Factors predisposing to the development of atrial fibrillation

Cardiac rehabilitation for heart failure and atrial fibrillation: a propensity- matched study

BACKGROUND

Atrial fibrillation (AF) is common in individuals with heart failure (HF). Individuals with HF and AF may have a reduced functional capacity and quality of life (QoL) which leads to hospital admission and burden on clinical services. Evidence supported the effect of exercise training in individuals with HF. However, there is no existing data on the effectiveness of comprehensive cardiac rehabilitation (CR) in individuals with coexisting HF and AF.

AIM

To explore the effect of CR in individuals with HF and AF compared with those with HF and no-coexisting AF.

METHODS

Using CR database, individuals with HF and AF were identified and propensity matched to those with no coexisting AF. The change in incremental shuttle walking test, Heart Disease Quality of Life questionnaire, Hospital Anxiety and Depression Scores were compared between groups pre-CR and post-CR.

RESULTS

149 individuals were propensity matched from each group. The mean±SD age of the matched sample was 73.4±8 years, body mass index 29±5.5 kg/m2, left ventricular ejection fraction 35.2±9.8% and 56% were male.A statistically significant improvements in exercise capacity, heart disease QoL, anxiety and depression scores were observed within each group. There were no significant differences between groups for any of these outcome measures.

CONCLUSIONS

Individuals with HF and AF gain a similar improvement in exercise capacity and health related QoL outcomes as individuals with no coexisting AF following CR. The presence of AF did not compromise the effectiveness of CR.

Overview of Cardiac Arrhythmias and Treatment Strategies

Maintenance of normal cardiac rhythm requires coordinated activity of ion channels and transporters that allow well-ordered propagation of electrical impulses across the myocardium. Disruptions in this orderly process provoke cardiac arrhythmias that may be lethal in some patients. Risk of common acquired arrhythmias is increased markedly when structural heart disease caused by myocardial infarction (due to fibrotic scar formation) or left ventricular dysfunction is present. Genetic polymorphisms influence structure or excitability of the myocardial substrate, which increases vulnerability or risk of arrhythmias in patients. Similarly, genetic polymorphisms of drug-metabolizing enzymes give rise to distinct subgroups within the population that affect specific drug biotransformation reactions. Nonetheless, identification of triggers involved in initiation or maintenance of cardiac arrhythmias remains a major challenge. Herein, we provide an overview of knowledge regarding physiopathology of inherited and acquired cardiac arrhythmias along with a summary of treatments (pharmacologic or non-pharmacologic) used to limit their effect on morbidity and potential mortality. Improved understanding of molecular and cellular aspects of arrhythmogenesis and more epidemiologic studies (for a more accurate portrait of incidence and prevalence) are crucial for development of novel treatments and for management of cardiac arrhythmias and their consequences in patients, as their incidence is increasing worldwide.

Reduction in atrial and pulmonary vein stretch as a therapeutic target for prevention of atrial fibrillation

Atrial fibrillation (AF) is a common cardiac arrhythmia that is associated with increased mortality. Heart failure, hypertension, valvular disease, and obstructive sleep apnea are risk factors for incident AF. A common characteristic of these diseases is that they increase atrial wall stretch. Multiple experimental studies confirm a proarrhythmic effect of atrial stretch. Conversely, a reduction in stretch is antiarrhythmic. A therapeutic target for AF, therefore, lies in local reduction of atrial stretch. This review focuses on atrial stretch and its clinical associations in patients with AF and its downstream effects on electrophysiology. We discuss the possible application of targeted atrial stretch reduction in AF prevention. We conclude that a reduction in local atrial stretch should be considered an essential element in rhythm control.

Early atrial remodeling predicts the risk of cardiovascular events in patients with metabolic syndrome: a retrospective cohort study

Background

This study aims to assess the prevalence of atrial cardiomyopathy (ACM) in patients with new-onset metabolic syndrome (MetS) and investigate whether ACM could be a predictor of hospital admission for cardiovascular (CV) events.

Methods

Patients with MetS who were free of clinically proven atrial fibrillation and other CV diseases (CVDs) at baseline were included in the present study. The prevalence of ACM was compared between MetS patients with and without left ventricular hypertrophy (LVH). The time to first hospital admission for a CV event between subgroups was assessed using the Cox proportional hazard model.

Results

A total of 15,528 MetS patients were included in the final analysis. Overall, LVH patients accounted for 25.6% of all newly diagnosed MetS patients. ACM occurred in 52.9% of the cohort and involved 74.8% of LVH patients. Interestingly, a significant percentage of ACM patients (45.4%) experienced MetS without LVH. After 33.2 ± 20.6 months of follow-up, 7,468 (48.1%) patients had a history of readmission due to CV events. Multivariable Cox regression analysis revealed that ACM was associated with an increased risk of admission for CVDs in the MetS patients with LVH [hazard ratio (HR), 1.29; 95% confidence interval (CI), 1.142-1.458; P < 0.001]. Likewise, ACM was found to be independently associated with hospital readmission due to CVD-related events in MetS patients without LVH (HR, 1.175; 95% CI, 1.105-1.250; P < 0.001).

Conclusion

ACM is a marker of early myocardial remodeling and predicts hospitalization for CV events in patients with MetS.

An Investigation of Left Ventricular Valve Disorders and the Mechano-Electric Feedback Using a Synergistic Lumped Parameter Cardiovascular Numerical Model

Cardiac diseases and failure make up one of largest contributions to global mortality and significantly detriment the quality of life for millions of others. Disorders in the valves of the left ventricle are a prominent example of heart disease, with prolapse, regurgitation, and stenoses—the three main valve disorders. It is widely known that mitral valve prolapse increases the susceptibility to cardiac arrhythmia. Here, we investigate stenoses and regurgitation of the mitral and aortic valves in the left ventricle using a synergistic low-order numerical model. The model synergy derives from the incorporation of the mechanical, chemical, and electrical elements. As an alternative framework to the time-varying elastance (TVE) method, it allows feedback mechanisms at work in the heart to be considered. The TVE model imposes the ventricular pressure–volume relationship using a periodic function rather than calculating it consistently. Using our synergistic approach, the effects of valve disorders on the mechano-electric-feedback (MEF) are investigated. The MEF is the influence of cellular mechanics on the electrical activity, and significantly contributes to the generation of arrhythmia. We further investigate stenoses and regurgitation of the mitral and aortic valves and their relationship with the MEF and generation of arrhythmia. Mitral valve stenosis is found to increase the sensitivity to arrhythmia-stimulating systolic stretch, and reduces the sensitivity to diastolic stretch. Aortic valve stenosis does not change the sensitivity to arrhythmia-stimulating stretch, and regurgitation reduces it. A key result is found when valve regurgitation is accompanied by diastolic stretch. In the presence of MEF disorder, ectopic beats become far more frequent when accompanied by valve regurgitation. Therefore, arrhythmia resulting from a disorder in the MEF will be more severe when valve regurgitation is present.

The use of MRI in quantification of the atrial fibrosis in patients with rheumatic mitral disease

Background

Atrial fibrillation (AF) is a common type of arrhythmia with higher incidence in countries with increased prevalence of rheumatic heart disease (RHD), where AF contributes to significant morbidity and mortality in young population. Atrial fibrosis is a common feature of AF. Delayed enhancement MRI (DE-MRI) is a well-established method for characterizing fibrosis in ventricles. The use of DE-MRI to detect left atrial fibrosis helps to evaluate the extent of atrial structural remodeling non-invasively. The aim of this study is to evaluate the atrial fibrosis in patients with mitral valve disease, using the DE MRI, regarding its amount, distribution, and relation to AF.

Results

Patients with AF were older and have longer duration of symptoms, smaller valve area, larger LA size, and more fibrosis at the left atrium (with the posterior wall most frequently involved) in comparison to those with sinus rhythm. Patients with atrial fibrosis were older and have longer duration of symptoms, smaller valve area, and larger LA, and most of them had AF compared to those without fibrosis. The comparison between types of AF showed a significant difference in the amount of atrial fibrosis that increases across the spectrum of AF.

Conclusion

In patients with rheumatic mitral valve diseases, AF is associated with more atrial fibrosis as assessed by DE-MRI. Atrial fibrosis is the best independent predictor of AF.

Cardiac Mechano-Electric Coupling: Acute Effects of Mechanical Stimulation on Heart Rate and Rhythm

The heart is vital for biological function in almost all chordates, including humans. It beats continually throughout our life, supplying the body with oxygen and nutrients while removing waste products. If it stops, so does life. The heartbeat involves precise coordination of the activity of billions of individual cells, as well as their swift and well-coordinated adaption to changes in physiological demand. Much of the vital control of cardiac function occurs at the level of individual cardiac muscle cells, including acute beat-by-beat feedback from the local mechanical environment to electrical activity (as opposed to longer term changes in gene expression and functional or structural remodeling). This process is known as mechano-electric coupling (MEC). In the current review, we present evidence for, and implications of, MEC in health and disease in human; summarize our understanding of MEC effects gained from whole animal, organ, tissue, and cell studies; identify potential molecular mediators of MEC responses; and demonstrate the power of computational modeling in developing a more comprehensive understanding of ‟what makes the heart tick.ˮ.

DACT2 regulates structural and electrical atrial remodeling in atrial fibrillation

Background

Atrial fibrillation (AF) is the most common sustained arrhythmia. DACT2 is a novel and important mediator of signaling pathways. The aim of this study was to investigate the clinical significance and functions of DACT2 expression in AF.

Methods

Immunohistochemistry was used to detect the DACT2 expression pattern in valvular disease patients. DACT2 was overexpressed in HL-1 cells and primary atrial fibroblasts. The expression levels of the potassium channel, the L-type calcium current channel, sodium ion channel proteins and collagen proteins were detected by real-time polymerase chain reaction (RT-PCR). The proteins involved in the Wnt and TGF-β signaling pathways were detected after DACT2 overexpression by western blotting.

Results

DACT2 expression was significantly associated with AF (P=0.016). The fibrosis ratio in the strong DACT2 expression group was significantly lower than that in the weak DACT2 expression group (weak: 0.198±0.091, strong: 0.129±0.064, P=0.048), and a negative correlation between DACT2 expression levels and fibrosis severity was observed (Spearman rho =−0.476, P=0.010). DACT2 significantly increased the expression levels of KCNE5 and decreased the levels of KCNH2 and SCN5A. Overexpression of DACT2 significantly inhibited the expression of collagen I and collagen III in primary rat atrial fibroblasts. DACT2 could facilitate β-catenin accumulation by reducing its phosphorylation at Thr41/Ser45 in HL-1 cells and inhibit the TGF-β signaling pathway in primary atrial fibroblasts.

Conclusions

DACT2 played a role in AF by regulating both structural and electrical atrial remodeling and by affecting β-catenin accumulation and TGF-β signaling, and it could serve as a protective factor against AF in valvular heart disease.

Does minimal invasive cardiac surgery reduce the incidence of post-operative atrial fibrillation?

Atrial fibrillation (AF) is the most common post-operative complication and tends to be the most common arrhythmia after cardiac surgery. The etiology and risk factors for post-operative AF are poorly understood, but older age, large left atrium, diffuse coronary artery disease, a history of AF paroxysms and in general, pre-existing cardiac conditions that cause restricting and susceptibility towards inflammation have been consistently linked with post-operative atrial fibrillation (POAF). It has been traditionally thought that post-operative AF is transient, well-tolerated, benign to the patient and self-limiting complication of cardiac surgery that was temporary and easily treated. However, recent evidence suggests that POAF may be more "malignant" than previously thought, associated with follow-up mortality and morbidity. Several minimally invasive approaches, including the right parasternal approach, upper and lower mini-sternotomy (MS), V-shaped, Z-shaped, inverse-T, J-, reverse-C and reverse-L partial MS, transverse sternotomy and right mini-thoracotomy, have been developed for cardiac surgery operations since 1993 and have been associated with better outcomes and lower perioperative morbidity compared to full sternotomy (FS). The common goal of several minimally invasive approaches is to reduce invasiveness and surgical trauma. According to a statement from the American Heart Association (AHA), the term "minimally invasive" refers to a small chest wall incision that does not include a FS. This review is aimed to evaluate the use of minimally invasive techniques like mini-sternotomy, mini-thoracotomy and hybrid techniques versus conventional techniques which are used in cardiac surgery and to compare the frequency of post-operative AF and its effect on post-operative complications, morbidity and mortality, after cardiac surgery operations with FS versus cardiac surgery operations with the use of minimally invasive techniques.

Intercalated Disk Extracellular Nanodomain Expansion in Patients With Atrial Fibrillation

Aims: Atrial fibrillation (AF) is the most common sustained arrhythmia. Previous evidence in animal models suggests that the gap junction (GJ) adjacent nanodomain – perinexus – is a site capable of independent intercellular communication via ephaptic transmission. Perinexal expansion is associated with slowed conduction and increased ventricular arrhythmias in animal models, but has not been studied in human tissue. The purpose of this study was to characterize the perinexus in humans and determine if perinexal expansion associates with AF.

Methods: Atrial appendages from 39 patients (pts) undergoing cardiac surgery were fixed for immunofluorescence and transmission electron microscopy (TEM). Intercalated disk distribution of the cardiac sodium channel Nav1.5, its β1 subunit, and connexin43 (C×43) was determined by confocal immunofluorescence. Perinexal width (Wp) from TEM was manually segmented by two blinded observers using ImageJ software.

Results: Nav1.5, β1, and C×43 are co-adjacent within intercalated disks of human atria, consistent with perinexal protein distributions in ventricular tissue of other species. TEM revealed that the GJ adjacent intermembrane separation in an individual perinexus does not change at distances greater than 30 nm from the GJ edge. Importantly, Wp is significantly wider in patients with a history of AF than in patients with no history of AF by approximately 3 nm, and Wp correlates with age (R = 0.7, p < 0.05).

Conclusion: Human atrial myocytes have voltage-gated sodium channels in a dynamic intercellular cleft adjacent to GJs that is consistent with previous descriptions of the perinexus. Further, perinexal width is greater in patients with AF undergoing cardiac surgery than in those without.

Incidence of cardiac arrhythmias in asymptomatic hereditary hemochromatosis subjects with C282Y homozygosity

It is not well known whether systemic iron overload per se in hereditary hemochromatosis (HH) is associated with cardiac arrhythmias before other signs and symptoms of cardiovascular disease occur. In the present study, we examined the incidence of cardiac arrhythmia in cardiac asymptomatic subjects with HH (New York Heart Association functional class I) and compared it to that in age- and gender-matched normal volunteers. The 42 subjects with HH and the 19 normal control subjects were recruited through the National Heart, Lung, and Blood Institute-sponsored "Heart Study of Hemochromatosis." They completed 48-hour Holter electrocardiography ambulatory monitoring at the baseline evaluation. The subjects with HH were classified as newly diagnosed (group A) and chronically treated (group B) subjects. All subjects with HH had C282Y homozygosity, and the normal volunteers lacked any HFE gene mutations known to cause HH. Although statistically insignificant, the incidence of ventricular and supraventricular ectopy tended to be greater in the combined HH groups than in the controls. Supraventricular ectopy was more frequently noted in group B compared to in the controls (ectopy rate per hour 11.1 ± 29.9 vs 1.5 ± 3.5, p < 0.05, using the Kruskal-Wallis test). No examples of heart block, other than first-degree atrioventricular node block, were seen in any of the subjects. The incidence of cardiac arrhythmias was not significantly reduced after 6 months of intensive iron removal therapy in the group A subjects. No life-threatening arrhythmias were observed in our subjects with HH. In conclusion, our data suggest that the incidence of cardiac arrhythmias is, at most, marginally increased in asymptomatic subjects with HH. A larger clinical study is warranted to further clarify our observation.

20-Hydroxyeicosatetraenoic acid induces apoptosis in neonatal rat cardiomyocytes through mitochondrial-dependent pathways

OBJECTIVE

20-Hydroxyeicosatetraenoic acid (20-HETE), a [omega]-hydroxylation product of arachidonic acid catalyzed by cytochrome P450 4A, may play a role in the cardiovascular system. It is well known that cytochrome P450 [omega]-hydroxylase inhibitors markedly reduced the cardiac ischemia reperfusion injury. However, the direct effect of 20-HETE on cardiomyocytes is still poorly investigated. Here, we studied the effect of 20-HETE on cardiomyocyte apoptosis and the apoptosis-associated signaling pathways.

METHODS AND RESULTS

The cardiomyocyte apoptosis was measured by fluorescein isothiocyanate conjugated annexin V/propidium iodide double staining cytometry, indicating that the percentage of early apoptotic cells increased from 15.6% +/- 2.6% to 25.5% +/- 2.5% in control and 20-HETE-treated cells, respectively. The mitochondrial membrane potential ([DELTA][PSI]m) was measured by detecting the ratio of JC-1 green/red emission intensity. A significant decrease in the ratio was observed after treatment with 20-HETE for 24 hours in comparison with control group, suggesting the disruptive effect of 20-HETE on mitochondrial [DELTA][PSI]m. In addition, 20-HETE stimulated caspase-3 activity and Bax mRNA expression in cardiomyocytes. In contrast, the Bcl-2 mRNA levels were significantly decreased by 20-HETE treatment.

CONCLUSION

These results demonstrate that 20-HETE induces cardiomyocyte apoptosis by activation of several intrinsic apoptotic pathways. The 20-HETE-induced apoptosis could contribute to the cytochrome P450 [omega]-hydroxylase-dependent cardiac injure during cardiac ischemia-reperfusion.

Effects on Atrial Fibrillation in Aged Hypertensive Rats by Ca 2+ -Activated K + Channel Inhibition

We have shown previously that inhibition of small conductance Ca 2+ -activated K + (SK) channels is antiarrhythmic in models of acutely induced atrial fibrillation (AF). These models, however, do not take into account that AF derives from a wide range of predisposing factors, the most prevalent being hypertension. In this study we assessed the effects of two different SK channel inhibitors, NS8593 and UCL1684, in aging, spontaneously hypertensive rats to examine their antiarrhythmic properties in a setting of hypertension-induced atrial remodeling. Male spontaneously hypertensive rats and the normotensive Wistar-Kyoto rat strain were divided in 2×3 groups of animals aged 3, 8, and 11 months, respectively. The animals were randomly assigned to treatment with NS8593, UCL1684, or vehicle, and open chest in vivo experiments including burst pacing–induced AF were performed. The aging spontaneously hypertensive rats were more vulnerable to AF induction both by S2 stimulation and burst pacing. Vehicle affected neither the atrial effective refractory period nor AF duration. SK channel inhibition with NS8593 and UCL1684 significantly increased the atrial effective refractory period and decreased AF duration in both the normotensive and hypertensive strains with no decline in efficacy as age increased. In conclusion, SK channel inhibition with NS8593 and UCL1684 possesses antiarrhythmic properties in a rat in vivo model of paroxysmal AF with hypertension-induced atrial remodeling. The present results support the notion that SK channels may offer a promising new therapeutic target in the treatment of AF.

Polymorphisms of the angiotensin-converting enzyme and angiotensinogen gene in patients with atrial fibrillation

Activation of the renin-angiotensin system (RAS) is associated with atrial fibrillation (AF). The aim of this study was to investigate the relation between AF and polymorphisms in RAS. One hundred and fifty patients with AF, 100 patients with no documented episode of AF and 100 healthy subjects were consecutively recruited into the study. The angiotensin-converting enzyme (ACE) insertion/deletion (I/D) polymorphism, and the M235T, A-20C, and G-6A polymorphisms of the angiotensinogen gene were genotyped. Patients with AF had significantly lower frequency of II genotype of ACE I/D and higher frequency of angiotensinogen M235T polymorphism T allele and TT genotype and G-6A polymorphism G allele and GG genotype compared with the controls. AF patients had significantly larger left atrium, higher left ventricular mass index (LVMI) and higher frequency of significant valvular pathology. ACE I/D polymorphism II genotype, angiotensinogen M235T polymorphism TT genotype and G allele and GG genotype of angiotensinogen G-6A polymorphism were still independently associated with AF when adjusted for left atrium, LVMI and presence of significant valvular pathology. Genetic predisposition might be underlying the prevalence of acquired AF. Patients with a specific genetic variation in the RAS genes may be more liable to develop AF.

Left atrial ganglion ablation as an adjunct to atrial fibrillation surgery in valvular heart disease

BACKGROUND

Our aim was to evaluate early results of ganglionic plexus (GP) ablation with modified Cox maze lesion sets for concomitant atrial fibrillation (AF) during corrective valve surgery.

METHODS

Between December 2006 and April 2008, 20 patients (7 men; median age, 65 years; range, 52 to 82 years) with valvular heart disease and AF (intermittent in 12 [60%]) underwent corrective valve surgery with maze and GP ablation. Patients were then compared with a case-matched control cohort who underwent radiofrequency ablation maze alone.

RESULTS

Procedures included mitral valve repair in 7 patients (35%), multivalve procedures in 5 (25%), mitral valve replacement in 4 (20%), aortic valve replacement in 3 (15%), and valve-sparing aortic root replacement in 1 (5%). All patients underwent concomitant AF ablation procedures (biatrial maze in 11 [55%], left-sided maze in 9 [45%]). Ganglionic plexus stimulation was performed in all patients. Sites at which the R-R interval doubled were considered active and were ablated. There were no early deaths. Freedom from AF at 1 year was significantly higher (90% versus 50%; p=0.01) and mean New York Heart Association functional class was better (1 versus 1.7; p<0.001) in the group that underwent maze and GP ablation compared with maze alone.

CONCLUSIONS

Active left atrial GP are frequently present in patients with AF and valvular heart disease, and GP ablation can be safely performed as an adjunct to AF ablation during valve surgery. Early results are promising and may yield higher freedom from AF compared with radiofrequency ablation maze alone.

Relationships of CRP and P wave dispersion with atrial fibrillation in hypertensive subjects

BACKGROUND

Although inflammation has been shown to be implicated in the pathophysiology of atrial fibrillation (AF), little is known about its involvement in the accompanying atrial electrical remodeling expressed by P wave dispersion (P(disp)).

METHODS

Fifty hypertensive subjects with documented paroxysmal AF (AF group) and 50 matched for body mass index, sex and office systolic blood pressure (BP) subjects with no history of AF (SR group) were subjected to electrocardiogram (ECG) and P(disp) assessment, hs-CRP determination, a complete echocardiographic study and 24-h ambulatory BP monitoring.

RESULTS

The AF as compared to the SR subjects were older by 14 years (P < 0.0001) and they exhibited lower office and 24-h diastolic BP (7 mm Hg, P < 0.0001 and by 8 mm Hg, P < 0.0001, respectively) and higher office and 24-h pulse pressure (by 4 mm Hg, P = 0.03 and 6 mm Hg, P = 0.001, respectively) mean values. A higher mean of left atrial (LA) diameter index (by 1.9 mm/m(2), P < 0.0001) and left ventricular mass index (by 16 g/m(2), P < 0.0001) were observed in the AF vs. SR group. P(disp) mean and hs-CRP median values were higher in the AF group (by 22 ms, P < 0.0005 and by 4.63 mg/l, P < 0.0005, respectively). Standard multiple and multiple logistic regression analysis identified log(10)(hs-CRP) as independent determinant of P(disp) and log(10)(CRP) and P(disp) as independent determinants of AF.

CONCLUSIONS

In hypertensive subjects hs-CRP and P(disp) are interrelated and associated with AF, suggesting an active implication of inflammation in the atrial electrophysiological remodeling predisposing to AF.

The effect of rapid blood pressure control on P-wave dispersion in hypertensive urgency

INTRODUCTION

A sharp increase in blood pressure, increase in atrial pressure and atrial strain, left ventricular diastolic dysfunction, and left ventricular hypertrophy (LVH) lead to heterogeneity and instability in atrial conduction. The resulting physiopathological situation may elevate maximum Pwave duration (P(max)) and P-wave dispersion (PWD) in electrocardiography. The objective of our study was to explore the effect of the sudden change in atrial hemodynamics on P(max) and PWD, which may indicate the risk of atrial fibrillation (AF) development in hypertensive urgency.

METHODS

The study included patients diagnosed as hypertensive urgency (systolic blood pressure > or =180 mmHg, diastolic blood pressure > or =110 mmHg). Nitroprusside was started at a dose of 0.2 microg/kg/min, and the ensuing dose was arranged according to blood pressure. Echocardiography and electrocardiography were used to noninvasively measure changes in diastolic function and PWD and P(max), respectively.

RESULTS

The study enrolled 102 patients (mean age 57.9+/-11.6 years; 32 [31.4%] males, and 70 [68.6%] females). P(max) decreased from 99.9+/-11.1 msec (95% confidence intervals [CI] 97.7, 102) to 88.5+/-9.3 msec (95% CI 86.6, 90.3) (P<0.001), while PWD decreased from 60.1+/-7.4 msec (95% CI 58.7, 61.6) to 43.9+/-6.7 msec (95% CI 42.5, 45.2) (P<0.001). In addition, most patients had LVH and diastolic dysfunction. After nitroprusside treatment improvements in indicators of diastolic functions such as E/A ratio, deceleration time, and isovolumetric relaxation time were observed.

CONCLUSION

The change observed in P(max) and PWD in hypertensive urgency may be associated with the rapid change in blood pressure and atrial strain, sympathetic nervous system activation, relative myocardial ischemia, and left ventricular diastolic dysfunction. Rapid regulation of blood pressure with nitroprusside brought about a marked decrease in P(max) and PWD in our patients. This improvement was interpreted as atrial conduction acquiring a stable and homogeneous character, which may reduce the risk of AF development in hypertensive urgency.

First diagnosis of colorectal or breast cancer and prevalence of atrial fibrillation

Aim of the present study was to assess the prevalence of atrial fibrillation (AF) in patients with two different types of cancer. Recent epidemiologic and clinical studies support the hypothesis that AF is promoted and maintained by a broad spectrum of modulating factors. A total of 2,339 patients admitted to the Surgery Department of "Luigi Sacco Hospital, Milan," over the period 1987-2004 were eligible for the study. One thousand three hundred and seventeen patients were admitted consecutively with a first diagnosis of colorectal or breast cancer (cases). The remaining 1,022 were patients admitted to undergo non-neoplastic surgery (controls). Routine pre-surgery electrocardiogram available in patient charts was analysed by a cardiologist who was not aware of the present study to evaluate the presence of atrial fibrillation or other arrhythmias. Overall, AF was present in 3.6% cases and 1.6% controls. This corresponded to at least two times higher likelihood of having AF in cases compared to controls. Prevalence of AF increased with age both in cases and controls. Our study describes an increased prevalence of AF in two different types of cancer. Autonomic, endocrine, coagulation, and inflammatory alterations were previously described in both AF and cancer, and can provide the physiopathological basis to our clinical observation.

Atrial fibrosis: mechanisms and clinical relevance in atrial fibrillation

Atrial fibrillation (AF) is the most common arrhythmia in the clinical setting, and traditional pharmacological approaches have proved to have important weaknesses. Structural remodeling has been observed in both clinical and experimental AF paradigms, and is an important feature of the AF substrate, producing fibrosis that alters atrial tissue composition and function. The precise mechanisms underlying atrial fibrosis are not fully elucidated, but recent experimental studies and clinical investigations have provided valuable insights. A variety of signaling systems, particularly involving angiotensin II and related mediators, seem to be centrally involved in the promotion of fibrosis. This paper reviews the current understanding of how atrial fibrosis creates a substrate for AF, summarizes what is known about the mechanisms underlying fibrosis and its progression, and highlights emerging therapeutic approaches aimed at attenuating structural remodeling to prevent AF.

Atrial Glutathione Content, Calcium Current, and Contractility

Atrial fibrillation (AF) is characterized by decreased L-type calcium current (I(Ca,L)) in atrial myocytes and decreased atrial contractility. Oxidant stress and redox modulation of calcium channels are implicated in these pathologic changes. We evaluated the relationship between glutathione content (the primary cellular reducing moiety) and I(Ca,L) in atrial specimens from AF patients undergoing cardiac surgery. Left atrial glutathione content was significantly lower in patients with either paroxysmal or persistent AF relative to control patients with no history of AF. Incubation of atrial myocytes from AF patients (but not controls) with the glutathione precursor N-acetylcysteine caused a marked increase in I(Ca,L). To test the hypothesis that glutathione levels were mechanistically linked with the reduction in I(Ca,L), dogs were treated for 48 h with buthionine sulfoximine, an inhibitor of glutathione synthesis. Buthionine sulfoximine treatment resulted in a 24% reduction in canine atrial glutathione content, a reduction in atrial contractility, and an attenuation of I(Ca,L) in the canine atrial myocytes. Incubation of these myocytes with exogenous glutathione also restored I(Ca,L) to normal or greater than normal levels. To probe the mechanism linking decreased glutathione levels to down-regulation of I(Ca), the biotin switch technique was used to evaluate S-nitrosylation of calcium channels. S-Nitrosylation was apparent in left atrial tissues from AF patients; the extent of S-nitrosylation was inversely related to tissue glutathione content. S-Nitrosylation was also detectable in HEK cells expressing recombinant human cardiac calcium channel subunits following exposure to nitrosoglutathione. S-Nitrosylation may contribute to the glutathione-sensitive attenuation of I(Ca,L) observed in AF.

Pharmacogenetics and cardiac ion channels

Ion channels control electrical excitability in living cells. In mammalian heart, the opposing actions of Na(+) and Ca(2+) ion influx, and K(+) ion efflux, through cardiac ion channels determine the morphology and duration of action potentials in cardiac myocytes, thus controlling the heartbeat. The last decade has seen a leap in our understanding of the molecular genetic origins of inherited cardiac arrhythmia, largely through identification of mutations in cardiac ion channels and the proteins that regulate them. Further, recent advances have shown that 'acquired arrhythmias', which occur more commonly than inherited arrhythmias, arise due to a variety of environmental factors including side effects of therapeutic drugs and often have a significant genetic component. Here, we review the pharmacogenetics of cardiac ion channels-the interplay between genetic and pharmacological factors that underlie human cardiac arrhythmias.

In vitro atrial flow dynamics: normal conditions versus atrial fibrillation

AIMS

The flow dynamics in the atrium is poorly described. The reasons are principally due to the complicated geometry of the cavity and its contractility. The present in vitro study focuses on the description of the flow in the left atrium in normal conditions (NC) and in atrial fibrillation (AF). The final objective is to give leads to understand, from the hemodynamic point of view, complications in case of AF.

METHODS AND RESULTS

An atrio-ventricular dual activation system is used to simulate physiological flow in the left atrium. The cavities are compliant and transparent. Velocity measurements are performed with Particle Image Velocimetry. Systolic peak of the pulmonary venous flow is about 0.4 m s(-1) and diastolic peak 0.6 m s(-1) in magnitude. Vortices appear during diastasis and systole and are of normal size and duration. In early and late diastole, the ventricular filling (in NC and AF) and the atrial contraction (in NC only) create a characteristic flow pattern that consists in directed flow towards the mitral valve. In AF an increased resident time (500 ms versus 300 ms) and a slow helical flow pattern (about 0.1 m s(-1)), similar to what is measured using ultrasound echocardiography are observed.

CONCLUSION

This study uses atrial flow dynamics description to help understand why thromboembolisms occur in AF.

The signal-averaged P-wave duration is longer in hypertensive patients with history of paroxysmal atrial fibrillation as compared to those without

BACKGROUND

Onset of atrial fibrillation in hypertensive patients is usually associated with a high occurrence of cardiovascular complications. Therefore, it is important to assess non-invasively the risk of developing paroxysmal atrial fibrillation (PAF) in hypertensive patients during sinus rhythm. This study was undertaken to determine if hypertensive patients with history of PAF could be identified while in sinus rhythm by measurement of signal-averaged ECG P-wave duration.

METHODS

Signal-averaged electrocardiography (SAECG) P-wave recording was performed in 44 hypertensive patients (30 men and 14 women; mean age 60+/-11 years, group A) who had a history of paroxysmal AF and in 50 hypertensive patients without history of AF (33 men and 17 women; mean age 57+/-12, group B). All patients were also evaluated by using echocardiography to measure left ventricular ejection fraction (LVEF) and left atrial diameter (LAD).

RESULTS

SAECG P-wave duration was found to be significantly higher in group A than in group B (146+/-14 ms vs. 128+/-11 ms, p<0.001). Left atrial diameter was not significantly different (40.1+/-3.4 mm vs. 39.3+/-3.0 mm, p>0.05), whereas LVEF was significantly lower in group A than group B (63+/-5% vs. 67+/-4%, p=0.03). There was a correlation between SAECG P-wave duration and age (r=0.32, p<0.05). In univariate analysis, SAECG P-wave duration and LVEF were significant predictors of PAF, but only SAECG P-wave duration remained a significant independent predictor of PAF in multivariate analysis.

CONCLUSION

The results of this study indicate that hypertensive patients with history of PAF can be detected while in sinus rhythm by signal-averaged ECG P-wave duration.

Sudden cardiac death in hereditary hemochromatosis: an underestimated cause of death?

Hereditary hemochromatosis (HH) is a frequent autosomal recessive disease which causes iron-overload of various organs. Of all northern European affected individuals, 90-95% show 1 of 3 known point mutations in the HFE gene. Symptoms and organs involved can vary considerably: Only a small fraction of the 200,000-400,000 persons affected in Germany develop the classical picture of liver cirrhosis and/or pancreatic fibrosis. Nevertheless, the life expectancy of persons with moderate or even subclinical symptoms is reduced, in many cases due to myocardial damage leading to cardiomyopathy with greatly increased risk of sudden cardiac death. Although the high prevalence of HH suggests that sudden cardiac death due to cardiac HH is a relatively common cause of death, the forensic literature lacks such reports. We present the case of sudden cardiac death in a young man with histological findings of massive cardial hemochromatosis which is characterized by the fact that none of the three known mutations for HH were found. This case demonstrates that genetic screening alone might not be sufficient to identify all persons at risk to developing HH.

Increased vulnerability to atrial fibrillation in transgenic mice with selective atrial fibrosis caused by overexpression of TGF-beta1

Studies on patients and large animal models suggest the importance of atrial fibrosis in the development of atrial fibrillation (AF). To investigate whether increased fibrosis is sufficient to produce a substrate for AF, we have studied cardiac electrophysiology (EP) and inducibility of atrial arrhythmias in MHC-TGFcys33ser transgenic mice (Tx), which have increased fibrosis in the atrium but not in the ventricles. In anesthetized mice, wild-type (Wt) and Tx did not show significant differences in surface ECG parameters. With transesophageal atrial pacing, no significant differences were observed in EP parameters, except for a significant decrease in corrected sinus node recovery time in Tx mice. Burst pacing induced AF in 14 of 29 Tx mice, whereas AF was not induced in Wt littermates (P<0.01). In Langendorff perfused hearts, atrial conduction was studied using a 16-electrode array. Epicardial conduction velocity was significantly decreased in the Tx RA compared with the Wt RA. In the Tx LA, conduction velocity was not significantly different from Wt, but conduction was more heterogeneous. Action potential characteristics recorded with intracellular microelectrodes did not reveal differences between Wt and Tx mice in either atrium. Thus, in this transgenic mouse model, selective atrial fibrosis is sufficient to increase AF inducibility.

How do HMG-CoA reductase inhibitors prevent stroke?

Stroke is a heterogeneous disorder with significantly high morbidity and mortality. The relationship between serum cholesterol level and the incidence of stroke remains controversial. Recent evidence from primary and secondary prevention trials suggests that treatment with hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors may reduce the incidence of stroke in patients with coronary artery disease (CAD). In this review, we attempt to outline and describe the potential mechanisms of HMG-CoA reductase inhibitors in the prevention of stroke. In addition to their lipid-lowering action HMG-CoA reductase inhibitors appear to exert their beneficial effects by various nonlipid-lowering mechanisms including anti-inflammatory effects, effect on endothelial function and coagulation cascade. Treatment with HMG-CoA reductase inhibitors is associated with decreased progression, plaque stablization and even regression of atheromatous plaque in the carotid arteries. HMG-CoA reductase inhibitors also inhibit the coagulation cascade at various levels such as activation of prothrombin, factor V, factor X and liberation of tissue factor in response to vascular injury. Inhibition of fibrinolysis occurs secondary to inhibition of plasmin generation. Pravastatin therapy is associated with a reduction in the size of aortic atheroma which is an independent risk factor for stroke. Lastly, left ventricular dysfunction after acute myocardial infarction is associated with an increased risk of stroke and HMG-CoA reductase inhibitors may indirectly decrease the incidence of stroke by reducing coronary events. Most of these effects are independent of the cholesterol-lowering effects of HMG-CoA reductase inhibitors. In conclusion, HMG-CoA reductase inhibitors may have a role in primary prevention of stroke in patients with CAD.

Left atrial maximum volume is a recurrence predictor in lone atrial fibrillation: an acoustic quantification study

Predictors of recurrence in lone atrial fibrillation have not been clearly identified. Acoustic quantification (AQ) is a promising method in the assessment of left atrial (LA) volumes. The purpose of the present study was to investigate the potential of LA volumes obtained by standard manual tracing and AQ methods in predicting AF-recurrence after restoring the sinus rhythm in patients with lone AF, and to test the agreement between the two approaches. Standard echocardiography combined with AQ was performed in 28 patients with lone AF one hour after the sinus rhythm was regained, and in 10 controls. LA volumes were determined by conventional manual tracing and AQ methods. AQ waveforms of LA were obtained by drawing a region of interest around the LA border. The agreement of the two methods was tested by Bland-Altman analysis. Patients were followed up for 6 months for the occurrence of AF recurrence. A good correlation was observed between AQ and manual tracing methods in determining both minimal (r=0.59) and maximal (r=0.88) LA volumes. Patients with AF recurrence had a significantly larger maximum LA volume as assessed with both methods (P<0.05 for both). M-mode derived LA dimension and isovolumic relaxation time were additional predictors of recurrence in patients with lone AF. In lone AF, patients prone to recurrence could be predicted by determining LA maximum volume assessed either by AQ or manual tracing methods. AQ provides on-line, accurate estimation of LA volumes.

The effect of insulin cardioplegia on atrial fibrillation after high-risk coronary bypass surgery: a double-blinded, randomized, controlled trial

Atrial fibrillation after coronary bypass (CABG) surgery is an important cause of morbidity and increased resource utilization. Insulin-enhanced cardioplegia may reduce postoperative arrhythmias by improving aerobic myocardial metabolism and mitigating the deleterious effects of ischemia. We performed a double-blinded, randomized, controlled clinical trial to determine if insulin-enhanced cardioplegia decreases the risk of post-CABG atrial fibrillation in a high-risk patient population. We randomized 501 patients undergoing urgent CABG to receive insulin-enhanced (Humulin R 10 IU/L, Insulin group, n = 243) or standard (Control group, n = 258) blood cardioplegia during cardiopulmonary bypass. Patients were monitored by using continuous electrocardiography for a minimum of 3 days postoperatively. All standard cardiac medications, including beta-adrenergic blockers, were continued postoperatively. Insulin-enhanced cardioplegia did not result in a significant reduction in postoperative atrial fibrillation. Furthermore, we failed to detect a difference in the incidence of conduction defects, ventricular tachycardia, or pacemaker requirements between insulin and placebo patients. Atrial fibrillation was the most common arrhythmia, occurring in 31% of all patients. Independent predictors of atrial fibrillation were elderly age, preoperative atrial fibrillation, and renal insufficiency. Right bundle branch block was the most common conduction abnormality. Predictors of right bundle branch block were elderly age, female sex, and circumflex coronary artery disease. The incidence of postoperative ventricular tachycardia, left bundle branch block, and permanent pacemaker requirement was small. We conclude that insulin-enhanced cardioplegia does not reduce the incidence of postoperative atrial fibrillation in high-risk CABG patients.

IMPLICATIONS

We conducted a double-blinded, randomized, placebo-controlled trial of insulin-enhanced cardioplegia in 501 patients undergoing urgent coronary bypass surgery. Insulin did not decrease the incidence of postoperative atrial fibrillation when compared with placebo. We also failed to demonstrate a difference in the incidence of other postoperative arrhythmias between the two groups of patients.