm control and their study in clinical trials are reviewed. Seven published trials that deal with a comparison of these two strategies are reviewed in some detail. In summary, no distinct advantage of the rhythm control strategy has been identified so far. With respect to pharmacologic therapies and the type of patient studied in most of these trials, advantages seem to accrue to the rate control strategy. Those advantages include fewer adverse drug effects, fewer hospitalizations, and lower cost. Two trials studying quite different patients, and in one case quite different drug therapies, are currently in progress, and these two trials are also briefly reviewed. Current guidelines have not taken into account fully the findings of the studies described in this review, and comment is offered on the current guidelines. Finally, some of the possibilities for future research around this question are highlighted.

Atrial fibrillation: how to approach rate control

The optimal management of atrial fibrillation is of considerable clinical importance, and with the recent publication of four studies suggesting the equivalence of rate and rhythm control strategies, new attention has been focused on rate control. Reasons for rate control include reduction of symptoms and the prevention of tachycardia-mediated cardiomyopathy; yet, evidence-based definitions of optimal rate control are lacking. This article examines an approach to rate control that includes serial assessment of heart rate and symptoms, both at rest and with exertion, and the use of therapy tailored to the individual and modified over time (as no single therapy demonstrates clear superiority). Often, multidrug regimens including digoxin and a calcium channel blocker or beta-blocker are required, and in a minority of patients atrioventricular nodal ablation and pacing are necessary. Several novel therapies currently under development are also discussed.

Carvedilol's antiarrhythmic properties: therapeutic implications in patients with left ventricular dysfunction

Carvedilol is a beta- and alpha-adrenergic-blocking drug with clinically important antiarrhythmic properties. It possesses anti-ischemic and antioxidant activity and inhibits a number of cationic channels in the cardiomyocyte, including the HERG-associated potassium channel, the L-type calcium channel, and the rapid-depolarizing sodium channel. The electrophysiologic properties of carvedilol include moderate prolongation of action potential duration and effective refractory period; slowing of atrioventricular conduction; and reducing the dispersion of refractoriness. Experimentally, carvedilol reduces complex and repetitive ventricular ectopy induced by ischemia and reperfusion. In patients, carvedilol is effective in controlling the ventricular rate response in atrial fibrillation (AF), with and without digitalis, and is useful in maintaining sinus rhythm after cardioversion, with and without amiodarone. In patients with AF and heart failure (HF), carvedilol reduces mortality risk and improves left ventricular (LV) function. Large-scale clinical trials have demonstrated that combined carvedilol and angiotensin-converting enzyme inhibitor therapy significantly reduces sudden cardiac death, mortality, and ventricular arrhythmia in patients with LV dysfunction (LVD) due to chronic HF or following myocardial infarction (MI). Despite intensive neurohormonal blockade, mortality rates remain relatively high in patients with post-MI and nonischemic LVD. Recent trials of implantable cardioverter-defibrillators added to pharmacologic therapy, especially beta blockers, have shown a further reduction in arrhythmic deaths in these patients.

Antiadrenergic therapy in the control of atrial fibrillation

Atrial fibrillation (AF) in heart failure develops commonly in older individuals and its prevalence increases as heart failure severity progresses. Because of deteriorating hemodynamics, patients with heart failure are at increased risk for developing AF and, conversely, AF in heart failure patients is associated with adverse hemodynamic changes. AF is believed to increase the mortality risk in heart failure, which may be minimized by treatment that includes the control of ventricular rate, prevention of thrombotic events, and conversion to normal sinus rhythm. Clinical guidelines recommend amiodarone or dofetilide in heart failure patients, but these drugs have certain drawbacks, such as an increased risk for bradyarrhythmias with amiodarone and proarrhythmic reaction with dofetilide. Some but not all clinical trials have suggested that rate control should be the primary therapeutic goal in high-risk heart failure patients with AF and, if unsuccessful, followed by rhythm control. The former is effectively achieved with rate-lowering beta-blockers alone or in combination with digoxin. Recent studies evaluating the effects of combination carvedilol/digoxin therapy demonstrate synergistic effects between the two drugs. This combination therapy decreased heart failure symptoms, effectively reduced ventricular rate, and improved ventricular function to a greater extent compared with that produced by either drug alone. Although digoxin alone is an effective heart failure treatment, its use as a single rate-control therapy is often ineffective in heart failure patients with AF associated with rapid ventricular response. Carvedilol is effective, alone or in combination, with digoxin in such heart failure patients with AF, and has been shown to reduce mortality risk in patients with chronic heart failure during prolonged therapy.

New antiarrhythmic agents for atrial fibrillation and atrial flutter

Atrial fibrillation is the most common sustained cardiac arrhythmia and is a frequent reason for antiarrhythmic therapy. Existing antiarrhythmic drugs have important side effects and presently the therapy to maintain sinus rhythm is not superior to a strategy of controlling excessive heart rate. This review summarises current strategies to improve antiarrhythmic therapy for atrial fibrillation. The most important strategies are: i) to develop drugs without proarrhythmic effects--development of drugs devoid of QT prolonging potential is the main strategy; ii) multiple channel-blocking drugs--inspired by the efficacy of amiodarone, several drugs are being developed that have similar electrophysiological properties as amiodarone, but without the extracardiac side effects; iii) drugs that act exclusively in the atria--the atria contain specific potassium channels, and several drugs that act only on these channels are in development; and iv) antiarrhythmic therapy without effects on ion channels--inhibition of the renin-angiotensin system and steroid therapy has been shown to have some effect in the treatment of atrial fibrillation. Many drugs are in development and the therapeutic scenario for treatment of atrial fibrillation may change quickly.

Management of atrial fibrillation in patients with congestive heart failure

An increase in the prevalence of both atrial fibrillation and congestive heart failure is occurring in part because of the demographic shift toward an aging population. These two clinical entities often coexist in the same patient, resulting in the worsening of symptoms and prognosis, rendering their management even more challenging. A large clinical trial is currently examining whether a rhythm-control strategy is superior to a rate-control strategy in patients with congestive heart failure. New nonpharmacologic therapies such as pulmonary vein isolation are undergoing clinical investigation and may also alter the management of these patients. At present, therapy for atrial fibrillation in patients with congestive heart failure should aim first at controlling heart rate to provide symptomatic relief; then sinus rhythm should be restored if symptoms persist or if congestive heart failure worsens. For a more definitive approach in managing these patients, the authors await further clinical trial data.

Management of new onset atrial fibrillation in previously well patients less than 60 years of age

OBJECTIVE

This study reviewed the ED management of new onset atrial fibrillation (AF) in previously well patients aged less than 60 years.

METHODS

We undertook a retrospective review of ED patients from 1998 to 2002 inclusive. The main outcome measures were approaches to rate or rhythm control and anticoagulation, the use of echocardiography, the value of diagnostic testing and the frequency of hospital admission.

RESULTS

Fifty-two patients were identified. In general, all patients were haemodynamically stable. One patient had mild cardiac failure and one was clinically thyrotoxic. Serum potassium was measured in 51 (98%) patients, magnesium in 23 (44%) and cardiac enzymes in 30 (58%); results were generally unhelpful. Thyroid function tests were carried out in 40 (77%) patients; results were unremarkable except for the clinically thyrotoxic patient. No patient had echocardiography in the ED; however, 6 patients (12%) were later found to have major cardiac abnormalities. Forty-four (85%) patients received a variety of medications; 37 (71%) received an anti-arrhythmic and 24 (46%) an antithrombotic. Overall, 17 (33%) patients received theoretically effective therapy for conversion to sinus rhythm. Twenty-two (42%) patients were admitted to hospital.

CONCLUSIONS

This study reveals variation in the management of acute AF in previously well, haemodynamically stable, young patients. Pathology testing was frequently carried out with a low yield. There were high rates of attempts to cardiovert, use of antithrombotics and of admission to hospital. Although cardioversion attempts appeared to be contrary to existing guidelines, decisions may have been based primarily on patient symptoms. Echocardiography should be considered prior to anti-arrhythmic therapy.

Atrial Fibrillation: Modern Concepts and Management

Atrial fibrillation (AF) is a common cardiac arrhythmia responsible for significant morbidity and mortality. In recent years, progress has been made in determining the genetic abnormalities that may lead to AF. New trials have shown that rate control and anticoagulation are acceptable as a primary treatment strategy in many patients who have a high risk of recurrence. Newer and safer antiarrhythmics are now available. Pacemaker and implantable cardiac defibrillator technology is rapidly evolving and may play a significant role in future treatment and prevention of AF. Direct thrombin inhibitors are likely to add a user-friendly option to the current standard therapy for stroke prevention.