Structural changes of atrial myocardium during chronic atrial fibrillation

Capillary supply to the sinus node in subjects with long-term atrial fibrillation

BACKGROUND

Atrial ischemia, and sinus node ischemia in particular, may be involved in the pathogenesis of atrial fibrillation. In this study we compared the sinus node blood capillary content in normal hearts in sinus rhythm and in pathologic hearts with chronic atrial fibrillation and we analyzed the ultrastructural features of such capillaries.

METHODS

Sinus node biopsy specimens were obtained from 16 patients in chronic atrial fibrillation undergoing open heart surgery. Control sinus node specimens of normal hearts were obtained at autopsy from 7 subjects. Specimens were processed for immunohistochemical, light microscopy and transmission electron microscopy analysis and compared grossly and with morphometric techniques.

RESULTS

The proportion of sinus node tissue corresponding to capillaries, defined as blood vessel density (or BVD), was estimated as 1.06 +/- 1.47% for the atrial fibrillation group versus 2.12 +/- 2.0% for controls (p < 0001). Internal capillary diameter averaged 21.6 microm in the atrial fibrillation group and 24.2 microm in controls (p = 0.175), whereas external diameter averaged 32.2 microm in the atrial fibrillation group and 38.9 microm in controls (p = 0.052). Ultrastructural analysis demonstrated scarce and interrupted myoendocardial bridges and abnormal deposits of elastic fibers under the endothelial basal membrane at the level of precapillary sphincters and metaarterioles of atrial fibrillation specimens.

CONCLUSIONS

There is a significant reduction in the amount of capillaries in the sinus node of hearts in chronic atrial fibrillation. Our findings would support a potential association between sinus node tissue ischemia and chronic atrial fibrillation.

Comparative expression of proteins in left and right atrial appendages from patients with mitral valve disease at sinus rhythm and atrial fibrillation

INTRODUCTION

The objective was to compare by proteomics the expression of proteins associated with the cytoskeleton, energetic metabolism, and cardiac cytoprotection between left atrial appendages (LAA) and right atrial appendages (RAA) obtained from patients with mitral valve disease both in sinus rhythm (SR, n = 6) and in permanent atrial fibrillation (AF, n = 11).

METHODS AND RESULTS

Samples from RAA and LAA were obtained from the same patient. Proteins were separated in 2-dimensional electrophoresis and identified by mass spectrometry. LAA from SR patients upexpressed alpha-actin isotype 1 and desmin isotypes 3 and 5 with respect to RAA. In LAA from AF patients were upexpressed cardiac alpha-actin isotypes 1 and 2, tropomyosin alpha- and beta-chains, and myosin light chain embryonic muscle/atrial isoform with respect to LAA from SR patients. In RAA from AF patients also upexpressed different cytoskeleton associated proteins with respect to RAA from SR patients. Different energetic metabolism-associated proteins were upexpressed in LAA and RAA from AF with respect those from SR patients. In AF patients, the expression of proteins associated with cardiac cytoprotection such as gluthatione-S-transferase, heat shock protein (Hsp) 27, and different Hsp60 isotypes, were higher in RAA but not in LAA with respect to the corresponding appendages in SR patients.

CONCLUSIONS

For each individual patient RAA and LAA showed a similar level of proteins expressed associated with cytoskeleton, energetic metabolism, and cardiac cytoprotection. There were more differences in the level of proteins associated with the above-mentioned mechanisms between the atrial appendages from AF with respect to SR patients, which may open new targets for drugs.

Atrial Ca2+ signaling in atrial fibrillation as an antiarrhythmic drug target

Atrial fibrillation (AF) is the most frequent arrhythmia and is associated with increased morbidity and mortality. Current drugs for AF treatment have moderate efficacy and increase the risk of life-threatening antiarrhythmias, making novel drug development crucial. Newer antiarrhythmic drugs like dronedarone and possibly vernakalant are efficient and may have less proarrhythmic potential. Emerging evidence suggests that abnormal intracellular Ca(2+) signaling is the key contributor to focal firing, substrate evolution, and atrial remodeling during AF. Accordingly, identification of the underlying atrial Ca(2+)-handling abnormalities is expected to discover novel mechanistically based therapeutic targets. This article reviews the molecular mechanisms of altered Ca(2+) signaling in AF and discusses the potential value of novel approaches targeting atrial Ca(2+)-handling abnormalities.

Probucol attenuates atrial structural remodeling in prolonged pacing-induced atrial fibrillation in dogs

AIMS

Oxidative stress has recently been implicated in atrial fibrillation (AF); however, the mechanisms remain unclear. Herein, we hypothesize that probucol can attenuate atrial structure remodeling.

METHODS

Twenty dogs were randomly divided into sham-operated, control, and probucol-treated groups. We identified apoptosis and histopathological changes in the atria. Oxidative stress was measured by lipid peroxidation and echocardiographic examinations were performed.

RESULTS

Atrial apoptosis indexes were dramatically decreased in the probucol-treated group compared to the control group. Relative to the control group, the percentage of myolysis was dramatically decreased in the probucol-treated group (p < 0.01). There was less lipid peroxidation in the probucol-treated group than the control group. Atrial function was dramatically elevated in the probucol-treated group.

CONCLUSIONS

The results of this study indicate that the antioxidant probucol suppresses atrial structural remodeling and may act as a new therapy for AF.

Energetic metabolism during acute stretch-related atrial fibrillation

BACKGROUND AND METHODS

Perturbations in energetic metabolism and impaired atrial contractility may play an important role in the pathogenesis of atrial fibrillation (AF). Besides, atrial stretch is commonly associated with AF. However, the atrial energetics of stretch-related AF are poorly understood. Here, we measured indicators of energy metabolism during acute stretch-related AF. PCr, adenine nucleotides, and derivatives concentrations as well as the activity of the F(0)F(1)-ATPase and Na,K-ATPase were obtained after 1 h of stretch and/or AF in isolated rabbit hearts and compared to control hearts without stretch and AF.

RESULTS

After 1 h of stretch-related AF, the total adenine nucleotides' pool was significantly lower (42.2 +/- 2.6 vs. 63.7 +/- 8.3 micromol/g protein in control group, P < 0.05) and the PCr/ATP ratio significantly higher (2.3 +/- 0.3 vs. 1.1 +/- 0.1 in control group P < 0.05), because of ATP, ADP, and AMP decrease and PCr increase. The sum of high-energy phosphate compounds did not change. There were no significant differences in F(0)F(1)-ATPase nor Na,K-ATPase activity between the groups.

CONCLUSIONS

Results show that in this experimental model, acute stretch-related AF induces specific modifications of atrial myocytes energetics that may play a pivotal role in the perpetuation of the arrhythmia.

Frequency of recurrence of atrial fibrillation within 48 hours after ablation and its impact on long-term outcome

Because of delayed structural and electrophysiologic effects of radiofrequency ablation of atrial fibrillation (AF), early recurrence of AF after ablation does not necessarily indicate long-term ablation failure. This study was intended to assess the prognostic value of early recurrence of AF within 48 hours after ablation. The study included 234 patients (aged 23 to 80 years; 72% men) with symptomatic drug-resistant paroxysmal (n = 165) or persistent AF (n = 69) who underwent either Lasso-guided segmental pulmonary vein isolation (n = 83) or CARTO-guided left atrial circumferential ablation (n = 151). After a median follow-up of 12.7 months, 64% of patients with paroxysmal and 45% of patients with persistent AF were AF free. Early recurrence of AF occurred in 43% of patients and was more frequently observed in the persistent-AF group (paroxysmal vs persistent 39% vs 54%; p = 0.037). Early recurrence of AF was a significant predictor of long-term ablation failure in univariate (hazard ratio [HR] 2.29, p <0.001) and multivariate (HR 2.17. p <0.001) Cox regression analysis. Nevertheless, 46% of patients with early recurrence of AF were AF free during long-term follow-up compared with 68% of patients without early recurrence of AF. The prognostic value of early recurrence of AF was found in patients with paroxysmal (HR 2.05, p = 0.005) and persistent AF (HR 2.35, p = 0.013). In conclusion, early recurrence of AF within 48 hours after ablation was a significant predictor of a poor long-term ablation outcome. However, because nearly half the patients with early recurrence of AF remained AF free during long-term follow-up, early recurrence of AF should not automatically result in an early repeated procedure.

Structural and functional remodeling of the left atrium: clinical and therapeutic implications for atrial fibrillation

Left atrial (LA) structural and functional remodeling reflects a spectrum of pathophysiological changes that have occurred in response to specific stressors. These changes include alterations at the levels of ionic channels, cellular energy balance, neurohormonal expression, inflammatory response, and physiologic adaptations. There is convincing evidence demonstrating an important pathophysiological association between LA remodeling and atrial fibrillation (AF). Measures that will prevent, attenuate, or halt these processes of LA remodeling may have a major public health impact with respect to the epidemic of AF. In this review, we describe the mechanisms involved in LA remodeling and highlight the existing and potential therapeutic options for its reversal, and implications for AF development.

Beat shock proteins and atrial fibrillation

In this mini-review, the role of heat shock proteins in susceptability to induction of atrial fibrillation (AF) or in the process of AF is discussed. AF is the most common arrhythmia in humans, is self-perpetuating in nature and hence tends to become more persistent in time. Some studies show a correlation between high Hsp70 (HspA1A) expression in cardiac tissue and a reduced susceptability to induction of postoperative AF. Expression of Hsp70, Hsc70 (HspA8), Hsp40 (DnaJB1), Hsp60 (HspD1), Hsp90 (HspC1) was not associated with progression of AF. However, both correlative studies in human and experimental studies suggest that Hsp27 (HspB1) may delay progression of AF to the more permanent forms and hence Hsp27 might be referred to as a "Beat shock protein".

Increased expression of extracellular matrix proteins in rapid atrial pacing-induced atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is characterized by structural remodeling of the extracellular matrix (ECM) in cardiac atrium.

OBJECTIVE

The purpose of this study was to gain further insight into atrial ECM remodeling at the molecular level and to test whether altered expression of ECM proteins was associated with the disease.

METHODS

Sustained AF was induced in nine adult pigs after 3-4 weeks of continuous rapid atrial pacing at a rate of 600 bpm. Histologic studies and immunohistochemical stain were performed to identify the potential pathologic substrate underlying abnormalities in atrial tissues with sustained AF.

RESULTS

In the pathologic findings, the fraction of myocardial ECM (ECM%) was measured, with a significantly greater ECM% found in the AF group compared with the sham operated group (n = 6; i.e., pigs with normal sinus rhythm [SR]). A set of 9,182 genes was screened with cDNA microarray analysis. In AF animals, expression of 121 genes increased and 24 genes decreased by > or =1.75-fold compared with SR animals. Significant up-regulation of fibronectin-1 (4.9-fold), fibrillin-1 (3.1-fold), and fibromodulin (1.9-fold) in the fibrillating atria was confirmed by quantitative real-time reverse transcriptase-polymerase chain reaction. Western blot analysis revealed significantly increased atrial fibronectin-1, fibrillin-1, and fibromodulin in the AF group compared with the SR group (1.5-, 2.7-, and 2.1-fold, respectively). Immunohistochemical staining of AF tissue displayed increased accumulation of fibronectin-1 and fibrillin-1 in the atrial interstitial space.

CONCLUSION

Increased expression of ECM proteins in fibrillating atria supports the hypothesis that ECM metabolism contributes to the development of AF.

The effects of cilazapril and valsartan on the mRNA and protein expressions of atrial calpains and atrial structural remodeling in atrial fibrillation dogs

Owing to relative inefficacy and side effects of currently available antiarrhythmic drugs, current interest has shifted to treatments that target atrial fibrillation (AF) substrate. It has been suggested that calpain-induced atrial structural remodelling is under the control of renin-angiotensin system during AF. The purpose of this study is to investigate the effects of cilazapril and valsartan on the mRNA and protein expression of atrial calpains and atrial structural remodelling in AF dogs induced by chronic rapid atrial pacing. Twenty-seven dogs were randomly divided into sham-operated group (n = 6), control group (n = 7), cilazapril group (n = 7) and valsartan group (n = 7). One thin silicon plaque containing 4 pairs of electrodes was sutured to each atrium. A pacemaker was implanted in a subcutaneous pocket and attached to a screw-in epicardial lead in the right atrial appendage. The dogs in control group, cilazapril group and valsartan group were paced at 400 beats per minutes for 6 weeks. The dogs in cilazapril and valsartan groups received cilazapril (1mg x kg(-1)x d(-1)) or valsartan (30mg x kg(-1) x d(-1)) 1 week before rapid atrial pacing until pacing stop respectively. Transthoracic and transoesophageal echocardiographic examinations were performed in order to detect the changes of left atrium volume and contractile function. The inducibility and duration of AF were measured in all the groups. The expressions of atrial calpain I and calpain II mRNA were semi-quantified by reverse transcription-polymerase chain reaction. The protein levels of calpain I and calpain II in atrial myocardium were measured by Western-blot method. Pathohistological and ultrastructural changes in atrial tissue were tested by light and electron microscopy. Compared with the sham-operated control group, dramatic smaller left atrium and left atrial appendage volumes and significant higher atrial contractile function were observed in the cilazapril and valsartan groups. After 6-week atrial tachy-pacing, the mRNA and protein expressions of calpain I increased dramatically in the control group than that in the sham group, tissue calpain protein expression in all groups significantly correlated with the myolysis (r = 0.89, P < 0.01). Cilazapril and valsartan could significantly inhibit the gene and protein expressions of calpain I. No differences were found in the expression of calpain II mRNA and protein between the groups. Compared with atrial myocytes obtained from sham dogs, atrial myocytes from the control group dogs showed a reduced number of sarcomeres, a significant higher myolytic area of atria (24.3% vs. 3.1%, P < 0.01), increased vacuolization and dissolution. Cilazapril and valsartan could effectively prevent the pathohistological and ultrastructural changes induced by chronic rapid atrial pacing, dramatically decrease the area of myolysis (P < 0.05) and significantly reduce the inducibility and duration of AF. The expression of calpain I mRNA and protein increased remarkably in AF dogs. Cilazapril and valsartan can inhibit calpain I up-regulation, suppress atrial structural remodeling, and prevent the induction and promotion of AF in chronic rapid atrial pacing dogs.

ST-segment abnormalities and premature complexes are predictors of new-onset atrial fibrillation: the Niigata preventive medicine study

BACKGROUND

Left ventricular hypertrophy is a known risk factor for atrial fibrillation (AF). However, it is not well understood whether other electrocardiogram abnormalities are associated with development of AF.

METHODS

This was a community-based cohort study based upon a database of annual health examinations. We included 63,386 subjects aged > or = 50 years, without baseline AF (including atrial flutter), structural heart disease, or heart failure, who completed the annual examination during a 10-year follow-up period (1991-2002). The electrocardiographic risk factors for AF were studied in the subjects.

RESULTS

Atrial fibrillation developed in 873 subjects. Age, male sex, body mass index, hypertension, systolic and diastolic blood pressure, and diabetes were significant risk factors for the development of AF. In multivariable logistic regression analysis adjusted for these risk factors, electrocardiographic left ventricular hypertrophy (odds ratio [OR], 1.43), ST-segment abnormality without left ventricular hypertrophy (OR, 1.89), and the presence of premature complexes during a 10-second recording (OR, 2.89) were significantly associated with AF, whereas either right (OR, 0.84) or left bundle branch block (OR, 0.96) was unrelated. The risk for AF increased progressively with the severity of both ST-segment change and premature complexes.

CONCLUSIONS

ST-segment abnormality and comparably high-frequency premature complexes were each associated with increased risk for the development of AF. These electrocardiographic findings may be useful to stratify high-risk subjects for new-onset AF.

Prognostic Implications of Preoperative Atrial Fibrillation in Patients Undergoing Aortic Valve Replacement: Is There an Argument for Concomitant Arrhythmia Surgery?

BACKGROUND

The prognostic significance of preoperative atrial fibrillation (AF) at the time of aortic valve replacement is unknown, as is the potential role for concomitant arrhythmia surgery.

METHODS

We performed a cohort comparison of patients with preoperative AF (n = 129) and preoperative sinus rhythm (SR, n = 252) undergoing aortic valve surgery between 1993 and 2002; patients were matched for age, gender, and left ventricular ejection fraction. Follow-up (mean interval, 4.5 years) was 98% complete. Primary endpoints were late cardiac and all-cause mortality, as well as major adverse cardiac or cerebrovascular event.

RESULTS

Patients with preoperative AF presented with more severe congestive heart failure (p = 0.03) and more often had significant tricuspid regurgitation (p = 0.01) preoperatively. They also had worse late survival (risk ratio [RR] for death = 1.5, p = 0.03) with 1-, 5-, and 7-year survival rates substantially reduced at 94%, 87%, and 50%, respectively, for those in AF versus 98%, 90%, and 61% for patients in sinus rhythm preoperatively. Individuals in AF had a greater probability of subsequent rhythm-related intervention (RR = 4.7, p = 0.0002), and more frequently developed congestive heart failure (25% vs 10%, p = 0.005) and stroke (16% vs 5%, p = 0.005). By multivariable analysis, preoperative AF was an independent predictor of late adverse cardiac and cerebrovascular events, but not late death.

CONCLUSIONS

Performance of concomitant arrhythmia surgery in patients undergoing aortic valve surgery may reduce late morbidity; however, its potential impact on late mortality in this high-risk subset of patients remains unclear.

Heat shock protein upregulation protects against pacing-induced myolysis in HL-1 atrial myocytes and in human atrial fibrillation

Atrial fibrillation (AF) causes myocyte stress by inducing structural changes, predominantly myolysis, which is related to the progression of AF. As heat shock proteins (Hsp) protect against cellular stress, their efficacy in preventing myolysis was investigated in a tachy-paced cell model for AF and in patients with AF. HL-1 atrial myocytes were subjected to tachy-pacing, which induced myolysis. Hsp overexpression was accomplished by a mild heat shock or by the drug geranylgeranylacetone (GGA). Hsp-gene-transfection studies were carried out to investigate roles of individual Hsp. In left and/or right atrial appendages from patients with paroxysmal (n=14), persistent (n=17) AF and controls (n=13) in sinus rhythm (SR), Hsp levels (Westerns) and localization (confocal microscopy) were determined. Heat shock and GGA administered prior to tachy-pacing resulted in almost complete protection against tachy-pacing-induced myolysis. Overexpression of Hsp27, but not of Hsp70, also provided complete protection against pacing-induced myolysis. In patients with paroxysmal AF, Hsp27 expression was significantly increased compared to SR and persistent AF. No changes in Hsp40, Hsc70, Hsp70 and Hsp90 expression levels were observed. Hsp27 levels correlated inversely with the duration of paroxysmal and persistent AF and the extent of myolysis. Furthermore, Hsp27 was localized on myofibrils in tachy-paced HL-1 myocytes and in human cardiomyocytes. These data demonstrate that upregulation of Hsp, especially Hsp27, protects tachy-paced atrial myocytes from myolysis. Therefore, the observed elevated Hsp27 expression in patients with paroxysmal AF might serve to protect myocytes from myolysis and limit the progression to persistent AF. Pharmacological induction of Hsp, with drugs such as GGA, may represent a novel therapeutic approach in AF.

Fibrosis in heart disease: understanding the role of transforming growth factor-beta in cardiomyopathy, valvular disease and arrhythmia

The importance of fibrosis in organ pathology and dysfunction appears to be increasingly relevant to a variety of distinct diseases. In particular, a number of different cardiac pathologies seem to be caused by a common fibrotic process. Within the heart, this fibrosis is thought to be partially mediated by transforming growth factor-beta1 (TGF-beta1), a potent stimulator of collagen-producing cardiac fibroblasts. Previously, TGF-beta1 had been implicated solely as a modulator of the myocardial remodelling seen after infarction. However, recent studies indicate that dilated, ischaemic and hypertrophic cardiomyopathies are all associated with raised levels of TGF-beta1. In fact, the pathogenic effects of TGF-beta1 have now been suggested to play a major role in valvular disease and arrhythmia, particularly atrial fibrillation. Thus far, medical therapy targeting TGF-beta1 has shown promise in a multitude of heart diseases. These therapies provide great hope, not only for treatment of symptoms but also for prevention of cardiac pathology as well. As is stated in the introduction, most reviews have focused on the effects of cytokines in remodelling after myocardial infarction. This article attempts to underline the significance of TGF-beta1 not only in the post-ischaemic setting, but also in dilated and hypertrophic cardiomyopathies, valvular diseases and arrhythmias (focusing on atrial fibrillation). It also aims to show that TGF-beta1 is an appropriate target for therapy in a variety of cardiovascular diseases.

Remodeling of myocardial sleeve and gap junctions in canine superior vena cava after rapid pacing

OBJECTIVE

We studied the response of the superior vena cava (SVC) myocardial sleeve to atrial fibrillation (AF).

METHODS AND RESULTS

We examined adult male dogs without pacing (N=6) and after rapid atrial pacing (600 bpm) for 2 weeks (P2w; N=5) and 6-8 weeks (P6-8w; N=5). After pacing, the sleeve was increased in thickness (non-paced vs. either paced group, both P<0.05). This was associated with an increase in proliferative activity, which was higher in the P2w than the P6-8w animals (P<0.05). In addition, collagen content increased, and the component cardiomyocytes become more unevenly oriented and shorter and narrower in shape (non-paced vs. either paced group, both P<0.05). Pacing had different effects on connexin40 (Cx40) and Cx43 gap junctions. There was a 98% increase in Cx43 signal in P2w, and a 74% increase in P6-8w animals (non-paced vs. each paced group, both P<0.05). In contrast, Cx40 signal decreased 47% in P2w but increased 44% in P6-8w animals (non-paced vs. each paced group, both P<0.05).

CONCLUSIONS

Rapid atrial pacing results in a specific pattern of remodeling of the canine SVC sleeve, including changes in size and shape, spatial orientation, and gap junction expression profile of the component cardiomyocytes. These changes may co-operatively affect the electrical properties and contribute to the formation and maintenance of the arrhythmogenic substrate of AF.

Wave Similarity Mapping Shows the Spatiotemporal Distribution of Fibrillatory Wave Complexity in the Human Right Atrium During Paroxysmal and Chronic Atrial Fibrillation

INTRODUCTION

The complexity of waveforms during atrial fibrillation may reflect critical activation patterns for the arrhythmia perpetuation. In this study, we introduce a novel concept of map, based on the analysis of the wave morphology, which gives a direct evidence in the human right atrium on the spatiotemporal distribution of fibrillatory wave complexity in paroxysmal (PAF) and chronic (CAF) atrial fibrillation.

METHODS AND RESULTS

Electrograms were recorded from a 64-electrode catheter in the right atrium of 15 patients during PAF (n = 8) and CAF (n = 7). Wave similarity maps were constructed by calculating the degree of morphological similarity of activation waves (S) at each atrial site and by following its temporal evolution. During PAF the spatiotemporal distribution of the waveforms was highly consistent across the subjects and was determined by the anatomic location. Wave similarity maps showed the existence of an extended area with low similarity index, which covered the low posteroseptal atrium (S = 0.28 +/- 0.09) and the septal region (S = 0.22 +/- 0.04), and the presence of a large tongue with high similarity index, which penetrated the lateral wall (S = 0.55 +/- 0.08) starting from the high anterolateral atrium (S = 0.54 +/- 0.06). A completely different spatiotemporal pattern was seen during CAF. No distinct regions with different similarity indexes were recognized, but a uniformly distributed low similarity index (S = 0.27 +/- 0.07) was found. The spatial pattern was highly stable in time with fluctuations of S < 0.04.

CONCLUSION

Quantification of the spatiotemporal distribution of fibrillatory wave complexity is feasible in humans by wave similarity mapping. Anatomic anchoring of waveforms during PAF and pattern destruction during CAF was determined.

Myocyte changes and their left atrial distribution in patients with chronic atrial fibrillation related to mitral valve disease

It has been found that the pulmonary veins and adjacent left atrial posterior wall (LAPW) are deeply involved in both the initiation and maintenance of atrial fibrillation (AF), and the identification of these high-risk sites has aroused great interest in investigating their histopathologic substrate. We used light and conventional electron microscopy to evaluate the differential myocyte and interstitial changes in LAPW and left atrial appendage (LAA) samples from 28 patients with chronic AF undergoing mitral valve surgery and from 12 autoptic controls. There were always more myocytes with loss of sarcomeres in the LAPW than in the LAA (19.9% +/- 7.7% versus 8.2% +/- 5.0%; P < .0001), and the LAPW showed more marked immunohistochemical evidence of dedifferentiation, characterized by the reexpression of smooth muscle actin. In pathological left atria, myocyte diameter in the LAPW and LAA was comparable (19.0 +/- 1.5 versus 18.5 +/- 2.0 microm; not significant) but larger than in the controls (11.9 +/- 0.8 and 12.1 +/- 1.3 microm, respectively; P < .0001). A terminal deoxynucleotidyltransferase assay did not reveal any myocyte apoptosis. The LAPW also showed more interstitial fibrosis than the LAA (7.49% +/- 3.34% versus 2.80% +/- 1.35%; P < .0001). Ultrastructural examination confirmed the presence of myocyte myocytolysis in the perinuclear area and showed changes in mitochondrial shape. In conclusion, the LAPW in patients with chronic AF related to mitral valve disease seems to be a particular anatomical site in which major myocyte and interstitial changes are concentrated, whereas the LAA is more protected. This remodeling may increase the heterogeneity of LAPW electrical conduction, thus confirming this location as an elective target for the ablation treatment of AF.

The dubious value of echocardiographic and plasma ANP measurements in predicting outcome of cardioversion in patients with persistent atrial fibrillation

Atrial fibrillation (AF) is a common arrhythmia with important therapeutic and prognostic implications. An attempt to restore sinus rhythm is considered in most patients with AF. The aim of this study was to assess the value of echocardiographic examination and plasma atrial natriuretic peptide (ANP) evaluation in predicting the outcome of cardioversion and maintenance of sinus rhythm in patients with persistent AF.

METHODS

Eighty-one consecutive patients, aged 62+/-9 years, with AF of duration 4.7 months were subjected to an echocardiography examination and ANP assessment before cardioversion. The patients were predominantly hypertensive men with moderately enlarged left atrium and ejection fraction of left ventricle of about 50%. All patients were in controlled AF and had normalized blood pressure. In order to predict the outcome of cardioversion, and maintenance of sinus rhythm over a 1 month period, a multivariate logistic regression method was performed using the following variables: left atrial and left ventricular dimensions, left ventricular ejection fraction and plasma ANP levels.

RESULTS

Sixty-nine out of the 81 patients were successfully converted to sinus rhythm. At 1 month 57 patients remained in sinus rhythm. There were no statistical differences between sinus rhythm and AF group in baseline ANP levels (59.4 vs 64.2 pg/ml, consecutively), clinical and echocardiographic characteristics. In logistic regression analysis neither baseline echocardiographic variable nor ANP level, predicts successful cardioversion over a 1-month period of observation.

CONCLUSION

Echocardiographic data and ANP level should not be included as an important variable when considering patients for cardioversion.

Prolonged signal-averaged P wave duration after elective cardioversion increases the risk of recurrent atrial fibrillation

OBJECTIVE

To assess the risk of atrial fibrillation (AF) recurrence after elective cardioversion of AF in relation to the signal-averaged P wave duration (SAPWD), clinical characteristics of the patient, and the duration of the AF disease.

DESIGN

We studied 131 consecutive patients (88 men, 43 women), median age 67 years (range 29-87 years), after elective cardioversion of AF into sinus rhythm. The SAPWD was measured on inclusion, and the follow-up period was 1 month. Recurrent AF within the first month after cardioversion was regarded as endpoint.

RESULTS

AF recurred in 73 patients (56%). Multiple logistic regression analysis showed that prolonged SAPWD above 160 ms was the only significant risk factor for recurrent AF, OR=2.22 (95% CI 1.07-4.60), p=0.03. There was no significant effect of age, diagnosed hypertension, diagnosed congestive heart failure, dilated left atrium, or long duration of AF on the risk of AF relapse.

CONCLUSION

Prolonged SAPWD above 160 ms is a risk factor for recurrent AF after elective cardioversion of persistent AF.

Expression of extracellular signal-regulated kinase and angiotensin-converting enzyme in human atria during atrial fibrillation

In order to investigate the changes in the expression of extracellular signal-regulated kinase (ERK1/ERK2) and angiotensin-converting enzyme (ACE) in the patients with atrial fibrillation (AF), 52 patients with rheumatic heart diseases were examined. Nineteen patients had chronic persistent AF (AF > or = 6 months, CAF), 12 patients had paroxymal AF (PAF) and 21 patients had no history of AF. The ERK expression was detected at the mRNA level by reverse transcription polymerase chain reaction, at the protein level by Western blotting and at atrial tissue level by immunohistochemistry. ERK-activating kinases (MEK1/2) and ACE were determined by Western blotting techniques. The expression of ERK2-mRNA was increased in the patients with CAF (74 +/- 19 U vs sinus rhythm: 32 +/- 24 U, P < 0.05). Activated ERK1/ERK2 and MEK1/2 were increased to more than 150% in the patients with AF compared to those with sinus rhythm. No significant difference between CAF and PAF was found. The expression of ACE was three-fold increased in the patients with CAF compared to those with sinus rhythm. Patients with AF showed an increased expression of ERK1/ERK2 in atrial interstitial cells and marked atrial fibrosis. An ACE-dependent increase in the amounts of activated ERK1/ERK2 in atrial interstitial cells may be one of molecular mechanisms for the development of atrial fibrosis in the patients with AF. These findings may have important impact on the treatment of AF.

Expression of the von Willebrand Factor in Atrial Endocardium is Increased in Atrial Fibrillation Depending on the Extent of Structural Remodeling

BACKGROUND

The incidence of stroke in patients suffering atrial fibrillation (AF) is increased when left atrial enlargement occurs. Recently, the platelet adhesive molecule, von Willebrand factor (vWF), located in the atrial endocardium, has been shown to be increased in patients with a variety of heart diseases compared with patients who have no cardiac problems.

METHODS AND RESULTS

We investigated the expression of vWF mRNA and protein in the endocardium as a possible prothrombotic alteration of AF in association with atrial structural remodeling. Atrial appendage specimens were obtained during either heart surgery or at an autopsy from AF patients with and without underlying heart disease. The immunohistochemical and in situ hybridization signals for vWF in the endocardium were well correlated and varied widely among the individual atrial appendages examined. The increased expression of vWF in the endocardium was associated with enlarged left atrial dimensions in mitral valvular disease or increased myocyte diameters in the underlying myocardium. Platelet adhesion/aggregation on the endocardium was always found under the fresh thrombi and was colocalized with strong vWF staining, but not necessarily with fibrinogen and/or fibrin staining.

CONCLUSIONS

Endocardial overexpression of vWF may occur during the process of atrial structural remodeling contributing to the thrombotic predilection of AF in association with underlying heart disease.

Oxidative damage to mitochondrial DNA in atrial muscle of patients with atrial fibrillation

Atrial fibrillation (AF) is the most common cause of arrhythmia and is an aging-related disease encountered in clinical practice. The electrophysiological remolding with Ca(2+) overloading and cellular structure changes were found in cardiomyocytes of AF patients. In previous studies, increased oxidative stress and oxidative damage was found in cardiomyocytes during the ischemia/reperfusion injury. Besides, mitochondrial DNA (mtDNA) deletion and mtDNA proliferation occur frequently in affected tissues of patients with certain degenerative diseases and during aging of the human. However, it remains unclear whether high oxidative stress and alteration of mtDNA play a role in the pathophysiology of AF. In this study, we first screened for large-scale deletions of mtDNA in the atrial muscle of AF patients by long-range polymerase chain reaction (PCR). The results showed that large-scale deletions between nucleotide positions 7900 and 16500 of mtDNA occurred at a high frequency. Among them, the 4977 bp deletion was the most frequent and abundant one, and the mean proportion of mtDNA with the 4977 bp deletion in the atrial muscle of the patients with AF was 3.75-fold higher than that of the patients without AF (p <.005). Furthermore, quantitative PCR was performed to evaluate lesions in mtDNA caused by oxidative damage. We found that the degree of mtDNA damage in the patients with AF was greater than that of the patients without AF (3.29 vs.1.60 per 10 kb, p <.0005). The 8-OHdG, which is one of the most common products of oxidative damage to DNA, was also found at a higher frequency in mtDNA of patients with AF as compared with those without AF. In addition, the mtDNA content was found to increase significantly in the patients with AF (p =.0051). The level of mtDNA lesion and the mtDNA content was positively correlated (r = 0.44). These results suggest that oxidative injury and deletion of mtDNA in cardiac muscle are increased in the patients with AF, which may contribute to the impairment of bioenergetic function of mitochondria and induction of the oxidative vicious cycle involved in the pathogenesis of atrial myopathy in AF.

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

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

Echocardiographic changes and predictors of arrhythmia recurrence after long-term use of the atrial defibrillator

BACKGROUND

The patient-activated atrial defibrillator allows patients to cardiovert themselves from atrial fibrillation soon after the onset of symptoms. The long-term effects of early cardioversion from persistent atrial fibrillation on left ventricular performance and left atrial size are unknown.

METHODS

Eighteen patients, mean age 63.4, 83% male, had the Jewel((R)) AF atrial defibrillator implanted for persistent atrial fibrillation only. Transthoracic echocardiography was performed 3-monthly following implant. Parasternal long axis measurements were taken using conventional M-mode techniques.

RESULTS

Over follow-up of 28.0+/-9 months, 377 episodes of persistent atrial fibrillation were terminated by patient-activated cardioversion (median 15 per patient). Echocardiographic measurements at implant were; left atrium 44+/-6 mm, left ventricular end-diastolic diameter 49+/-7 mm, left ventricular end-systolic diameter 34+/-7 mm, fractional shortening 33+/-10% and ejection fraction 65+/-17%. After 1 year there had been a significant decrease in mean left atrial size to 41+/-6 mm (P=0.02) and an increase in mean ejection fraction to 73+/-8% (P=0.04). At long-term follow-up however, all parameters reverted to pre-implant levels. Baseline echocardiographic variables did not predict which patients would demonstrate serial increases in sinus rhythm duration between shocks during long-term follow-up. Patients on antiarrhythmic drug therapy however were more likely to demonstrate "sinus rhythm begetting sinus rhythm".

CONCLUSIONS

Use of the atrial defibrillator for spontaneous persistent atrial fibrillation is associated with a medium-term (1 year) reduction in left atrial size and an increase in ejection fraction. These changes were not maintained in the long-term. Synergistic therapy with antiarrhythmic drugs may prolong periods of sinus rhythm between arrhythmia recurrences.

P wave morphology during spontaneous and paced pulmonary vein activity: differences between patients with atrial fibrillation and normal controls

P wave morphology (PWM) has been used to predict the location of ectopic foci responsible for triggering atrial fibrillation (AF). With bi-atrial mapping, this study examined PWM during spontaneous ectopy and during pulmonary vein (PV) pacing, comparing the results with published algorithms in 40 AF patients and 15 controls. PWM during PV pacing is similar to spontaneous ectopy, if performed at similar coupling intervals. PWM during ectopic activity from the PVs is affected by cycle length and the presence of underlying atrial electrical and structural abnormalities. Changes in PWM during decremental pacing were observed in 5% of controls but in over 25% of persistent AF patients. The algorithms are accurate in over 90% of controls and paroxysmal AF patients with normal atria, but less than 60% in those with persistent AF or electrical or structural atrial abnormalities. The accuracy of non-invasive localization of arrhythmogenic PV is limited.

Effects of MgSO4 and glucose, insulin and potassium (GIK) on atrial conduction during the first 12 hours after DC-conversion of chronic atrial fibrillation

OBJECTIVE

To investigate changes in atrial conduction induced by MgSO4 and glucose, insulin and potassium (GIK) during the first 12-h period of sinus rhythm after successful DC-conversion of chronic atrial fibrillation (CAF).

METHODS

Signal-averaged P-wave duration, QRS-duration and PQ-time were recorded in 20 patients who were randomly assigned to control or intervention. Ten patients received no infusates (control group) and 10 patients received MgSO4 and GIK infusions (intervention group). P-wave duration was determined from the X-, Y- and Z-leads, which were further combined to obtain a spatial magnitude. P-wave morphology was studied by analysing global activation patterns and discrete components from the calculated spatial magnitude signal.

RESULTS

No changes in the measured parameters were seen in the control group. The P-wave duration, QRS-duration and PQ-time increased from 139(13) [mean(SD)] to 149(15) (p < 0.01), 90(7) to 94(9) (p < 0.05) and 188(10) to 207(13) ms (p < 0.01). respectively, after bolus infusion of MgSO4. The time from the start of the P-wave to its 1st and 2nd max. locations increased by 6 ms (p < 0.01) in both cases after bolus infusion of MgSO4 and had reversed after 10 h of MgSO4 and GIK infusion. P-wave duration and PQ-time decreased after 10 h of MgSO4 and GIK infusion, from 149(34) (bolus) to 138(12) and from 207(13) to 195(27) ms (p < 0.05), respectively, in spite of an even higher serum Mg concentration at the end of this period.

CONCLUSION

Bolus infusion of MgSO4 2 h after DC-conversion of CAF produced an intra-atrial conduction delay that could be reversed by adding a GIK infusion, in spite of a concomitant increase in serum Mg concentration. No recovery of the intra-atrial conduction delay, seen after DC-conversion of CAF, was observed in either of the two groups during the 12-h study period.

Clinical pathophysiology of hibernating myocardium

Our current knowledge of the pathophysiology of chronic hibernating myocardium is mainly based on results from clinical studies, because of the absence of appropriate and validated animal models. These clinical observations have given rise to two major controversies: the role of reduced blood flow and that of histological changes in the hibernating segments. In this review, these two subjects will be briefly discussed, and put into the perspective of findings emerging from recently developed animal models.

Impaired myofibrillar energetics and oxidative injury during human atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is associated with severe contractile dysfunction and structural and electrophysiological remodeling. Mechanisms responsible for impaired contractility are undefined, and current therapies do not address this dysfunction. We have found that myofibrillar creatine kinase (MM-CK), an important controller of myocyte contractility, is highly sensitive to oxidative injury, and we hypothesized that increased oxidative stress and energetic impairment during AF could contribute to contractile dysfunction. Methods and Results-- Right atrial appendages were obtained from AF patients undergoing the Maze procedure and from control patients who were in normal sinus rhythm and undergoing cardiac surgery. MM-CK activity was reduced in AF patients compared with controls (25.4+/-3.4 versus 18.2+/-3.8 micromol/mg of myofibrillar protein per minute; control versus AF; P<0.05). No reduction in total CK activity or myosin ATPase activity was detected. This selective reduction in MM-CK activity was associated with increased relative expression of the beta-myosin isoform (25+/-6 versus 63+/-5%beta, CTRL versus AF; P<0.05). Western blotting of AF myofibrillar isolates demonstrated no changes in protein composition but showed increased prevalence of protein oxidation as detected by Western blotting for 3-nitrotyrosine (peroxynitrite biomarker) and protein carbonyls (hydroxyl radical biomarker; P<0.05). Patterns of these oxidative markers were distinct, which suggests discrete chemical events and differential protein vulnerabilities in vivo. MM-CK inhibition was statistically correlated to extent of nitration (P<0.01) but not to carbonyl presence.

CONCLUSIONS

The present results provide novel evidence of oxidative damage in human AF that altered myofibrillar energetics may contribute to atrial contractile dysfunction and that protein nitration may be an important participant in this condition.

Recovery of electrophysiological parameters after conversion of atrial fibrillation

We investigated the recovery of electrophysiological parameters from electrical remodeling after conversion of chronic lone atrial fibrillation in humans. Clinical studies have shown that the longer atrial fibrillation lasts, the more difficult it becomes to maintain the sinus rhythm after cardioversion. To explore the effects of the duration of atrial fibrillation on changes of electrophysiological parameters after conversion, we determined the atrial effective refractory period and P wave duration during right atrial pacing at 1 and 24 h after electrical cardioversion in 15 patients with chronic lone atrial fibrillation (median duration, 6 months). By 24 h after cardioversion, the effective refractory period at a pacing cycle length of 600 ms increased from 225+/-19 to 254+/-27 ms. However, the P wave duration did not decrease significantly 24 h after conversion. As the duration of atrial fibrillation became longer, the prolongation of effective refractory period was more delayed (P<0. 001, r=0.82), and the shortening of P wave duration was significantly smaller within 24 h after cardioversion (P<0. 001, r=0.67). After cardioversion of chronic lone atrial fibrillation, the recovery of shortened atrial refractoriness and prolonged intraatrial conduction time is dependent on the duration of preexisting atrial fibrillation.

Atrial fibrillation--Where do we stand today?

The basic underlying mechanisms behind atrial fibrillation (AF), the most abundant therapy demanding cardiac dysrhythmia, have until recently being largely unknown. Once established, AF is not only self-perpetuating but also self-destructive, prompting rapid treatment against possible initiating mechanisms. Recent observations reveal that the ectopic beats, initiating AF, often originate in the walls of the pulmonary veins and that the deterioration of the ectopic impulse to AF may be linked to an impaired inferoposterior interatrial conduction. The underlying mechanisms behind these functional defects are still obscure. The observations has however, permitted evaluation of new types of treatment, directly interfering with the newly verified findings.