Assessment of Intersignal Variability for Discrimination of Atrial Fibrillation from Atrial Flutter

The analysis of endocardial signals obtained from an electrode located in the right atrium enabled by new dual chamber implantable cardioverter defibrillators may be helpful to provide additional therapies such as overdrive pacing or low energy atrial cardioversion for the treatment of concomitant atrial flutter (AFL) or atrial fibrillation (AF). Algorithms for discrimination of atrial tachyarrhythmias based on rate counting are of limited efficacy. The aim of this study was to assess the intersignal variability by using fast discrete wavelet transforms (FDWT) as a new method of discrimination of AF from AFL. Patients with spontaneous episodes of AF/AFL or patients who developed AF/AFL during an electrophysiological study were studied. The endocardial signals were recorded from the high right atrium using a transvenous 5 Fr bipolar electrode catheter (interelectrode spacing: 1 cm). The signals were digitized (2 kHz, 12-bit resolution) after amplification and filtering (40–500 Hz). Within data segments of 10-second duration, 25 consecutive signals were selected and normalized and FDWT was applied. Standard deviations of the wavelet coefficients (SD) from coarse scales (scale 4–8) were calculated. A total of 94 data segments (AF: 52, AFL: 42) from 28 patients were analyzed. SD at each considered scale was higher for AF than for AFL (P < 0.001). SD at scale 8 discriminated between AF from AFL with 100% sensitivity and specificity. We conclude that assessment of intersignal variability of bipolar endocardial recordings using FDWT is an effective method for the discrimination of AF from AFL. The implementation of this tool in a discrimination algorithm of an implantable device may help provide the appropriate differential therapy for atrial tachyarrhythmias.     

Comparison of Bipolar Atrial Electrogram Amplitude in Sinus Rhythm, Atrial Fibrillation, and Atrial Flutter

Automatic mode switching pacemakers revert to non-atrial tracking modes in response to sensed atrial tachyarrhythmias. It is unclear how atrial electrogram amplitudes in sinus rhythm compare to those during atrial tachyarrhythmias. In this study, peak-to-peak bipolar atrial electrogram amplitudes were measured during sinus rhythm and either atrial fibrillation or atrial flutter in 69 patients. The mean atrial electrogram amplitudes were 1,59 ± 1.36 m V during sinus rhythm and 0.77 ± 0,58 mV during atrial fibrillation (P < 0.0001) for 25 patients with atrial fibrillation and 1.81 ± 2.07 mV during sinus and 1.5 ± 1.81 mV(P < 0.0001) for 44 patients with atrial flutter. The mean electrogram amplitudes during both atrial fibrillation and flutter correlated significantly with amplitudes during sinus rhythm (R = 0.79, R = 0.94. respectively, both P < 0,0001). The coefficient of variance of individual electrogram amplitudes was greater in atrial fibrillation than sinus (P < 0.0001). By comparing 20th percentile electrogram amplitudes in atrial fibrillation and flutter to mean sinus amplitudes, intermittent very low electrogram amplitudes (< 0.3 mV) were more likely during atrial fibrillation and flutter if the mean sinus electrogram amplitudes were < 1.5 mV and < 0.5 mV, respectively (P < 0.01). Eightieth percentile electrogram amplitude values in atrial fibrillation and flutter were equally likely to exceed mean sinus amplitude values in respective patients, in conclusion, mean atrial electrogram amplitudes during atrial fibrillation and flutter are less than but correlated to sinus rhythm electrogram amplitudes. Very low amplitude individual electrograms during these atrial arrhythmias are associated with low mean sinus rhythm electrogram amplitudes. These findings may have implications for the programming of permanent dual chamber pacemakers in patients with paroxysmal atrial fibrillation and flutter.     

The Importance of Atrial Fibrillation Burden and the Origin of Device‐Tailored Anticoagulation

The current paradigm for anticoagulation in patients with atrial fibrillation is based upon clinical risk factors for stroke without reference to the frequency or duration (i.e., burden) of atrial fibrillation episodes. In the last decade, increasing evidence derived from device‐based surveillance of atrial fibrillation has suggested that in some patients the burden of atrial fibrillation may be associated with thromboembolic risk. The development of rapidly acting oral anticoagulants and devices with remote monitoring capability has allowed the testing of a strategy of tailored or “pill‐in‐the‐pocket” anticoagulation based upon atrial fibrillation burden.     

Atrial Vulnerability in Patients with Paroxysmal "Lone" Atrial Fibrillation

Little is known about the electrophysiological properties of the atrium predisposing to paroxysmal atrial fibrillation (AF), especially in patients without structural heart disease. This study was conducted to analyze intraatrial conduction, atrial refractoriness, and arrhythmia inducibility in patients with lone paroxysmal AF. An electrophysiological study was performed in 24 patients with a documented history of lone paroxysmal AF but in sinus rhythm at the time of the electrophysiological study. Twelve patients without any history of atrial arrhythmias served as controls. The patients with lone paroxysmal AF showed a significant prolonged local conduction time S1A1 (70 ± 21 ms vs 36 ± 12 ms, P < 0.0001), a lack of rate adaptation of the functional refractory period (FRP changes/cycle length changes < 10% in 15 of 24 patients with lone paroxysmal AF vs 1/12 controls, P = 0.002) and a higher incidence of inducible AF with only one extrastimulus (13/24 vs 0/12, P = 0.0014). The total P wave duration in the surface ECG (89 ± 14 ms vs 83 ± 8 ms, P = 0.15), the intraatrial conduction time (36 ± 14 ms vs 28 ± 8 ms, P = 0.07), the presence of a fragmented atrial electrogram (16/24 vs 7/12, P = 0.62), the absolute value of the effective refractory period (204 ± 28 ms vs 212 ± 23 ms, P = 0.42), and the vulnerability index (3.0 ± 1.5 vs 3.6 ± 1.5, P = 0.26) were not statistically different between the two groups. The presence of a prolonged (> 50 ms) S1A1 and/or the presence of a lack of rate adaptation of the FRP and/or the presence of inducible AF identified patients with spontaneous lone paroxysmal AF with a sensitivity of 96%, a specificity of 67%, a positive predictive value of 85%, and a negative predictive value of 89%. In patients with lone paroxysmal AF. the electrophysiological study using conventional techniques allows not only to detect AF inducibility using a nonaggressive protocol, but also to reveal several electrophysiological abnormalities related to the atrial substrate itself. This atrial vulnerability may explain the high incidence of recurrences in patients with lone paroxysmal AF.     

Magnesium Sulfate versus Placebo for Paroxysmal Atrial Fibrillation: A Randomized Clinical Trial

Objectives: The objective was to investigate the efficacy of magnesium sulfate (MgSO₄) in decreasing the ventricular rate in emergency department (ED) patients presenting with new‐onset, rapid atrial fibrillation (AF). Methods: A double‐blinded, placebo‐controlled randomized clinical trial was conducted in an adult university hospital. Patients aged ≥18 years with AF onset of less than 48 hours and a sustained ventricular rate of >100 beats/min were randomized to either intravenous (IV) MgSO₄ 10 mmol or normal saline (NSal). Rhythm and instantaneous heart rate as measured by the monitor were recorded at baseline and every 15 minutes for 2 hours after starting the trial drug. Heart rate and rhythm were compared at 2 hours. A multilevel modeling analysis was performed to adjust for differences in baseline heart rate and any additional treatment and to examine changes in heart rate over time. Results: Twenty‐four patients were randomized to MgSO₄ and 24 to NSal. Baseline heart rate was lower in the MgSO₄ group (mean ± standard deviation [±SD] = 125 ± 24 vs. 140 ± 21 beats/min]. One and 3 patients in the MgSO₄ and NSal groups, respectively, were given another antiarrhythmic or were electrically cardioverted within 2 hours after starting the trial drug. Heart rate (mean ± SD) at 2 hours in both MgSO₄ (116 ± 30 beats/min) and NSal groups (114 ± 31 beats/min) decreased below their respective baseline levels. However, the rate of heart rate decrease across time did not differ between groups (p = 0.124). The proportion of patients who converted to sinus rhythm 2 hours post–trial drug did not differ (MgSO₄ 8.7% vs. NSal 25.0%, p = 0.25). Conclusions: This study was unable to demonstrate a difference between IV MgSO₄ 10 mmol and saline placebo for reducing heart rate or conversion to sinus rhythm at 2 hours posttreatment in ED patients with AF of less than 48 hours duration.     

Conversion of Recent-Onset Atrial Fibrillation to Sinus Rhythm: Effects of Different Drug Protocols

In a population of 417 hospitalized patients, the efficacy and safety of different drug regimens administered to convert atrial fibrillation (AF) of recent anset (≤ 7 days duration) to sinus rhythm were evaluated. All patients were in NYHA Class ≤ 2, and free of heart failure. They were randomly allocated to treatment with placebo in 121 patients; IV amiodarone, 5 mg/kg bolus, followed by 1.8 g/24 hours in 51 patients; IV propafenone, 2 mg/kg bolus, followed by 0.0078 mg/kg/min in 57 patients; p.o. propafenone, 600 mg p.o. in a single dose in 119 patients; and p.o. flecainide, 300 mg p.o. in a single dose in 69 patients. All patients were continuously monitored by Holter ECG, and the number of conversions to sinus rhythm was measured at 1, 3, and 8 hours. Results: (1) IV propafenone resulted in a higher conversion rate within 1 hour compared with the oral loading regimens of propafenone or flecainide, but the conversion rates at 3 and 8 hours were comparable, approximately 75% at 8 hours; 2) IV amiodarone was not different from placebo until 8 hours when it was associated with 57% of conversions; (3) conversion to sinus rhythm at 8 hours was observed in 37% of the placebo treated patients. Serious adverse effects occurred in few patients: two patients treated with flecainide and one treated with IV propafenone experienced left ventricular decompensation; one patient treated with placebo and two treated with flecainide had atrial flutter with rapid ventricular response. In conclusion, single-dose, oral loading with propafenone or flecainide are acceptable alternatives to conventional drug regimens in selected hospitalized patients. In addition, the measure of a placebo effect is mandatory in studies of recent-onset AF.     

Impact of Atrial Fibrillation Termination on Clinical Outcome after Ablation in Relation to the Duration of Persistent Atrial Fibrillation

Background: Whether procedural termination of persistent atrial fibrillation (AF) is necessary for optimal clinical efficacy still remains controversial. We sought to characterize the patients with persistent AF in whom procedural AF termination impacted an improved clinical outcome after ablation. Methods: We retrospectively assessed 132 patients (61.0 ± 9.3 years, 114 males) undergoing catheter ablation of persistent AF (duration 3 years, median). A stepwise ablation approach including pulmonary vein isolation and atrial substrate ablation targeting complex fractionated and high‐frequency electrograms was performed with desired endpoint of AF termination. Results: Overall, 90 patients (68%) were free from recurrent arrhythmias at 20 ± 11 months of follow‐up after one or two procedures. The left atrial diameter and continuous AF duration according to medical history were associated with the outcome (P = 0.002 and P< 0.001, respectively). In multivariate Cox regression analysis, the continuous AF duration was the only independent predictor of recurrent arrhythmias (hazard ratio 1.17, 95% confidence interval 1.10–1.23, P < 0.001). In patients with AF duration of ≥3 years, the clinical success was comparable regardless of whether AF termination was achieved or not (log‐rank, P = 0.27). In the remaining patients with AF duration of <3 years, procedural AF termination was associated with a higher arrhythmia‐free rate than when AF was sustained after ablation (log‐rank, P = 0.023). Conclusion: Extensive ablation to terminate AF might not be warranted in patients with a longer AF duration. On the contrary, procedural AF termination could be associated with maintenance of sinus rhythm in patients with a shorter AF duration with a less proarrhythmic substrate. (PACE 2012;35:1436–1443)     

Contemporary Challenges of Catheter Ablation for Atrial Fibrillation

Purpose

Catheter ablation of atrial fibrillation (AF) is now one of the most frequently performed ablation procedures, but there are currently 2 important challenges: achieving permanent/durable rather than transient pulmonary vein isolation (PVI) and improving the results of ablation for the wider patient population with persistent AF.

Methods

Recent technical advances in the technique of ablation and the results of clinical trials aimed at achieving more permanent and durable PVI are reviewed. We also summarize recent advances in identifying atrial fibrosis and in understanding the pathophysiology of AF relevant to selecting patients for ablation of persistent AF.

Findings

The use of contact force–sensing technology, adenosine testing after ablation, and pace capture–guided ablation all have the potential for achieving more durable ablation. Selection of patients suitable for ablation of persistent AF may be improved by assessing the extent of atrial fibrosis with delayed enhancement imaging with cardiac magnetic resonance or by assessing the pattern of atrial electrical activity with the use of complex atrial electrograms. Advances in treatment are likely to result from the recognition of localized rotors and focal sources as primary sustaining mechanisms for all types of human AF and in the use of noninvasive mapping for their identification. Linear ablation to supplement PVI may improve the results of AF ablation.

Implications

Rapidly unfolding advances in the techniques of AF ablation and the understanding of mechanisms of AF hold promise for improving the durability of PVI and for extending the technique to carefully selected patients with persistent AF.     

Computer Discrimination of Atrial Fibrillation and Regular Atrial Rhythms from Intra-Atrial Electrograms

Reliable detection of atrial fibrillation from intra-atrial data is an important requirement for automatic implantable anti-tachycardia devices. Simultaneous filtered and unfiltered intra-atrial electrograms were recorded from patients in regular rhythms (12 sinus rhythms and six regular atrial tachycardias) and atrial fibrillation (nine rhythms). Each rhythm was broken down into consecutive 4-second data segments for analysis by atrial rate calculation, power spectrum analysis and amplitude probability density function generation. Significant differences were found between regular rhythms and atrial fibrillation for atrial rate, for the percentage of the total power in the 4-9 hertz band and for amplitude probability density close to the isoelectric region. There was no overlap for any of these three parameters. For each method of analysis, algorithms were generated to discriminate individual data segments from regular rhythms and atrial fibrillation with high sensitivity and specificity. Comparable results were found when sinus rhythm was excluded from the analysis. Characteristics of intra-atrial recordings during atrial fibrillation were remarkably similar to previously published reports of intra-ventricular recordings during ventricular fibrillation. Each of the three methods of analysis may provide an algorithm for accurate detection of atrial fibrillation by anti-tachycardia devices.     

Noninvasive Evidence of Shortened Atrial Refractoriness during Sinus Rhythm in Patients with Paroxysmal Atrial Fibrillation

Background: Shortening of the atrial refractory period is the key feature of atrial electrical remodeling during atrial fibrillation (AF). During sinus rhythm (SR), assessment of the atrial refractoriness is hampered by the fact that the atrial repolarization wave (Ta wave) is largely obscured by the following QRST complex. The purpose of this study was to study the Ta wave in subjects with paroxysmal AF during SR with third‐degree atrioventricular (AV) block, and in matched controls. Methods: Fifteen patients (mean age 70 ± 10 years, five males) with paroxysmal AF undergoing AV‐nodal ablation were studied. Fifteen age‐ and gender‐matched subjects (mean age 71 ± 9 years, five males) with third‐degree AV block, without a history of heart disease, were used as controls. Standard 12‐lead electrocardiograms (ECGs) were recorded and transformed to orthogonal leads and studied using P‐wave signal averaging technique. Results: The P to Ta interval was shorter (408 ± 47 ms vs 451 ± 53 ms, P = 0.017) and in Lead Y the Ta peak location was earlier (156 ± 31 ms vs 187 ± 34 ms, P = 0.002) in subjects with paroxysmal AF than in the controls. The P‐wave duration (126 ± 15 ms vs 129 ± 17 ms, P = 0.59) and morphology was similar in AF patients and controls. Conclusions: In this study, the ECG signs of shorter atrial refractoriness associated with a history of AF are visualized for the first time during SR. The finding of the earlier location of the PTa peak in AF subjects implies that a possible indicator of increased arrhythmia susceptibility may be visible already in the unprocessed ECG.     

Long-Term Sinus Rhythm Stability after Intraoperative Ablation of Permanent Atrial Fibrillation

Introduction: Short‐ and medium‐term sinus rhythm (SR) rates after intraoperative radiofrequency ablation to treat permanent atrial fibrillation (AF) are well documented. Is rhythm success stable during a long‐term follow‐up? Methods and Results: A total of 130 patients who had undergone intraoperative radiofrequency cooled‐tip endocardial ablation (SICTRA) of permanent AF (mean AF duration 6±5 years) concomitant to open heart surgery more than 3 years ago were followed up using electrocardiogram (ECG), Holter‐ECG, and echocardiography and compared with 12‐month follow‐up data. In 55% of patients, only the left atrium and in 45%, both atria were treated using SICTRA. Mitral valve replacement was performed in 21, mitral valve reconstruction in 25, aortic valve replacement in 13, CABG procedures in 51 (including 11 patients with additional mitral valve surgery), and complex procedures in 20 patients. Sixty‐nine percent of patients (90/130) were in stable SR after a median period of 48 months, whereas 28% (36/130) were in AF and 3% (4/130) were in atrial flutter. In between the 12‐month follow‐up and the long‐term follow‐up, seven patients converted to AF after having documented SR, two patients converted to typical right atrial flutter after being in SR, and two patients from AF to left atrial macroreentry. After left and biatrial SICTRA, SR rates were comparable (73% vs 66%, P = 0.45). Echocardiography revealed 73% of patients in SR to have effective left atrial contraction. Conclusions: SICTRA restores long‐term stable SR in 69% of all patients. Nine percent of patients reconverted back to atrial arrhythmia after having documented SR at 12 months.     

Atrial Fibrillation from Thyroid Storm

Background: Thyroid storm is an often-discussed but rare presentation to emergency departments (EDs). The clinical presentation of a thyroid storm is the result of a hyperthyroid state that may result in significant morbidity or disability, or even death. Typically, patients are aware of their hyperthyroid condition, and may be able to recognize an episode of thyroid storm. However, the first presentation of hyperthyroidism could, in fact, be from thyrotoxic crisis. Objectives: To review the presentation of thyroid storm, including tachycardia, hyperpyrexia, agitation, and altered mental status, which can be easily misdiagnosed as drug intoxication. Case Report: We present the case of an otherwise healthy young adult who was sent to the ED by an outpatient care provider for generalized and vague symptoms of “feeling unwell” that was eventually diagnosed in the ED as thyrotoxic crisis. Conclusion: We use this case to emphasize that thyrotoxic crisis should be at least considered in the differential diagnosis of a patient with this presentation, and to highlight how, even with apparently usual and effective treatments, a patient may still decompensate.     

Regular Ventricular Rhythms Before Conversion of Recent Onset Atrial Fibrillation to Sinus Rhythm

The incidence of fast atrial tachycardias with regular ventricular rhythm was assessed in a population of 243 patients with recent onset (< 72 hours) atrial fibrillation (AF), without heart failure, randomly treated with single loading oral dose of propafenone (600 mg), flecainide (300 mg), digoxin (1 mg), or placebo for acute conversion to sinus rhythm (SR). Fast atrial arrhythmias developed in 14 (6%) patients: 6/92 treated with propafenone, 3/34 treated with flecainide, 1/25 treated with digoxin, and 4/ 92 who received placebo (P = NS). Heart rate > 175 beats/min with 1:1 AV conduction ensued in 4 cases: 2 treated with flecainide and 2 treated with placebo; in the other cases 2:1 AV conduction was observed. Widening of QRS during regular tachycardia was observed in 4 patients; 3 who received propafenone and 1 who received flecainide. Conversion to SR within 4 hours was achieved in 55/92 (60%) patients treated with propafenone, 20/34 (59%) patients treated with flecainide, 7/25 (28%) patients treated with digoxin, and 19/92 (20%) treated with placebo (P < 0.001 propafenone vs placebo and flecainide vs placebo; P < 0.05 propafenone vs digoxin and flecainide vs digoxin). Periods of regular tachycardia are expected in recent onset AF and may not necessarily represent a proarrhythmic effect of Class 1C drugs, rather than mark the transition from AF to SR. Class 1C agents are probably responsible for widening of the QRS complex seen during these tachycardias. Propafenone and flecainide appear equally effective in converting recent onset AF.     

Contemporary Management of Atrial Fibrillation

Nurse practitioners (NPs) frequently treat adults with atrial fibrillation. With new oral antithrombotic agents available, NPs need to be knowledgeable of treatment options to prevent stroke and systemic emboli. This article reviews the latest American College of Cardiology Foundation/American Heart Association guideline on the management of atrial fibrillation. Emphasis is placed on the changing landscape of pharmacological agents. Use of guideline-directed medical therapy will ultimately improve patients’ quality of life and prevent stroke and premature death.     

Persistent Atrial Fibrillation Converts to Common Type Atrial Flutter during CFAE Ablation

Background: Catheter ablation of persistent and long‐standing persistent atrial fibrillation (AF) is still challenging. So far different ablation techniques have been reported, including pulmonary vein isolation, additional linear lesions, ablation of complex fractionated atrial electrograms (CFAE), and combinations of these techniques. During ablation of CFAE, the occurrence of left atrial (LA) tachycardia is well known. The occurrence of right atrial flutter on the other hand is less well described. Methods: Here, we report three patients who had been ablated because of symptomatic persistent atrial fibrillation. Summary: In all patients, AF changed into a cavotricuspid isthmus = dependent right atrial flutter during ablation of CFAE in the LA. (PACE 2010; 33:304–308)