Age-related changes in the electrophysiologic properties of the atrium in patients with no history of atrial fibrillation

Atrial Fibrillation Structural Substrates: Aetiology, Identification and Implications

Atrial remodelling in AF underlines the electrical, structural and mechanical changes in the atria of patients with AF. Several risk factors for AF contribute to the development of the atrial substrate, with some evidence that atrial remodelling reversal is possible with targeted intervention. In this article, the authors review the electrophysiological changes that characterise the atrial substrate in patients with AF risk factors. They also discuss the pitfalls of mapping the atrial substrate and the implications for developing tailored ablation strategies to improve outcomes in patients with AF.

Age as a Critical Determinant of Atrial Fibrillation: A Two-sided Relationship

The incidence of atrial fibrillation (AF), the most common sustained arrhythmia and a major public health burden, increases exponentially with age. However, mechanisms underlying this long-recognized association remain incompletely understood. Experimental and human studies have demonstrated the involvement of aging in several arrhythmogenic processes, including atrial electrical and structural remodelling, disturbed calcium homeostasis, and enhanced atrial ectopic activity/increased vulnerability to re-entry induction. Given this wide range of putative mechanisms, the task of delineating the specific effects of aging responsible for AF promotion is not simple, as aging is itself associated with increasing prevalence of a host of AF-predisposing conditions, including heart failure, coronary artery disease, and hypertension. Although we usually think of old age promoting AF, there is also evidence that young age may actually have a protective effect against AF occurrence. For example, the low AF incidence among populations of young patients with significant structural congenital heart disease and substantial atrial enlargement/remodelling suggests that younger age might protect against fibrillation in the diseased atrium; efforts at understating how younger age may prevent AF might be helpful in elucidating missing mechanistic links between AF and age. The goal of this paper is to review the epidemiologic and pathophysiologic evidence regarding mechanisms underlying age-related AF. Although the therapeutic options for AF have recently improved, major gaps still remain and a better understanding of the special relationship between age and AF may be important for the identification of new targets for therapeutic innovation.

Characteristics of Cardiac Rhythm and Conduction Abnormalities Diagnosed in Mobile Emergency Units in Central Romania

Background: Cardiac arrhythmias and conduction abnormalities are frequently identified by emergency medical service staff in patients requesting emergency services.

Methods: We conducted a prospective observational study that aimed to analyze the characteristics of rhythm and conduction abnormalities in prehospital settings, in patients who requested emergency medical assistance for symptoms indicative for an arrhythmia or conduction abnormalities.

Results: From 180 patients included in the study (90 from a tertiary and 90 from a non-tertiary medical center), 92.78% presented an arrhythmia and 15.56% a conduction abnormality. A clear etiology was found in only 29.44% of cases. Ischemic patients presented a higher rate of atrial fibrillation (AF) (p <0.0001), while sinus tachycardia was more common in non-ischemic subjects (p = 0.02). Patients younger than 50 years of age presented higher rates of sinus tachycardia (p <0.0001) and right bundle branch block (p = 0.001), while those older than 50 years presented higher rates of AF (p <0.0001) and ventricular extrasystole (p = 0.014). There were no differences regarding the type of arrhythmia diagnosed in emergency settings, neither between genders or provenance environments, nor between regions served by a tertiary versus non-tertiary base station hospital.

Conclusions: The most frequently diagnosed arrhythmias in prehospital settings were atrial fibrillation and sinus tachycardia, while atrioventricular blocks were the most frequent conduction disturbances. Young patients more frequently present sinus tachycardia or right bundle branch blocks, while older subjects are more prone to develop ischemia-related AF and ventricular extrasystole. The lack of any significant differences between systems served by a tertiary vs. non-tertiary medical center indicates an efficient emergency system of care regardless of the geographical region.

Longitudinal relationships of periodic limb movements during sleep and incident atrial fibrillation

OBJECTIVES

This study aimed to examine relationship between periodic limb movements during sleep (PLMS) and incident atrial fibrillation/flutter (AF).

METHODS

Prospective multicenter cohort (n = 2273: adjudicated AF group; n = 843: self-reported AF group) of community-dwelling men without prevalent AF were followed for an average of 8.3 years (adjudicated) and 6.5 years (self-reported). PLMS index (PLMI, <5 (ref), ≥5 to <30, ≥30) and PLM arousal index (PLMAI, <1 (ref), ≥1 to <5, ≥5) were measured by polysomnography. Incident adjudicated and self-reported AF were analyzed by Cox proportional hazards and logistic regression, respectively, and adjusted for age, clinic, race, body mass index (BMI), alcohol use, cholesterol level, cardiac medications, pacemaker, apnea-hypopnea index, renal function, and cardiac risk. The interaction of age and PLMS was examined.

RESULTS

In this primarily Caucasian (89.8%) cohort of older men (mean age 76.1 ± 5.5 years) with BMI of 27.2 ± 3.7, there were 261 cases (11.5%) of adjudicated and 85 cases (10.1%) of self-reported incident AF. In the overall cohort, PLMI and PLMAI were not associated with adjudicated or self-reported AF. There was some evidence of an interaction of age and PLMI (p = 0.08, adjudicated AF) and PLMAI (p ≤ 0.06, both outcomes). Among men aged ≥76 years, the highest PLMI tertile was at increased risk of adjudicated AF (≥30 vs. <5; hazard ratio (HR) = 1.63, 1.01-2.63) and the middle PLMAI tertile predicted increased risk of both outcomes (1 to <5 vs. <1; adjudicated, HR = 1.65, 1.05-2.58; self-reported HR = 5.76, 1.76-18.84). No such associations were found in men aged <76 years.

CONCLUSIONS

Although PLMS do not predict AF incidence in the overall cohort, the findings suggest PLMS increases incident AF risk in the older subgroup.

Central Sleep-disordered Breathing Predicts Incident Atrial Fibrillation in Older Men

RATIONALE

Although research supports a sleep-disordered breathing and atrial fibrillation association, prospective data examining sleep-disordered breathing predicting incident atrial fibrillation are lacking.

OBJECTIVES

To investigate sleep-disordered breathing indices as predictors of incident atrial fibrillation.

METHODS

A cohort (n = 843) of ambulatory older men without prevalent atrial fibrillation was assessed for baseline sleep indices: apnea-hypopnea index, central sleep apnea (central apnea index, ≥5 vs. <5), central sleep apnea or Cheyne-Stokes respiration, obstructive apnea-hypopnea index, and percentage of sleep time with less than 90% oxygen saturation. Incident clinically symptomatic adjudicated or self-reported atrial fibrillation outcome was ascertained (mean follow-up, 6.5 ± 0.7 yr). We used logistic regression models adjusted for age, race, body mass index, cardiopulmonary disease, alcohol use, pacemaker, cholesterol, cardiac medications, and alternate apnea type for obstructive and central apnea. Age interaction terms and median age-stratified analyses were performed.

MEASUREMENTS AND MAIN RESULTS

Central sleep apnea (odds ratio [OR], 2.58; 95% confidence interval [CI], 1.18-5.66) and Cheyne-Stokes respiration with central sleep apnea (OR, 2.27; 95% CI, 1.13-4.56), but not obstructive apnea or hypoxemia, predicted incident atrial fibrillation. Central apnea, Cheyne-Stokes respiration, and sleep-disordered breathing-age interaction terms were significant (P < 0.05). Unlike the case with younger participants, among participants aged 76 years or older (albeit with small atrial fibrillation counts), atrial fibrillation was related to central apnea (OR, 9.97; 95% CI, 2.72-36.50), Cheyne-Stokes respiration with central apnea (OR, 6.31; 95% CI, 1.94-20.51), and apnea-hypopnea index (OR, 1.22; 95% CI, 1.08-1.39 [per 5-unit increase]).

CONCLUSIONS

In older men, central apnea and Cheyne-Stokes respiration predicted increased atrial fibrillation risk, with findings being strongest in older participants in whom overall sleep-disordered breathing also increased atrial fibrillation risk.

The Stress-Response MAP Kinase Signaling in Cardiac Arrhythmias

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

High risk factors of atrial fibrillation in type 2 diabetes: results from the Chinese Kailuan study

BACKGROUND

The pathophysiological mechanisms for atrial fibrillation (AF) vulnerability in diabetic patients are largely unclear.

AIM

To investigate the high risk factors of AF in Chinese Kailuan diabetes.

DESIGN

A retrospective review of AF in Chinese Kailuan diabetes.

METHODS

Research and statistic analysis on the clinical data of 9050 diabetic patients from Kailuan Coal Mine Group Corporation who participated in a health survey from July 2006 to October 2007.

RESULTS

Sixty diabetic patients (50 males and 10 females) were diagnosed with AF during the health checkup, with a prevalence of 0.66% (0.67% in males and 0.62% in females). Univariate analysis showed that patients with AF were older and had higher levels of serum uric acid (UA), pulse pressure, serum c-reactive protein and anti-hypertensive medication usage, but lower levels of fasting blood glucose and triglycerides (TG). Multivariate analysis indicated that older age (OR = 1.09; 95% CI: 1.06-1.12), increased UA (OR = 1.01; 95% CI: 1.00-1.01) and decreased TG (OR = 0.71; 95% CI: 0.55-0.92) were independent predictive factors of AF after adjusting for other variables. After gender stratification, age and UA remained as independent predictive factors of AF in both male and female patients. However, TG had an independent inverse association with AF in male patients only.

CONCLUSIONS

Age and UA are independent predictive factors of AF in both male and female diabetic patients. TG is inversely correlated with AF in male diabetic patients only.

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

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

Comparison of Atrial Fibrillation in the Young versus That in the Elderly: A Review

The incidence and prevalence of atrial fibrillation (AF) are projected to increase significantly worldwide, imposing a significant burden on healthcare resources. The disease itself is extremely heterogeneous in its epidemiology, pathophysiology, and treatment options based on individual patient characteristics. Whilst ageing is well recognised to be an independent risk factor for the development of AF, this condition also affects the young in whom the condition is frequently symptomatic and troublesome. Traditional thinking suggests that the causal factors and pathogenesis of the condition in the young with structurally normal atria but electrophysiological "triggers" in the form of pulmonary vein ectopics leading to lone AF are in stark contrast to that in the elderly who have AF primarily due to an abnormal substrate consisting of fibrosed and dilated atria acting in concert with the pulmonary vein triggers. However, there can be exceptions to this rule as there is increasing evidence of structural and electrophysiological abnormalities in the atrial substrate in young patients with "lone AF," as well as elderly patients who present with idiopathic AF. These reports seem to be blurring the distinction in the pathophysiology of so-called idiopathic lone AF in the young versus that in the elderly. Moreover with availability of improved and modern investigational and diagnostic techniques, novel causes of AF are being reported thereby seemingly consigning the diagnosis of "lone AF" to a rather mythical existence. We shall also elucidate in this paper the differences seen in the epidemiology, causes, pathogenesis, and clinical features of AF in the young versus that seen in the elderly, thereby requiring clearly defined management strategies to tackle this arrhythmia and its associated consequences.

Angiotensin II receptor type 1 is upregulated in atrial tissue of patients with rheumatic valvular disease with atrial fibrillation

OBJECTIVE

The purpose of this study was to examine the changes in expression of angiotensin II receptor type 1/2 in left or right atrial tissue from patients with rheumatic valvular disease with or without atrial fibrillation.

METHODS

Atrial tissue samples were obtained from 39 patients with rheumatic mitral valve disease during cardiac surgery. Among these patients, there were 25 with atrial fibrillation and 14 with sinus rhythm. The level of angiotensin II receptor type 1 or type 2 mRNA transcription was measured by means of a semiquantitative reverse transcription-polymerase chain reaction technique. Expression of angiotensin II receptor type 1 or type 2 protein was detected by means of immunohistochemistry assay and Western blot analysis.

RESULTS

The inner diameter of the left atrium was clearly enlarged in the atrial fibrillation group in comparison with that seen in the sinus rhythm group. The expression levels of both angiotensin II receptor type 1 mRNA and protein in the left atrial tissue were significantly increased in the patients with atrial fibrillation compared with those seen in patients with sinus rhythm (P < .05). Interestingly, the comparison of angiotensin II receptor type 2 expression levels in the left atrial tissue between these 2 groups is not statistically significant. In addition, the results of angiotensin II receptor type 1 or 2 expression in the right atrial tissue did not show any obvious change in the patients with atrial fibrillation versus those with sinus rhythm.

CONCLUSIONS

Expression of angiotensin II receptor type 1 but not type 2 is highly upregulated only in the left atrial tissue of patients with rheumatic valvular disease with atrial fibrillation. This suggests that there is a possible pathophysiologic role of the renin-angiotensin system in patients with atrial fibrillation and that a series of effects mediated by the activation of angiotensin II receptor type 1 in the left atrial tissue might be one of the molecular mechanisms involved in the process of atrial remodeling in atrial fibrillation.

Ageing to arrhythmias: conundrums of connections in the ageing heart

The proportion of the population that is elderly continues to increase, leading to an increasing need to address problems chiefly associated with old age. Progressive ageing of the heart is associated with an increasing incidence of arrhythmias and disorders of the normal origin of the heartbeat, the sinoatrial node. This intrinsic pacemaker of the heart has an increasing tendency with age to lose its dominant role in pacing the heart, and regulation of heart rate becomes erratic. This 'sick sinus syndrome' is associated with fainting, palpitations, shortness of breath and sudden death. Current treatment of this condition is by implantation of an artificial pacemaker, an intervention increasingly required with age. The current evidence suggests that the normal heartbeat fails due to changes in the expression of critical proteins that ensure the correct production and conduction of the cardiac action potential. Depletion of a protein directly responsible for providing electrical connections between the cells of the heart, connexin 43, appears to leave the normal cardiac pacemaker disconnected and unable to drive the heart. This process may be associated with age-dependent changes in stress-related signalling. Simple interventions such as exercise could impact on the processes hypothesized to be involved and may offer a means to preserve the stability of the electrical activity of the heart into old age without pharmacological manipulation.

Electrophysiologic characteristics of atria in patients without heart disease

BACKGROUND

The significance of atrial fibrillation or tachycardia (AF) induction remains debatable. Some believe that the presence of heart disease (HD) increases the sensitivity and decreases the specificity of programmed atrial stimulation (PAS). There are few data in patients without HD. The purpose of the study was to evaluate the results of PAS in asymptomatic patients without HD and in those with documented spontaneous AF, but without HD, to know the diagnosis value of the technique.

METHODS

A total of 4,900 PAS were consecutively performed. The control group (I, N=67) was defined by the absence of preexcitation syndrome, dizziness/syncope, hypertension, history of tachycardia, or other documented HD together with a normal 2D echocardiogram and 24-hour Holter monitoring. They were compared to a group (II) of 54 patients with documented paroxysmal AF and without HD. PAS used one and two extrastimuli, delivered during sinus rhythm and two drive rates (600, 400 ms). Atrial-effective refractory periods (ARP), their adaptation to cycle length, and conduction times were noted. AF induction was defined as the induction of AF lasting more than 1 minute.

RESULTS

Group I patients (1.4% of 4,900) were younger than group II (51 +/- 17 vs 65 +/- 11 years, P < 0.001). A single extrastimulus never induced sustained AF in group I, but did so in 11 group II patients (20%); sustained AF was induced by two extrastimuli in 15 group I patients (22%) and in 31 group II patients (57%) (P < 0.001). There were no ARP and conduction time differences in group I patients with and without inducible AF, but there was a longer sinus cycle length in patients with inducible AF (977 +/- 164 vs 838 +/- 141 ms, P < 0.02). There were no electrophysiological differences in group II patients with and without inducible AF. No group I patient developed spontaneous AF (follow-up 4 +/- 2 years). The sensitivity of PAS with one extrastimulus was 20% and the specificity 100%; the sensitivity of PAS with two extrastimuli was 57% and the specificity 78%.

CONCLUSION

Sustained AF was not induced by one extrastimulus in control patients without symptoms, nor heart disease, but sustained AF was induced by two extrastimuli in 22% of these patients. The induction of a sustained AF by two extrastimuli should be interpreted cautiously, particularly in patients with a relative sinus bradycardia. However, the sensitivity of PAS with one extrastimulus was very low and two extrastimuli were required in patients with spontaneous AF to induce the tachycardia. Other electrophysiological parameters were not useful to differentiate patients with and without inducible AF.