Hybrid Epicardial-Endocardial Approach to Atrial Fibrillation Ablation

Who should undergo hybrid AF ablation?

Patients with symptomatic persistent or long-standing persistent atrial fibrillation refractory to pharmacological or routine catheter ablation can be considered for hybrid epicardial-endocardial AF ablation. Although it seems clear that patient selection should be important when considering hybrid AF ablation for optimal results, unfortunately, available data on the outcomes of hybrid epicardial-endocardial ablation is limited. Hybrid ablation is rarely compared to stand-alone catheter ablation, the surgical approach (access site, lesion set, ablation tool) is inconsistent, and the patient population studied is often suitable for a catheter ablation approach (paroxysmal AF, minimal structural heart disease). We believe that the hybrid approach should be considered in patients who either have had unsuccessful catheter ablations or have significant structural heart disease evident by enlarged left atrial size or atrial fibrosis. These are the patients who warrant the added risk of a hybrid approach and who stand to benefit from a more extensive ablation including isolation of the posterior wall of the left atrium. Multi-center studies with a uniform hybrid ablation approach and comparison with a stand-alone catheter ablation approach are needed to help clarify the role of hybrid AF ablation.

     

In-Hospital Approach to Newly Recognized Atrial Fibrillation

This research was designed to test the hypothesis that ischemic preconditioning can be transferred between animals via whole blood transfusion. Preconditioning at a distance refers to the reduction in myocardial infarct size seen when coronary artery occlusion is preceded by brief ischemic episodes of noncardiac tissue. Isolation of the trigger signal responsible for this effect may be useful in the diagnosis and treatment of acute coronary occlusive syndromes. Rabbits were paired by crossmatching blood samples prior to experimentation. Crossmatched pairs were placed into either preconditioned (P) or control sets. Rabbits in the preconditioned sets were further divided into donor (PD) and acceptor (PA) animals. PD animals underwent five episodes of circumflex and renal artery occlusion followed by reperfusion. Before and after each preconditioning episode, a whole blood exchange was performed between PD and PA animals. Alternatively, control rabbits underwent the same surgical procedures and time-sequenced transfusion without preconditioning. All animals then underwent prolonged circumflex occlusion (60 minutes) followed by reperfusion (30 minutes). The area of myocardium at risk (R) was determined by isotope-labeled microsphere injection. Infarct size (I) was determined by NBT staining. The percent infarct within the risk area (I/R) was then compared. The I/R was significantly lower in the PA (14.0% ± 12.2) and PD (14.3% ± 11.2) groups as compared with controls (61% ± 20.6). There was no significant difference between the tPA and TPD groups. In conclusion, the ischemic preconditioning effect can be transferred to nonpreconditioned animals via whole blood transfusion, suggesting a humoral mechanism for preconditioning at a distance.     

Management of Atrial Fibrillation: Out-of-Hospital Approach

Atrial fibrillation is increasingly common with advancing age and is responsible for 10% of the half-million strokes that occur annually in the United States. When a patient presents with atrial fibrillation, the physician's first task is to use the history, physical examination, and electrocardiogram to determine whether hospitalization is necessary. Factors indicating a need for hospital care include evidence of infarction or ischemia, congestive heart failure, hypotension or hypoperfusion, excessive rate, or pre-excitation. In addition, if the episode began within 48 hours, consider early cardioversion, which also requires hospitalization. Next, the need for control of the ventricular rate should be assessed. A heart rate under 90 beats/min at rest and under 120 beats/min after 1 minute of step exercise is a reasonable goal. Dixogin usually controls the resting rate, but sometimes beta-blockers or calcium channel blockers are needed to control the exercise rate. The need for anticoagulation is determined by the presence of clinical risk factors such as valvular heart disease, previous thromboembolism, hypertension, age over 65 years, congestive heart failure, and left atrial enlargement. An echocardiogram is necessary to complete this assessment. Patients having one or more of these risk factors are most effectively treated with warfarin, as evident from several clinical trials. Although patients over age 65 demonstrate reduced thromboembolism with warfarin therapy, they also are more prone to cerebral hemorrhage, thus, their international normalization ratio (INR) should be kept at the lower end of the therapeutic range [2,3]. Other patients can be treated with aspirin, although stroke reduction in these patients may be more related to reduction of arterial thrombosis than thromboembolism. Patients under age 65 with no risk factors have a very low annual risk of stroke without therapy (approximately 1%). If symptoms persist or if this is a first episode in someone without left atrial enlargement, cardioversion can be considered after 3 weeks of warfarin therapy with INR in the therapeutic range. Otherwise, warfarin should be continued indefinitely. Prevention of recurrence with antiarrhythmic drugs is somewhat problematic because of incomplete efficacy (30% recurrence at 1 year) and the potential for inducing other, life-threatening arrhythmias.     

Taking the Pulse of Atrial Fibrillation: A Practical Approach to Rate Control

Despite major advances in atrial fibrillation (AF) catheter ablation, rate control remains the most widely used management strategy for AF in the general population. In addition to its use as a primary approach to control symptoms and prevent complications of AF, rate control is often a necessary complement to rhythm-control strategies, especially with antiarrhythmic drugs. The value of rate-control therapy is supported by several large randomized clinical trials showing no difference in major cardiovascular outcomes between rate-control and rhythm-control strategies with currently available therapeutic approaches (antiarrhythmic drugs and/or catheter ablation). Despite its extensive use, the rational basis for rate-control therapy is underemphasized in clinical teaching and practice. In this article, we aim to provide evidence-based thoughts on important practical aspects of rate-control therapy in AF by reviewing 5 clinically relevant issues. We (1) highlight the pharmacological differences between the mechanisms of action of β-blockers and Ca²⁺-channel blockers for AF rate control and the practical implications for therapeutic decision making; (2) review the controversies surrounding the use of digoxin for AF rate control in the light of recently published work; (3) discuss the evidence for rate-control heart rate targets in patients with AF and preserved left-ventricular function; (4) examine how heart rate targets may differ in patients with heart failure and reduced vs preserved left-ventricular ejection fraction and the importance of heart-rate lowering for the effectiveness of cardiac resynchronization therapy in patients with heart failure and AF; (5) discuss the relationship between AF, exercise capacity, and rate-controlling drug class.     

Applying the Atrial Fibrillation Guidelines Update to Manage Your Patients With Atrial Fibrillation

Guidelines can be lengthy and complex to apply. We provide a concise summary of important components of outpatient atrial fibrillation management, based on the updated Canadian Cardiovascular Society guidelines. Common questions arising when caring for such patients are addressed, including: what underlying causes should be investigated and treated, how to assess and treat symptoms, how to determine and reduce stroke risk, and when to arrange subspecialty referral. The guidelines emphasize that emergency room visits are rarely necessary and quality of life for most patients with atrial fibrillation can be quite good. The guidelines also clarify that bleeding risk factors should be assessed to identify modifiable issues, rather than as a reason to permanently withhold oral anticoagulant therapy. There is an opportunity to substantially reduce the morbidity and health-system costs related to atrial fibrillation through patient education related to symptom management and adherence to appropriate stroke prevention therapy.     

Atrial Ectopics Prior to Atrial Fibrillation Onset

Background: This study examined the possible role of atrial ectopics and short runs of atrial tachycardia in the initiation of episodes of paroxysmal atrial fibrillation (PAF). Methods: Holter recordings from patients participating in pharmacotherapy trials for the prevention of PAF were examined. Treatment comprised placebo, digoxin, disopyramide, or atenolol. The frequency of atrial ectopic beats during each 30 seconds over the 5 minutes prior to PAF and whether this was also associated with atrial tachycardia (3 or more ectopics in succession) was calculated. Results: The mean number of ectopics was 4.1 in the final minute, but patients receiving disopyramide or atenolol had significantly more ectopics than those on placebo (P > 0.05 for both). Those on digoxin had a similar number of ectopics to placebo patients. There was no relationship between heart rate at PAF onset and ectopic frequency, nor any association between the presence of one or more episodes of atrial tachycardia and ectopic frequency. Conclusion: Atrial ectopics increase in frequency prior to PAF onset, and this study suggests that antiarrhythmic therapy may increase the number of ectopics required to initiate PAF.     

The Burden of Atrial Fibrillation on the Hospital Sector in Canada

Background

Atrial fibrillation (AF) is a common disease that frequently requires acute hospital care; however, the cost of hospital care in Canada has not been reported. The purpose of this study was to estimate the cost of AF related to hospital-based care in Canada.

Methods

Analyses were conducted with 2 national administrative databases for the fiscal year 2007-2008. Databases included information for hospital admissions, day operations, and ambulatory care. Records with a most responsible diagnosis of AF, atrial flutter, or a diagnosis related to AF with a concomitant comorbidity of AF were included. Hospital costs were estimated, in 2010 Canadian dollars, by applying an average cost per weighted case to the resource intensity weight for each admission or visit and then adding the separate billable fee for admissions, surgical procedures, and interventions.

Results

In 2007-2008, the number of acute care admissions with AF as the most responsible diagnosis was 22,823, same-day surgical procedures was 5707, and emergency department visits was 58,066. The hospital costs attributable to AF were $815 million in 2010 Canadian dollars: $710 million for hospitalizations; $32 million for same-day surgical procedures; and $73 million for emergency department visits. Most of the acute care costs were for hospitalizations when AF was listed as a comorbidity ($558 million, or 69%).

Conclusion

AF results in a substantial cost burden to the acute care hospital sector. Current hospital costs in AF patients are driven by the consequences of AF, while the costs for specific treatments for AF are relatively low.     

Integrated Management Approach to Atrial Fibrillation Care: A Cost Utility Analysis

BackgroundAtrial fibrillation (AF) is a substantial burden on health care. Combined specialist and nurse-based AF clinics are associated with improved outcomes. However, Canadian data on the cost-effectiveness of this integrated management approach to AF care are lacking.MethodsWe evaluated health care costs and outcomes of 413 patients with newly-diagnosed AF in 3 emergency departments in Nova Scotia between January 1, 2011 and January 31, 2014. Using a before-after study design, patients were divided into usual care (228 patients) and intervention (185 patients) groups. The intervention was a nurse-run, physician-supervised AF clinic. Costs and quality-adjusted life years (QALYs) were compared between usual care and intervention. Costs were those incurred because of the clinical outcome, bleeding events, medications, and cardiovascular-related procedures. Probabilistic analysis was conducted to assess uncertainty.ResultsThe AF clinic was associated with an average cost reduction of CAD$210.83 and an average improvement in QALY of 0.0007 per patient. The AF clinic was dominant over usual care despite higher operational and medication costs over 1 year. It provided greater cost-saving in approximately 66% of probabilistic analysis simulations and generated more QALYs in approximately 92% of simulations. An incremental cost-effectiveness ratio < $50,000 was found in 68% of simulations.ConclusionsThe present study provides guidance regarding the cost-effectiveness of an integrated management approach compared with usual specialty care of AF in a Canadian setting. We recommend further study be undertaken that prospectively plans for economic evaluation before definitive assessments of cost-effectiveness can be made.     

Pharmacological Approach for the Prevention of Atrial Fibrillation After Cardiovascular Surgery

Atrial fibrillation (AF) is a common complication of cardiovascular surgery. The two most important risk factors for its development are advancing age and a preoperative history of AF. Long-term sequelae, such as a stroke, are uncommon, however, atrial fibrillation frequently results in increased length and cost of hospitalization. Strategies to prevent postoperative AF include perioperative beta-blockers, amiodarone, and atrial pacing. These strategies are most effective in high-risk patients. When AF does occur, treatment includes control of the ventricular rate, systemic anticoagulation, and conversion to sinus rhythm.     

Pacing to Prevent Atrial Fibrillation

Introduction: Pacing has been proposed as a nonpharmacologic treatment option to prevent atrial tachyarrhythmias (ATs) in drug-refractory patients. This article reviews the current state of pacing to prevent ATs.
Methods and Results: Different pacing modalities have been assessed with regard to their ability to prevent AT: conventional DDDR pacing with elevated lower rate limit, biatrial pacing, dual-site right atrial pacing, atrial septal pacing, and pacing with the use of dedicated pacing algorithms. Small studies suggest a benefit of conventional pacing for AT prevention in patients with bradycardia, but a randomized trial did not reveal any AT reduction by conventional pacing in patients without bradycardia. AT prevention by biatrial or dual-site right atrial pacing has been reported in small studies, but randomized trials did not show a clear benefit of these pacing techniques. Small studies showed a reduced AT recurrence rate in patients with septal pacing at the triangle of Koch or at Bachmann's bundle. Two large randomized trials with preventive pacing algorithms showed a significant AT reduction compared to conventional pacing, but this was not confirmed in four trials.
Conclusion: Pacing seems to be able to suppress ATs in a minority of patients; however, prospective identification of responders to different pacing modalities does not appear to be feasible at the present time. (J Cardiovasc Electrophysiol, Vol. 14, pp. S20-S26, September 2003, Suppl.)     

Susceptibility to Atrial Fibrillation:

Propensity for Extrastimulus to Induce AF. Introduction : The development of susceptibility to atrial fibrillation (AF) is a common consequence of many forms of cardiovascular disease, especially heart failure. In this study we used a sheep model of pacing-induced stable early heart failure to describe, quantify, and relate the level of susceptibility to AF to changes in structural and electrophysiologic parameters.
Methods and Results : Epicardial electrodes were implanted on the atria and right ventricles of nine sheep. The AF thresbold, atrial vulnerability period, atrial effective refractory period (ERP), and interatrial conduction time were examined during control and over a 6-week period of ventricular pacing at 190 beats/min. Left atrial (LA) area and left ventricular (LV) fractional shortening were monitored using echocardiography. There were significant increases in LA susceptibility to AF (P < 0.0003), LA area (P < 0.0002), and LA FRP400 (P < 0.0002). Rate of increase in LA area was related positively to AF susceptibility (P = 0.02) and inversely to LA ERP400 (P = 0.002). LV fractional shortening decreased to approximately 50% of control value (P < 0.00001). No changes were observed in right atrial electrophysiology.
Conclusion : In this study, susceptibility (the ability of an extrastimulus to induce AF) was rigorously measured within a predetermined format. Significant relationships were found to exist between susceptibility, certain of the observed changes in atrial electrophysiology and structure.     

消融心房脂肪垫治疗心房颤动的研究现状

近年研究表明,迷走神经过度兴奋与一部分心房颤动的发生密切相关。由于支配心房的迷走神经丛主要分布于心房外膜的脂肪垫中,因此,以心房去迷走神经化为终点的脂肪垫消融成为一项新的心房颤动治疗措施。初步研究的结果显示,该术式治疗心房颤动确实有效,但同时也存在若干弊端。现就消融心房脂肪垫治疗心房颤动的现状作一综述。     

Nonpharmacologic Approaches to the Treatment of Atrial Fibrillation and Atrial Flutter

Nonpharmacologic Approaches to Atrial Fibrillation and Flutter. The high prevalence of atrial fibrillation, the associated morbidity and mortality, the absence of safe and effective drug therapy, and an increased understanding of the pathophysiologic basis of atrial fibrillation and flutter have collectively led to the development of novel nonpharmacologic treatments for the management of these arrhythmias, including the CORRIDOR and MAZE surgical procedures, catheter-based ablation and modification of AV conduction, catheter-based ablation of atrial flutter and fibrillation, and internal atrial defibrillation. These surgical and catheter-based techniques offer potentially curative therapy while sparing the long-term risks of antiarrhythmic drug therapy. For patients with typical atrial flutter, catheter ablation affords cure rates in excess of 70%. As technological innovations further facilitate identification and ablation of the critical isthmus in the floor of the right atrium, success rates should improve substantially. For patients with atrial fibrillation, AV junction ablation with implantation of a rate-responsive ventricular pacemaker should be considered palliative therapy, as should modification of AV junction conduction. The MAZE procedure offers very high cure rates, but because it currently involves open heart surgery, patient selection is critical. Catheter-based procedures emulating aspects of the MAZE procedure may one day offer cure rates comparable to those of the surgery itself, but additional research and technological development are necessary to further define and refine the minimal effective procedure, and then to facilitate the placement of contiguous, full-thickness lesions in precise three-dimensional configurations. In the interim, the implantable automatic atrial defibrillator may offer a means for rapidly restoring sinus rhythm without the risks of long-term antiarrhythmic drug therapy.