Treatment strategies for atrial fibrillation

Therapeutic effects of selective atrioventricular node vagal stimulation in atrial fibrillation and heart failure

INTRODUCTION

Atrial fibrillation (AF) and heart failure (HF) frequently coexist. We have previously demonstrated that selective atrioventricular node (AVN) vagal stimulation (AVN-VS) can be used to control ventricular rate during AF. Due to withdrawal of vagal activity in HF, the therapeutic effects of AVN-VS may be compromised in the combined condition of AF and HF. Accordingly, this study was designed to evaluate the therapeutic effects of AVN-VS to control ventricular rate in AF and HF.

METHODS AND RESULTS

A combined model of AF and HF was created by implanting a dual chamber pacemaker in 24 dogs. A newly designed bipolar electrode was inserted into the ganglionic AVN fat pad and connected to a nerve stimulator for delivering AVN-VS. In all dogs, HF was induced by high rate ventricular pacing at 220 bpm for 4 weeks. AF was then induced and maintained by rapid atrial pacing at 600 bpm after discontinuation of ventricular pacing. These HF + AF dogs were randomized into control (n = 9) and AVN-VS (n = 15) groups. In the latter group, vagal stimulation (310 μs, 20 Hz, 3-7 mA) was delivered continuously for 6 months. Compared with the control, AVN-VS had a consistent effect on ventricular rate slowing (by >50 bpm, all P < 0.001) during the entire 6-month observation period that was associated with left ventricular functional improvement. Moreover, AVN-VS was well tolerated by the treated animals.

CONCLUSIONS

AVN-VS achieved consistent rate slowing, which was associated with improved ventricular function in a canine AF and HF model. Thus, AVN-VS may be a novel, effective therapeutic option in the combined condition of AF and HF.

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.

Thromboembolism in patients with atrial fibrillation with and without left atrial thrombus documented by transesophageal echocardiography

The incidence of cerebrovascular events (CVEs) was investigated in 95 consecutive patients with atrial fibrillation (AF) with left atrial thrombus (LAT) diagnosed by transesophageal echocardiography (TEE) and in 131 age- and sex-matched AF patients without LAT. Compared with patients without LAT, patients with LAT had a larger left atrial diameter (49 versus 44 mm, P < 0.0001), a lower left ventricular ejection fraction (40% versus 50%, P < 0.0001), a higher prevalence of spontaneous echocardiographic contrast (88% versus 25%, P < 0.001), a reduced left atrial appendage emptying velocity (0.25 versus 0.41 cm/s, P < 0.0001), and less use of antiarrhythmic drugs (61% versus 76%, P = 0.03). Before TEE, the prevalence of prior CVE was higher in LAT patients (20%) compared with patients without LAT (8%) (P = 0.01). Fifty-four of 95 LAT patients (57%) and 81 of 131 non-LAT patients (62%) were on warfarin before TEE. The incidence of prior CVE in LAT patients without warfarin (32%) was higher than that in non-LAT patients without warfarin (10%) (P = 0.02). The mortality rate in LAT patients with an international normalized ratio (INR) >or= 2.0 (42%) was higher than that in patients without LAT and an INR >or= 2.0 (11%) (P < 0.001). Fifty-one of 95 LAT patients (54%) underwent repeat TEE before cardioversion (48 patients received warfarin therapy). The thrombus resolved in 40 of 51 patients (78%) after the first TEE. There was no significant difference in INR between the patients with persistent and resolved LAT. AF patients with persistent LAT had a higher incidence of CVE (45%) than the patients with resolved LAT (5%) (P = 0.003). We suggest that patients with LAT be treated with warfarin to maintain an INR between 2.5 and 3.5 rather than between 2.0 and 3.0 because they are at a high risk for new thromboembolism.

A comparative study of the efficacy and safety of procainamide versus propafenone versus amiodarone for the conversion of recent-onset atrial fibrillation

The appropriate treatment for the restoration of sinus rhythm in patients with atrial fibrillation (AF) of recent onset is still the subject of controversy. In this prospective, randomized, single-blind, placebo-controlled clinical study, we investigated the effectiveness and safety of procainamide, propafenone, and amiodarone, administered intravenously, for the conversion of recent-onset AF. We enrolled 362 consecutive patients (183 men; age 34 to 86 years; mean 65+/-10) with AF duration of no >48 hours. Of these patients, 89 were given procainamide, 91 propafenone, 92 amiodarone, and 90 placebo. Treatment was considered successful if conversion to sinus rhythm was achieved within the 24-hour study period. Baseline clinical characteristics were similar in the 4 groups. The treatment was successful in 61 of the 89 patients who received procainamide (68.53%; median time 3 hours), 73 of the 91 patients who received propafenone (80.21%; median time 1 hour), 82 of the 92 patients who received amiodarone (89.13%; median time 9 hours), and 55 of the 90 patients who received placebo (61.11%; median time 17 hours; p<0.05 for all medicated groups vs placebo; p<0.05 for amiodarone and propafenone vs procainamide). In conclusion, all 3 medications, when administered intravenously, are effective in the restoration of sinus rhythm in recent-onset AF. Amiodarone and propafenone are more effective whereas procainamide and propafenone are faster.

Warfarin Therapy Initiated before Is More Beneficial Than after Transesophageal Echocardiography Detected Left Atrial Thrombus

OBJECTIVE

Warfarin anticoagulation significantly reduces the risk of thromboembolism in patients with atrial fibrillation (AF). However, there are many patients with AF who begin anticoagulation only after left atrial thrombus (LAT) is detected by transesophageal echocardiography (TEE). The impact of anticoagulation in these patients has not been clearly described. The purpose of this study was to investigate the incidence of cerebrovascular accident (CVA) among AF patients who began warfarin before LAT was detected by TEE compared to those who began warfarin only after TEE demonstrated LAT and those did not receive warfarin at any point.

METHOD

Of the 90 consecutive AF patients with LAT (male 48, female 42, age 71.5 +/- 10.1 years), 49 began warfarin more than 3 weeks before TEE (Group I); 29 began warfarin after TEE (Group II); and 12 did not receive warfarin at all (Group III).

RESULTS

The incidence of CVA in Group I (14%, 7/49, prior CVA 5, new CVA after TEE 2) was significantly lower than Group II (45%, 13/29, prior CVA 10, new CVA after TEE 3, P = 0.006) and III (42%, 5/12, prior CVA 3, new CVA after TEE 2, P = 0.047). Patients with persistent LAT had significantly higher incidence (64% vs 23%, P = 0.024) of CVA and lower CVA free survival than those with resolved LAT.

CONCLUSION

The incidence of CVA among AF patients, who began warfarin before LAT detection, is significantly lower than those who began warfarin after LAT detection as well as those who did not receive warfarin at all.

Atrial Fibrillation

Our understanding of the pathophysiology and clinical consequences of atrial fibrillation has led to an evidence-based revolution in the management of atrial fibrillation over the last decade. As we improve in our ability to detect recurrent atrial fibrillation and treat it definitively, the patients who benefit from long-term anticoagulation may change. We can expect, however,that stroke prevention through systemic anticoagulation will be a cornerstone of atrial fibrillation management for decades to come. Innovations in anticoagulation therapy will make the use of these medications safer. Finally, as we further understand the underlying mechanisms of the development of atrial fibrillation, the pursuit of preventative therapy will be an investigational focus of great import.

Management of Atrial Fibrillation in the Emergency Department

Although atrial fibrillation remains the most common cardiac arrhythmia, the treatment and disposition remain varied. An accept-able standard of practice requires an evidence-based approach. This approach has revealed that half of the patients who present with acute atrial fibrillation will convert to sinus rhythm without intervention. In the hemodynamically stable subset, ascertaining the on-set of atrial fibrillation within 48 hours is critical because this period dictates when and if anticoagulation should be instituted and if and where electrical or chemical cardioversion needs be performed. The hemodynamically unstable patient, however, requires emergent cardioversion, irrespective of the chronicity of atrial fibrillation. An evidence-based approach may serve to optimize treatment and obviate the need for unnecessary hospital admissions.

Chronic atrioventricular nodal vagal stimulation: first evidence for long-term ventricular rate control in canine atrial fibrillation model

BACKGROUND

We have previously demonstrated that selective atrioventricular nodal (AVN) vagal stimulation (AVN-VS) can be used to control ventricular rate during atrial fibrillation (AF) in acute experiments. However, it is not known whether this approach could provide a long-term treatment in conscious animals. Thus, this study reports the first observations on the long-term efficacy and safety of this novel approach to control ventricular rate during AF in chronically instrumented dogs.

METHODS AND RESULTS

In 18 dogs, custom-made bipolar patch electrodes were sutured to the epicardial AVN fat pad for delivery of selective AVN-VS by a subcutaneously implanted nerve stimulator (pulse width 100 micros or 1 ms, frequency 20 or 160 Hz, amplitude 6 to 10 V). Fast-rate right atrial pacing (600 bpm) was used to induce and maintain AF. ECG, blood pressure, and body temperature were monitored telemetrically. One week after the induction of AF, AVN-VS was delivered and maintained for at least 5 weeks. It was found that AVN-VS had a consistent effect on ventricular rate slowing (on average 45+/-13 bpm) over the entire period of observation. Echocardiography showed improvement of cardiac indices with ventricular rate slowing. AVN-VS was well tolerated by the animals, causing no signs of distress or discomfort.

CONCLUSIONS

Beneficial long-term ventricular rate slowing during AF can be achieved by implantation of a nerve stimulator attached to the epicardial AVN fat pad. This novel concept is an attractive alternative to other methods of rate control and may be applicable in a selected group of patients.

Errors and pitfalls in the non-invasive management of atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia encountered in clinical practice while it has a significant impact on morbidity and mortality. The errors and pitfalls in the management of AF patients are not uncommon. These include errors in detection and management of the underlying conditions that promote and perpetuate the arrhythmia, in the selection and monitoring of antithrombotic treatment, in the selection of appropriate strategy for arrhythmia management (rate or rhythm control), in the cardioversion procedure, in the prevention of recurrence after cardioversion, in the acute or chronic control of heart rate, and in the monitoring of drug toxicities. The heterogeneity of the disease along with the diversity of current treatment options mainly account for these problems. Nevertheless, deep knowledge of the evidence-based therapeutic approaches, as well as the development of individualized therapeutic strategies, can substantially improve the effective management of such patients.

Pulmonary vein ablation of atrial fibrillation: beyond the traditional

The present review aims at giving a synthesis on the evolution in the last decade of the catheter-based ablative treatments for atrial fibrillation (AF). We report the rationale of current pulmonary vein (PV) ablation techniques: segmental PV isolation and circumferential PV ablation. The endpoint is the electrical isolation of the PVs from the left atrium, as they house foci triggering AF in 80% to 95% of cases and seem to play a key role in arrhythmia maintenance. Recurrence rates of AF after these PV ablation strategies are very encouraging. Two recent randomized trials, AFFIRM and RACE, showed no significant difference in outcomes between a strategy of pharmacological heart rate control and that of restoration and maintenance of sinus rhythm with antiarrhythmic drugs. However, multicenter randomized trials comparing PV ablation with drug therapy are required. Future refinements in catheter technology and navigation systems should provide simpler and faster procedures and render PV ablation more widespread and accepted from the scientific and medical communities.

Drug-induced atrial fibrillation

Atrial fibrillation (AF) is the most common sustained rhythm disorder observed in clinical practice and predominantly associated with cardiovascular disorders such as coronary heart disease and hypertension. However, several classes of drugs may induce AF in patients without apparent heart disease or may precipitate the onset of AF in patients with preexisting heart disease. We reviewed the literature on drug-induced AF, using the PubMed/Medline and Micromedex databases and lateral references. Successively, we discuss the potential role in the onset of AF of cardiovascular drugs, respiratory system drugs, cytostatics, central nervous system drugs, genitourinary system drugs, and some miscellaneous agents. Drug-induced AF may play a role in only a minority of the patients presenting with AF. Nevertheless, it is important to recognize drugs or other agents as a potential cause, especially in the elderly, because increasing age is associated with multiple drug use and a high incidence of AF. This may contribute to timely diagnosis and management of drug-induced AF.

Surgical Treatment of Atrial Fibrillation

This article reviews the fundamentals of surgical treatment of atrial fibrillation. The clinical classification, pathophysiology, medical treatment strategy, and catheter-based interventions are also included. The Cox-Maze III procedure was developed over based on experiences of several operations which proceeded it. The operation is complex but results are excellent with over 90% of patients in normal sinus rhythm or regular atrial rhythm. Several modifications have been devised using various energies to ablate atrial myocardium as a means of extending surgical incisions to simplify the Maze III operation. Techniques and results of these operations are reviewed. Modified operations offering about 80% restoration of sinus rhythm are attractive to more surgeons because of the reduced complexity and time of operation.

Electrical cardioversion of emergency department patients with atrial fibrillation

STUDY OBJECTIVE

Electrical cardioversion of emergency department (ED) patients with atrial fibrillation has not been well investigated. The objective of this study is to identify the outcomes and complications associated with ED electrical cardioversion of patients with atrial fibrillation.

METHODS

This retrospective health records survey investigated a consecutive cohort of ED patients with atrial fibrillation who underwent electrical cardioversion in 4 EDs during a 42-month period. Trained personnel reviewed medical records for demographic characteristics, clinical descriptors, medical interventions, complications, and ED return visits within 7 days. Data were analyzed using descriptive statistics.

RESULTS

The study population consisted of 388 patients (mean age 61 years; range 20 to 93 years). Duration of atrial fibrillation was less than 48 hours in 99% of the cohort. Electrical cardioversion was successful in 332 (86%) patients. Twenty-eight complications were noted in 25 electrical cardioversion encounters: 22 attributed to procedural sedation and analgesia and 6 attributed to electrical cardioversion. Three hundred thirty-three (86%) patients were discharged to home from the ED: 301 after electrical cardioversion success and 32 with electrical cardioversion failure. Thirty-nine patients (10%) returned to the ED within 7 days, 25 of these patients (6% of successful electrical cardioversion patients) returned because of relapse of atrial fibrillation.

CONCLUSION

In this multicenter cohort, selected ED patients with atrial fibrillation had high rates of electrical cardioversion success, infrequent hospital admission, and few immediate and short-term complications.

Antiarrhythmic drug therapy of atrial fibrillation

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

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.

Obstructive sleep apnea and the recurrence of atrial fibrillation

BACKGROUND

We tested the hypothesis that patients with untreated obstructive sleep apnea (OSA) would be at increased risk for recurrence of atrial fibrillation (AF) after cardioversion.

METHODS AND RESULTS

We prospectively obtained data on history, echocardiogram, ECG, body mass index, hypertension, diabetes, NYHA functional class, ejection fraction, left atrial appendage velocity, and medications in patients with AF/atrial flutter referred for DC cardioversion. Forty-three individuals were identified as having OSA on the basis of a previous sleep study. Data regarding the use of continuous positive airway pressure (CPAP) and recurrence of AF were obtained for 39 of these patients. Follow-up data were also obtained in 79 randomly selected postcardioversion patients (controls) who did not have any previous sleep study. Twenty-seven of the 39 OSA patients either were not receiving any CPAP therapy (n=25) or were using CPAP inappropriately (n=2). Recurrence of AF at 12 months in these 27 patients was 82%, higher than the 42% recurrence in the treated OSA group (n=12, P=0.013) and the 53% recurrence (n=79, P=0.009) in the 79 control patients. Of the 25 OSA patients who had not been treated at all, the nocturnal fall in oxygen saturation was greater (P=0.034) in those who had recurrence of AF (n=20) than in those without recurrence (n=5).

CONCLUSIONS

Patients with untreated OSA have a higher recurrence of AF after cardioversion than patients without a polysomnographic diagnosis of sleep apnea. Appropriate treatment with CPAP in OSA patients is associated with lower recurrence of AF.

Evolution of non-pharmacological curative therapy for atrial fibrillation. Where do we stand today?

The present review aims at giving a comprehensive synthesis regarding not only the epidemiological aspects but also the evolution, over the last decades, of the curative surgical and catheter-based ablative treatments for atrial fibrillation (AF), with particular emphasis on the experience of Milan working group which has always been committed to the on-going and fascinating therapeutic challenges inherent in this type of cardiac arrhythmia. After discussing the surgical treatment of AF we report the rationale basis of current pulmonary vein (PV) ablation techniques. In particular, we report on circumferential PV ablation, an intellectually appealing strategy, aimed at creation of RF lesions around each PV ostia using a non-fluoroscopic electro-geometric mapping system to reconstruct the anatomy of venous-atrial junction, allowing to tailor number and size of lesions to the complex morphology of the PV-LA junction in each patient. This purely anatomic approach not only disconnects PVs (as demonstrated by elimination of PV ostial potentials and absence of discrete electrical activity inside the lesion during pacing outside the ablation line), but also, like surgery, reduces the "electrically active" atrial tissue, involving substantial parts of the posterior LA wall, with a profound atrial electroanatomic remodeling, as expressed by voltage abatement (<0.1 mV) inside and around the encircled areas.

[Permanent atrial fibrillation in heart disease in Spain. The CARDIOTENS study 1999]

INTRODUCTION AND OBJECTIVE

Atrial fibrillation is the most common arrhythmia seen in clinical practice. The objective of this study was to know the frequency of atrial fibrillation and the characteristics of patients with atrial fibrillation in the Cardiotens study.

MATERIAL AND METHOD

A cross-section study with systematic selection of the study sample. All 32,051 outpatients seen on the same day by 1,159 physicians specialized in primary-care (79%) and cardiology (21%) were prospectively added to a database including history of cardiac disease (heart failure, coronary disease or atrial fibrillation), blood pressure, and ongoing treatment.

RESULTS

Atrial fibrillation was present in 25% of patients with previous cardiovascular disease (6,194 patients), the prevalence being 4.8% (1,540/32,051) of the study population. Atrial fibrillation was more frequent in females 29%, (810/2,837) than in males, 22% (730/3,367), p < 0.005). Atrial fibrillation was present in 33% (469/1,420) of patients with heart failure and in 12% (387/3,226) of those with coronary heart disease. Arterial hypertension was diagnosed in 25% of the patients with atrial fibrillation. Only 33% of them were treated with oral anticoagulants (41% of the patients seen by cardiologists and 26% by primary-care physicians, p < 0.005). The antiarrhythmic drug most often used was digoxin (36%).

CONCLUSIONS

Atrial fibrillation had the same frequency and epidemiology in Spain as in other Western countries. Antithrombotic therapy is underused by primary-care physicians and cardiologists.

Ventricular rate control by selective vagal stimulation is superior to rhythm regularization by atrioventricular nodal ablation and pacing during atrial fibrillation

BACKGROUND

Selective atrioventricular nodal (AVN) vagal stimulation (AVN-VS) has emerged as a novel strategy for ventricular rate (VR) control in atrial fibrillation (AF). Although AVN-VS preserves the physiological ventricular activation sequence, the resulting rate is slow but irregular. In contrast, AVN ablation with pacemaker implantation produces retrograde activation (starting at the apex), with regular ventricular rhythm. We tested the hypothesis that, at comparable levels of VR slowing, AVN-VS provides hemodynamic benefits similar to those of ablation with pacemaker implantation.

METHODS AND RESULTS

AVN-VS was delivered to the epicardial fat pad that projects parasympathetic nerve fibers to the AVN in 12 dogs during AF. A computer-controlled algorithm adjusted AVN-VS beat by beat to achieve a mean ventricular RR interval of 75%, 100%, 125%, or 150% of spontaneous sinus cycle length. The AVN was then ablated, and the right ventricular (RV) apex was paced either irregularly (i-RVP) using the RR intervals collected during AVN-VS or regularly (r-RVP) at the corresponding mean RR. The results indicated that all 3 strategies improved hemodynamics compared with AF. However, AVN-VS resulted in significantly better responses than either r-RVP or i-RVP. i-RVP resulted in worse hemodynamic responses than r-RVP. The differences among these modes became less significant when mean VR was slowed to 150% of sinus cycle length.

CONCLUSIONS

AVN-VS can produce graded slowing of the VR during AF without destroying the AVN. It was hemodynamically superior to AVN ablation with either r-RVP or i-RVP, indicating that the benefits of preserving the physiological antegrade ventricular activation sequence outweigh the detrimental effect of irregularity.

Mechanisms of antiarrhythmic drug actions and their clinical relevance for controlling disorders of cardiac rhythm

This review on antiarrhythmic drugs traces the evolution of the fundamental mechanisms of action of drugs that have been used to control disorders of cardiac rhythm. It describes the very earliest data from experimental studies that dealt with the effects of acute and chronic administration of drugs in whole animals combined with the measurements of the action potential duration and the effective refractory period in isolated tissues. Antiarrhythmic drugs were found to have properties consistent with the block of fast sodium channel conduction, adrenergic blockade, repolarization block, and the block of slow-channel mediated conduction especially in the atrioventricular node. Over the past 15 years, the attention has focused on atrial tissue with atrial fibrillation emerging as the most common arrhythmia in clinical practice. Drug-induced increases in refractoriness as a function rate and in wavelength (product of refractoriness and conduction velocity), and a reduction in numbers of wavelets have been found to be critical in the conversion of atrial fibrillation and maintenance of sinus rhythm. The continued development of newer pharmacologic agents is likely to lead to the resolution of the controversy regarding rhythm versus rate control in various clinical subsets of the arrhythmia by controlled clinical trials.

Cardioversion of atrial fibrillation with ibutilide: when is it most effective?

BACKGROUND

Atrial fibrillation (AF) is found in 1% of persons above the age of 60 years. More than 5% of the population older than 69 years and about 14% of octogenarians are at risk for this arrhythmia. It is estimated that 1.5 to 3 million persons in the United States alone suffer from AF. The public health implications and attendant morbidity are a significant drain on our health care system.

HYPOTHESIS

The purpose of this study was to determine the clinical and echocardiographic predictors of success in converting AF of > or = 24 h duration.

METHODS

Demographic and clinical and echocardiographic parameters of 101 patients with recent onset AF (> 24 h) who received ibutilide were studied.

RESULTS

Of 101 patients, 56 (55%) converted to sinus rhythm. Age, gender, hypertension, diabetes mellitus, left ventricular ejection fraction (< or = 35%), congestive heart failure, and previous medication for rate control had no significant effect on the conversion rate. Conversion rate was only 30% (9/30 patients) in the presence of an enlarged left atrium (LA > or = 5 cm) and 37.7% (23/61 patients) in the presence of mitral valve disease (MVD), whereas the conversion rate was 82.5% (33/40 patients) in the absence of MVD and 85% (29/34 patients) in the absence of both enlarged LA and MVD (p = <0.001). Patients with coronary artery disease (CAD) also exhibited a significantly greater response to ibutilide than patients without CAD (77 vs. 46%, p-value 0.005).

CONCLUSION

As a therapy for cardioversion of AF, ibutilide is most effective in a selected subgroup patients, such as in patients with CAD and in patients without MVD and/or markedly enlarged left atrium.

Remodeling of the left atrium in pacing-induced atrial cardiomyopathy

Rapid atrial pacing produces atrial systolic and diastolic failure characterized by absent atrial booster pump function, increased atrial chamber stiffness, enhanced atrial conduit function, and atrial enlargement. However, the processes underlying these abnormalities are poorly understood. Therefore, we examined left atrial myocardium from dogs with rapid pacing-induced atrial failure (400 bpm for 6 weeks) and from control dogs. Western blotting was used to determine the levels of proteins involved in calcium homeostasis (SERCA 2A, phospholamban, Na+-Ca2+ exchanger). Matrix metalloproteinase (MMP) activity was measured using gelatin and casein zymography, and levels of tissue inhibitor of metalloproteinase-4 (TIMP-4) and the TIMP-4 complexed with MMPs were measured with Western blot analysis. There were no differences in SERCA 2A or Na+-Ca2+ exchanger protein levels, but phospholamban level was significantly decreased in atrial samples from rapidly paced dogs (51.2 +/- 7.8 vs. 77.0 +/- 10.0, p < 0.01). The activity of MMP-9 was selectively and significantly increased by approximately 50%, and the level of complexed TIMP-4 protein was significantly decreased by approximately 50% in samples from dogs with atrial failure. Thus, rapid pacing-induced atrial failure is associated with differential changes in MMP activity, an unchanged number of calcium pumps, and compensatory changes in the level of phospholamban.

Optimal ventricular rate slowing during atrial fibrillation by feedback AV nodal-selective vagal stimulation

Although the beneficial effects of ventricular rate (VR) slowing during atrial fibrillation (AF) are axiomatic, the precise relationship between VR and hemodynamics has not been determined. We hypothesized that selective atrioventricular node (AVN) vagal stimulation (AVN-VS) by varying the nerve stimulation intensity could achieve precise graded slowing and permit evaluation of an optimal VR during AF. The aims of the present study were the following: 1) to develop a method for computerized vagally controlled VR slowing during AF, 2) to determine the hemodynamic changes at each level of VR slowing, and 3) to establish the optimal anterograde VR during AF. AVN-VS was delivered to the epicardial fat pad that projects parasympathetic nerve fibers to the AVN in 14 dogs. Four target average VR levels, corresponding to 75%, 100%, 125%, and 150% of the sinus cycle length (SCL), were achieved by computer feedback algorithm. VR slowing resulted in improved hemodynamics and polynomial fit analysis found an optimum for the cardiac output at VR slowing of 87% SCL. We conclude that this novel method can be used to maintain slow anterograde conduction with best hemodynamics during AF.

Risk of mortality in a cohort of patients newly diagnosed with chronic atrial fibrillation

OBJECTIVE

To estimate the mortality rate of patients newly diagnosed with chronic atrial fibrillation (AF) and compare it with the one in the general population. To evaluate the role of co-morbidity and other factors on the risk of dying among AF patients.

METHODS

We used the General Practice Research Database in the UK to perform a retrospective cohort study. We followed a cohort of chronic AF patients (N = 1,035) and an age and sex matched cohort of 5,000 subjects sampled from the general population. We used all deceased AF patients as cases (n = 234) and the remaining AF patients as controls to perform a nested case-control analysis. We estimated mortality risk associated with AF using Cox regression. We computed mortality relative risks using logistic regression among AF patients.

RESULTS

During a mean follow-up of two years, 393 patients died in the general population cohort and 234 in the AF cohort. Adjusted relative risk of death in the cohort of AF was 2.5 (95%CI 2.1 - 3.0) compared to the general population. Among AF patients, mortality risk increased remarkably with advancing age. Smokers carried a relative risk of dying close to threefold. Ischaemic heart disease was the strongest clinical predictor of mortality with a RR of 3.0 (95% CI; 2.1-4.1). Current use of calcium channel blockers, warfarin and aspirin was associated with a decreased risk of mortality.

CONCLUSIONS

Chronic AF is an important determinant of increased mortality. Major risk factors for mortality in the AF cohort were age, smoking and cardiovascular co-morbidity, in particular ischaemic heart disease.

Efficacy of amiodarone for the termination of chronic atrial fibrillation and maintenance of normal sinus rhythm: a prospective, multicenter, randomized, controlled, double blind trial

OBJECTIVE

We sought to assess the efficacy and safety of amiodarone for restoration and maintenance of sinus rhythm in patients with chronic atrial fibrillation in a prospective, randomized, double blind trial.

BACKGROUND

Restoration and preservation of sinus rhythm is difficult in patients with chronic atrial fibrillation. The efficacy of oral amiodarone has not been conclusively established.

METHODS

Ninety-five patients with chronic atrial fibrillation, lasting an average of 35.6 months, were randomized to either amiodarone (600 mg/d) (47 patients) or placebo (48 patients) during four weeks. Nonresponders underwent electric cardioversion, and those who reverted continued with amiodarone (200 mg/d) or placebo. End-points were successful cardioversion and sinus rhythm maintenance.

RESULTS

Sixteen patients (34.04%) in the amiodarone group reverted within 27.28 +/- 8.85 days in comparison with 0% in the placebo group (P < 0.000009). The conversion rate rose to 51.72% in patients with chronic atrial fibrillation lasting less than 12 months. Twenty-eight patients in the amiodarone group and 39 in the placebo group underwent electric cardioversion, which was successful in 19 patients (67.8%) of the amiodarone group and in 15 (38.46%) of the placebo group (P = 0.017). Altogether, conversion was obtained in 79.54% of the amiodarone group patients and in 38.46% of the placebo group patients (P < 0.0001). During follow-up, atrial fibrillation relapsed in 13 (37.14%) of 35 patients of the amiodarone group within 8.84 +/- 8.57 months and in 12 (80%; P = 0.009) of 15 patients of the placebo group within 2.74 +/- 3.41 months.

CONCLUSIONS

Oral amiodarone restored sinus rhythm in one third of patients with chronic atrial fibrillation, increased the success rate of electric cardioversion, decreased the number of relapses and delayed their occurrence.

Selective AV nodal vagal stimulation improves hemodynamics during acute atrial fibrillation in dogs

Although the atrioventricular node (AVN) plays a vital role in blocking many of the atrial impulses from reaching the ventricles during atrial fibrillation (AF), a rapid irregular ventricular rate nevertheless persists. The goals of the present study were to explore the feasibility of novel epicardial selective vagal nerve stimulation for slowing of the ventricular rate during AF and to characterize the hemodynamic benefits in vivo. Electrophysiological-echocardiographic experiments were performed on 11 anesthetized open-chest dogs. Hemodynamic measurements were performed during three distinct periods: 1) sinus rate, 2) AF, and 3) AF with vagal nerve stimulation. AF was associated with significant deterioration of all measured parameters (P < 0.025). The vagal nerve stimulation produced slowing of the ventricular rate, significant reversal of the pressure and contractile indexes (P < 0.025), and a sharp reduction in one-half of the abortive ventricular contractions. The present study provides comprehensive evidence that slowing of the ventricular rate during AF by selective ganglionic stimulation of the vagal nerves that innervate the AVN successfully improved the hemodynamic responses.

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

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

Does acute-phase beta blockade reduce left atrial appendage function in patients with chronic nonvalvular atrial fibrillation?

To investigate whether acute-phase beta-blocker therapy has a harmful effect on left atrial appendage (LAA) function in patients with chronic nonvalvular atrial fibrillation by transesophageal echocardiography (TEE), we evaluated 21 patients with normal left ventricular systolic function and a poorly controlled ventricular rate, despite the use of digoxin. Baseline parameters that were obtained included heart rate, blood pressure, LAA emptying velocities, and left atrial spontaneous echo contrast intensity. Then, each patient was given a bolus dose of 5 mg metoprolol. Ten minutes later, a second set of assessments was performed. After the first TEE studies, each patient began treatment with metoprolol (50 mg orally twice daily for 1 week). A second TEE study was performed after 1 week of continuous oral metoprolol therapy at maintenance dose, and values were again determined. The average resting apical heart rate was 91 +/- 7 bpm. As expected, beta-blocker therapy showed a marked decrease in heart rate at 10 minutes (79 +/- 6 bpm, P <.001) and at 1 week (71 +/- 4 bpm, P <.001). Beta-blocker therapy caused a significant reduction in systolic and diastolic blood pressures (144 +/- 16 / 93 +/- 6 mm Hg at baseline, 137 +/- 16 / 87 +/- 9 mm Hg at 10 minutes, and 135 +/- 12 / 86 +/- 8 mm Hg at 1 week, P <.001). With the beta-blocker therapy, the baseline transesophageal Doppler parameter of LAA emptying velocities (at baseline 24 +/- 7 cm/s) fell significantly at 10 minutes (19 +/- 7 cm/s, P <.001) and at 1 week (17 +/- 6 cm/s, P <.001) after initiation of beta-blocker therapy. After a bolus of metoprolol, spontaneous echo contrast intensity did not change in any patients, but 1 week later, it increased in 1 patient. In 2 patients who had not been found to have an LAA thrombus at baseline TEE study, the second TEE examination demonstrated new thrombi in the LAA. In conclusion, our findings suggest that in patients with chronic nonvalvular atrial fibrillation who have normal left ventricular systolic function and a poorly controlled ventricular rate despite the use of digoxin, acute-phase beta blockade may have a harmful effect on LAA function.

Atrial fibrillation: treatment rationale and clinical utility of nonpharmacologic therapies

Atrial fibrillation (AF) is the most common sustained cardiac dysrhythmia requiring therapy. Nonpharmacologic therapies for the treatment of AF, namely, catheter ablation, cardiac pacing, internal defibrillation, and dysrhythmia surgery are playing an increasingly important role in the overall management of AF. Although usually prescribed when traditional pharmacologic therapy is not effective, not tolerated, or contraindicated, these therapies are rapidly assuming a more prominent role as they mature. These modern therapies for AF, offering the promise of prevention and cure of AF, potential elimination from the sequelae of AF, and significant improvements in quality of life, are increasingly becoming more frequent in clinical practice. Further investigation is needed to determine which therapy is ideally suited for an individual patient and the impact of these varying therapies on morbidity and mortality.

Antidysrhythmics. Emergent

The emergent treatment of dysrhythmias in the ED continues to evolve. Classic medications such as bretylium and lidocaine are given with newer drugs like amiodarone, ibutilide, and sotalol. Studies in progress will examine their efficacy in the ED. The emergency physician must keep abreast of the growing body of literature.

Cost effectiveness of therapies for atrial fibrillation. A review

Atrial fibrillation is the most common supraventricular tachyarrhythmia encountered in clinical practice, affecting over 5% of persons over the age of 65 years. A common pathophysiological mechanism for arrhythmia development is atrial distention and fibrosis induced by hypertension, coronary artery disease or ventricular dysfunction. Less frequently, atrial fibrillation is caused by mitral stenosis or other provocative factors such as thyrotoxicosis, pericarditis or alcohol intoxication. Depending on the extent of associated cardiovascular disease, atrial fibrillation may produce haemodynamic compromise, or symptoms such as palpitations, fatigue, chest pain or dyspnoea. Arrhythmia-induced atrial stasis can precipitate clot formation and the potential for subsequent thromboembolism. Comprehensive management of atrial fibrillation requires a multifaceted approach directed at controlling symptoms, protecting the patient from ischaemic stroke or peripheral embolism and possible conversion to or maintenance of sinus rhythm. Numerous randomised trials have demonstrated the efficacy of warfarin--and less so aspirin (acetylsalicylic acid)--in reducing the risk of embolic events. Furthermore, therapeutic strategies exist that can favourably modify symptoms by restoring and maintaining sinus rhythm with cardioversion and antiarrhythmic prophylaxis. However, the risks and benefits of various treatments is highly dependent on patient-specific features, emphasising the need for an individualised approach. This article reviews the findings of cost-effectiveness studies published over the past decade that have evaluated different components of treatment strategies for atrial fibrillation. These studies demonstrate the economic attractiveness of acute management options, long term warfarin prophylaxis, telemetry-guided initiation of antiarrhythmic therapy, approaches to restore and maintain sinus rhythm, and the potential role of transoesophageal echocardiographic screening for atrial thrombus prior to pharmacological or electrical cardioversion. Further, we discuss the merits and limitations of the cost-effectiveness analyses in the context of overall treatment strategies. Finally, we identify areas that will require additional research to achieve the goal of effective and economically efficient management of atrial fibrillation.

Appropriate outcome measures in trials evaluating treatment of atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is a widespread disease that has only recently received the focused attention of arrhythmia specialists despite being the most frequently occurring significant cardiac arrhythmia.

METHODS AND RESULTS

The wide variety of trial designs used to evaluate AF treatment is a reflection of the diverse outcomes associated with this condition. The best trials assess the impact of treatment on a clearly measured outcome that is of clinical relevance to patients. This review discusses the different designs of AF treatment trials and analyzes the utility of the various outcomes that can be assessed.

CONCLUSIONS

A sensible goal of AF treatment is to reduce the frequency of recurrences and to prolong the time between them. The most appropriate trials focus on AF recurrences that are symptomatic and therefore relevant to the patient. We still do not know if there is value in AF prevention, beyond preventing symptoms. However, ongoing and future studies will show whether AF suppression reduces the longer-term risks of stroke or death and improves patient quality of life. Cost of care will increasingly be studied in future trials of AF management.

The tachycardia-induced dog model of atrial fibrillation. clinical relevance and comparison with other models

In the past, investigators have relied extensively on acute in vivo models of atrial fibrillation (AF), in which AF was induced either pharmacologicly or by vagal stimulation. More recently, there is a need and desire for more clinically relevant models that can only be achieved with the use of chronically instrumented animals. One of these models is the atrial tachycardia-induced AF dog model, which is the main focus of this review. The model produces a persistent AF in 80% of animals paced at 400 beats/min for 6 weeks. Atrial tachycardia also induces various pathophysiologic and ultrastructural changes that often resemble electrical remodeling of atria in patients that have a high susceptibility to AF. This model can also be used to evaluate drug efficacy with respect to attenuation of AF duration or conversion of AF to sinus rhythm. The model may therefore be used to provide further insights into the discovery of new therapeutic approaches to modifying this atrial arrhythmic disorder in man.

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.

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.