Immediate reinitiation of atrial fibrillation following internal atrial defibrillation

Does conduction heterogeneity determine the supervulnerable period after atrial fibrillation?

Atrial fibrillation (AF) resumes within 90 s in 27% of patients after sinus rhythm (SR) restoration. The aim of this study is to compare conduction heterogeneity during the supervulnerable period immediately after electrical cardioversion (ECV) with long-term SR in patients with AF. Epicardial mapping of both atria was performed during SR and premature atrial extrasystoles in patients in the ECV (N = 17, age: 73 ± 7 years) and control group (N = 17, age: 71 ± 6 years). Inter-electrode conduction times were used to identify areas of conduction delay (CD) (conduction times 7-11 ms) and conduction block (CB) (conduction times ≥ 12 ms). For all atrial regions, prevalences and length of longest CB and continuous CDCB lines, magnitude of conduction disorders, conduction velocity, biatrial activation time, and voltages did not differ between the ECV and control group during both SR and premature atrial extrasystoles (p ≥ 0.05). Hence, our data suggest that there may be no difference in biatrial conduction characteristics between the supervulnerable period after ECV and long-term SR in AF patients. The supervulnerable period after AF termination is not determined by conduction heterogeneity during SR and PACs. It is unknown to what extent intra-atrial conduction is impaired during the supervulnerable period immediately after ECV and whether different right and left atrial regions are equally affected. This high-resolution epicardial mapping study (upper left panel) of both atria shows that during SR the prevalences and length of longest CB and cCDCB lines (upper middle panel), magnitude of conduction disorders, CV and TAT (lower left panel), and voltages did not differ between the ECV and control group. Likewise, these parameters were comparable during PACs between the ECV and control group (lower left panel). †Non-normally distributed. cm/s = centimeters per second; mm = millimeter; ms = millisecond; AF = atrial fibrillation; AT = activation time; BB = Bachmann's bundle; cCDCB = continuous lines of conduction delay and block; CB = conduction block; CD = conduction delay; CT = conduction time; CV = conduction velocity; ECV = electrical cardioversion; LA = left atrium; LAT = local activation times; PAC = premature atrial complexes; PVA = pulmonary vein area; RA = right atrium; SR = sinus rhythm; TAT = total activation time.

Transvenous electrical cardioversion of atrial fibrillation in horses: Horse and procedural factors correlated with success and recurrence

Background

Transvenous electrical cardioversion (TVEC) is 1 of the main treatment options for atrial fibrillation (AF) in horses. Large‐scale studies on factors affecting success and prognosis have primarily been performed in Standardbred populations.

Hypothesis/Objectives

To determine factors affecting cardioversion success, cardioversion difficulty and recurrence in a predominant Warmblood study sample.

Animals

TVEC records of 199 horses.

Methods

Retrospective study of TVEC procedures of horses admitted for AF without severe echocardiographic abnormalities. Horse and procedural factors for success and cumulative amount of energy (≤ 600 J vs > 600 J) were determined using multivariable logistic regression. A survival analysis was performed to determine risk factors for recurrence.

Results

Two hundred and thirty‐one TVEC procedures were included, with a 94.4% success rate and 31.9% recurrence rate (51/160). Mitral regurgitation (OR 0.151, 95% CI 0.032‐0.715, P = .02) and AF cycle length (OR 1.05, 95% CI 1.01‐1.09, P = .02) were independent determinants for success. Catheter type (OR 0.154, 95% CI 0.074‐0.322, P < .001), previous AF episode (OR 3.10, 95% CI 1.20‐8.01, P = .02), tricuspid regurgitation (OR 2.54, 95% CI 1.25‐5.13, P = .01), and body weight (OR 1.009, 95% CI 1.003‐1.015, P = .004) were significantly correlated with cumulative amount of energy delivered. Significant risk factors for recurrence after a first AF episode were sex (stallion; HR 3.05, 95% CI 1.34‐6.95, P = .008), mitral regurgitation (HR 1.91, 95% CI 1.08‐3.38, P = .03), and AF duration (HR 1.001, 95% CI 1.0001‐1.0026, P = .04).

Conclusions and Clinical Importance

Both horse and procedural factors should be considered when assessing treatment options and prognosis in horses with AF.

Deep Learning Approaches to Detect Atrial Fibrillation Using Photoplethysmographic Signals: Algorithms Development Study

Background

Wearable devices have evolved as screening tools for atrial fibrillation (AF). A photoplethysmographic (PPG) AF detection algorithm was developed and applied to a convenient smartphone-based device with good accuracy. However, patients with paroxysmal AF frequently exhibit premature atrial complexes (PACs), which result in poor unmanned AF detection, mainly because of rule-based or handcrafted machine learning techniques that are limited in terms of diagnostic accuracy and reliability.

Objective

This study aimed to develop deep learning (DL) classifiers using PPG data to detect AF from the sinus rhythm (SR) in the presence of PACs after successful cardioversion.

Methods

We examined 75 patients with AF who underwent successful elective direct-current cardioversion (DCC). Electrocardiogram and pulse oximetry data over a 15-min period were obtained before and after DCC and labeled as AF or SR. A 1-dimensional convolutional neural network (1D-CNN) and recurrent neural network (RNN) were chosen as the 2 DL architectures. The PAC indicator estimated the burden of PACs on the PPG dataset. We defined a metric called the confidence level (CL) of AF or SR diagnosis and compared the CLs of true and false diagnoses. We also compared the diagnostic performance of 1D-CNN and RNN with previously developed AF detectors (support vector machine with root-mean-square of successive difference of RR intervals and Shannon entropy, autocorrelation, and ensemble by combining 2 previous methods) using 10 5-fold cross-validation processes.

Results

Among the 14,298 training samples containing PPG data, 7157 samples were obtained during the post-DCC period. The PAC indicator estimated 29.79% (2132/7157) of post-DCC samples had PACs. The diagnostic accuracy of AF versus SR was 99.32% (70,925/71,410) versus 95.85% (68,602/71,570) in 1D-CNN and 98.27% (70,176/71,410) versus 96.04% (68,736/71,570) in RNN methods. The area under receiver operating characteristic curves of the 2 DL classifiers was 0.998 (95% CI 0.995-1.000) for 1D-CNN and 0.996 (95% CI 0.993-0.998) for RNN, which were significantly higher than other AF detectors (P<.001). If we assumed that the dataset could emulate a sufficient number of patients in training, both DL classifiers improved their diagnostic performances even further especially for the samples with a high burden of PACs. The average CLs for true versus false classification were 98.56% versus 78.75% for 1D-CNN and 98.37% versus 82.57% for RNN (P<.001 for all cases).

Conclusions

New DL classifiers could detect AF using PPG monitoring signals with high diagnostic accuracy even with frequent PACs and could outperform previously developed AF detectors. Although diagnostic performance decreased as the burden of PACs increased, performance improved when samples from more patients were trained. Moreover, the reliability of the diagnosis could be indicated by the CL. Wearable devices sensing PPG signals with DL classifiers should be validated as tools to screen for AF.

The Stress-Response MAP Kinase Signaling in Cardiac Arrhythmias

Stress-response kinases, the mitogen-activated protein kinases (MAPKs) are activated in response to the challenge of a myriad of stressors. c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinases (ERKs), and p38 MAPKs are the predominant members of the MAPK family in the heart. Extensive studies have revealed critical roles of activated MAPKs in the processes of cardiac injury and heart failure and many other cardiovascular diseases. Recently, emerging evidence suggests that MAPKs also promote the development of cardiac arrhythmias. Thus, understanding the functional impact of MAPKs in the heart could shed new light on the development of novel therapeutic approaches to improve cardiac function and prevent arrhythmia development in the patients. This review will summarize the recent findings on the role of MAPKs in cardiac remodeling and arrhythmia development and point to the critical need of future studies to further elucidate the fundamental mechanisms of MAPK activation and arrhythmia development in the heart.

Vernakalant-facilitated electrical cardioversion: comparison of intravenous vernakalant and amiodarone for drug-enhanced electrical cardioversion of atrial fibrillation after failed electrical cardioversion

AIMS

Electrical cardioversion is one cornerstone for the rhythm control strategy of atrial fibrillation (AF), which is, however, hampered by immediate AF recurrence (IRAF) or failed electrical cardioversion (FECV). We aimed to investigate the potential role of vernakalant for facilitated electrical cardioversion in cardioversion-resistant AF.

METHODS AND RESULTS

The subjects of this study were 63 patients referred to the Heart Centre Leipzig between November 2011 and May 2014 for transthoracic electrical cardioversion of AF. All patients experienced after antiarrhythmic-naïve electrical cardioversion either IRAF (n = 44; 70%) or FECV (n = 19; 30%). After drug infusion, electrical cardioversion was successful in 66.7% of vernakalant-treated as opposed to 46.7% of amiodarone-treated patients (P = 0.109). Multivariate analysis revealed treatment with vernakalant (OR 0.057, 95% CI 0.006-0.540, P = 0.013), treatment with ACEI or ARB (OR 0.101, 95% CI 0.015-0.691 P = 0.019), and IRAF after initial CV (OR 0.047, 95% CI 0.004-0.498, P = 0.011) as predictors for successful, drug-facilitated electrical cardioversion. Subgroup analysis of 18 patients with previous AF ablation revealed a significantly higher success rate of electrical cardioversion after infusion of vernakalant than after infusion of amiodarone (66.7 vs. 11.1%, P = 0.016).

CONCLUSION

Vernakalant may therefore be considered as a useful agent for facilitated electrical cardioversion in cardioversion-resistant AF.

SR calcium handling dysfunction, stress-response signaling pathways, and atrial fibrillation

Atrial fibrillation (AF) is the most common sustained arrhythmia. It is associated with a markedly increased risk of premature death due to embolic stroke and also complicates co-existing cardiovascular diseases such as heart failure. The prevalence of AF increases dramatically with age, and aging has been shown to be an independent risk of AF. Due to an aging population in the world, a growing body of AF patients are suffering a diminished quality of life and causing an associated economic burden. However, effective pharmacologic treatments and prevention strategies are lacking due to a poor understanding of the molecular and electrophysiologic mechanisms of AF in the failing and/or aged heart. Recent studies suggest that altered atrial calcium handling contributes to the onset and maintenance of AF. Here we review the role of stress-response kinases and calcium handling dysfunction in AF genesis in the aged and failing heart.

Contemporary approach to electrical and pharmacological cardioversion of atrial fibrillation

In patients with atrial fibrillation (AF), a rhythm-control strategy may be adopted when there are unacceptable symptoms from AF, failure of rate control, and/or the presence of comorbidities, such as heart failure, that may improve with restoration of sinus rhythm. When a rhythm-control strategy is chosen and the patient is in persistent AF, cardioversion will be necessary to convert the rhythm to sinus. Patients with AF present for > 48 hours must be effectively anticoagulated both prior to and after cardioversion. With newer oral anticoagulants, achieving effective anticoagulation is faster and more reliable, with no requirement for blood test monitoring. Cardioversion can be accomplished either electrically or pharmacologically, and in some cases, electrical cardioversion may be facilitated pharmacologically. Electrical cardioversion has a higher success rate compared with pharmacological cardioversion in the short-term. Pharmacological cardioversion is usually accomplished with intravenous ibutilide, oral flecainide or propafenone, or intravenous amiodarone. Oral amiodarone and dofetilide also result in chemical cardioversion in some patients over a longer period of time. Long-term success in the maintenance of sinus rhythm post-cardioversion can be increased with the use of antiarrhythmic drugs. Alternatively, when AF is recurrent and symptomatic despite the use of antiarrhythmic drugs, catheter ablation is a reasonable option for many patients. Cardioversion may be incorporated into the management approach of persistent AF when the primary therapeutic option chosen is catheter ablation.

Burden and timing of premature atrial contractions after electrical cardioversion of persistent atrial fibrillation do not predict its recurrence

BACKGROUND

The heart is susceptible to recurrence of atrial fibrillation (AF) during the period immediately following conversion to sinus rhythm (SR). It is less clear whether various onset or trigger mechanisms can predict AF recurrence after direct current (DC) cardioversion of persistent AF.

METHODS

In this study, 172 patients (117 men), mean age 69 +/- 11 y, and with persistent AF underwent elective electrical cardioversion. A detailed analysis was made of the heart rhythm and potential AF trigger mechanisms based on 5 min electrocardiogram (ECG) recordings after conversion.

RESULTS

Of 151 patients discharged in SR, 45 (30%) had a recurrence of AF within 1 wk. Premature atrial contractions (PACs) were the most common potential trigger, occurring on an average of 3/min. They were equally frequent in patients with and without immediate and early reinitiation of AF, and in patients with and without AF recurrence at the 1-wk follow-up visit. Other trigger mechanisms were too infrequent to allow conclusions.

CONCLUSION

Premature atrial contractions were the most common potential trigger mechanism occurring immediately after cardioversion in patients with persistent AF. However, they neither predicted immediate and/or early reinitiations, nor recurrences during the first wk after cardioversion.

Clinical importance of short-long-short sequences: analysing the mode of onset of ventricular tachycardias and atrial fibrillation

Clinical importance of atrial and ventricular ectopic beats are investigated in some experimental and clinical trials. They are common and occur in a broad spectrum of the population. This includes patients without structural heart disease and those with any form of cardiac disease, independent of severity. Although we know something about the mechanisms and etiology of serious ventricular arrhythmias and atrial fibrillation, we don't know a lot about mode of onset of those arrhythmias. Can short-long-short sequences, related ectopic beats predict AF and ventricular tachycardias in some selected groups of patients? In this paper we will try to answer this important question.

Electrical and pharmacologic cardioversion for atrial fibrillation

In this article, electrical and pharmacologic cardioversion for atrial fibrillation is described in detail. Indications for cardioversion and management of pericardioversion anticoagulation also are discussed. Finally, management strategies for immediate recurrence of atrial fibrillation and cardioversion failure are offered.

Transvenous electrical cardioversion of atrial fibrillation in six horses using custom made cardioversion catheters

Pharmacological conversion of atrial fibrillation (AF) to sinus rhythm in horses can be difficult. The objective of this study was to investigate the feasibility of transvenous electrical cardioversion with custom made catheters in eight horses, of which three had failed cardioversion using quinidine sulfate. Two cardioversion catheters and one pacing/sensing electrode were inserted via the right jugular vein and placed using ultrasound guidance into the left pulmonary artery, the right atrium and the right ventricle, respectively. Because immediate recurrence of AF was encountered in the second horse treated, pre-treatment with amiodarone was given to each of the remaining six horses. Induction of general anaesthesia was associated with dislocation of the cardioversion catheter in three horses, requiring a second catheterisation procedure. During general anaesthesia, biphasic R wave synchronised shocks of up to 360 J were delivered between both cardioversion electrodes. In six horses (75%), including two which had failed quinidine sulfate treatment, sinus rhythm was restored with a mean energy level of 295+/-62 J. No side effects were observed. Blood analysis 3 h after cardioversion revealed normal parameters, including cardiac troponin I values. Transvenous electrical cardioversion of atrial fibrillation with custom made cardioversion catheters can be considered as a treatment option for atrial fibrillation in horses, especially when conventional drugs fail.

Can short-long-short sequences predict atrial fibrillation in acute inferior myocardial infarction?

Short-long-short sequences (SLSS), related to atrial ectopic beats (AEBs), predict the recurrence of atrial fibrillation (AF) in some clinical situations. We investigated whether SLSS predict the occurrence of AF in acute phase of inferior myocardial infarction (MI). In patients who developed AF AEBs were more frequent. We concluded that the presence of frequent SLSS could be predictors or preceding factors of the occurrence of AF in acute inferior MI.

Prospective randomized trial of transthoracic versus low-energy internal cardioversion in persistent atrial fibrillation: long term follow-up

Low energy internal cardioversion (ICV) is a relatively new method. This report describes the long-term follow-up results of a prospective randomized comparison of low energy ICV and transthoracic cardioversion (TT CV) in patients with persistent atrial fibrillation (AF). Fifty-two patients (mean age, 60.6 +/- 10.1 years, 23 males) with persistent AF were randomly assigned to either TT (n = 26) or ICV (n = 26). The baseline characteristics of the 2 groups were similar. Transthoracic CV was performed under sedation with hand-held electrodes in the apex-anterior position and high energy (100-360 J) monophasic shocks. ICV was performed by a dedicated balloon-directed catheter utilizing truncated, biphasic shocks of low energy (1-15 J). Sinus rhythm (SR) was restored in 24/26 (92%) patients in the ICV group and in 22/26 (85%) patients in the TT CV group (P > 0.05). Immediate recurrence of AF (IRAF), defined as reappearance of AF within 2 minutes of successful CV, occurred in 5 patients (21%) in the ICV group and in 1 patient (4.5%) in the TT group (P > 0.05). Successfully cardioverted patients in whom no IRAF occurred were followed-up for 18 months under both warfarin and Class 1 or 3 antiarrhythmic drugs, as guided by the current ACC/AHA/ESC Guidelines. The rate of SR at 1, 3, 6, 12, and 18 months of follow-up was not significantly different between the 2 groups, and in an intention-to-treat analysis at 18 months, SR was present in 6 patients (23%) in the ICV group and in 10 patients (38%) in the TT group (P > 0.05). The majority of AF recurrences occurred within a month of successful CV in both groups (8/12 [67%] in the TT group and 15/18 [83%] in the ICV group, P > 0.05). The mortality, thromboembolic, and bleeding complication rates were similar in the 2 groups. In this prospective randomized comparison of TT and low energy ICV in patients with persistent AF, the 18-month rates of SR and major adverse clinical events were found to be similar.

Late-phase 3 EAD. A unique mechanism contributing to initiation of atrial fibrillation

Early (EAD) and delayed (DAD) afterdepolarizations-induced triggered activity is capable of initiating and maintaining cardiac arrhythmias. EAD-induced triggered responses are traditionally thought to be involved in the generation of ventricular arrhythmias under long QT conditions and are precipitated by bradycardia or long pauses. In contrast, DAD-induced triggered activity commonly underlies arrhythmias precipitated by tachycardia. Spontaneous release of calcium from the sarcoplasmic reticulum (SR) secondary to cellular calcium overload induces DADs and some forms of EADs. Recent studies from our laboratory have uncovered a novel mechanism giving rise to triggered activity, termed "late-phase 3 EAD," which combines properties of both EAD and DAD, but has its own unique character. Late-phase 3 EAD-induced triggered extrasystoles represent a new concept of arrhythmogenesis in which abbreviated repolarization permits "normal SR calcium release" to induce an EAD-mediated closely coupled triggered response, particularly under conditions permitting intracellular calcium loading. This review briefly describes the mechanisms and properties of late-phase 3 EADs, how they differ from conventional EADs and DADs, as well as their role in the initiation of cardiac arrhythmias, such as atrial fibrillation.

Electrical cardioversion of atrial fibrillation: different methods for a safe and effective technique

Atrial fibrillation is the most common cardiac arrhythmia observed in clinical practice. Many different therapeutic approaches are available at present but none may be considered the gold standard treatment. Antiarrhythmic drugs are not very effective agents to cardiovert persistent atrial fibrillation and, therefore, the technique most frequently used to restore sinus rhythm is external direct current cardioversion, which has proved to be safe and very effective. Esophageal cardioversion is an alternative method that could obviate some of the limitations of the external technique, such as the high energy required, need for anesthesia and longer hospital stay. Another technique performed during the last two decades is internal cardioversion, but at present, the advantage of this technique is limited to the small proportion of cases of unsuccessful external cardioversion.

Supraventricular ectopy and recurrence of atrial fibrillation after electrical cardioversion

AIMS

Paroxysmal atrial fibrillation (AF) is usually preceded by a premature atrial complex (PAC). We hypothesized that patients with a high frequency of atrial ectopic activity after restoration of sinus rhythm following direct current cardioversion would be more likely to experience recurrence of AF.

METHODS AND RESULTS

Forty-four patients with documented persistent AF were studied. A 24 h Holter recording was performed from the day of external direct current cardioversion. Patients were reviewed at 1 week, 1 month, and 6 months. After 6 months, 59% of patients had experienced a recurrence of AF. Neither the frequency of PACs nor the frequency or duration of supraventricular tachycardia (SVT) episodes predicted AF recurrence (P=0.60, 0.30, and 0.42, respectively). There was a trend towards maximum rate of SVT predicting recurrence of AF (P=0.08).

CONCLUSION

Frequency of supraventricular ectopy or the number and length of SVT runs in the 24 h after restoration of sinus rhythm are not strong predictors of recurrence of AF after electrical cardioversion. A larger study would be required to detect a small predictive effect.

New Insights Into the Initiation of Atrial Fibrillation

BACKGROUND

This study investigated onset scenarios of atrial fibrillation (AF), the first phase of the Atrial Fibrillation Therapy (AFT) trial, to determine potential arrhythmogenic triggers as targets for atrial pacing algorithms that have been proposed for prevention of AF.

METHODS AND RESULTS

Ninety-eight patients (58 men; age 65+/-11 years) with recurrent, symptomatic, drug-refractory AF and a conventional pacemaker indication in 31 of 98 received a dual-chamber pacemaker. Using novel diagnostic pacemaker features AF onset scenarios were prospectively evaluated in 612 AF episodes during a 2-month monitoring period, with atrial pacing limited to 40 bpm. The most common onset scenario was premature atrial complexes (PACs) before AF (48% onsets per patient), followed by bradycardia (33%), sudden onset (17%), and tachycardia (0%). Combinations of onset scenarios were frequent (median 2 different scenarios per patient). A main study finding was the significance of repetitive AF, with 33% of onsets per patient being initiated within 5 minutes of a previous AF episode. Sudden onsets were more frequent among patients with than without repetitive AF (24% versus 0% onsets per patient, P=0.011), whereas the proportion of PACs before AF was not statistically different (50% versus 37%, P=0.52); however, patients with repetitive AF had more PACs per hour (72 versus 29, P=0.023) and a higher number of AF episodes per day (17 versus 0, P=0.001) and were more likely to have at least 1 PAC-related onset (90% versus 53%, P<0.0001).

CONCLUSIONS

Novel diagnostic pacemaker features allowed a detailed individual analysis of rate and rhythm changes before AF and thus uncovered a substantial intraindividual and interindividual variability of AF onset scenarios.

Impact of atrial fibrillation duration on postcardioversion recurrence

BACKGROUND

"Begetting," a mechanistic tenet of atrial fibrillation (AF), stipulates that the rate of recurrence of AF after cardioversion is proportional to the preceding arrhythmia duration. However, recent reports suggest that, for brief durations, the incidence of early recurrence of AF (ERAF) is inversely proportional to duration. These reports were based on potentially biased data.

OBJECTIVES

We performed a prospective study to examine the impact of AF duration on postcardioversion recurrence.

METHODS

Forty-four patients underwent placement of an implantable cardioverter-defibrillator (ICD) capable of delivering patient-elicited AF cardioversion shocks. Subsequently, in the ambulatory setting, the timing of shocks in relationship to perceived AF onset was randomly assigned within individuals to early (as soon as possible) or delayed (1 day later).

RESULTS

During a follow-up averaging 199 days per patient, a total of 61 AF episodes among 17 patients occurred for which a patient-elicited cardioversion shock was delivered. Twenty-three shocks were delivered using early protocol (mean 6.8 hours after AF onset), and 38 shocks were delivered using delayed protocol (mean 34.7 hours after AF onset). The incidence of ERAF was significantly lower using the delayed protocol.

CONCLUSION

A strategy of approximately 24-hour delay in cardioversion shock timing decreased the incidence of ERAF, relative to a shock delivered within a few hours of AF onset. This observation has important mechanistic and therapeutic implications.

A retrospective evaluation of transthoracic biphasic electrical cardioversion for atrial fibrillation in dogs

OBJECTIVES

To evaluate safety, efficacy, and clinical usefulness of biphasic transthoracic cardioversion for management of dogs with atrial fibrillation (AF).

BACKGROUND

In dogs AF is usually managed with heart rate control rather than by restoration of sinus rhythm (SR). However, restoration of SR has potential advantages of improving cardiac output and reducing ventricular filling pressures, and biphasic cardioversion provides an improved benefit/risk ratio compared to traditional monophasic cardioversion.

ANIMALS, MATERIALS AND METHODS

Retrospective analysis of data from 39 dogs with spontaneous AF managed with biphasic transthoracic cardioversion was done. Conversion characteristics, adverse effects, and duration of SR were evaluated. Effects of heart disease and pretreatment with amiodarone on success of cardioversion and on duration of SR were also evaluated.

RESULTS

Restoration of SR was achieved in 36 of 39 dogs (92.3%). Presence of heart disease or atrial enlargement had no effect on cardioversion characteristics or ability to restore SR. Median duration of SR following cardioversion and treatment with amiodarone was 120 days. Dogs with lone AF remained in SR longer than those with heart disease.

CONCLUSIONS

Biphasic cardioversion is safe and effective. Although duration of SR varied, a majority of dogs remained in SR long enough to benefit.

Randomized comparison of anterolateral versus anteroposterior electrode position for biphasic external cardioversion of atrial fibrillation

BACKGROUND

In biphasic external cardioversion (CV) of atrial fibrillation (AF), the influence of different electrode positions on efficacy and incidence of early recurrent atrial fibrillation is not known. This study compared anteroposterior (AP) vs anterolateral (AL) electrode positioning.

METHODS

Consecutive patients referred for CV of persistent AF were randomized either to an AP or an AL electrode position. Biphasic external CV was performed with standardized electrode positions and rising energy delivery.

RESULTS

Both groups (N = 123, mean age 66 years, 71% male, 83% with structural cardiovascular disease or hypertension) did not differ concerning age, sex, body mass index, chronic antiarrhythmic therapy, duration of AF, left ventricular ejection fraction, and left atrial diameter. Cumulative success rates were comparable (AP 94.9% vs AL 95.2%, P = ns). First-shock efficacy did not differ (AP 78.3% vs AL 74.6%, P = ns). Early recurrent atrial fibrillation (AF relapse < 1 minute after successful CV) occurred in 8.1% (AP 11.6% vs AL 4.8%, P = ns). Mean number of shocks was 1.3 per patient with the AP configuration and 1.4 per patient with the AL configuration (P = ns). Mean cumulative energy delivery was also comparable (AP 171 WS vs AL 198 WS, P = ns).

CONCLUSIONS

Both electrode positions are similar in biphasic external CV of AF with regard to acute success and early recurrent atrial fibrillation. Also, the number of shocks needed and energy delivery are comparable with both electrode configurations.

Defective Cardiac Ryanodine Receptor Regulation During Atrial Fibrillation

Background— Ca 2+ leak from the sarcoplasmic reticulum (SR) may play an important role in triggering and/or maintaining atrial arrhythmias, including atrial fibrillation (AF). Protein kinase A (PKA) hyperphosphorylation of the cardiac ryanodine receptor (RyR2) resulting in dissociation of the channel-stabilizing subunit calstabin2 (FK506-binding protein or FKBP12.6) causes SR Ca 2+ leak in failing hearts and can trigger fatal ventricular arrhythmias. Little is known about the role of RyR2 dysfunction in AF, however.

Methods and Results— Left and right atrial tissue was obtained from dogs with AF induced by rapid right atrial pacing (n=6 for left atrial, n=4 for right atrial) and sham instrumented controls (n=6 for left atrial, n=4 for right atrial). Right atrial tissue was also collected from humans with AF (n=10) and sinus rhythm (n=10) and normal cardiac function. PKA phosphorylation of immunoprecipitated RyR2 was determined by back-phosphorylation and by immunoblotting with a phosphospecific antibody. The amount of calstabin2 bound to RyR2 was determined by coimmunoprecipitation. RyR2 channel currents were measured in planar lipid bilayers. Atrial tissue from both the AF dogs and humans with chronic AF showed a significant increase in PKA phosphorylation of RyR2, with a corresponding decrease in calstabin2 binding to the channel. Channels isolated from dogs with AF exhibited increased open probability under conditions simulating diastole compared with channels from control hearts, suggesting that these AF channels could predispose to a diastolic SR Ca 2+ leak.

Conclusions— SR Ca 2+ leak due to RyR2 PKA hyperphosphorylation may play a role in initiation and/or maintenance of AF.

Determinants and Prognostic Significance of Immediate Atrial Fibrillation Recurrence Following Cardioversion in Patients Undergoing Pulmonary Vein Isolation

BACKGROUND

Immediate recurrence of atrial fibrillation (IRAF) occurs frequently after electrical cardioversion, its electrophysiological determinants and prognostic significance have, however, not been studied in detail. This study aimed to explore (1) the association of IRAF with clinical characteristics, pulmonary vein (PV) arrhythmogenicity as well as atrial electrophysiologic properties and (2) the prognostic significance of IRAF for outcome of PV isolation for atrial fibrillation (AF).

METHODS AND RESULTS

The subjects of this study were 41 consecutive patients (30 males, 11 females) who underwent PV isolation for drug-refractory AF. Following successful initial cardioversion, 19 patients (46%) had IRAF within 2 minutes. Coupling intervals of AF reinitiating beats arising from PVs were shorter (386 +/- 39 vs 490 +/- 136 ms, P = 0.008) and prematurity indices (0.38 +/- 0.06 vs 0.51 +/- 0.12, P = 0.01) smaller than those of premature beats not initiating AF. Patients with IRAF had more frequently AF duration <1 month, a longer P-wave duration, and a longer mid coronary sinus AF cycle length. Multivariate regression analysis revealed coronary sinus AF cycle length (beta= 0.186, P = 0.049), which was closely correlated with conduction time along the coronary sinus (R = 0.716, P = 0.003) to be independently associated with IRAF. While early AF recurrence rate (within the first 5 days) following the procedure was higher in the IRAF group (53 vs 18%, P = 0.02), outcome was not different between the two groups thereafter.

CONCLUSIONS

(1) IRAF is common in patients undergoing PV isolation for AF, (2) is initiated by premature atrial beats with short coupling intervals, and (3) seems to be associated with conduction disturbances along the coronary sinus. It reflects susceptibility of arrhythmia recurrence within the first 5 days after the procedure, but not thereafter.

Impact of biphasic electrical cardioversion of atrial fibrillation on early recurrent atrial fibrillation and shock efficacy

INTRODUCTION

Early recurrent atrial fibrillation (ERAF) after external cardioversion of atrial fibrillation (AF) occurs in 12% to 26% of patients. Whether biphasic cardioversion has an impact on the incidence of ERAF after cardioversion of AF is unclear.

METHODS AND RESULTS

Consecutive patients (n = 216, mean age 66 years, 71% male, 88% with structural cardiovascular disease or hypertension) underwent cardioversion with a biphasic (Bi) or monophasic (Mo) shock waveform in randomized fashion. Energies used were 120-150-200-200 Ws (Bi) or 200-300-360-360 Ws (Mo). The two study groups (Bi vs Mo) did not differ with regard to age, sex, body mass index, underlying cardiovascular disease, left atrial diameter, left ventricular ejection fraction, duration of AF fibrillation, and antiarrhythmic drug therapy. Mean delivered energy was significantly lower in the Bi group (Bi: 186 +/- 143 Ws vs Mo: 324 +/- 227 Ws; P < 0.001). Overall incidence of ERAF (AF relapse within 1 minute after successful cardioversion) was 8.9% and showed no difference between the two groups (Bi: 8.1% vs Mo: 9.7%, P = NS). Cardioversion was successful in 95.4% of patients. The success rate was comparable in both groups (Bi: 94.3% vs Mo 96.8%; P = NS). First shock efficacy did not differ between Bi and Mo (76.4% vs 67.7%; P = NS). Mean number of shocks were 1.4 shocks per patient in both groups.

CONCLUSION

Biphasic cardioversion allows comparable success rates with significantly lower energies. However, the incidence of ERAF is not influenced by biphasic cardioversion. With the energies used, biphasic and monophasic shock waveforms are comparable with regard to first shock and cumulative shock efficacy.

Efficacy of internal cardioversion for chronic atrial fibrillation in patients with and without left ventricular dysfunction

Internal cardioversion can restore sinus rhythm with energies below 6-10 J, often without anaesthesia/sedation. We investigated its safety and short-/medium-term efficacy in patients with persistent atrial fibrillation (AF) with left ventricular dysfunction (defined as ejection fraction < or = 40%). Among 34 patients with persistent AF who agreed to receive internal cardioversion, 16 had left ventricular dysfunction and 18 did not (the groups were similar as regards age, duration of AF and pretreatment with amiodarone). Internal CV was performed delivering 3.0/3.0-ms biphasic shocks between coil catheters using a step-up protocol. Sinus rhythm was always restored. General anaesthesia (administered only when discomfort was not tolerated) was required only in 2 of the 16 (12.5%) patients with left ventricular dysfunction. The defibrillation threshold was similar in patients with and without left ventricular dysfunction (10.2+/-6.9 vs. 8.4+/-4.9 J; p=0.37). Short-term (within 72 h) AF recurrence rates in the presence and absence of left ventricular dysfunction were 19% (3/16) and 6% (1/18), respectively (p=0.51). After cardioversion, all patients received antiarrhythmic drugs (mostly amiodarone in patients with left ventricular dysfunction and class IC agents in the remainder). With mean follow-up periods of about 220 days, AF recurrence rates among patients with and without left ventricular dysfunction were 50% (8/16) and 28% (5/18), respectively (p=0.328). We conclude that even in patients with left ventricular dysfunction, internal CV is safe and effective, minimizing risks from anaesthesia. Although these patients may have a higher risk of short- or medium-term AF recurrence, 6-month maintenance of sinus rhythm is possible in about 50% of cases.

Randomized study of surgery for patients with permanent atrial fibrillation as a result of mitral valve disease

BACKGROUND

The Cox Maze procedure has been used to treat atrial fibrillation in patients with mitral valve disease. Recently, ectopic foci, originating in the pulmonary veins, were demonstrated in patients with atrial fibrillation, and the indication was that their arrhythmia could have a focal origin. In the light of this new evidence, a simplified surgical technique to isolate the pulmonary veins was developed to eliminate permanent atrial fibrillation in patients undergoing mitral valve surgery. This study compares three surgical procedures proposed to maintain sinus rhythm after mitral valve surgery.

METHODS

A prospective clinical trial of 30 patients with mitral valve disease and permanent atrial fibrillation who had undergone mitral valve surgery were randomized in accordance with the type of surgery used on each: (1). associated en bloc isolation of pulmonary veins, (2). the Maze procedure, or (3). mitral valve correction alone. The preoperative clinical characteristics were similar in the three groups.

RESULTS

The overall postoperative complications were similar in all three groups. The cardiopulmonary bypass time and the aortic cross-clamping time were shorter in the control group, but this factor bore no relation to increased morbidity in the intervention groups. The relative risk of atrial fibrillation after surgery was 0.08 in the group undergoing isolation of pulmonary veins (p = 0.010; 95% confidence interval, 0.01 to 0.71) and 0.20 in the Maze group (p = 0.044; 95% confidence interval, 0.04 to 1.02) compared with the control group.

CONCLUSIONS

En bloc isolation of pulmonary veins associated with mitral valve surgery appears to be safe and just as effective as the Maze procedure in maintaining sinus rhythm in patients with permanent atrial fibrillation.

Increase in QT/QTc dispersion after low energy cardioversion of chronic persistent atrial fibrillation

BACKGROUND

The effects of atrial internal cardioversion on QT interval and QT dispersion (parameters associated with increased risk of ventricular tachyarrhythmias) are unknown. We investigated changes in QT interval, QTc and QT dispersion immediately after shock delivery for internal cardioversion in patients with chronic persistent atrial fibrillation.

METHOD

Twenty-two patients with chronic persistent atrial fibrillation (mean duration, 17+/-23 months) underwent transvenous low-energy internal atrial cardioversion with a step-up protocol of shocks delivered between catheters in the right atrium and coronary sinus. (successful shock, 7.2+/-4.2 J). RR interval, QT interval, QTc interval, QT dispersion, and QTc dispersion were all measured on three consecutive beats (at 75 mm/s on at least 9 of 12 leads) and then averaged both before and after (1) the last unsuccessful shock, and (2) sinus rhythm restoration.

RESULTS

All parameters remained similar in the minute before and after the last unsuccessful shock. At 1 min after the successful shock, abrupt increases in QT dispersion (+43.8% vs. pre-shock; P<0.001 at least significant difference analysis) and QTc dispersion (+30.0%; P<0.05) were observed, followed by a gradual return to pre-shock values at 15 min.

CONCLUSIONS

These findings strongly suggest the likely existence of a brief period of increased electrical vulnerability immediately after restoration of sinus rhythm by internal cardioversion. Particular caution should therefore be applied whenever class III antiarrhythmic drugs are administered immediately after successful internal atrial cardioversion.

Echocardiographic and electrocardiographic predictors for atrial fibrillation recurrence following cardioversion

INTRODUCTION

Identification of suitable candidates for cardioversion currently is not based on individual electrical and mechanical atrial remodeling. Therefore, this study analyzed the meaning of atrial fibrillatory rate obtained from the surface ECG (as a measure of electrical remodeling) and left atrial size (as measure of mechanical remodeling) for prediction of early atrial fibrillation (AF) recurrence following cardioversion.

METHODS AND RESULTS

Forty-four consecutive patients (26 men and 18 women, mean age 62 +/- 11 years, no antiarrhythmic medication at baseline) with persistent AF were studied. Fibrillatory rate was obtained from high-gain, high-resolution surface ECG using digital signal processing (filtering, QRST subtraction, Fourier analysis) before electrical cardioversion. Univariate and multivariate regression analysis revealed larger systolic left atrial area (Beta = 0.176, P = 0.031) obtained by precardioversion echocardiogram from the apical four-chamber view and higher atrial fibrillatory rate (Beta = 0.029, P = 0.021) to be independent predictors for AF recurrence (n = 13). Stratification based on the regression equation (electromechanical index [EMI] = 0.176 systolic left atrial area + 0.029 fibrillatory rate - 17.674) allowed identification of groups at low, intermediate, or high risk. No patient with an EMI < -1.85 had early AF recurrence, as opposed to 78% with an EMI > -0.25. Intermediate results (40% recurrence rate) were obtained when the calculated EMI ranged between -1.85 and -0.25 (P < 0.001).

CONCLUSION

Fibrillatory rate obtained from the surface ECG and systolic left atrial area obtained by echocardiography may predict early AF recurrence in patients with persistent AF. These parameters might be useful in identifying candidates with a high likelihood of remaining in sinus rhythm after cardioversion.

Atrial fibrillation and cardiac surgery

PURPOSE OF REVIEW

To discuss the pathophysiology, risk factors, and treatments for atrial fibrillation occurring after cardiac surgery.

RECENT FINDINGS

Atrial fibrillation occurs frequently after cardiac surgery and it may lead to patient morbidity. Many variables have been suggested to be associated with this arrhythmia, but only advanced patient age can consistently identify risk for this complication. Immediate electrical cardioversion is indicated when the arrhythmia leads to hemodynamic instability or myocardial ischemia. Otherwise treatment is aimed at heart rate control, elective cardioversion with drugs or electrical means, and anticoagulation when the arrhythmia persists. Multiple investigations have evaluated methods for preventing postoperative atrial fibrillation, but only beta-adrenergic receptor blocking drugs have been consistently shown to be effective, and then not in all patients. Surgical treatments are increasingly being considered as a therapeutic means for ameliorating chronic atrial fibrillation. The use of these procedures has been simplified with the development of devices that can generate linear scars in the atrium and around the pulmonary vein orifices. These simplifications will allow for broader application of these techniques to patients undergoing other cardiac surgery (e.g. mitral valvular surgery).

SUMMARY

Atrial fibrillation is one of the most common complications of cardiac surgery. There are three major aims for treating atrial fibrillation: conversion to sinus rhythm, heart rate control, and anticoagulation. Only beta-blockers can be recommended for prophylaxis against postoperative atrial fibrillation. Further refinements in surgical treatments for atrial fibrillation may allow for wider applications of this therapy with lower rates of complications.

Mechanism of Immediate Recurrences of Atrial Fibrillation After Restoration of Sinus Rhythm

An immediate recurrence of AF may occur after restoration of sinus rhythm. Although pulmonary vein (PV) isolation has been shown to prevent immediate recurrence of AF, the specific trigger for immediate recurrence of AF has not been described. In 89 consecutive patients (mean age 53 +/- 11 years) who had sinus rhythm restored by spontaneous or transthoracic cardioversion in the course of a PV isolation procedure, electrograms recorded within a PV and in the adjacent left atrium were analyzed to determine the mechanism of initiation of immediate recurrence of AF. Immediate recurrence of AF was defined as a recurrence of AF within 90 seconds after restoration of sinus rhythm. There were 124 episodes of immediate recurrence of AF at a mean of 18 +/- 23 seconds after cardioversion. Recordings within the PV that triggered the immediate recurrence of AF were available in 23 (19%) of the 124 immediate recurrence of AF episodes. Among these 23 episodes of immediate recurrence of AF, all (100%) were triggered by a burst of PV tachycardia (P < 0.001). The coupling interval and prematurity index (coupling interval/preceding sinus cycle length) of the premature depolarizations that did and did not trigger immediate recurrence of AF were 246 +/- 67 ms and 0.30 +/- 0.11 vs 378 +/- 117 ms and 0.49 +/- 0.16, respectively (P < 0.01). Immediate recurrence of AF was abolished by PV isolation. The mechanism of immediate recurrence of AF is a burst of PV tachycardia, not a single premature depolarization. Immediate recurrence of AF identifies patients with AF in whom the PVs may play a major role in the initiation of AF.

Prevention of immediate reinitiation of atrial tachyarrhythmias by high-rate overdrive pacing: results from a prospective randomized trial

INTRODUCTION

Immediate reinitiation of atrial tachyarrhythmia (IRAT) is an important cause of failure to maintain sinus rhythm. IRAT prevention by overdrive pacing has not been evaluated in a prospective randomized trial.

METHODS AND RESULTS

Patients with a DDDRP pacemaker offering temporary atrial overdrive pacing after AT termination (Post Mode Switching Overdrive Pacing [PMOP]) were enrolled into the prospective PIRAT (Prevention of IRAT) trial if paroxysmal AT episodes occurred after implantation. PMOP was randomly activated (120 beats/min for 2 min) or inactive. After 3 months, device memory was interrogated, symptoms and quality of life assessed, and patients crossed over to the alternative treatment arm for another 3 months. Primary study endpoint was the number of AT episodes; secondary endpoints were the cumulative time in AT (AT burden), percentage of AT episodes with IRAT, symptoms, and quality of life with PMOP active versus inactive. In 37 patients (21 men; 69 +/- 9 years), there was no difference in the median number of AT episodes (0.37 vs 0.34 per day), AT burden (both 1%), percentage of episodes with IRAT (30%vs 28%), symptoms, and quality of life during PMOP off versus on. With PMOP active, 29% of 439 ATs restarted during and 18% before PMOP intervention. The PMOP-induced rate increase appeared to be associated with IRAT in 9% of AT episodes.

CONCLUSION

Automatic overdrive pacing after AT termination did not prevent IRAT, mainly due to insufficient overdrive suppression even at 120 beats/min and the delay between AT termination and PMOP intervention.

Recent advances in drug therapy for atrial fibrillation

Despite the major new insights into our knowledge of the mechanisms underlying initiation and perpetuation of atrial fibrillation (AF) gained in the last decade, the treatment of this common arrhythmia remains unsatisfactory in many patients. Although several new treatment modalities (e.g., internal cardioversion, pulmonary vein ablation, preventive pacing) have been developed, pharmacologic therapy remains the first-line therapy in most patients with AF. As illustrated by recent trials comparing rhythm control and rate control, current antifibrillatory drugs are hampered by a relatively low success rate in maintaining long-term sinus rhythm and the occurrence of proarrhythmic and other adverse events. This article discusses currently available antiarrhythmic drugs for rhythm and rate control, with special emphasis on more recently developed drugs and drugs still under development. Selective blockers of atrial ion channels (IKur and IK.ACh), multi-ion channel blockers, and selective A1-adenosine receptor antagonists are examples of the newer antiarrhythmic drugs that are expected to be more effective and safer than those currently available.

Clinical predictors and time course of arrhythmia recurrence in patients with early reinitiation of atrial fibrillation after successful internal cardioversion

Early reinitiation of atrial fibrillation (ERAF) was commonly observed after successful electrical cardioversion, however, the effect of ERAF on the subsequent time course of arrhythmia recurrence remains unclear. The aim of this study was to evaluate the clinical predictors and time course of AF recurrence with respect to the occurrence of ERAF after successful cardioversion. The clinical predictors and time course of AF recurrence were prospectively evaluated in 124 patients (94 men, 30 women; mean age 65 +/- 9 years) with persistent AF (mean AF duration 36 +/- 40 months), who underwent internal cardioversion. After cardioversion, all patients received treatment with sotalol and were monitored for AF recurrence. Successful restoration of sinus rhythm was achieved in 104 (84%) of 124 patients. ERAF was observed in 28 (27%) of 104 patients in whom 26 of them were successfully treated acutely with intravenous sotalol and repeated cardioversion. After a mean follow-up of 26 months, 29 (28%) of 104 patients remained in sinus rhythm. Kaplan-Meier analysis revealed a significantly poorer outcome with regard to the recurrence of AF in patients with ERAF (hazard ratio 1.7,P = 0.03) and in those with AF for more than 3 years (hazard ratio 1.6,P = 0.03). Despite treatment with sotalol, patients with ERAF had a significantly higher AF recurrence rate within the first day (13/26 [50%] vs 12/76 [16%],P < 0.01), but not during long-term follow-up (21/26 [81%] vs 52/76 [68%],P = 0.3). In contrast, patients with AF for more than 3 years had a similar AF recurrence rate within the first day (7/29 [24%] vs 18/73 [25%],P = 1.0), but a significantly higher recurrence rate during long-term follow-up (27/29 [93%] vs 46/73 [37%],P < 0.01). In conclusion, the occurrence of ERAF and long AF duration were independent predictors for AF recurrence after successful internal cardioversion. The difference in the time course of AF recurrence in patients with ERAF from those with long AF duration suggests distinct arrhythmogenic mechanisms.

P wave amplitude and duration may predict immediate recurrence of atrial fibrillation after internal cardioversion

BACKGROUND

Although internal cardioversion (IC) for atrial fibrillation (AF) is effective at restoring sinus rhythm, immediate recurrence (IR) of AF after IC is a major and largely unpredictable clinical problem. The purpose of the study was to determine the role of P wave duration and amplitude in prediction of IR of AF after IC. Forty-five consecutive patients undergoing IC for chronic AF were evaluated.

MATERIAL AND METHODS

After successful IC, 1-minute ECG recording was obtained in all patients. P wave duration and amplitude in Lead II and V1 were measured using computer. Forty patients (88%) had successful IC. Thirteen patients experienced IR of AF within 1 minute of restoring sinus rhythm.

RESULTS AND CONCLUSION

As a result, the incidence of IR of AF after IC was higher in the patients with shorter P wave amplitude (for lead II P<0.01, for V1 P<0.01) and larger P wave duration (for lead II P<0.01, for V1 P<0.05).

Immediate reinitiation of atrial tachyarrhythmias after spontaneous restoration of sinus rhythm in patients with an implanted monitoring device

Immediate reinitiation of atrial tachyarrhythmia (IRAT) has been observed after cardioversion. After spontaneous restoration of sinus rhythm (SR), incidence and characteristics of IRAT have not been described. Therefore, in patients with atrial tachyarrhythmias (ATs) and bradycardia, a pacemaker with dedicated memory functions was implanted. Devices were interrogated after 1 month and stored episodes of AT were analyzed: incidence of IRAT, duration and rate of the preceding episode, sinus rate before AT, coupling interval of atrial premature beats (APBs) initiating AT, and incidence of repetitive APBs. A potential association with IRAT was assessed for clinical characteristics. In 36 of 68 patients, stored electrograms confirmed correct detection of AT onset and termination in 545 episodes. IRAT was present in 212 (39%, 24 patients) episodes of AT. Episodes of AT preceding IRAT were longer than those before non-IRAT (156 vs 46 s, P < 0.001), and occurred during a higher atrial rate before onset of AT (cycle length 775 +/- 111 vs 856 +/- 133 ms, P < 0.001). The coupling interval of APBs initiating IRAT was shorter (502 +/- 83 vs 538 +/- 89 ms; P < 0.001) while the percentage of episodes with repetitive APBs before AT onset and the median atrial cycle length of the preceding AT were not different. On stepwise logistic regression analysis, none of the clinical factors evaluated independently predicted IRAT. In conclusion, IRAT is frequent after spontaneous restoration of SR. Changes of atrial electrophysiological properties promoting IRAT may already develop during AT of short duration.

Reinduction of atrial fibrillation immediately after termination of the arrhythmia is mediated by late phase 3 early afterdepolarization-induced triggered activity

BACKGROUND

Atrial fibrillation (AF) at times recurs immediately after termination of the arrhythmia. The mechanism(s) responsible for the extrasystole that reinduces AF is largely unknown. We hypothesized that abbreviation of action potential duration (APD) would permit very rapid rates of excitation, known to induce intracellular calcium loading, which in turn could promote delayed and/or early afterdepolarizations (EADs).

METHODS AND RESULTS

Acetylcholine (ACh, 1 micromol/L) was used to abbreviate atrial APD and permit rapid-pacing induction of AF in isolated coronary-perfused canine right atria. Transmembrane action potentials, pseudo-ECG, and tension development were recorded. AF or rapid pacing was associated with an increase in tonic tension. Termination of AF or rapid pacing (cycle length, 150 to 80 ms) resulted in a dramatic rise of phasic tension, prolongation of repolarization of the initial beats at the regular rate (cycle length, 700 ms), and the development of late phase 3 EADs and extrasystoles. These extrasystoles initiated AF in 15 cases (involving 9 right atria) within the first 11 seconds after termination of AF or rapid pacing. This novel EAD mechanism is observed only in association with marked APD abbreviation. The calcium channel blocker nifedipine reduced, and the sarcoplasmic reticulum calcium release blocker ryanodine eliminated, the post-rapid pacing-induced increase in phasic tension, late phase 3 EADs, and extrasystoles that initiate AF.

CONCLUSIONS

These data suggest that calcium overload conditions present after termination of vagally mediated AF contribute to the development of late phase 3 EAD-induced triggered activity and that this mechanism may be responsible for the extrasystolic activity that reinitiates AF.

Reverse structural and gap-junctional remodeling after prolonged atrial fibrillation in the goat

BACKGROUND

Prolonged atrial fibrillation (AF) results in electrical, structural, and gap-junctional remodeling. We examined the reversibility of the changes in (ultra)structure and gap junctions.

METHODS AND RESULTS

Four groups of goats were used: (1) sinus rhythm (SR), (2) 4 months' AF (4 mo AF), (3) 2 months' SR after 4 mo AF (2 mo post-AF), and (4) 4 months' SR after 4 mo AF (4 mo post-AF). Atria were characterized electrophysiologically, (ultra)structure was studied by light and electron microscopy, and structural and gap-junctional protein expression was studied by immunohistochemistry or Western blotting. The atrial effective refractory period had completely returned to normal values 2 mo post-AF. Induced AF episodes still lasted for minutes at 2 and 4 mo post-AF, compared with seconds in the SR group. Structural abnormalities were still present at 2 and 4 mo post-AF, although to a lesser extent. The increased atrial myocyte diameter was back to normal at 4 mo post-AF. The number of myocytes with severe myolysis had almost normalized 4 mo post-AF, whereas myocytes with mild myolysis remained significantly increased. Extracellular matrix area fraction after 4 mo AF was similar to SR. However, the extracellular matrix fraction per myocyte had increased after 4 mo AF and remained higher post-AF. Changes in expression of structural proteins were partially restored post-AF. The reduction of connexin 40 that was observed during AF was completely reversed at 4 mo post-AF.

CONCLUSIONS

Recovery from structural remodeling after 4 mo AF is a slow process and is still incomplete 4 mo post-AF. Several months post-AF, the duration of AF episodes is still prolonged (minutes).

Atrial pacing for the prevention and termination of atrial fibrillation

Atrial fibrillation (AF) affects about 2% of the general population and 8%-11% of those older than 65 years. The demand for effective therapeutic strategies for AF is anticipated to increase substantially as the proportion of the elderly population increases. Atrioventricular nodal ablation accompanied by permanent pacemaker implantation is an established option in elderly patients with intractable arrhythmia and poor ventricular rate control. However, it renders most patients pacemaker dependent and does not eliminate symptoms associated with loss of atrial transport or reduce the risk of stroke. The considerable limitations of rhythm or rate control strategies prompted interest in preventative atrial pacing, which may reduce the incidence of AF by either eliminating the triggers and/or by modifying the substrate of AF. Atrial or dual-chamber pacing has been proven to prevent or delay progression to permanent AF in elderly patients with sinus node dysfunction as compared with ventricular pacing. Patients with advanced atrial conduction delay may benefit from atrial resynchronization pacing. There may be additional benefits associated with the use of particular sites of pacing, specific pacing algorithms designed to target potential triggers of AF, and pace-termination of atrial tachycardia. Preventive and antitachycardia pacing algorithms incorporated in implantable cardioverter-defibrillators and pacemakers are currently under investigation and may offer a valuable alternative to antiarrhythmic drug therapy in elderly patients with left ventricular dysfunction at high risk of proarrhythmia or worsening heart failure. The evolution of hybrid therapy, in which two or more different strategies are employed in the same patient, may be the most effective approach to management of AF.