Onset mechanism of paroxysmal atrial fibrillation detected by ambulatory Holter monitoring

Autonomic Nervous System Activity before Atrial Fibrillation Onset as Assessed by Heart Rate Variability

Background

Neuromodulation has been shown to increase the efficacy of atrial fibrillation (AF) ablation procedures. However, despite its ability to influence the autonomic nervous system (ANS), the exact mechanism of action remains unclear. The activity of the ANS via the intracardiac nervous system (ICNS) can be inferred from heart rate variability (HRV). Therefore, this study aims to investigate the significance of changes in the ICNS prior to the onset of AF by analyzing the evolution of HRV in a large new cohort of patients.

Methods

We selected and annotated recordings with AF and atrial flutter from our database of 95,871 Holter recordings. Each recording included both sinus rhythm and one or more AF episodes. We computed parameters estimating parasympathetic activity (root mean square of successive RR interval differences (RMSSD) and percentage of successive RR intervals that differ by more than 50 ms (pNN50)), as well as HRV frequential parameters a few minutes before AF onset. To allow a minute-by-minute assessment of the parameter changes, we computed their values over 5-minute sliding windows, starting at 35 minutes before AF onset.

Results

The mean age of the whole group of patients was 71.1 ± 11.3 years (range 35-99), the total number of episodes was 1319 on 623 recordings from 570 patients, with an average of 2.1 ± 2.2 episodes per recording (range 1-17) and 2.3 ± 2.6 episodes per patient (range 1-21). The proportion of premature atrial contractions (PACs) increased from 4.8 ± 0.3%, 35 minutes before the onset of AF to 8.3 ± 0.4%, 5 minutes before the AF episode. We measured a statistically significant increase in very-low-frequency (VLF), low-frequency (LF), high-frequency (HF), RMSSD and pNN50 between 35 minutes and 5 minutes before AF onset.

Conclusions

Our data suggest that a significant short-term increase in vagal activity precedes most AF events. Dynamic changes in HRV parameters could be considered when determining the optimal neuromodulation strategies.

Impact of lifestyle risk factors on atrial fibrillation: Mechanisms and prevention approaches - A narrative review

Both the development and progression of atrial fibrillation (AF) are affected by a range of modifiable lifestyle risk factors. These key modifiable risk factors encompass obesity, hypertension, hypercholesterolemia, diabetes mellitus, smoking, chronic obstructive pulmonary disease, alcohol consumption, exercise, sedentary lifestyle and obstructive sleep apnoea. These lifestyle-dependent factors rarely exist in isolation, but rather exist together, exerting a complex influence on the development of AF. This comprehensive review elucidates the interplay and interdependency of these lifestyle factors in the arrhythmogenesis of AF, by exploring their role in AF substrate formation, modulating properties and triggering mechanisms. We emphasize the importance of targeted prevention strategies by discussing available literature on the effectiveness of treatment strategies targeting multiple risk factors. Additionally, the clinical impacts of integrated care, nurse-led care and mobile health are discussed in the context of lifestyle improvement. These management strategies have favourable applicability in both paroxysmal and persistent AF, and are also beneficial for patients receiving AF ablation. Despite the challenges accompanying lifestyle and prevention strategies, substantial benefits are apparent, such as improved quality of life and better ablation outcomes. This review further emphasizes the essential nature of awareness of appropriate lifestyle modifications as fundamental pillars in the management of individuals with AF.

When the Clock Strikes A-fib

Within the broad spectrum of atrial fibrillation (AF) symptomatology, there is a striking subset of patients with predominant or even solitary nocturnal onset of the arrhythmia. This review covers AF with nocturnal onset, with the aim of defining this distinctive subgroup among patients with AF. A periodicity analysis is provided showing a clear increased onset between 10:00 pm and 7:00 am. Multiple interacting mechanisms are discussed, such as circadian modulation of electrophysiological properties, vagal tone, and sleep disorders, as well as the potential interaction and synergism between these factors, to provide a better understanding of this clinical entity. Lastly, potential therapeutic targets for AF with nocturnal onset are addressed such as upstream therapy for underlying comorbidities, type of drug and timing of drug administration and pulmonary vein isolation, ablation of the ganglionated plexus, and autonomic nervous system modulation. Understanding the underlying AF mechanisms in the individual patient with nocturnal onset will contribute to patient-specific therapy.

Unusual atrial pacing induced by type II far-field p-wave sensing in a patient with complete atrioventricular block

An 88-year-old Japanese woman underwent DDD pacemaker (MicroPort KORA 250 DR, V lead: VEGA R52) implantation for complete atrioventricular block. A 12-lead electrocardiogram for a routine examination showed atrial pacing within the intrinsic P wave, followed by inhibition of ventricular pacing. Pacemaker interrogation revealed no abnormalities in the basic parameters; however, ventricular pacing was inhibited by far-field sensing of intrinsic atrial waves before atrial events; type II far-field P-wave sensing. As a result, unusual atrial pacing occurred due to the pause suppression algorithm, which is the one of the functions that prevent atrial fibrillation development.

Utility of short-time electrocardiogram to assess risk for atrial arrhythmia recurrence: Impact of atrial premature beat occurrence 1 day after pulmonary vein isolation for atrial fibrillation

INTRODUCTION

Atrial premature beats (APBs) are the trigger for atrial fibrillation (AF). We sought to investigate the clinical significance of APB occurrence 1 day after pulmonary vein isolation (PVI) for AF using a short-time electrocardiogram.

METHODS

A total of 206 patients undergoing PVI for paroxysmal AF were included. Electrocardiogram recording for 100 consecutive beats was performed 1 day after PVI. The patients were divided into two groups: those with reproducible APBs (≥1 beat) during reassessment (APB group, n = 49) or those without (non-APB group, n = 157). Late recurrence was defined as atrial tachyarrhythmia recurrence 3-12 months after PVI. The impact of APB occurrence on outcomes was investigated.

RESULTS

Late recurrence occurred in 19 patients (9.2%). The presence of low-voltage areas, left atrial volume, and recurrence rate were higher in the APB group than in the non-APB group. In the APB group, the patients with recurrence had lower prematurity index (PI, coupling interval of APB/previous cycle length) compared to those without. Receiver-operating characteristic analysis revealed PI (<59.3) to be a predictive factor of recurrence (area under the curve: 0.733). The study subjects were then reclassified into three groups according to the absence of APB occurrence (n = 157), presence thereof with PI ≥ 59.3 (n = 33), and presence with PI < 59.3 (n = 16). The multivariate Cox models revealed that APB with PI < 59.3 was an independent predictor for recurrence (hazard ratio, 8.735; p < 0.001).

CONCLUSION

A short-time electrocardiogram enables risk assessment for arrhythmia recurrence, and APB with low PI 1 day after PVI is a powerful predictor.

Atrial extrasystoles enhance low-voltage fractionation electrograms in patients with atrial fibrillation

BACKGROUND AND AIMS

Atrial extrasystoles (AES) provoke conduction disorders and may trigger episodes of atrial fibrillation (AF). However, the direction- and rate-dependency of electrophysiological tissue properties on epicardial unipolar electrogram (EGM) morphology is unknown. Therefore, this study examined the impact of spontaneous AES on potential amplitude, -fractionation, -duration, and low-voltage areas (LVAs), and correlated these differences with various degrees of prematurity and aberrancy.

METHODS AND RESULTS

Intra-operative high-resolution epicardial mapping of the right and left atrium, Bachmann's Bundle, and pulmonary vein area was performed during sinus rhythm (SR) in 287 patients (60 with AF). AES were categorized according to their prematurity index (>25% shortening) and degree of aberrancy (none, mild/opposite, moderate and severe). In total, 837 unique AES (457 premature; 58 mild/opposite, 355 moderate, and 154 severe aberrant) were included. The average prematurity index was 28% [12-45]. Comparing SR and AES, average voltage decreased (-1.1 [-1.2, -0.9] mV, P < 0.001) at all atrial regions, whereas the amount of LVAs and fractionation increased (respectively, +3.4 [2.7, 4.1] % and +3.2 [2.6, 3.7] %, P < 0.001). Only weak or moderate correlations were found between EGM morphology parameters and prematurity indices (R2 < 0.299, P < 0.001). All parameters were, however, most severely affected by either mild/opposite or severely aberrant AES, in which the effect was more pronounced in AF patients. Also, there were considerable regional differences in effects provoked by AES.

CONCLUSION

Unipolar EGM characteristics during spontaneous AES are mainly directional-dependent and not rate-dependent. AF patients have more direction-dependent conduction disorders, indicating enhanced non-uniform anisotropy that is uncovered by spontaneous AES.

Ablation of ectopic atrial foci for successful management of symptomatic bradycardia: A case series (bradycardia and ectopic atrial beats)

Atrial premature contractions (PACs) that block at the atrio-ventricular (AV) nodal level and occurring in a bigeminal frequency are recognized as a cause of symptomatic bradycardia. Appropriate suppression of the PACs often results in restoration of a regular rhythm with resolution of bradycardia-related symptoms. We report a series of three patients with non-conducted bigeminal PACs arising from the mitral annulus that resulted in symptomatic bradycardia and who were referred for consideration of cardiac pacing. Focal ablation suppressed PACs restoring a normal heart rate and resolution of symptoms without resorting to cardiac pacing.

Novel Score to Predict Very Late Recurrences After Catheter Ablation of Atrial Fibrillation

Various predictors of atrial fibrillation (AF) recurrence have been shown based on the baseline characteristics before catheter ablation (CA). This study aimed to develop a novel scoring system for predicting very late recurrences of AF (VLRAFs) after an initial CA, taking the postprocedural clinical data into account and reassessing VLRAFs in 12-month patients' condition using previously known preprocedural predictors of AF recurrences. We retrospectively studied 327 patients who underwent an initial CA with freedom from AF for over 12 months. We elucidated the predictors of VLRAFs and created a new score to predict VLRAFs in the discovery AF cohort (n = 181). Thereafter, we investigated whether the new scoring system could accurately predict VLRAFs in the validation AF cohort (n = 146). In the discovery AF cohort, VLRAFs were observed in 53 patients (29%) during the follow-up period (mean follow-up duration: 55 months). The univariate and multivariate Cox proportional-hazards model demonstrated that non-pulmonary vein foci, early recurrences of AF (ERAFs), atrial premature contraction (APC) burden ≥ 142/24 hours, and minimum prematurity index of the APCs ≤ 48% were associated with VLRAFs after CA. We created a new scoring system to predict VLRAFs, the n-PReDCt score (non-pulmonary vein: 1 point, early recurrences of AFs (Recurrences of AF in early phase after CA): 1 point, APC burden ≥ 142/24 hours: 1 point, and minimum prematurity index (= Coupling interval) of the APCs of ≤ 48%: 1 point). The n-PReDCt score was significantly associated with VLRAFs by a Kaplan-Meier analysis in the discovery AF and validation AF cohorts (p < 0.0001 and p < 0.0001, respectively).

Risk Factors for Atrial Fibrillation Progression

Atrial fibrillation is a chronic, progressive condition that presents a major health burden. This review summarizes recent studies assessing atrial fibrillation progression and its associated risk factors, describes the mechanisms underlying atrial fibrillation progression, and discusses the clinical implications of the progressive nature of atrial fibrillation. Progression of atrial fibrillation burden, and clinical progression from paroxysmal to more advanced (persistent/permanent) forms is common, but progression rates are variable. Atrial fibrillation progression parallels progressive atrial remodeling induced by atrial fibrillation risk factors and atrial fibrillation itself, and is associated with worse clinical outcomes.

Association between P wave polarity in atrial premature complexes and cardiovascular events in a community-dwelling population

OBJECTIVE

To examine the association between polarity of atrial premature complexes (APCs) and stroke.

DESIGN

A prospective study.

SETTING AND PARTICIPANTS

A total of 11 092 participants in the Jichi Medical School cohort study were included after excluding patients with atrial fibrillation. We analysed stroke events in patients with (n=136) and without (n=10 956) APCs. With regard to polarity of APCs, patients were subcategorised into having (1) negative (n=39) or non-negative (n=97) P waves in augmented vector right (aVR), and (2) positive (n=28) or non-positive (n=108) P waves in augmented vector left (aVL).

OUTCOME MEASURES

The primary endpoint was stroke.

RESULTS

Patients with APCs were significantly older than those without APCs (64.1±9.2 vs 55.1±11.6 years, p<0.001). The mean follow-up period was 11.8±2.4 years. Stroke events were observed in patients with (n=13 events) and without (n=411 events) APCs. This difference was significant (log-rank 12.9, p<0.001); however, APCs were not an independent predictor of stroke after adjusting for age, sex, height, body mass index, current drinking, diabetes, systolic blood pressure, prior myocardial infarction, prior stroke and high-density lipoprotein-cholesterol (p=0.15). The incidence of stroke in patients with APCs and non-negative P wave in aVR was significantly higher than in patients without APCs (log-rank 20.1, p<0.001), and non-negative P wave in aVR was revealed to be an independent predictor of stroke (HR 1.84, 95% CI 1.02 to 3.30). The incidence of stroke in patients with APC with non-positive P wave in aVL was also significantly higher than in patients without APC (log-rank 15.3, p<0.001), and non-positive P wave in aVL was an independent predictor of stroke (HR 1.92, 95% CI 1.05 to 3.54).

CONCLUSIONS

The presence of APCs with non-negative P wave in aVR or non-positive P wave in aVL on 12-lead ECG was associated with a higher risk of incident stroke.

New Predictor of Very Late Recurrence After Catheter Ablation of Atrial Fibrillation Using Holter Electrocardiogram Parameters

This study aimed to evaluate the predictors of very late recurrence of atrial fibrillation (VLRAF) after an initial AF catheter ablation (CA) by analyzing the follow-up Holter electrocardiogram. We retrospectively studied patients (n = 253, mean age: 66 years, woman: 30%, paroxysmal AF: 73%) without recurrence of AF within 12 months and the use of antiarrhythmic drugs. In the Holter electrocardiogram analysis, the atrial premature complexes (APCs) burden, the profile of the APCs run and prematurity index of the APCs were evaluated. Fifty-one patients (20%) had VLRAF during the follow-up period (mean follow up: 46 months). Patients with VLRAF had a significantly greater APCs burden (0.318% [0.084 to 1.405] vs 0.132% [0.051 to 0.461], p = 0.022), longer number of APCs run (5 [3 to 11] vs 4 [0 to 7], p = 0.019), and shorter minimum prematurity index of the APCs (47 ± 7 vs 51 ± 6, p = 0.001) than those without VLRAF. The optimal cutoff value for the APCs burden, maximum number of APCs run, and minimum prematurity index of the APCs to predict VLRAF was 0.159%, 10, and 48%, respectively. The minimum prematurity index of the APCs (≤48%) was significantly associated with VLRAF in the multivariate analysis. In conclusion, the minimum prematurity index of the APCs (≤48%) at 12 months after CA was shown to be an independent predictor of VLRAF in patients without antiarrhythmic drugs. Although the index is a very simple parameter automatically calculated by analysis software, it can be an important index for following patients after CA over the long-term.

Pulmonary vein volume and myocardial sleeve extension estimated by 3D computed tomography and voltage mapping predict arrhythmogenic triggers of paroxysmal atrial fibrillation

PURPOSE

Relationship between pulmonary vein (PV) anatomy and the pathophysiology of paroxysmal atrial fibrillation (PAF) remains incompletely studied. The aim of this study was to determine whether PV anatomy predicts arrhythmogenic PVs.

METHODS

Twenty-six consecutive PAF patients with spontaneous PAF or consistently frequent ectopic beats during electrophysiological study were enrolled. Computed tomography (CT) images for PVs were reconstructed into 3D images. The PV diameter and volume were measured based on the 3D images. The PV myocardial sleeve area was measured based on the 3D voltage mapping results. The PV myocardial sleeve area index was calculated by dividing the sleeve area of each PV by the average sleeve area of all PVs in each patient.

RESULTS

The diameter and volume of the arrhythmogenic PVs were larger than those of the non-arrhythmogenic PVs (21.08 ± 4.57 mm vs. 16.47 ± 3.31 mm, P < 0.001 and 7.70 ± 3.28 cm³ vs. 4.09 ± 1.99 cm³, P < 0.001, respectively). The myocardial sleeve area and sleeve area index of the arrhythmogenic PVs were also larger than those of the non-arrhythmogenic PVs (8.62 ± 5.33 cm² vs. 4.77 ± 3.84 cm², P < 0.001 and 1.59 ± 0.35 vs. 0.81 ± 0.38, P < 0.001, respectively). Multivariate analysis showed the PV myocardial sleeve area index was the independent predictor for arrhythmogenic PVs (P < 0.001).

CONCLUSIONS

PV size plays an important role in triggering PAF. A large myocardial sleeve extension is a powerful and independent predictor for arrhythmogenic PV, which may be useful anatomical markers to facilitate PAF ablation.

Temporal Dispersion of Atrial Activation Causes Postoperative Atrial Fibrillation

BACKGROUND

Spatial dispersion of atrial activation is a cause of postoperative atrial fibrillation (PoAF) after cardiac surgery. This study evaluated whether temporal dispersion of atrial activation causes PoAF after surgery in a clinical setting.

METHODS

Nineteen patients were enrolled. Postoperative atrial activation was evaluated by 24-hour Holter electrocardiography, with atrial pacing wires on the right atrium, for 5 days after cardiac surgery. No patient received antiarrhythmic drugs, including beta-blockers. The cycle length of 15 continuous atrial beats was measured at 4 time points: (i) earlier than 12 hours before PoAF, as a control, (ii) just before PoAF onset, (iii) during PoAF, and (iv) just before cessation of PoAF. Inhomogeneity of atrial activation was quantified by using the variation coefficient for a cycle length of 15 atrial beats during each phase.

RESULTS

The median inhomogeneity index of atrial activation (interquartile range) was 0.102 (0.046-0.136) in controls, 0.943 (0.582-1.610) just before PoAF onset (vs. control; p=0.009), 0.966 (0.631-1.117) during PoAF, and 0.471 (0.138-0.645) just before cessation of PoAF.

CONCLUSIONS

Dispersion of atrial activation significantly increased just before PoAF onset. Temporal dispersion of atrial activation is a precursory variation of PoAF.

Molecular Basis of Atrial Fibrillation Pathophysiology and Therapy: A Translational Perspective

Atrial fibrillation (AF) is a highly prevalent arrhythmia, with substantial associated morbidity and mortality. There have been significant management advances over the past 2 decades, but the burden of the disease continues to increase and there is certainly plenty of room for improvement in treatment options. A potential key to therapeutic innovation is a better understanding of underlying fundamental mechanisms. This article reviews recent advances in understanding the molecular basis for AF, with a particular emphasis on relating these new insights to opportunities for clinical translation. We first review the evidence relating basic electrophysiological mechanisms to the characteristics of clinical AF. We then discuss the molecular control of factors leading to some of the principal determinants, including abnormalities in impulse conduction (such as tissue fibrosis and other extra-cardiomyocyte alterations, connexin dysregulation and Na+-channel dysfunction), electrical refractoriness, and impulse generation. We then consider the molecular drivers of AF progression, including a range of Ca2+-dependent intracellular processes, microRNA changes, and inflammatory signaling. The concept of key interactome-related nodal points is then evaluated, dealing with systems like those associated with CaMKII (Ca2+/calmodulin-dependent protein kinase-II), NLRP3 (NACHT, LRR, and PYD domains-containing protein-3), and transcription-factors like TBX5 and PitX2c. We conclude with a critical discussion of therapeutic implications, knowledge gaps and future directions, dealing with such aspects as drug repurposing, biologicals, multispecific drugs, the targeting of cardiomyocyte inflammatory signaling and potential considerations in intervening at the level of interactomes and gene-regulation. The area of molecular intervention for AF management presents exciting new opportunities, along with substantial challenges.

Autonomic modulation before and after paroxysmal atrial fibrillation events in patients with ischemic heart disease

BACKGROUND

The autonomic activity plays a critical role in generating paroxysmal atrial fibrillation (PAF). This study aimed to evaluate the changes in the autonomic nerve activity before and after PAF events in patients with and without ischemic heart disease (IHD).

METHODS

The study included 49 patients (71.43 ± 12.24 years old, 26 males) with PAF events lasting more than 30 s during 24-hr ambulatory Holter monitoring. The 20-min intervals before and after PAF events were divided into eight segments of 5 min each. Heart rate variability (HRV) analyses of the time and frequency domains were applied to each time segment.

RESULTS

Patients with IHD had significant increases in the root mean square successive differences (r-MSSD, p = .008) and HF component (p = .04), followed by a significant increase in the LF/HF ratio (p = .02) preceding the onset of PAF. Patients without IHD had only a significant increase in the r-MSSD (p = .045) preceding the onset of PAF. During the termination of PAF events, patients in both the IHD and control groups had a significantly decreased r-MSSD and HF, respectively.

CONCLUSION

Ischemic heart disease causes a sympathovagal imbalance in the initiation of PAF. Decreased parasympathetic activity regulated the termination of PAF in both the IHD and control groups. The modification of the autonomic nervous system (ANS) activity should be individualized due to the autonomic complexity in AF arrhythmogenesis and termination.

Excessive Supraventricular Ectopic Activity and Adverse Cardiovascular Outcomes: a Systematic Review and Meta-analysis

PURPOSE OF REVIEW

Excessive supraventricular ectopic activity (ESVEA), in the form of frequent premature atrial contractions (PACs) and runs of PACs, is commonly observed in clinical practice and is frequently considered to be benign. Yet, recent studies have demonstrated a link between ESVEA and adverse cardiovascular outcomes. The aim of this meta-analysis was to examine the association between ESVEA and the risk of atrial fibrillation (AF), stroke, and mortality.

RECENT FINDINGS

A systematic search was performed in PubMed, EMBASE, and the Cochrane Library up to December 2017 to identify studies assessing adverse cardiovascular outcomes in patients with ESVEA, recorded on ambulatory electrocardiography. ESVEA was defined as a burden of PACs > 30 PACs/h or any runs of ≥20 PACs. The risk estimates for EVSEA and each clinical endpoint were pooled and analyzed separately.

RESULTS

Five studies comprising 7545 participants were included in this meta-analysis. The pooled analysis showed that ESVEA doubled the risk of AF (HR 2.19, 95% CI 1.70-2.82). ESVEA was also associated with a higher incidence of stroke (HR 2.23, 95% CI 1.24-4.02). Finally, ESVEA was associated with higher all-cause mortality (HR 1.61, 95% CI 1.25-2.07). Our meta-analysis found that ESVEA is closely associated with AF, stroke, and all-cause mortality. Further studies are required to examine the implication of therapeutic strategies in patients with ESVEA, in order to prevent potential subsequent adverse cardiovascular outcomes.

Atrial Ectopy Increases Asynchronous Activation of the Endo- and Epicardium at the Right Atrium

The predisposition of atrial extrasystoles (AES) to trigger cardiac tachyarrhythmia may arise from intramural conduction disorders causing endo-epicardial asynchrony (EEA). This study aimed to determine whether spontaneous AES disturb endo-epicardial conduction. Simultaneous endo-epicardial mapping of the right atrium was performed in patients during cardiac surgery with two 128-electrode arrays. Sixty spontaneous AES were observed in 23 patients and were analyzed for incidence of conduction delay, conduction block and amount of EEA compared to the previous sinus rhythm beat. Both conduction delay and block occurred more often in AES compared to sinus rhythm. The difference in lines of conduction block between the epicardium and endocardium increased in AES causing a greater imbalance of conduction disorders between the layers. The incidence of EEA with differences ≥10 ms increased significantly in AES. AES caused delays between the epicardium and endocardium up to 130 ms and EEA to increase for up to half (47%) of the mapping area. Conduction disturbances between the epicardial and endocardial layer giving rise to EEA increase during AES. Asynchronous activation of the atrial layers increases during AES which may be a mechanism for triggering cardiac tachyarrhythmia under the right conditions but EEA cannot be recognized by current mapping tools.

The Subcellular Distribution of Ryanodine Receptors and L-Type Ca2+ Channels Modulates Ca2+-Transient Properties and Spontaneous Ca2+-Release Events in Atrial Cardiomyocytes

Spontaneous Ca²⁺-release events (SCaEs) from the sarcoplasmic reticulum play crucial roles in the initiation of cardiac arrhythmias by promoting triggered activity. However, the subcellular determinants of these SCaEs remain incompletely understood. Structural differences between atrial and ventricular cardiomyocytes, e.g., regarding the density of T-tubular membrane invaginations, may influence cardiomyocyte Ca²⁺-handling and the distribution of cardiac ryanodine receptors (RyR2) has recently been shown to undergo remodeling in atrial fibrillation. These data suggest that the subcellular distribution of Ca²⁺-handling proteins influences proarrhythmic Ca²⁺-handling abnormalities. Here, we employ computational modeling to provide an in-depth analysis of the impact of variations in subcellular RyR2 and L-type Ca²⁺-channel distributions on Ca²⁺-transient properties and SCaEs in a human atrial cardiomyocyte model. We incorporate experimentally observed RyR2 expression patterns and various configurations of axial tubules in a previously published model of the human atrial cardiomyocyte. We identify an increased SCaE incidence for larger heterogeneity in RyR2 expression, in which SCaEs preferentially arise from regions of high local RyR2 expression. Furthermore, we show that the propagation of Ca²⁺ waves is modulated by the distance between RyR2 bands, as well as the presence of experimentally observed RyR2 clusters between bands near the lateral membranes. We also show that incorporation of axial tubules in various amounts and locations reduces Ca²⁺-transient time to peak. Furthermore, selective hyperphosphorylation of RyR2 around axial tubules increases the number of spontaneous waves. Finally, we present a novel model of the human atrial cardiomyocyte with physiological RyR2 and L-type Ca²⁺-channel distributions that reproduces experimentally observed Ca²⁺-handling properties. Taken together, these results significantly enhance our understanding of the structure-function relationship in cardiomyocytes, identifying that RyR2 and L-type Ca²⁺-channel distributions have a major impact on systolic Ca²⁺ transients and SCaEs.

Frequent premature atrial complexes as a predictor of atrial fibrillation: Systematic review and meta-analysis

BACKGROUND

Frequent premature atrial complexes (PACs) are associated with higher morbidity and mortality. Recent studies suggest that frequent PACs are associated with new onset atrial fibrillation (AF). However, a systematic review and meta-analysis of the literature has not been done. We assessed the association between frequent PACs and new onset AF by a systematic review and a meta-analysis.

METHODS

We comprehensively searched the databases of MEDLINE and EMBASE from inception to September 2017. Included studies were published cohort (prospective or retrospective) that compared new onset AF among patients with and without frequent PACs documented by Holter monitoring or 12-lead electrocardiogram. Data from each study were combined using the random-effects, generic inverse variance method of DerSimonian and Laird to calculate risk ratios and 95% confidence intervals.

RESULTS

Twelve studies from 2009 to 2017 were included in this meta-analysis involving 109,689 subjects (9217frequent and 100,472 non-frequent PACs). Frequent PACs were associated with increased risk of new onset AF (pooled risk ratio = 2.76, 95% confidence interval: 2.05-3.73, p < 0.000, I² = 90.6%).

CONCLUSION

Frequent PACs are associated with up to three-fold increased risk of new onset AF. Our study suggests that frequent PACs in general population is an independent predictor of new onset AF.

Supraventricular premature beats and risk of new-onset atrial fibrillation in coronary artery disease

INTRODUCTION

The significance of premature atrial contraction (PAC) count and supraventricular runs (SVR) for the risk of development of new-onset atrial fibrillation (AF) in patients with coronary artery disease (CAD) is not well established.

METHODS

The Innovation to Reduce Cardiovascular Complications of Diabetes at the Intersection (ARTEMIS) study cohort consisted of 1,946 patients with CAD who underwent clinical and echocardiographic examinations, 24-hour ambulatory ECG monitoring, and laboratory tests. After excluding patients who were not in sinus rhythm at baseline or were lost from the follow-up, the present study included 1,710 patients. SVR was defined as at least four PACs in a row with a duration <30 seconds.

RESULTS

During a follow-up for an average 5.6 ± 1.5 years, new-onset AF was identified in 143 (8.4%) patients. In the univariate analysis, both SVR and PAC count were associated with the development of new-onset AF. When SVR and PAC count were adjusted with the established AF risk markers of the modified CHARGE-AF model in the Cox multivariate regression analysis, both parameters remained significant predictors of the occurrence of new-onset AF (HR = 2.529, 95 % CI = 1.763-3.628, P ˂ 0.001 and HR = 8.139 for ≥1,409 PACs [the fourth quartile] vs. ≤507 PACs [the first quartile], 95 % CI = 3.967-16.696, P ˂ 0.001, respectively). Together these parameters improved the C-index of the established AF risk model from 0.649 to 0.718, P < 0.001.

CONCLUSION

Including SVR and PAC count to the established AF risk model improves the discrimination accuracy in predicting AF in patients with CAD.

Early, de novo atrial fibrillation after coronary artery bypass grafting: Facts and features

Knowledge of the mechanism underlying post-operative atrial fibrillation (PoAF) is essential for development of preventive measures. The incidence and characteristics of both PoAF and supraventricular premature beats triggering PoAF, their interrelationship and alterations over time have never been examined. The goal of this study is therefore to examine the correlation between the incidence and characteristics of supraventricular premature beats (SVPBs) and PoAF episodes in patients undergoing CABG in the first five post-operative days.

METHODS

PoAF episodes (N=327) and SVPBs (N=141,873) were characterized in 29 patients (63±9 years; 22 (76%) male) undergoing coronary artery bypass grafting and compared with a control group of patients without PoAF by using continuous cardiac rhythm monitoring during the first 5 days after surgery.

RESULTS

Most patients (N=18, 62%) had multiple PoAF episodes; the median number of PoAF episodes per patient was 3 and varied between 1 and 139. The majority of PoAF episodes developed on the second and third post-operative day (55%). The averaged median duration of PoAF episodes per patient was 469±1085 min. Patients with PoAF had a higher SVPBs burden compared to subjects without PoAF (0.9% vs 0.2%, P<.001). SVPBs initiating PoAF had shorter coupling intervals than SVPBs which did not initiate PoAF episodes (58% vs 64% (P<.001) and were preceded by heart rate acceleration.

CONCLUSION

PoAF episodes are mainly repetitive though transient in nature. There was a considerable inter-individual variation in both AF and SVPB characteristics, despite a similar underlying clinical profile. The SVPB burden is higher in patients with PoAF and the mode of onset is characterized by short coupled SVPBs. Determination of individual post-operative dysrhythmia profiles enables identification of patients at risk for developing PoAF.

Electrophysiological and molecular mechanisms of paroxysmal atrial fibrillation

Atrial fibrillation (AF) is an extremely prevalent arrhythmia that presents a wide range of therapeutic challenges. AF usually begins in a self-terminating paroxysmal form (pAF). With time, the AF pattern often evolves to become persistent (nonterminating within 7 days). Important differences exist between pAF and persistent AF in terms of clinical features, in particular the responsiveness to antiarrhythmic drugs and ablation therapy. AF mechanisms have been extensively reviewed, but few or no Reviews focus specifically on the pathophysiology of pAF. Accordingly, in this Review, we examine the available data on the electrophysiological basis for pAF occurrence and maintenance, as well as the molecular mechanisms forming the underlying substrate. We first consider the mechanistic insights that have been obtained from clinical studies in the electrophysiology laboratory, noninvasive observations, and genetic studies. We then discuss the information about underlying molecular mechanisms that has been obtained from experimental studies on animal models and patient samples. Finally, we discuss the data available from animal models with spontaneous AF presentation, their relationship to clinical findings, and their relevance to understanding the mechanisms underlying pAF. Our analysis then turns to potential factors governing cases of progression from pAF to persistent AF and the clinical implications of the basic mechanisms we review. We conclude by identifying and discussing questions that we consider particularly important to address through future research in this area.

Lessons from computer simulations of ablation of atrial fibrillation

This paper reviews the simulations of catheter ablation in computer models of the atria, from the first attempts to the most recent anatomical models. It describes how postulated substrates of atrial fibrillation can be incorporated into mathematical models, how modelling studies can be designed to test ablation strategies, what their current trade-offs and limitations are, and what clinically relevant lessons can be learnt from these simulations. Drawing a parallel between clinical and modelling studies, six ablation targets are considered: pulmonary vein isolation, linear ablation, ectopic foci, complex fractionated atrial electrogram, rotors and ganglionated plexi. The examples presented for each ablation target illustrate a major advantage of computer models, the ability to identify why a therapy is successful or not in a given atrial fibrillation substrate. The integration of pathophysiological data to create detailed models of arrhythmogenic substrates is expected to solidify the understanding of ablation mechanisms and to provide theoretical arguments supporting substrate-specific ablation strategies.

Development of an alert system for subjects with paroxysmal atrial fibrillation

Background

Knowledge of the onset of atrial fibrillation (AF) episodes in patients with paroxysmal atrial fibrillation (PAF) will enable them to better manage this condition. Current advances in mobile technology allow RR interval data to be obtained in real time. An analysis technique using RR interval data is presented with a view to alert a subject before a PAF episode.

Method

The method is based on a time series of standard deviation and 0.99 quantile values of the spectral entropy, constructed from RR data. The RR data are taken from three time periods. The first time period has no occurrences of AF for 45 min to either side of the time period. The second time period just precedes an AF attack. Both of these are of thirty minutes duration. The third time period of approximately 5 min follows the second, and is when AF occurs.

Results

Twenty-two PAF subjects were studied and in all cases there was a steady increase in the values of these indices as the onset of the AF attack approached.

Conclusion

This method of analysis of RR interval data shows potential use to alert a PAF subject before the onset of an AF episode.

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A method to alert the PAF subject before the onset of paroxysms of AF, based on a time series of standard deviation and 0.99 quantile values of the spectral entropy, obtained from the RR interval data.

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The RR data used in analysis each subject was obtained from three time periods. The first two are of thirty minute duration while the third set is of 5 min duration.

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RR data from the first time period had no occurrences of AF, 45 min on either side of it. The time period of the second set just precedes an AF attack. The third set which follows the second is when AF occurs.

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22 PAF subjects were studied and in all cases there was a steady increase in the values of the standard deviation and 0.99 quantile values of the spectral entropy.

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Such a signature of these indices shows that this analysis technique of RR data could be useful to PAF patients to better manage the onset of AF attacks.

Frequent Atrial Premature Complexes and Their Association With Risk of Atrial Fibrillation

Identification of precursors of atrial fibrillation (AF) may lead to early detection and prevent associated morbidity and mortality. This study aimed to examine the association between frequent atrial premature complexes (APCs) and incidence of AF. For this retrospective cohort study, we analyzed Holter recordings obtained from 2000 to 2010 of 1,357 veterans free of AF at baseline. All pertinent data in electronic medical records were reviewed to ascertain baseline characteristics. Holter groups with frequent (≥100/day) and infrequent (<100/day) APCs were compared for development of new AF over a median follow-up of 7.5 years. Multivariate Cox regression analyses were performed before and after propensity score matching. Mean age was 64 years with 93% men. Mean body mass index, hemoglobin A1C, low-density lipoprotein, left atrial size, and heart rate were 31.24 kg/m(2), 6.42%, 107.92 mg/dl, 4.26 cm, and 73 beats/min, respectively. AF was noted in 21.8% of patients with frequent APCs compared to 5.6% of those with infrequent APCs. After adjusting for demographics, medication use, co-morbidities, and laboratory and echocardiographic findings, multivariate Cox regression analyses confirmed frequent APCs to be independently associated with higher incidence of AF (hazard ratio [HR] 2.97, 95% confidence interval [CI] 1.85 to 4.80; p <0.001). In propensity-matched groups, this association remained significant (HR 2.87, 95% CI 1.65 to 4.98; p <0.001). Additionally, atrial couplets (≥50/day), atrial bigeminy (≥50/day), frequent runs of ≥3 APCs (≥20 runs/day), and longer runs (≥10 beats/run) were significantly associated with AF (HR 3.11, 3.67, 2.94, and 1.73, respectively, all p <0.05). In conclusion, frequent APCs (≥100/day) are associated with greater risk of AF.

Atrial Septal Aneurysms and Supraventricular Arrhythmias: The Role of Atrial Electromechanical Delay

BACKGROUND

Paroxysmal supraventricular arrhythmias (SVAs) frequently occur in patients with atrial septal aneurysm (ASA). The aim of the current study was to evaluate the electrocardiographic (P-wave duration and dispersion) and echocardiographic (atrial electromechanical delay, AEMD) noninvasive indicators of atrial conduction heterogeneity in healthy ASA subjects without interatrial shunt and to assess the AEMD role in predicting the SVAs onset in this population.

MATERIALS AND METHODS

One hundered ASA patients (41 males, mean age of 32.5 ± 8 years) and 100 healthy subjects used as controls, matched for age and gender, were studied for the occurrence of SVAs during a 4-year follow-up, through 30-day external loop recorder (ELR) monitoring performed every 3 months. ASAs were diagnosed by transthoracic echocardiography based on the criteria of a minimal aneurismal base of ≥15 mm and an excursion of ≥10 mm. Intra-AEMD and inter-AEMD of both atria were measured through tissue Doppler echocardiography. P-wave dispersion (PD) was carefully measured using 12-lead electrocardiogram (ECG).

RESULTS

Compared to the healthy control group, the ASA group showed a statistically significant increase in inter-AEMD, intra-left AEMD, maximum P-wave duration, and PD. Dividing the ASA group into 2 subgroups (patients with or without SVAs), the inter-AEMD, intra-left AEMD, P max, and PD were significantly higher in the subgroup with SVAs compared to the subgroup without SVAs. There were significant good correlations of intra-left AEMD and inter-AEMD with PD. A cutoff value of 40.1 msec for intra-left AEMD had a sensitivity of 82% and a specificity of 83% in identifying ASA patients at risk for SVA.

CONCLUSION

Our results showed that the echocardiographic AEMD indices (intra-left and inter-AEMD) and the PD were significantly increased in healthy ASA subjects without interatrial shunt. PD and AEMD represent noninvasive, inexpensive, useful, and simple parameters to assess the SVAs' risk in ASA patients.

Obstructive respiratory events and premature atrial contractions after cardioversion

Recurrence of atrial fibrillation (AF) after electrical cardioversion (ECV) is increased in patients with obstructive sleep apnoea (OSA).

In patients with persistent AF, with (n=40) and without (n=32) obstructive respiratory events (OREs) during sedation for ECV, we determined the occurrence of premature atrial contractions (PACs) before and after insertion of a nasopharyngeal tube. The influence of acute obstructive respiratory events on atrial electrophysiology after termination of AF was studied in pigs.

Incidence of PACs directly after ECV was higher in patients with OREs compared to those without OREs (7±2 versus 1±1 per 10 s, respectively; p<0.01). Occurrence of PACs could be reduced by 79% by insertion of a nasopharyngeal tube. In a subsequent sleeping study, patients with OREs had higher apnoea–hypopnoea indices and more PACs during night. 16 patient with and four patients without OREs had a relapse of AF during 1 week after ECV (p<0.01). In pigs, acute OREs after 30 min of AF increased occurrence of PACs and vulnerability for reinduction of AF, which could be attenuated by atropine, beta-blockers and renal denervation.

OREs are associated with increased occurrence of PACs and more early relapse of AF. OREs increase occurrence of PACs and vulnerability for reinduction of AF by sympathovagal imbalance.

Recurrent intradialytic paroxysmal atrial fibrillation: hypotheses on onset mechanisms based on clinical data and computational analysis

Atrial fibrillation (AF) incidence is high in end-stage renal disease (ESRD) patients, and haemodialysis (HD) session may induce paroxysmal AF episodes. Structural atrium remodelling is common in ESRD patients, moreover, HD session induces rapid plasma electrolytes and blood volume changes, possibly favouring arrhythmia onset. Therefore, HD session represents a unique model to study in vivo the mechanisms potentially inducing paroxysmal AF episodes. Here, we present the case report of a patient in which HD regularly induced paroxysmal AF. In four consecutive sessions, heart rate variability analysis showed a progressive reduction of low/high frequency ratio before the AF onset, suggesting a relative increase in vagal activity. Moreover, all AF episodes were preceded by a great increase of supraventricular ectopic beats. We applied computational modelling of cardiac cellular electrophysiology to these clinical findings, using plasma electrolyte concentrations and heart rate to simulate patient conditions at the beginning of HD session (pre-HD) and right before the AF onset (pre-AF), in a human atrial action potential model. Simulation results provided evidence of a slower depolarization and a shortened refractory period in pre-AF vs. pre-HD, and these effects were enhanced when adding acetylcholine effect. Paroxysmal AF episodes are induced by the presence of a trigger that acts upon a favourable substrate on the background of autonomic nervous system changes and in the described case report all these three elements were present. Starting from these findings, here we review the possible mechanisms leading to intradialytic AF onset.

A brief review and clinical application of heart rate variability biofeedback in sports, exercise, and rehabilitation medicine

CONTEXT

An important component of the effective management of chronic noncommunicable disease is the assessment and management of psychosocial stress. The measurement and modulation of heart rate variability (HRV) may be valuable in this regard.

OBJECTIVE

To describe the measurement and physiological control of HRV; to describe the impact of psychosocial stress on cardiovascular disease, metabolic syndrome, and chronic respiratory disease, and the relationship between these diseases and changes in HRV; and to describe the influence of biofeedback and exercise on HRV and the use of HRV biofeedback in the management of chronic disease.

DATA SOURCES AND STUDY SELECTION

The PubMed, Medline, and Embase databases were searched (up to August 2013). Additional articles were obtained from the reference lists of relevant articles and reviews. Articles were individually selected for further review based on the quality and focus of the study, and the population studied.

RESULTS

Heart rate variability is reduced in stress and in many chronic diseases, and may even predict the development and prognosis of some diseases. Heart rate variability can be increased with both exercise and biofeedback. Although the research on the effect of exercise is conflicting, there is evidence that aerobic training may increase HRV and cardiac vagal tone both in healthy individuals and in patients with disease. Heart rate variability biofeedback is also an effective method of increasing HRV and cardiac vagal tone, and has been shown to decrease stress and reduce the morbidity and mortality of disease.

CONCLUSION

The assessment and management of psychosocial stress is a challenging but important component of effective comprehensive lifestyle interventions for the management of noncommunicable disease. It is, therefore, important for the sports and exercise physician to have an understanding of the therapeutic use of HRV modulation, both in the reduction of stress and in the management of chronic disease.

Orthostatic change in blood pressure and incidence of atrial fibrillation: results from a bi-ethnic population based study

Background

Autonomic fluctuations are associated with the initiation and possibly maintenance of atrial fibrillation (AF). However, little is known about the relationship between orthostatic blood pressure change, a common manifestation of autonomic dysfunction, and incident AF.

Methods

We examined whether supine-to-standing changes in systolic blood pressure (SBP) are associated with incident AF in 12,071 African American and white men and women aged 45–64 years, enrolled in the Atherosclerosis Risks in Communities (ARIC) study. Orthostatic hypotension (OH) was defined as a supine-standing drop in SBP by ≥20 mmHg or diastolic blood pressure by ≥10 mmHg. AF cases were identified based on study scheduled 12-lead ECG, hospital discharge ICD codes, and death certificates through 2009.

Results

OH was seen in 603 (5%) at baseline. During an average follow-up of 18.1 years, 1438 (11.9%) study participants developed AF. Incident AF occurred more commonly among those with OH than those without, a rate of 9.3 vs. 6.3 per 1000 person years, (p<0.001). The age, gender, and race adjusted hazard ratio (95%CI) of AF among those with OH compared to those without was 1.62 (1.34, 2.14). This association was attenuated after adjustment for common AF risk factors to HR 1.40 (1.15, 1.71), a strength similar to that of diabetes or hypertension with AF in the same model. A non-linear relationship between orthostatic change in SBP and incident AF was present after multivariable adjustment.

Conclusions

OH is associated with higher AF incidence. Whether interventions that decrease OH can reduce AF risk remains unknown.

Renal sympathetic denervation provides ventricular rate control but does not prevent atrial electrical remodeling during atrial fibrillation

Renal denervation (RDN) reduces renal efferent and afferent sympathetic activity thereby lowering blood pressure in resistant hypertension. The effect of modulation of the autonomic nervous system by RDN on atrial electrophysiology and ventricular rate control during atrial fibrillation (AF) is unknown. Here we report a reduction of ventricular heart rate in a patient with permanent AF undergoing RDN. Subsequently, we investigated the effect of RDN on AF-induced shortening of atrial effective refractory period, AF inducibility, and ventricular rate control during AF maintained by rapid atrial pacing in 12 pigs undergoing RDN (n=7) or sham procedure (n=5). During sinus rhythm, RDN reduced heart rate (RR-interval, 708±12 versus 577±19 ms; P=0.0021) and increased atrioventricular node conduction time (PQ-interval, 112±12 versus 88±9 ms; P=0.0001). Atrial tachypacing for 30 minutes increased AF inducibility and decreased AF cycle length. This was not influenced by RDN. RDN reduced ventricular rate during AF episodes by ≈24% (119±9 versus 158±19 bpm; P=0.0001). AF episodes were shorter after RDN compared with sham (12±3 versus 34±4 s; P=0.0091), but atrial effective refractory period was not modified by RDN. RDN reduced heart rate and reduced atrioventricular node conduction time during sinus rhythm and provided rate control during AF. AF-induced atrial electrical remodeling, AF inducibility, and AF cycle length were not modified, but duration of AF episodes was shorter after RDN. Modulation of the autonomic nervous system by RDN might provide rate control and reduce susceptibility to AF. Whether RDN may provide rate control in a larger number of patients with AF deserves further clinical studies.

Modeling atrial arrhythmias: impact on clinical diagnosis and therapies

Atrial arrhythmias are the most frequent sustained rhythm disorders in humans and often lead to severe complications such as heart failure and stroke. Despite the important insights provided by animal models into the mechanisms of atrial arrhythmias, direct translation of experimental findings to new therapies in patients has not been straightforward. With the advances in computer technology, large-scale electroanatomical computer models of the atria that integrate information from the molecular to organ scale have reached a level of sophistication that they can be used to interpret the outcome of experimental and clinical studies and aid in the rational design of therapies. This paper reviews the state-of-the-art of computer models of the electrical dynamics of the atria and discusses the evolving role of simulation in assisting the clinical diagnosis and treatment of atrial arrhythmias.

Evaluation of the relationship between atrial septal aneurysm and cardiac arrhythmias via P-wave dispersion and signal-averaged P-wave duration

OBJECTIVE

The aim of the study was to investigate the relationship between atrial septal aneurysms (ASAs) and cardiac arrhythmias via signal-averaged P-wave duration (SAPWD) and P-wave dispersion (Pd).

METHODS

Sixty-six patients with ASA served as the study group (group 1; 28 men and 38 women; mean age, 34 +/- 10 years) and 62 healthy volunteers served as the control group (group 2; 29 men and 33 women; mean age, 31 +/- 8 years) in the current study. ASAs were diagnosed by transthoracic echocardiography based on the criteria of a minimal aneurysmal base of > or =15 mm; and an excursion of > or =10 mm. All subjects were evaluated by 24-hour Holter monitoring, 12 lead body surface electrocardiogram for P-wave analysis, and signal-averaged electrocardiogram for P-wave duration (PWD).

RESULTS

There was no significant difference between the study and control groups in terms of age, gender, left atrium diameter, and left ventricular ejection fraction. Supraventricular arrhythmias (SVAs) were detected in 29 patients with ASA (43.9%) and 5 controls (8.1%; P < 0.001). The mean Pd in patients with ASA was significantly longer compared to the control group (14.1 +/- 8 ms vs 7.0 +/- 2.9 ms; P < 0.001). Similarly, the mean SAPWD in group 1 was significantly longer compared to group 2 (127.4 +/- 17.6 ms vs 99.8 +/- 12.3 ms; P < 0.001).

CONCLUSION

Prolonged SAPWD and Pd were determined to indicate electrical disturbances in the atrial myocardium, and predict the increase in the prevalence of SVA in patients with ASA.

Relationship between atrial septal aneurysms and atrial electromechanical delay

Atrial septal aneurysm (ASA) is a saccular deformity located in the atrial septum. Atrial arrhythmias are common in patients with ASA. Atrial electromechanical delay (AEMD) can be used to evaluate development of atrial arrhythmias in various settings. The aim of the study was to investigate the relationship between ASA, cardiac arrhythmias and AEMD. Seventy patients with ASA served as the study group (30 men; mean age, 33.6 ± 10.9 years) and 70 healthy volunteers served as the control group (34 men; mean age, 31.4 ± 7.8 years). ASAs were diagnosed by transthoracic echocardiography based on the criteria of a minimal aneurysmal base of ≥ 15 mm; and an excursion of ≥ 10 mm. Inter-AEMD and intra-AEMDs of both atrium were measured from parameters of tissue Doppler imaging. There was no significant difference between the study and control groups in terms of age, gender, left atrium diameter, and left ventricular ejection fraction. Inter-AEMD (50.7 ± 22.5 ms vs. 36.9 ± 12.0 ms) and intra-left AEMD (44.6 ± 17.4 ms vs. 30.7 ± 11.6 ms) were significantly higher in patients with ASA with respect to control group. Inter-AEMD (63.6 ± 20.1 ms vs. 45.1 ± 21.5 ms, P = 0.001), intra-left AEMD (55.3 ± 15.6 ms vs. 40.1 ± 16.2 ms, P = 0.001), diameter of the ASA (19.9 ± 3.6 mm vs. 17.1 ± 2.7 mm, P = 0.001) and P wave dispersion (18.5 ± 6.7 ms vs. 11.8 ± 7.3 ms, P = 0.001) were significantly greater in the subgroup with arrhythmias compared to the subgroup without arrhythmias. Inter-AEMD and intra-left AEMD were found to be significantly prolonged in patients with ASA. Being a non-invasive, inexpensive and simple technique AEMD may provide significant contributions to assess the risk for paroxysmal supraventricular arrhythmia in patients with ASA.

Severe obstructive sleep apnea elicits concentric left ventricular geometry

BACKGROUND

Obstructive sleep apnea (OSA) has several negative effects on the heart including increase in myocardial end-systolic stress, venous return and sympathetic activity, all potential stimuli of left ventricular (LV) hypertrophy. The impact of the severity of OSA on LV geometry is unknown. We hypothesized that OSA is related to concentric LV geometry.

METHODS

One hundred and fifty-seven patients with suspected OSA underwent echocardiography, ambulatory 24-h blood pressure and ECG monitoring. On the basis of the severity of OSA, patients were divided into controls, mild OSA and moderate/severe OSA (apnea-hypopnea index <5, 5-15 and >15/h, respectively). Patients with LV hypertrophy were defined as LV mass at least 49.2 g/m2.7 for men and at least 46.7 for women. Relative wall thickness of at least 0.43 identified patients with concentric LV geometry.

RESULTS

Patients with moderate/severe OSA (n = 86) had a higher body mass index and a higher prevalence of paroxysmal atrial fibrillation than those (n = 51) with mild OSA and controls (n = 20). Prevalence of hypertension, diabetes, obesity, LV mass and blood pressure did not differ between the groups. Relative wall thickness was positively related to apnea-hypopnea index (r = 0.30; P = 0.003) and the prevalence of concentric LV geometry was 20% in controls, 12% in mild OSA and 58% in moderate/severe OSA (P < 0.001). In logistic regression analysis concentric LV geometry was associated with moderate/severe OSA [odds ratio (OR) 7.6, P < 0.001], low stress-corrected midwall shortening (OR 3.38, P = 0.004), and higher body mass index (OR 1.09, P = 0.03).

CONCLUSIONS

Moderate/severe OSA is associated with high prevalence of concentric LV geometry. This increased prevalence may in part explain the increased rate of cardiovascular events in these patients.

Novel KCNA5 mutation implicates tyrosine kinase signaling in human atrial fibrillation

BACKGROUND

Emerging evidence has strongly implicated hereditary determinants for atrial fibrillation (AF). Loss-of-function mutations in KCNA5 encoding the ultrarapid delayed rectifier potassium current I(Kur) have been identified in AF families.

OBJECTIVE

The purpose of this study was to determine the clinical and biophysical phenotypes in a KCNA5 mutation with deletion of 11 amino acids in the N-terminus of the protein, which was identified in patients with lone AF.

METHODS

Patients with AF confirmed by ECG were prospectively enrolled in the Vanderbilt AF Registry, which comprises clinical and genetic databases. A KCNA5 mutation was generated by mutagenesis for electrophysiologic characterization.

RESULTS

We identified a novel 33-bp coding region deletion in two Caucasian probands. One proband was part of a kindred that included four other members with AF, and all were mutation carriers. The mutation results in deletion of 11 amino acids in the N-terminus of the protein, a proline-rich region as a binding site for Src homology 3 (SH3) domains associated with Src-family protein tyrosine kinase (TK) pathway. In transfected cells, the mutant caused approximately 60% decreased I(Kur) versus wild-type (WT) (75 +/- 8 pA/pF vs 180 +/- 15 pA/pF, P <.01) and dominant-negative effect on WT current (105 +/- 10 pA/pF, P <.01). Pretreatment with the Src inhibitor PP2 prevented v-Src TK from 90% suppressed WT current. In contrast, the mutant channel displayed no response to v-Src TK.

CONCLUSION

Our data implicate abnormal atrial repolarization control due to variable TK signaling as a mechanism in familial AF and thereby suggest a role for modulation of this pathway in AF and its treatment.

Circadian distribution of paroxysmal atrial fibrillation in patients with and without structural heart disease in untreated state

BACKGROUND

This study aimed to compare the circadian distribution of the onset, maintenance and termination of paroxysmal atrial fibrillation (PAF) between structural and non-structural heart diseases (SHD and NSHD, respectively) in the untreated state.

SUBJECTS AND METHODS

We included 217 patients with 338 PAF (79 SHD patients with 131 episodes; 138 NSHD patients with 207 episodes). The probabilities for the onset, maintenance and termination of PAF for each hour were analyzed using Holter monitoring data and harmonic models being fitted into a cosinusoidal function.

RESULTS

The SHD group had a triphasic circadian pattern at the onset with higher peaks at midnight, in the early morning and in the late afternoon (p < 0.05), whereas the NSHD group showed a single peak at midnight (p < 0.01). The probability of maintenance revealed a single peak during midnight (SHD, p < 0.0001; NHD, p < 0.01). The termination showed a peak at noon in the SHD group (p < 0.05), whereas there was a double peak at 10:00 am and 8:00 pm in the NSHD group (p=0.06). RR intervals just after the PAF onset showed marked shortening in the daytime initiation PAF as compared to the nighttime initiation PAF in both SHD and NSHD groups (p < 0.01).

CONCLUSION

These observations suggest that the SHD group has very complex onset hours, whereas the NSHD group shows complex termination hours. Reflexly accelerated sympathetic tone just after the PAF onset is suggested in the daytime initiation PAF.

Augmented potassium current is a shared phenotype for two genetic defects associated with familial atrial fibrillation

Mutations in multiple genes have been implicated in familial atrial fibrillation (AF), but the underlying mechanisms, and thus implications for therapy, remain ill-defined. Among 231 participants in the Vanderbilt AF Registry, we found a mutation in KCNQ1 (encoding the alpha-subunit of slow delayed rectifier potassium current [I(Ks)]) and separately a mutation in natriuretic peptide precursor A (NPPA) gene (encoding atrial natriuretic peptide, ANP), both segregating with early onset lone AF in different kindreds. The functional effects of these mutations yielded strikingly similar I(Ks) "gain-of-function." In Chinese Hamster Ovary (CHO) cells, coexpression of mutant KCNQ1 with its ancillary subunit KCNE1 generated approximately 3-fold larger currents that activated much faster than wild-type (WT)-I(Ks). Application of the WT NPPA peptide fragment produced similar changes in WT-I(Ks), and these were exaggerated with the mutant NPPA S64R peptide fragment. Anantin, a competitive ANP receptor antagonist, completely inhibited the changes in I(Ks) gating observed with NPPA S64R. Computational simulations identified accelerated transitions into open states as the mechanism for variant I(Ks) gating. Incorporating these I(Ks) changes into computed human atrial action potentials (AP) resulted in 37% shortening (120 vs. 192 ms at 300 ms cycle length), reflecting loss of the phase II dome which is dependent on L-type calcium channel current. We found striking functional similarities due to mutations in KCNQ1 and NPPA genes which led to I(Ks) "gain-of-function", atrial AP shortening, and consequently altered calcium current as a common mechanism between diverse familial AF syndromes.

Paroxysmal atrial fibrillation initiated by late coupled atrial extrasystoles

A Holter recording was taken from a 62-year-old man, in whom paroxysmal atrial fibrillation was often initiated by late coupled extrasystoles rather than by close coupled ones. Coupling intervals of the extrasystoles to the preceding sinus P waves were considerably variable. When the coupling interval of an extrasystole was shorter than a critical period of 0.47 s, the extrasystole failed to be followed by another ectopic atrial deflection. On the other hand, when the coupling of an extrasystole was longer than 0.47 s, the extrasystole was followed by another atrial deflection, or it was followed by a short run of atrial tachycardia, which initiated paroxysmal atrial fibrillation. To our knowledge, such atrial fibrillation initiated by late coupled atrial extrasystoles has never been reported previously. Longitudinal dissociation in the re-entrant pathway of the extrasystoles is suggested as a possible mechanism for such initiation of paroxysmal atrial fibrillation.

Frequent Atrial Premature Beats Predict Paroxysmal Atrial Fibrillation in Stroke Patients

Background and Purpose— For patients having suffered ischemic stroke, the current diagnostic strategies often fail to detect atrial fibrillation as a potential cause of embolic events. The aim of the study was to identify paroxysmal atrial fibrillation in stroke patients. We hypothesized that patients with frequent atrial premature beats (APBs) recorded in 24-hour ECG will show more often atrial fibrillation when followed by repeated long-term ECG recordings than patients without or infrequent APBs.

Methods— 127 patients with acute ischemic stroke and without known AF were enrolled in a prospective study to detect paroxysmal AF. Patients were stratified according to the number of APBs recorded in a 24-hour ECG (≥70 APBs versus <70 APBs). Subsequently, they all underwent serial 7-day event-recorder monitoring at 0, 3, and 6 months.

Results— Serial extended ECG monitoring identified AF in 26% of patients with frequent APBs but only in 6.5% when APBs were infrequent ( P =0.0021). A multivariate analysis showed that the presence of frequent APBs in the initial 24-hour ECG was the only independent predictor of paroxysmal AF during follow-up (odds ratio 6.6, 95% confidence intervals 1.6 to 28.2, P =0.01).

Conclusions— In patients with acute ischemic stroke, frequent APBs (≥70/24 hours) are a marker for individuals who are at greater risk to develop or have paroxysmal AF. For such patients, we propose a diagnostic workup with repeated prolonged ECG monitoring to diagnose paroxysmal AF.