Irregular rhythm adversely influences calcium handling in ventricular myocardium: implications for the interaction between heart failure and atrial fibrillation

Heart rate variability in patients with atrial fibrillation of sinus rhythm or atrial fibrillation: chaos or merit?

Atrial fibrillation (AF) is the most common sustained cardiac arrhythmia characterized by consistently irregular atrial and ventricular contractions. Heart rate variability (HRV) refers to the changes in the intervals between consecutive ventricular heartbeats. In sinus rhythm, HRV may be subtle and is quantitatively reflecting the dynamic interplay of the cardiac autonomic nervous system, which plays a crucial role in the onset, development, and maintenance of AF. HRV metrics, consisting of time-domain, frequency-domain, and nonlinear parameters, have been verified to vary significantly before and after AF episodes, and AF treatment-related procedures such as electrical cardioversion, ablation, and surgery of AF. Therefore, HRV may serve as a digital biomarker in predicting AF risk in long-term and acute risk period, identification of patients with AF risk in sinus rhythm and recurrence risk stratification after procedures. HRV in AF rhythm, predominantly influenced by dynamic atrioventricular node conduction under the onslaught of irregular atrial impulses, shows a huge disparity compared to that in sinus rhythm. Despite this, HRV in AF rhythm still provides valuable prognostic information, as reduced HRV may indicate a poor heart function and outcomes in patients with AF. Despite being influenced by lots of variables, HRV can still serve as an independent digital biomarker in the clinical management of AF throughout its entire lifecycle.

Atrial Fibrillation-Induced Cardiomyopathy

Atrial fibrillation (AF) is one of the most prevalent cardiac arrhythmias in the world. Patients with AF also suffer from heart failure (HF). The relationship between AF and HF is often considered bidirectional and both share very similar risk factors. The mechanism of AF-induced cardiomyopathy lies in 3 distinct components: tachycardia-related cardiac dysfunction, heart rhythm irregularity, and AF-induced atrial myopathy. These components are mediated by calcium mishandling, neurohormonal activation, oxidative stress, myocardial supply-demand mismatch, and irreversible fibrosis and remodeling. Managing AF-induced cardiomyopathy should focus on early rhythm control to mitigate the development of irreversible remodeling and atrial myopathy.

Atrial Tachyarrhythmias With Ultra-Rapid Ventricular Response and Sudden Death in Patients Without Structural Heart Disease

BACKGROUND

Sudden cardiac death (SCD) is generally associated with life-threatening ventricular arrhythmias. Supraventricular arrhythmias are an accepted cause of SCD in Wolff-Parkinson-White syndrome and complex congenital heart disease. However, the role of atrial tachyarrhythmias (ATAs) in SCD in patients with structurally normal hearts is unclear.

OBJECTIVES

The goal of this study was to present data on resuscitated patients without structural heart disease (SHD), experiencing recurrent implantable cardioverter-defibrillator (ICD) shocks, who share common clinical and electrical features suggesting that ATAs can cause SCD.

METHODS

We describe the clinical characteristics and ICD analysis of syncopal events terminated with shock delivery in 5 young SCD survivors without SHD. Details on the follow-up after ablation of the arrhythmia causing the syncopal episode are also reported.

RESULTS

In all patients (4 male, 1 female; median age 23 years; age range 15-47 years), a surface electrocardiogram recording in the resuscitation setting suggested ventricular fibrillation. After the index event, all patients exhibited recurrent arrhythmic syncopal episodes in a setting of elevated adrenergic tone, treated with ICD shocks. ICD interrogation suggested ATAs (atrial fibrillation in 4 patients, atrial tachycardia in 1 patient), conducting to the ventricles at rates approaching 300 beats/min, as the underlying arrhythmia leading to the syncopal events. ATA ablation abolished episodes of arrhythmic syncope and shock delivery in all patients after a median follow-up of 34 months. No patient died suddenly during follow-up.

CONCLUSIONS

Common clinical and electrical features define a distinct entity of SCD caused by ATAs with ultra-rapid ventricular response in otherwise healthy patients. Catheter ablation of the ATA is an effective treatment in these patients.

Atrioventricular node ablation for atrial fibrillation in the era of conduction system pacing

Despite key advances in catheter-based treatments, the management of persistent atrial fibrillation (AF) remains a therapeutic challenge in a significant subset of patients. While success rates have improved with repeat AF ablation procedures and the concurrent use of antiarrhythmic drugs, the likelihood of maintaining sinus rhythm during long-term follow-up is still limited. Atrioventricular node ablation (AVNA) has returned as a valuable treatment option given the recent developments in cardiac pacing. With the advent of conduction system pacing, AVNA has seen a revival where pacing-induced cardiomyopathy after AVNA is felt to be overcome. This review will discuss the role of permanent pacemaker implantation and AVNA for AF management in this new era of conduction system pacing. Specifically, this review will discuss the haemodynamic consequences of AF and the mechanisms through which 'pace-and-ablate therapy' enhances outcomes, analyse historical and more recent literature across various pacing methods, and work to identify patient groups that may benefit from earlier implementation of this approach.

Renal Outcomes of Rhythm Control in Patients Recently Diagnosed With Atrial Fibrillation

BACKGROUND

Atrial fibrillation (AF) is associated with impaired renal function and chronic kidney disease (CKD).

OBJECTIVES

This study assessed the effects of rhythm control on renal function compared with rate control among patients recently diagnosed with AF.

METHODS

A total of 20,886 patients with AF and available baseline estimated glomerular filtration rate (eGFR) data undergoing rhythm control (antiarrhythmic drugs or ablation) or rate control therapy, initiated within 1 year of AF diagnosis in 2005 to 2015, were identified from the Korean National Health Insurance Service database. The composite outcome of ≥30% decline in eGFR, acute kidney injury, kidney failure, or death from renal or cardiovascular causes was compared with the use of propensity overlap weighting between rhythm or rate control strategies in patients with or without significant CKD (eGFR <60 mL/min/1.73 m2).

RESULTS

Of the included patients (median age 62 years, 32.7% female), 2,213 (10.6%) had eGFR <60 mL/min/1.73 m2. Among patients with significant CKD, early rhythm control, compared with rate control, was associated with a lower risk of the primary composite outcome (weighted incidence rate: 2.77 vs 3.92 per 100 person-years; weighted HR: 0.70; 95% CI: 0.52-0.95). In patients without significant CKD, there was no difference in the risk of the primary composite outcome between rhythm and rate control groups (weighted incidence rate: 3.41 vs 3.21 per 100 person-years; weighted HR: 1.06; 95% CI: 0.96-1.18). No differences in safety outcomes were found between rhythm and rate control strategies in patients without or with significant CKD.

CONCLUSIONS

Among patients with AF and CKD, early rhythm control was associated with lower risks of adverse renal outcomes than rate control was.

Clinical Features of Tachycardia-induced Cardiomyopathy in Patients with Atrial Fibrillation

Objective Atrial fibrillation (AF) is the most common cause of tachycardia-induced cardiomyopathy (TIC). However, which patients with AF are prone to developing TIC remains unclear. In this study, we investigated the clinical features of AF patients with TIC. Methods This single-center study included 722 patients with AF (average age, 63.1±10.2 years old; 191 women) who underwent radiofrequency catheter ablation. We defined TIC as an initial left ventricular ejection fraction (LVEF) of <40% and a >20% recovery of the LVEF after successful AF ablation and compared the clinical characteristics between the TIC and control groups. Results The proportions of type 2 diabetes (30.5% vs. 14.7%), renal dysfunction (34.2% vs. 23.8%), hypertension (67.1% vs. 54.8%), and persistent AF (62.2% vs. 32.2%) were significantly higher in the TIC group (n=82) than in the control group (n=640). The atrioventricular nodal effective refractory period (AVNERP) (303±72 ms vs. 332±86 ms; p=0.017) was significantly shorter in the TIC group than in the control group. A multivariable analysis found that persistent AF [odds ratio (OR), 3.19; 95% confidence interval (CI), 1.94-5.24], renal dysfunction (OR, 1.87; 95% CI, 1.06-3.32), and type 2 diabetes (OR, 2.30; 95% CI, 1.31-4.05) were significantly associated with TIC. Conclusion Comorbid renal dysfunction and type 2 diabetes were clinical features of AF patients with TIC. Persistent AF, and short AVNERP may be involved in the development of TIC.

Comparison of His-Purkinje Conduction System Pacing with Atrial-Ventricular Node Ablation and Pharmacotherapy in HFpEF Patients with Recurrent Persistent Atrial Fibrillation (HPP-AF study)

BACKGROUND

There is currently no particularly effective strategy for patients with persistent atrial fibrillation accompanying heart failure with preserved ejection fraction (HFpEF), especially with recurrent atrial fibrillation after ablation. In this study, we will evaluate a new treatment strategy for patients with persistent atrial fibrillation who had at least two attempts (≧2 times) of radio-frequency catheter ablation but experienced recurrence, and physiologic conduction was reconstructed after atrioventricular node ablation or drug therapy, to control the patient's ventricular rate to maintain a regular heart rhythm, which is called His-Purkinje conduction system pacing (HPCSP) with atrioventricular node ablation.

METHODS AND RESULTS

This investigator-initiated, multicenter prospective randomized controlled trial aimed to recruit 296 randomized HFpEF patients with recurrent atrial fibrillation. All the enrolled patients were randomly assigned to the pacing group or the drug treatment group. The primary endpoint is differences in cardiovascular events and clinical composite endpoints (all-cause mortality) between patients in the HPCSP and drug-treated groups. Secondary endpoints included heart failure hospitalization, exercise capacity assessed by cardiopulmonary exercise tests, quality of life, echocardiogram parameters, 6-minute walk distance, NT-ProBNP, daily patient activity levels, and heart failure management report recorded by the CIED. It is planned to compete recruitment by the end of 2023 and report in 2025.

CONCLUSIONS

The study aims to determine whether His-Purkinje conduction system pacing with atrioventricular node ablation can better improve patients' symptoms and quality of life, postpone the progression of heart failure, and reduce the rate of rehospitalization and mortality of patients with heart failure.

CLINICAL TRIAL REGISTRATION NUMBER

ChiCTR1900027723, URL: http://www.chictr.org.cn/edit.aspx?pid=46128&htm=4.

Arrhythmia-Induced Cardiomyopathy: JACC State-of-the-Art Review

Arrhythmias frequently accompany heart failure and left ventricular dysfunction. Tachycardias, atrial fibrillation, and premature ventricular contractions can induce a reversible form of dilated cardiomyopathy (CM) known as arrhythmia-induced CM (AiCM). The intriguing question is why certain individuals are more susceptible to AiCM, despite similar arrhythmia burdens. The primary challenge is determining the extent of arrhythmias' contribution to left ventricular systolic dysfunction. AiCM should be considered in patients with a mean heart rate of >100 beats/min, atrial fibrillation, or a PVC burden of >10%. Confirmation of AiCM occurs when CM reverses upon eliminating the responsible arrhythmia. Therapy choice depends on the specific arrhythmia, patient comorbidities, and preferences. After left ventricular function is restored, ongoing follow-up is essential if an abnormal myocardial substrate persists. Accurate diagnosis and treatment of AiCM have the potential to enhance patients' quality of life, improve clinical outcomes, and reduce hospital admissions and overall health care costs.

Real-World Outcomes of a Rhythm Control Strategy for Atrial Fibrillation Patients with Reduced Left Ventricular Ejection Fraction (<50%)

Background/Objectives: The effectiveness of a rhythm control strategy in patients with atrial fibrillation (AF) and reduced left ventricular ejection fraction (LVEF < 50%) in real-world practice remains uncertain. Our objective was to evaluate the real-world outcomes of a rhythm control strategy in patients with AF and reduced LVEF, focusing on changes in LV systolic function and brain natriuretic peptide (BNP) levels. Methods: The study retrospectively reviewed the medical records of 80 patients with concurrent AF and reduced LVEF who underwent rhythm control therapy between March 2015 and December 2021. Results: The patients had an average age of 63.6 years and an initial LVEF of 34.3%. Sinus rhythm was restored using anti-arrhythmic drugs (38, 47.5%) or electrical cardioversion (42, 52.5%). Over a follow-up period of 53.0 months, AF recurred in 65% of patients, with 57.7% undergoing catheter ablation. Significant improvements were noted in LVEF (from 34.3% to 55.1%, p < 0.001) and BNP levels (from 752 pg/mL to 72 pg/mL, p < 0.001) at the last follow-up. Nearly all patients (97.5%) continued with the rhythm control strategy during the follow-up period. Conclusions: In real-world settings, a rhythm control strategy proves to be feasible and effective for improving LVEF and reducing BNP levels in AF patients with reduced LVEF.

2023 Cardiac Society of Australia and New Zealand Expert Position Statement on Catheter and Surgical Ablation for Atrial Fibrillation

Catheter ablation for atrial fibrillation (AF) has increased exponentially in many developed countries, including Australia and New Zealand. This Expert Position Statement on Catheter and Surgical Ablation for Atrial Fibrillation from the Cardiac Society of Australia and New Zealand (CSANZ) recognises healthcare factors, expertise and expenditure relevant to the Australian and New Zealand healthcare environments including considerations of potential implications for First Nations Peoples. The statement is cognisant of international advice but tailored to local conditions and populations, and is intended to be used by electrophysiologists, cardiologists and general physicians across all disciplines caring for patients with AF. They are also intended to provide guidance to healthcare facilities seeking to establish or maintain catheter ablation for AF.

Tachycardia-induced metabolic rewiring as a driver of contractile dysfunction

Prolonged tachycardia-a risk factor for cardiovascular morbidity and mortality-can induce cardiomyopathy in the absence of structural disease in the heart. Here, by leveraging human patient data, a canine model of tachycardia and engineered heart tissue generated from human induced pluripotent stem cells, we show that metabolic rewiring during tachycardia drives contractile dysfunction by promoting tissue hypoxia, elevated glucose utilization and the suppression of oxidative phosphorylation. Mechanistically, a metabolic shift towards anaerobic glycolysis disrupts the redox balance of nicotinamide adenine dinucleotide (NAD), resulting in increased global protein acetylation (and in particular the acetylation of sarcoplasmic/endoplasmic reticulum Ca2+-ATPase), a molecular signature of heart failure. Restoration of NAD redox by NAD+ supplementation reduced sarcoplasmic/endoplasmic reticulum Ca2+-ATPase acetylation and accelerated the functional recovery of the engineered heart tissue after tachycardia. Understanding how metabolic rewiring drives tachycardia-induced cardiomyopathy opens up opportunities for therapeutic intervention.

Tachycardia and Atrial Fibrillation-Related Cardiomyopathies: Potential Mechanisms and Current Therapies

Atrial fibrillation (AF) is associated with an increased risk of new-onset ventricular contractile dysfunction, termed arrhythmia-induced cardiomyopathy (AIC). Although cardioembolic stroke remains the most feared and widely studied complication of AF, AIC is also a clinically important consequence of AF that portends significant morbidity and mortality to patients with AF. Current treatments are aimed at restoring sinus rhythm through catheter ablation and rate and rhythm control, but these treatments do not target the underlying molecular mechanisms driving the progression from AF to AIC. Here, we describe the clinical features of the various AIC subtypes, discuss the pathophysiologic mechanisms driving the progression from AF to AIC, and review the evidence surrounding current treatment options. In this review, we aim to identify key knowledge gaps that will enable the development of more effective AIC therapies that target cellular and molecular mechanisms.

Predictors of improvement in left ventricular systolic function after catheter ablation in patients with persistent atrial fibrillation complicated with heart failure

AIMS

The current management of patients with atrial fibrillation (AF) and concomitant heart failure (HF) remains a significant challenge. Catheter ablation (CA) has been shown to improve left ventricular ejection fraction (LVEF) in these patients, but which patients can benefit from CA is still poorly understood. The aim of our study was to determine the predictors of improved ejection fraction in patients with persistent atrial fibrillation (PeAF) complicated with HF undergoing CA.

METHODS AND RESULTS

A total of 435 patients with persistent AF underwent an initial CA between January 2019 and March 2023 in our hospital. We investigated consecutive patients with left ventricular systolic dysfunction (LVEF < 50%) measured by transthoracic echocardiography (TTE) within one month before CA. According to the LVEF changes at 6 months, these patients were divided into an improved group (fulfilling the '2021 Universal Definition of HF' criteria for LVEF recovery) and a nonimproved group. Eighty patients were analyzed, and the improvement group consisted of 60 patients (75.0%). In the univariate analysis, left ventricular end-diastolic diameter (P = 0.005) and low voltage zones in the left atrium (P = 0.043) were associated with improvement of LVEF. A receiver operating characteristic analysis determined that the suitable cutoff value for left ventricular end-diastolic diameter (LVDd) was 59 mm (sensitivity: 85.0%, specificity: 55.0%, area under curve: 0.709). A multivariate analysis showed that LVDd (OR = 0.85; 95% CI: 0.76-0.95, P = 0.005) and low voltage zones (LVZs) (OR = 0.26; 95% CI: 0.07-0.96, P = 0.043) were significantly independently associated with the improvement of LVEF. Additionally, parameters were significantly improved regarding the left atrial diameter, LVDd and ventricular rate after radiofrequency catheter ablation (all p < 0.05).

CONCLUSIONS

The improvement of left ventricular ejection fraction (LVEF) occurred in 75.0% of patients. Our study provides additional evidence that LVDd < 59 mm and no low voltage zones in the left atrium can be used to jointly predict the improvement of LVEF after atrial fibrillation ablation.

Conduction system pacing and atrioventricular node ablation in heart failure: The PACE-FIB study design

AIMS

Atrial fibrillation (AF) worsens the prognosis of patients with heart failure (HF). Successful treatments are still very scarce for those with permanent AF and preserved (HFpEF) or mildly reduced (HFmrEF) ejection fraction. In this study, the long-term benefits and safety profile of heart rate regularization through left-bundle branch pacing (LBBP) and atrioventricular node ablation (AVNA) will be explored in comparison with pharmacological rate-control strategy.

METHODS AND RESULTS

The PACE-FIB trial is a multicentre, prospective, open-label, randomized (1:1) clinical study that will take place between March 2022 and February 2027. A total of 334 patients with HFpEF/HFmrEF and permanent AF will receive either LBBP followed by AVNA (intervention arm) or optimal pharmacological treatment for heart rate control according to European guideline recommendations (control arm). All patients will be followed up for a minimum of 36 months. The primary outcome measure will be the composite of all-cause mortality, HF hospitalization, and worsening HF at 36 months. Other secondary efficacy and safety outcome measures such as echocardiographic parameters, functional status, and treatment-related adverse events, among others, will be analysed too.

CONCLUSION

LBBP is a promising stimulation mode that may foster the clinical benefit of heart rate regularization through AV node ablation compared with pharmacological rate control. This is the first randomized trial specifically addressing the long-term efficacy and safety of this pace-and-ablate strategy in patients with HFpEF/HFmrEF and permanent AF.

Association Between Catheter Ablation for Nonparoxysmal Atrial Fibrillation and Functional Mitral Regurgitation in Patients With Heart Failure With Preserved Ejection Fraction

Functional mitral regurgitation (FMR) often coexists with atrial fibrillation (AF) and may have a causal relation with AF persistence and exacerbation of heart failure (HF). The purpose of this study was to investigate the impact of FMR on AF catheter ablation (AFCA) outcomes and improvement in FMR after AFCA in patients with HF with preserved ejection fraction (HFpEF) and nonparoxysmal AF. Excluding patients with primary valve disease or post-mitral valve repair, 280 patients with HFpEF who underwent CA for nonparoxysmal AF were retrospectively included. All patients completed 1-year follow-up and were assessed for FMR, AF recurrence and HF parameters, including echocardiography. At baseline, FMR was present in 153 (54.6%) patients (mild, n = 112; moderate, n = 40; severe, n = 1), and these were decreased to 70 (25%) significantly 1 year after AFCA (mild, n = 64; moderate, n = 6), 119 patients (78%) had improvement in MR (a decrease of ≥1 level in the severity from baseline to 1 year on echocardiography). Overall, 274 patients (97.9%) had sinus rhythm at the 1-year examination, and recurrent AF-free survival did not differ in patients with and without MR improvement (83.2% vs 82.4%, p = 0.908). However, the MR improvement group had a significantly lower cardiothoracic ratio, left atrial diameter, E/e', and B-type natriuretic peptide levels after 1 year than those in the MR nonimprovement group. In conclusion, the majority of the HFpEF patients with nonparoxysmal AF had improvement of FMR after AFCA with the high maintenance of sinus rhythm, leading to a virtuous cycle of cardiac function.

Right Heart Structure and Function after Electrical Cardioversion for Atrial Fibrillation

INTRODUCTION

Atrial fibrillation (AF) adversely impacts right ventricular (RV) and right atrial (RA) structure and function. There are limited data on these changes after electrical cardioversion (ECV) and the relative contribution of heart rate to evaluate the immediate (1-2 h) and short-term (4-6 weeks) changes in right cardiac chamber dimensions and RV function after ECV in patients with persistent AF.

METHODS

Right cardiac chamber dimensions and RV function were measured in 64 patients using transthoracic echocardiography 1-2 h before, immediately after, and 4-6 weeks after ECV. Associations between changes in right-heart measures and rhythm status at follow-up were assessed using linear regression models.

RESULTS

For patients who remained in sinus rhythm 4-6 weeks after ECV (n = 48), median fractional area change (FAC) at baseline, immediately after ECV, and 4-6 weeks after ECV were 39 (Q1:35, Q3:42) %, 42 (Q1:39, Q3:46) %, 46 (Q1:43, Q3:49) % (p < 0.01); median tricuspid annular plane systolic excursion (TAPSE) values at the same time points were 18 (Q1:17, Q3:20) mm, 20 (Q1:18, Q3:23) mm, and 24 (Q1:22, Q3:26) mm (p < 0.01), respectively. There was no significant difference in RV end systolic area and RA volume index before and after ECV. However, RV end systolic area and RA volume index decreased significantly after 4-6 weeks from a median of 10 (Q1:8, Q3:13) cm2 to 8 (Q1:7, Q3:10) cm2 (p < 0.01), and from a median of 30 (Q1:24, Q3:36) mL/m2 to 24 (Q1:20, Q3:27) mL/m2 (p < 0.01). Changes in TAPSE were significantly associated with sinus rhythm at follow-up (p = 0.027), changes in FAC showed a strong trend to association with sinus rhythm (p = 0.053), and this was not true for RA measures (p = 0.64).

CONCLUSIONS

Among AF patients who remained in sinus rhythm after ECV, RV function improved immediately after ECV with further improvement at 4-6 weeks following sinus rhythm restoration.

Electrical management of heart failure: from pathophysiology to treatment

Electrical disturbances, such as atrial fibrillation (AF), dyssynchrony, tachycardia, and premature ventricular contractions (PVCs), are present in most patients with heart failure (HF). While these disturbances may be the consequence of HF, increasing evidence suggests that they may also cause or aggravate HF. Animal studies show that longer-lasting left bundle branch block, tachycardia, AF, and PVCs lead to functional derangements at the organ, cellular, and molecular level. Conversely, electrical treatment may reverse or mitigate HF. Clinical studies have shown the superiority of atrial and pulmonary vein ablation for rhythm control and AV nodal ablation for rate control in AF patients when compared with medical treatment. Ablation of PVCs can also improve left ventricular function. Cardiac resynchronization therapy (CRT) is an established adjunct therapy currently undergoing several interesting innovations. The current guideline recommendations reflect the safety and efficacy of these ablation therapies and CRT, but currently, these therapies are heavily underutilized. This review focuses on the electrical treatment of HF with reduced ejection fraction (HFrEF). We believe that the team of specialists treating an HF patient should incorporate an electrophysiologist in order to achieve a more widespread use of electrical therapies in the management of HFrEF and should also include individual conditions of the patient, such as body size and gender in therapy fine-tuning.

Effects of Atrial Fibrillation on the Human Ventricle

RATIONALE

Atrial fibrillation (AF) and heart failure often coexist, but their interaction is poorly understood. Clinical data indicate that the arrhythmic component of AF may contribute to left ventricular (LV) dysfunction.

OBJECTIVE

This study investigates the effects and molecular mechanisms of AF on the human LV.

METHODS AND RESULTS

Ventricular myocardium from patients with aortic stenosis and preserved LV function with sinus rhythm or rate-controlled AF was studied. LV myocardium from patients with sinus rhythm and patients with AF showed no differences in fibrosis. In functional studies, systolic Ca2+ transient amplitude of LV cardiomyocytes was reduced in patients with AF, while diastolic Ca2+ levels and Ca2+ transient kinetics were not statistically different. These results were confirmed in LV cardiomyocytes from nonfailing donors with sinus rhythm or AF. Moreover, normofrequent AF was simulated in vitro using arrhythmic or rhythmic pacing (both at 60 bpm). After 24 hours of AF-simulation, human LV cardiomyocytes from nonfailing donors showed an impaired Ca2+ transient amplitude. For a standardized investigation of AF-simulation, human iPSC-cardiomyocytes were tested. Seven days of AF-simulation caused reduced systolic Ca2+ transient amplitude and sarcoplasmic reticulum Ca2+ load likely because of an increased diastolic sarcoplasmic reticulum Ca2+ leak. Moreover, cytosolic Na+ concentration was elevated and action potential duration was prolonged after AF-simulation. We detected an increased late Na+ current as a potential trigger for the detrimentally altered Ca2+/Na+-interplay. Mechanistically, reactive oxygen species were higher in the LV of patients with AF. CaMKII (Ca2+/calmodulin-dependent protein kinase IIδc) was found to be more oxidized at Met281/282 in the LV of patients with AF leading to an increased CaMKII activity and consequent increased RyR2 phosphorylation. CaMKII inhibition and ROS scavenging ameliorated impaired systolic Ca2+ handling after AF-simulation.

CONCLUSIONS

AF causes distinct functional and molecular remodeling of the human LV. This translational study provides the first mechanistic characterization and the potential negative impact of AF in the absence of tachycardia on the human ventricle.

Atrial fibrillation-induced tachycardiomyopathy and heart failure: an underappreciated and elusive condition

Many patients with persistent, chronic, or frequently recurring paroxysmal atrial fibrillation (AF) may develop a tachycardiomyopathy (TCM) with left ventricular (LV) dysfunction and heart failure (HF), which is reversible upon restoration and maintenance of sinus rhythm, when feasible, or via better and tighter ventricular rate (VR) control. Mechanisms involved in producing this leading cause of TCM (AF-TCM) include loss of atrial contraction, irregular heart rate, fast VR, neurohumoral activation, and structural myocardial changes. The most important of all mechanisms relates to optimal VR control, which seems to be an elusive target. Uncontrolled AF may also worsen preexisting LV dysfunction and exacerbate HF symptoms. Data, albeit less robust, also point to deleterious effects of slow VRs on LV function. Thus, a J-shaped relationship between VR and clinical outcome has been suggested, with the optimal VR control hovering at ~ 65 bpm, ranging between 60 and 80 bpm; VRs above and below this range may confer higher morbidity and mortality rates. A convergence of recent guidelines is noted towards a stricter rather than a more lenient VR control with target heart rate < 80 bpm at rest and < 110 bpm during moderate exercise which seems to prevent TCM or improve LV function and exercise capacity and relieve TCM-related symptoms and signs. Of course, restoring and maintaining sinus rhythm is always a most desirable target, when feasible, either with drugs or more likely with ablation. All these issues are herein reviewed, current guidelines are discussed and relevant data are tabulated and pictorially illustrated.

Premature ventricular complexes and development of heart failure in a community-based population

OBJECTIVE

A higher premature ventricular complex (PVC) frequency is associated with incident congestive heart failure (CHF) and death. While certain PVC characteristics may contribute to that risk, the current literature stems from patients in medical settings and is therefore prone to referral bias. This study aims to identify PVC characteristics associated with incident CHF in a community-based setting.

METHODS

The Cardiovascular Health Study is a cohort of community-dwelling individuals who underwent prospective evaluation and follow-up. We analysed 24-hour Holter data to assess PVC characteristics and used multivariable logistic and Cox proportional hazards models to identify predictors of a left ventricular ejection fraction (LVEF) decline and incident CHF, respectively.

RESULTS

Of 871 analysed participants, 316 participants exhibited at least 10 PVCs during the 24-hour recording. For participants with PVCs, the average age was 72±5 years, 41% were women and 93% were white. Over a median follow-up of 11 years, 34% developed CHF. After adjusting for demographics, cardiovascular comorbidities, antiarrhythmic drug use and PVC frequency, a greater heterogeneity of the PVC coupling interval was associated with an increased risk of LVEF decline and incident CHF. Of note, neither PVC duration nor coupling interval duration exhibited a statistically significant relationship with either outcome.

CONCLUSIONS

In this first community-based study to identify Holter-based features of PVCs that are associated with LVEF reduction and incident CHF, the fact that coupling interval heterogeneity was an independent risk factor suggests that the mechanism of PVC generation may influence the risk of heart failure.

A prospective STudy using invAsive haemodynamic measurements foLLowing catheter ablation for AF and early HFpEF: STALL AF-HFpEF

AIMS

The impact of atrial fibrillation (AF) ablation in early heart failure with preserved ejection fraction (HFpEF) is unknown. Our aim was to determine the impact of AF ablation on symptoms and exercise haemodynamic parameters of early HFpEF.

METHODS AND RESULTS

Symptomatic AF patients referred for index AF ablation with ejection fraction ≥50% underwent baseline quality of life questionnaires, echocardiography, cardiac magnetic resonance imaging, exercise right heart catheterisation (exRHC), and brain natriuretic peptide (BNP) testing. HFpEF was defined by resting pulmonary capillary wedge pressure (PCWP) ≥15 mmHg or peak exercise PCWP ≥25 mmHg. Patients with HFpEF were offered AF ablation and follow-up exRHC ≥6 months post-ablation. Of 54 patients undergoing baseline evaluation, 35 (65%) had HFpEF identified by exRHC. HFpEF patients were older (64 ± 10 vs. 54 ± 13 years, P < 0.01), and more frequently female (54% vs. 16%, P < 0.01), hypertensive (63% vs. 16%, P < 0.001), and suffering persistent AF (66% vs. 11%, P < 0.001), compared to those without HFpEF. Twenty HFpEF patients underwent AF ablation and follow-up exRHC 12 ± 6 months post-ablation. Nine (45%) patients no longer fulfilled exRHC criteria for HFpEF at follow-up. Patients remaining arrhythmia free (n = 9, 45%) showed significant improvements in peak exercise PCWP (29 ± 4 to 23 ± 2 mmHg, P < 0.01) and Minnesota Living with Heart Failure (MLHF) score (55 ± 30 to 22 ± 30, P < 0.01) while the remainder did not (PCWP 31 ± 5 to 30.0 ± 4 mmHg, P = NS; MLHF score 55 ± 23 to 25 ± 20, P = NS).

CONCLUSION

Heart failure with preserved ejection fraction frequently coexists in patients with symptomatic AF and preserved ejection fraction. Restoration and maintenance of sinus rhythm in patients with comorbid AF and HFpEF improves haemodynamic parameters, BNP and symptoms associated with HFpEF.

Atrial Fibrillation and Heart Failure: Epidemiology, Pathophysiology, Prognosis, and Management

Atrial fibrillation (AF) and heart failure (HF) have similar risk factors, frequently coexist, and potentiate each other in a vicious cycle. Evidence suggests the presence of AF in both HF with reduced ejection fraction (HFrEF) and HF with preserved ejection fraction (HFpEF) increases the risk of all-cause mortality and stroke, particularly when AF is incident. Catheter ablation may be an effective strategy in controlling symptoms and improving quality of life in AF-HFrEF. Strong data guiding management of AF-HFpEF are lacking largely due to its challenging diagnosis. Improving outcomes associated with these coexistent conditions requires further careful investigation.

Sarcoplasmic reticulum calcium mishandling: central tenet in heart failure?

Excitation-contraction coupling links excitation of the sarcolemmal surface membrane to mechanical contraction. In the heart this link is established via a Ca²⁺-induced Ca²⁺ release process, which, following sarcolemmal depolarisation, prompts Ca²⁺ release from the sarcoplasmic reticulum (SR) though the ryanodine receptor (RyR2). This substantially raises the cytoplasmic Ca²⁺ concentration to trigger systole. In diastole, Ca²⁺ is removed from the cytoplasm, primarily via the sarcoplasmic-endoplasmic reticulum Ca²⁺-dependent ATPase (SERCA) pump on the SR membrane, returning Ca²⁺ to the SR store. Ca²⁺ movement across the SR is thus fundamental to the systole/diastole cycle and plays an essential role in maintaining cardiac contractile function. Altered SR Ca²⁺ homeostasis (due to disrupted Ca²⁺ release, storage, and reuptake pathways) is a central tenet of heart failure and contributes to depressed contractility, impaired relaxation, and propensity to arrhythmia. This review will focus on the molecular mechanisms that underlie asynchronous Ca²⁺ cycling around the SR in the failing heart. Further, this review will illustrate that the combined effects of expression changes and disruptions to RyR2 and SERCA2a regulatory pathways are critical to the pathogenesis of heart failure.

Association Between Atrial Fibrillation and Sudden Cardiac Death

Emerging evidence suggests that atrial fibrillation (AF) may be associated with an increased risk of sudden cardiac death (SCD). However, AF shares risk factors with numerous cardiac conditions, including coronary heart disease and heart failure—the 2 most common substrates for SCD—making the AF-SCD relationship particularly challenging to address. A careful consideration of confounding factors is essential, since interventions for AF will be effective in reducing SCD only if there is a causal association between these 2 conditions. In this translational review, we detail the plausible underlying pathophysiological mechanisms through which AF may promote or lead to SCD, as well as the existing epidemiological evidence supporting an association between AF and SCD. While the role of AF in predicting SCD in the general population appears limited and not established, AF might be integrated to improve risk stratification in some specific phenotypes. Optimal AF management, including that of its associated conditions, appears to be of interest to prevent AF-related SCD, especially because the AF-SCD relationship is in part driven by heart failure.

Metformin therapy confers cardioprotection against the remodeling of gap junction in tachycardia-induced atrial fibrillation dog model

OBJECTIVE

Metformin, introduced in 1957, is widely used as an anti-diabetic drug and has considerable benefits in cardiovascular disease reportedly, dependent or independent on its glucose-lowering effects. Aim of this study was to investigate the effect of metformin on gap junction and the inducibility of AF.

METHODS

Beagle dogs were subjected to acute or chronic pacing at right atrial appendage by a pacemaker to develop an AF model and electrophysiological parameters were measured. In vitro study, a cell fast pacing model was developed by CardioExcyte 96. We performed Western blot, histology immunohistochemical staining and electron microscopy to detect the effect of metformin.

RESULTS

In chronic AF model, the inducibility and duration of AF increased obviously after pacing for 6 weeks compared with sham-operated group (Inducibility, 3.33 ± 5.77 vs. 85.33 ± 7.89%, P<0.0001; Duration, 0.8 ± 0.84 vs. 11 ± 2.67 ms, P<0.0001). Effective refractory periods (ERP) decreased at left and right left atrium and atrial appendages compared with sham-operated group (123.95 ± 6.57 vs. 89.96 ± 7.39 ms P<0.0001). Metformin attenuated the pacing-induced increase in EPR (89.96 ± 7.39 vs. 105.83 ± 7.45 ms, P<0.05), AF inducibility and AF duration (Inducibility, 85.33 ± 7.89 vs. 64.17 ± 7.36%, Duration, 11 ± 2.67 vs. 8.62 ± 1.15 ms, P<0.05). The expression of Cx43 shows a significant downregulation(about 38%, P<0.001) after chronic pacing and treating with metformin could alleviate this decrease(P<0.01). However, the effect of metformin in acute pacing model is limited. The immunohistochemical staining of cardiac tissue also shown that there is more lateralized Cx43 under pacing condition (87.67 ± 2.52 vs. 60.8 ± 9.13%, P<0.005). These pacing-induced lateralize Cx43 could be alleviated by the metformin (48.4 ± 8.62 vs. 60.8 ± 9.13%, P<0.05). Additionally, metformin could affect the interactions of ZO-1 with p-Src/Cx43 via decrease the abnormal cAMP level after pacing (84.04 ± 4.58 vs. 69.34 ± 4.5 nmol/L, P<0.001).

CONCLUSIONS

Metformin could alleviate the vulnerability of AF and attenuate the downregulation of gap junction under pacing condition via AMPK pathway and decreasing the P-Src level.

Efficacy and Safety of Outpatient Clinic-based Elective External Electrical Cardioversion in Patients with Atrial Fibrillation

BACKGROUND AND OBJECTIVES

Little is known about the outcomes of outpatient clinic-based elective external cardioversion (OPC-ECV) for persistent atrial fibrillation (PeAF). We investigated the acute, short-term, and long-term elective external cardioversion (ECV) outcomes.

METHODS

We included 1,718 patients who underwent OPC-ECV (74% male, 61.1±11.0 years old, 90.9% long-standing PeAF, 9.1% after atrial fibrillation [AF] ablation) after excluding patients with atrial tachycardia or inappropriate antiarrhythmic drug medication, and in-patient ECV. Biphasic shocks were delivered sequentially until successful cardioversion was achieved (70-100-150-200-250 J). If ECV failed at 150 J, we administered intravenous amiodarone 150 mg and delivered 200 J.

RESULTS

ECV failed in 11.4%, and the complication rate was 0.47%. Within 3 months, AF recurred in 55.5% (44.7% as sustaining AF, 10.8% as paroxysmal AF), and the AF duration was independently associated (odds ratio [OR], 1.01 [1.00-1.02]; p=0.006), but amiodarone was independently protective (OR, 0.46 [0.27-0.76]; p=0.002, Log rank p<0.001) against an early recurrence. Regarding the long-term recurrence, pre-ECV heart failure was protective against an AF recurrence (hazard ratio, 0.63 [0.41-0.96], p=0.033) over 32 (9-66) months of follow-up. ECV energy (p<0.001) and early recurrence rate within 3 months (p=0.007, Log rank p=0.006) were significantly lower in post-ablation patients than in those with long-standing persistent AF.

CONCLUSIONS

The success rate of OPC-ECV was 88.6%, and the complication rate was low. However, AF recurred in 55.5% within 3 months. Amiodarone was protective against short-term AF recurrences, and long-term AF recurrences were less in patients with baseline heart failure.

Arrhythmia-Induced Cardiomyopathy: JACC State-of-the-Art Review

Arrhythmias coexist in patients with heart failure (HF) and left ventricular (LV) dysfunction. Tachycardias, atrial fibrillation, and premature ventricular contractions are known to trigger a reversible dilated cardiomyopathy referred as arrhythmia-induced cardiomyopathy (AiCM). It remains unclear why some patients are more prone to develop AiCM despite similar arrhythmia burdens. The challenge is to determine whether arrhythmias are fully, partially, or at all responsible for an observed LV dysfunction. AiCM should be suspected in patients with mean heart rate >100 beats/min, atrial fibrillation, and/or premature ventricular contractions burden ≥10%. Reversal of cardiomyopathy by elimination of the arrhythmia confirms AiCM. Therapeutic choice depends on the culprit arrhythmia, patient comorbidities, and preferences. Following recovery of LV function, patients require continued follow-up if an abnormal myocardial substrate is present. Appropriate diagnosis and treatment of AiCM is likely to improve quality of life and clinical outcomes and to reduce hospital admission and health care spending.

Value of Index Beat in Evaluating Left Ventricular Systolic and Diastolic Function in Patients with Atrial Fibrillation: A Dual Pulsed-Wave Doppler Study

Atrial fibrillation (AF) poses challenges in use of the echocardiogram to assess left ventricular (LV) function. The index beat method has been found to agree well with the average method. We aimed to assess the value of the index beat method in evaluation of LV function using the dual pulsed wave Doppler technique. Peak early diastolic mitral inflow velocity (E) and diastolic (e') and systolic (s') mitral annulus velocity were simultaneously obtained and measured beat-to-beat in patients with AF. The index beat s' exhibited the best correlation (r = 0.96 and 0.92, respectively, for septal and lateral wall, both p values = 0.000) with the mean, while E/e' at the pre-index beat, rather than at the index beat-initiated cycle, had the best correlation with the mean (r = 0.88 for septal and 0.97 for lateral wall, both p values = 0.000).

Atrial Fibrillation–Mediated Cardiomyopathy

AF-mediated cardiomyopathy (AMC) is an important reversible cause of heart failure that is likely underdiagnosed in today’s clinical practice. AMC describes AF either as the sole cause for ventricular dysfunction or exacerbating ventricular dysfunction in patients with existing cardiomyopathy or heart failure. Studies suggest that irreversible ventricular and atrial remodeling can occur in AMC, making timely diagnosis and intervention critical to optimize clinical outcome. Clinical correlation between AF onset/burden and progression of cardiomyopathy/heart failure symptoms provides strong evidence for the diagnosis of AMC. Cardiac MRI, continuous cardiac monitoring, and biomarkers are important diagnostic tools. From the therapeutic standpoint, early data suggest that AF ablation may improve long-term outcomes in AMC patients compared with medical rate and rhythm control. Patients with more AF burden and less severe underlying structural heart disease are more likely to experience left ventricle function recovery with successful AF ablation. Despite recent advances, significant knowledge gaps exist in our understanding of the epidemiology, mechanisms, diagnosis, management strategies, and prognosis of AMC.

Five-Year Change in the Renal Function After Catheter Ablation of Atrial Fibrillation

Background

Although it has been reported that renal function can improve after catheter ablation of atrial fibrillation (AF), long‐term changes in renal function and its relationship to rhythm outcomes have not yet been evaluated. We explored the 5‐year change in estimated glomerular filtration rate (eGFR) in AF patients depending on medical therapy and catheter ablation.

Methods and Results

Among 1963 patients who underwent AF catheter ablation and 14 056 with AF under medical therapy in the National Health Insurance Service database, we compared 571 with AF catheter ablation (59±10 years old, 72.3% male, and 66.5% paroxysmal AF) and 1713 with medical therapy after 1:3 propensity‐score matching. All participants had 5 years of serial eGFR data (Chronic Kidney Disease‐Epidemiology Collaboration [CKD‐EPI] method). Catheter ablation improved eGFR_5 yrs (P<0.001), but medical therapy did not. In 2284 matched patients, age (adjusted odds ratio [OR], 0.98 [0.97–0.99]; P<0.001) and AF catheter ablation (adjusted OR, 2.02 [1.67–2.46]; P<0.001) were independently associated with an improved eGFR_5 yrs. Among 571 patients who underwent AF ablation, freedom from AF/atrial tachycardia recurrence after the last AF ablation procedure was independently associated with an improved eGFR_5 yrs (adjusted OR, 1.44 [1.01–2.04]; P=0.043), especially in patients without diabetes mellitus (adjusted OR, 1.78 [1.21–2.63]; P=0.003, P for interaction=0.012). Although underlying renal dysfunction (<60 mL/min/1.73m²) was associated with atrial structural remodeling (adjusted OR, 1.05 [1.00–1.11]; P=0.046), it did not affect the AF ablation rhythm outcome.

Conclusions

AF catheter ablation significantly improved renal function over a 5‐year follow‐up, especially in patients maintaining sinus rhythm without preexisting diabetes mellitus.

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Consequences of chronic frequent premature atrial contractions: Association with cardiac arrhythmias and cardiac structural changes

INTRODUCTION

Frequent premature ventricular contractions (PVCs) can cause cardiomyopathy (CM). Postextrasystolic potentiation (PESP) and irregularity have been in implicated as triggers of PVC-CM. Because both phenomena can also be found in premature atrial contractions (PACs), it is speculated that frequent PACs have similar consequences.

METHODS AND RESULTS

A single-center, retrospective study included all consecutive patients undergoing a 14-day Holter monitors (November 2014 to October 2016). Patients were divided into four groups by ectopy burden group 1 (<1%) and remaining by tertiles (group 2-4). Echocardiographic and arrhythmic data were compared between PAC and PVC burdens. In addition, a translational PAC animal model was used to assess the chronic effects of frequent PACs. A total 846 patients were reviewed. In contrast to PVCs, we found no difference in left ventricular ejection fraction (LVEF), end-systolic and end-diastolic dimensions and presence of CM (LVEF <50%) between different PAC groups. Multivariate regression analysis demonstrated that only PVC burden predicted low EF (odds ratio, 1.1; confidence interval, 1.03-1.13; P = .001). While there was a weak correlation between PAC burden and supraventricular tachycardia (SVT) episodes and atrial fibrillation (AF) burden (r = 0.19; P < .001), there was no correlation between PAC burden and LVEF or CM. Finally, atrial bigeminy in our animal model did not significantly decrease LVEF after 3 months.

CONCLUSION

PAC burden is associated with increased AF and SVT episodes. In contrast to a high PVC burden, a high PAC burden is not associated with CM. Our findings suggest that heart rate irregularity and/or PESP may play a minimal role in the pathophysiology of PVC-CM.

Increased baseline ECG R-R dispersion predicts improvement in systolic function after atrial fibrillation ablation

Background

Atrial fibrillation (AF) is associated with left ventricular (LV) systolic dysfunction which may improve after AF ablation. We hypothesised that increased ventricular irregularity, as measured by R-R dispersion on the baseline ECG, would predict improvement in the left ventricular ejection fraction (LVEF) after AF ablation.

Methods

Patients with LVEF <50% at two US centres (2007–2016), having both a preablation and postablation echocardiogram or cardiac MRI, were included. LVEF improvement was defined as absolute increase in LVEF by >7.5%. Multivariable logistic regression (restricted to echocardiographic/ECG variables) was performed to evaluate predictors of LVEF improvement.

Results

Fifty-two patients were included in this study. LVEF improved in 30 patients (58%) and was unchanged/worsened in 22 patients (42%). Those with versus without LVEF improvement had an increased baseline R-R dispersion (645±155 ms vs 537±154 ms, p=0.02, respectively). The average baseline heart rate in all patients was 93 beats per minute. After multivariable logistic regression, increased R-R dispersion (OR 1.59, 95% CI 1.00 to 2.55, p=0.03) predicted LVEF improvement.

Conclusions

Increased R-R dispersion on ECG was independently associated with improved systolic function after AF ablation. This broadens the existing knowledge of arrhythmia-induced cardiomyopathy, demonstrating that irregular electrical activation (as measured by increased R-R dispersion on ECG) is associated with a cardiomyopathy capable of improving after AF ablation.

Post-cardioversion Improvement in LV Function Defined by 4D Flow Patterns and Energetics in Patients With Atrial Fibrillation

Background

Atrial fibrillation (AF) is a prevalent cause of cardiovascular morbidity, including thromboembolism and heart failure. Left ventricular dysfunction (LVD) detected in AF patients may be either precursor or consequence of the arrythmia. Successful cardioversion of chronic AF is often followed by a transient period of left atrial (LA) stunning, where depressed mechanical atrial contraction persists despite reinstitution of sinus rhythm. To determine if AF-associated LVD would improve with resolution of LA dysfunction, AF patients were examined immediately and 4 weeks after cardioversion to sinus rhythm. 4D flow cardiovascular magnetic resonance (CMR) assesses ventricular function according to the volumes and energetics of functional components of the LV volume. Previously, described 4D CMR markers of LVD include decreased volume and end-diastolic kinetic energy (KE) of the Direct flow, which is the portion of LV volume that passes directly from inflow to outflow in a single cycle. We hypothesize that impaired LV flow patterns and energetics will be found immediately after cardioversion during atrial stunning, and that those parameters will improve as atrial function returns.

Methods

Ten patients with a history of AF underwent CMR 2-3 h (Time-1) and 4 weeks (Time-2), following electrical cardioversion to sinus rhythm. 4D phase-contrast velocity data and morphological images were acquired at a 3T CMR system. Using a previously evaluated method, pathlines were emitted from the LV end diastolic volume (LVEDV) and traced forward and backward in time until end-systole. The LVEDV was automatically separated into four functional flow components whose volume and KE were calculated.

Results

Left atrial fractional area change increased over the follow-up period (P = 0.001), indicating recovery of LA mechanical function. LVEF increased between Time-1 and Time-2 (P = 0.003); LVEDVI did not change (P = 0.319). Over that interval, the ratios of Direct flow/LVEDV volume and KE increased (P = 0.001 and P = 0.003, respectively), while the ratios of Residual volume/LVEDV volume and KE decreased (P = 0.001 and P = 0.005, respectively).

Conclusion

Post-cardioversion recovery of LA function was associated with improvements in conventional and 4D CMR markers of LV function. Flow-specific measures demonstrate the negative but potentially reversible impact of LA dysfunction on volume and energetic aspects of LV function.

The Evolving Role of Catheter Ablation in Patients With Heart Failure and AF

AF and heart failure are emerging epidemics worldwide. Several recent trials have provided a growing evidence base for the benefits of catheter ablation in this patient group, which are yet to be universally adopted in clinical practice guidelines. This paper provides a summary of recent developments in this field and provides pragmatic advice to the treating physician regarding the appropriate role of catheter ablation in the overall management of patients with comorbid AF and heart failure.

Calcium in the Pathophysiology of Atrial Fibrillation and Heart Failure

Atrial fibrillation (AF) is commonly associated with heart failure. A bidirectional relationship exists between the two-AF exacerbates heart failure causing a significant increase in heart failure symptoms, admissions to hospital and cardiovascular death, while pathological remodeling of the atria as a result of heart failure increases the risk of AF. A comprehensive understanding of the pathophysiology of AF is essential if we are to break this vicious circle. In this review, the latest evidence will be presented showing a fundamental role for calcium in both the induction and maintenance of AF. After outlining atrial electrophysiology and calcium handling, the role of calcium-dependent afterdepolarizations and atrial repolarization alternans in triggering AF will be considered. The atrial response to rapid stimulation will be discussed, including the short-term protection from calcium overload in the form of calcium signaling silencing and the eventual progression to diastolic calcium leak causing afterdepolarizations and the development of an electrical substrate that perpetuates AF. The role of calcium in the bidirectional relationship between heart failure and AF will then be covered. The effects of heart failure on atrial calcium handling that promote AF will be reviewed, including effects on both atrial myocytes and the pulmonary veins, before the aspects of AF which exacerbate heart failure are discussed. Finally, the limitations of human and animal studies will be explored allowing contextualization of what are sometimes discordant results.

Predictors of sudden cardiac death in atrial fibrillation: The Atherosclerosis Risk in Communities (ARIC) study

We previously reported that incident atrial fibrillation (AF) is associated with an increased risk of sudden cardiac death (SCD) in the general population. We now aimed to identify predictors of SCD in persons with AF from the Atherosclerosis Risk in Communities (ARIC) study, a community-based cohort study. We included all participants who attended visit 1 (1987-89) and had no prior AF (n = 14,836). Incident AF was identified from study electrocardiograms and hospitalization discharge codes through 2012. SCD was physician-adjudicated. We used cause-specific Cox proportional hazards models, followed by stepwise selection (backwards elimination, removing all variables with p>0.10) to identify predictors of SCD in participants with AF. AF occurred in 2321 (15.6%) participants (age 45-64 years, 58% male, 18% black). Over a median of 3.3 years, SCD occurred in 110 of those with AF (4.7%). Predictors of SCD in AF included higher age, body mass index (BMI), coronary heart disease, hypertension, diabetes, current smoker, left ventricular hypertrophy, increased heart rate, and decreased albumin. Predictors associated only with SCD and not other cardiovascular (CV) death included increased BMI (HR per 5-unit increase, 1.15, 95% CI, 0.97-1.36, p = 0.10), increased heart rate (HR per SD increase, 1.18, 95% CI 0.99-1.41, p = 0.07), and low albumin (HR per SD decrease 1.23, 95% CI 1.02-1.48, p = 0.03). In the ARIC study, predictors of SCD in AF that are not associated with non-sudden CV death included increased BMI, increased heart rate, and low albumin. Further research to confirm these findings in larger community-based cohorts and to elucidate the underlying mechanisms to facilitate prevention is warranted.

Atrial Fibrillation and Heart Failure - Cause or Effect?

There are emerging epidemics of atrial fibrillation (AF) and heart failure in most developed countries, with a significant health burden. Due to many shared pathophysiological mechanisms, which facilitate the maintenance of each condition, AF and heart failure co-exist in up to 30% of patients. In the circumstance where known structural causes of heart failure (such as myocardial infarction) are absent, patients presenting with both conditions present a unique challenge, particularly as the temporal relationship of each condition can often remain elusive from the clinical history. The question of whether the AF is driving, or significantly contributing to the left ventricular (LV) dysfunction, rather than merely a consequence of heart failure, has become ever more pertinent, especially as catheter ablation now offers a significant advancement over existing rhythm control strategies. This paper will review the inter-related physiological drivers of AF and heart failure before considering the implications from the outcomes of recent clinical trials in patients with AF and heart failure.

Impaired Sarcoplasmic Reticulum Calcium Uptake and Release Promote Electromechanically and Spatially Discordant Alternans: A Computational Study

Cardiac electrical dynamics are governed by cellular-level properties, such as action potential duration (APD) restitution and intracellular calcium (Ca) handling, and tissue-level properties, including conduction velocity restitution and cell-cell coupling. Irregular dynamics at the cellular level can lead to instabilities in cardiac tissue, including alternans, a beat-to-beat alternation in the action potential and/or the intracellular Ca transient. In this study, we incorporate a detailed single cell coupled map model of Ca cycling and bidirectional APD-Ca coupling into a spatially extended tissue model to investigate the influence of sarcoplasmic reticulum (SR) Ca uptake and release properties on alternans and conduction block. We find that an intermediate SR Ca uptake rate and larger SR Ca release resulted in the widest range of stimulus periods that promoted alternans. However, both reduced SR Ca uptake and release promote arrhythmogenic spatially and electromechanically discordant alternans, suggesting a complex interaction between SR Ca handling and alternans characteristics at the cellular and tissue level.

New Features of Electrocardiogram in a Case Report of Arrhythmogenic Right Ventricular Cardiomyopathy: A Care-Compliant Article

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is a crucial health problem. With sudden death often being the first presentation, early diagnosis for ARVC is essential. Up to date, electrocardiogram (ECG) is a widely used diagnostic method without invasive harms. To diagnose and treat ARVC as well as possible, we should clearly elucidate its pathophysiological alterations. A 66-year-old farmer presented to the Emergency Department with continuous palpitation, chest tightness, profuse sweating, and nausea with no obvious predisposing causes. An ECG indicated ventricular tachycardia (VT). The patient experienced a sudden drop in blood pressure and acute confusion. After an immediate electrical conversion, his consciousness was gradually restored, and symptoms relieved. The patient was then transferred to the Department of Cardiology to receive ECG, echocardiography, coronary angiogram, biochemical assays, endocardiac tracing, and radiofrequency ablation. In the end, he was diagnosed with ARVC, evidenced by bilateral ventricle dilation and epsilon waves in leads V1-V3. Appropriate therapies were provided for this patient including pharmacological intervention and radiofrequency ablation. Although the diagnosis of ARVC is not difficult, this patient's ECG manifested several interesting features and should be further investigated: T wave inversions were found extensively in the anterior and inferior leads, revealing the involvement of bilateral ventricles; VTs with different morphologies and cycle lengths were found, and some VTs manifested the feature of irregularly irregular rhythm, reminding us to carefully differentiate some special VTs from atrial fibrillation (AF); and epsilon waves gradually appeared in leads V1-V3 and avR since the onset of ARVC. Most importantly, the epsilon waves behind QRS complex appeared in both sinus rhythm and ventricular premature beats/VT originating from cardiac apex, whereas the epsilon waves prior to QRS complex occurred in VT originating from right ventricular outflow tract (RVOT). The features of T wave inversion and epsilon wave in ECGs and the appearance of VTs with different morphologies can reflect the progression of ARVC. The position relationship between epsilon wave and QRS complex in VT depends on ventricular activation sequence, that is, the localization of epsilon wave depends on where VT is originating from.

Comorbidity of atrial fibrillation and heart failure

Atrial fibrillation (AF) and heart failure (HF) are evolving epidemics, together responsible for substantial human suffering and health-care expenditure. Ageing, improved cardiovascular survival, and epidemiological transition form the basis for their increasing global prevalence. Although we now have a clear picture of how HF promotes AF, gaps remain in our knowledge of how AF exacerbates or even causes HF, and how the development of HF affects the outcome of patients with AF. New data regarding HF with preserved ejection fraction and its unique relationship with AF suggest a possible role for AF in its aetiology, possibly as a trigger for ventricular fibrosis. Deciding on optimal treatment strategies for patients with both AF and HF is increasingly difficult, given that results from trials of pharmacological rhythm control are arguably obsolete in the age of catheter ablation. Restoring sinus rhythm by catheter ablation seems successful in the medium term and improves HF symptoms, functional capacity, and left ventricular function. Long-term studies to examine the effect on rates of stroke and death are ongoing. Guidelines continue to evolve to keep pace with this rapidly changing field.

Heart Rate, Life Expectancy and the Cardiovascular System: Therapeutic Considerations

It has long been known that life span is inversely related to resting heart rate in most organisms. This association between heart rate and survival has been attributed to the metabolic rate, which is greater in smaller animals and is directly associated with heart rate. Studies have shown that heart rate is related to survival in apparently healthy individuals and in patients with different underlying cardiovascular diseases. A decrease in heart rate due to therapeutic interventions may result in an increase in survival. However, there are many factors regulating heart rate, and it is quite plausible that these may independently affect life expectancy. Nonetheless, a fast heart rate itself affects the cardiovascular system in multiple ways (it increases ventricular work, myocardial oxygen consumption, endothelial stress, aortic/arterial stiffness, decreases myocardial oxygen supply, other) which, in turn, may affect survival. In this brief review, the effects of heart rate on the heart, arterial system and survival will be discussed.

Atrial fibrillation: effects beyond the atrium?

Atrial fibrillation (AF) is the most common sustained clinical arrhythmia and is associated with significant morbidity, mostly secondary to heart failure and stroke, and an estimated two-fold increase in premature death. Efforts to increase our understanding of AF and its complications have focused on unravelling the mechanisms of electrical and structural remodelling of the atrial myocardium. Yet, it is increasingly recognized that AF is more than an atrial disease, being associated with systemic inflammation, endothelial dysfunction, and adverse effects on the structure and function of the left ventricular myocardium that may be prognostically important. Here, we review the molecular and in vivo evidence that underpins current knowledge regarding the effects of human or experimental AF on the ventricular myocardium. Potential mechanisms are explored including diffuse ventricular fibrosis, focal myocardial scarring, and impaired myocardial perfusion and perfusion reserve. The complex relationship between AF, systemic inflammation, as well as endothelial/microvascular dysfunction and the effects of AF on ventricular calcium handling and oxidative stress are also addressed. Finally, consideration is given to the clinical implications of these observations and concepts, with particular reference to rate vs. rhythm control.