Yi-Chih Wang

Increased Expression of Mineralocorticoid Receptor in Human Atrial Fibrillation and a Cellular Model of Atrial Fibrillation

OBJECTIVES This study was designed to evaluate the status of steroidogenesis proteins and de novo synthesis of aldosterone in the atrium, and relationships of these factors to atrial fibrillation (AF). BACKGROUND The role of mineralocorticoid in the pathogenesis of AF is unknown. METHODS We studied atrial expression of steroidogenesis proteins and aldosterone level in patients with and without AF, and in HL-1 atrial myocytes. We also investigated the electrophysiologic effects and signal transduction of aldosterone on atrial myocytes. RESULTS We found basal expressions of mineralocorticoid receptors (MRs), glucocorticoid receptors, and 11-beta-hydroxysteroid dehydrogenase type 2 (11bHSD2) but not 11-beta-hydroxylase (CYP11B1) or aldosterone synthase (CYP11B2) in human atria and HL-1 myocytes. There was no significant difference of mean atrial aldosterone level between patients with AF and those with normal sinus rhythm. However, patients with AF had a significantly higher atrial MR expression compared with those with normal sinus rhythm (1.73 +/- 0.24-fold, p < 0.001). Using mouse HL-1 atrial myocytes as a cellular AF model, we found that rapid depolarization increased MR expression (1.97 +/- 0.72-fold, p = 0.008) through a calcium-dependent mechanism, thus augmenting the genomic effect of aldosterone signaling as evaluated by MR reporter. Aldosterone increased intracellular oxidative stress through a nongenomic pathway, which was attenuated by nicotinamide adenine dinucleotide phosphate oxidase inhibitor diphenyleneiodonium, but not by MR-blockade spironolactone. Aldosterone increased expression of the alpha-1G and -1H subunits of the T-type calcium channel and thus increased the T-type calcium current (-13.6 +/- 2.9 pA/pF vs. -4.5 +/- 1.6 pA/pF, p < 0.01) and the intracellular calcium load through a genomic pathway, which were attenuated by spironolactone, but not by diphenyleneiodonium. CONCLUSIONS Expression of MR increased in AF, thus augmenting the genomic effects of aldosterone. Aldosterone induced atrial ionic remodeling and calcium overload through a genomic pathway, which was attenuated by spironolactone. These results suggest that aldosterone may play a role in AF electrical remodeling and provide insight into the treatment of AF with MR blockade.

Mechanical Stretch of Atrial Myocyte Monolayer Decreases Sarcoplasmic Reticulum Calcium Adenosine Triphosphatase Expression and Increases Susceptibility to Repolarization Alternans

OBJECTIVES The purpose of this study was to investigate the effect of stretch (the major risk factor for atrial fibrillation [AF]) on spatial and temporal alternations of action potential duration (APD-ALT) and calcium transient in cultured atrial myocyte monolayer. BACKGROUND How rapid firings or premature beats trigger AF is not completely understood. Discordant repolarization alternans, characterized by simultaneous prolongation and shortening of APD in different myocardial regions, is central to the genesis of ventricular fibrillation. We hypothesized that repolarization alternans also is central to the initiation of multiple re-entry circuits and AF. METHODS Confluent HL-1 atrial myocyte monolayer with spontaneous depolarization was cultured in silicone membrane and subjected to mechanical stretch. Rapid field pacing was used to induce alternans. A high-resolution dual optical mapping system was used to record action potentials and calcium transients. RESULTS High-rate pacing induced APD-ALT and calcium transient in atrial myocyte monolayer. Mechanical stretch significantly decreased the thresholds for APD-ALT and calcium transient. Mechanical stretch decreased the expression of sarcoplasmic reticulum adenosine triphosphatase 2, and thus slower calcium reuptake kinetics, which was responsible for the susceptibility to alternans. Mechanical stretch did not alter the APD restitution kinetics. Mechanical stretch also enhanced spatially discordant alternans. Overexpression of sarcoplasmic reticulum adenosine triphosphatase 2 reversed all the effects of stretch on susceptibility to alternans. In intact atrium, mechanical stretch also enhanced discordant alternans. CONCLUSIONS Mechanical stretch increased the susceptibility to alternans in atrial myocytes, which may explain the susceptibility to AF in conditions of atrial stretch, such as mitral valvular heart disease, heart failure, and hypertension.

Atorvastatin prevents atrial fibrillation in patients with bradyarrhythmias and implantation of an atrial-based or dual-chamber pacemaker: a prospective randomized trial.

BACKGROUND Increasing evidence suggests that atrial fibrillation (AF) is an inflammatory disease. Statins is an anti-inflammatory agent. The present study was conducted to test the efficacy of atorvastatin in preventing paroxysmal AF or atrial high rate episodes (AHEs) in patients with bradyarrhythmias and implantation of an atrial-based or dual-chamber pacemaker. METHODS The effect of atorvastatin on time to the first attack of AF or AHE (> or =180 per minute and > or =1 or 10 minutes), which was accurately detected by pacemaker interrogation, was evaluated in an open-label prospective randomized design for 1 year of follow-up. RESULTS Fifty-two patients (23 males, 70 +/- 13 years old) were randomized to the statin group (atorvastatin 20 mg/d) and 54 (25 males, 72 +/- 13 years old) to the nonstatin group. Event-free survivals from AHE > or =1 minute were not significantly different between the 2 groups (log-rank P = .410). However, patients in the nonstatin group were more likely to develop AHE > or =10 minutes than those in the statin group (log-rank P = .028). Atrial high rate episode > or =10 minutes occurred in 3 (5.8%) of 51 patients in the statin group after 1 year of follow-up, and 10 (19.2%) of 52 patients (odds ratio 0.26, P = .041) in the nonstatin group. The mean left atrial volume of the statin group was significantly lower than that of the nonstatin group at the end of follow-up (39.7 +/- 1.7 vs 43.7 +/- 1.9 mL, P < .0001). CONCLUSIONS The present study demonstrated the efficacy of atorvastatin in preventing significant AF (> or =10 minutes) and left atrial enlargement in patients with bradyarrhythmias and implantation of a pacemaker.

In-vitro recording of adult zebrafish heart electrocardiogram — A platform for pharmacological testing

BACKGROUND Recently zebrafish has become a powerful vertebrate model system for cardiac arrhythmia and another advantage is that the heart could be rapidly excised for in-vitro electrophysiological recording. METHODS We made direct in-vitro recordings of adult zebrafish heart ECG using the microelectrode and tested the effects of various drugs on zebrafish heart ECG. RESULTS The QT interval change in the ECG was verified by optically mapped action potential duration (APD). The mean in-vitro heart rate (HR) of the adult zebrafish was 118 ± 22 beats/min. The mean QT interval was 312 ± 36 ms and mean HR corrected QT interval (QTc) 439 ± 39 ms. The mean optically mapped APD was 308 ± 30 ms, which was close to the QT interval in ECG (p=0.815). We found that sympathomimetic drug isoproterenol increased HR, whereas L-type calcium channel blocker verapamil decreased HR. Sodium channel blocker quinidine and L-type calcium channel activator BayK8644 prolonged QTc interval in a dose-dependent manner (515 ± 24 ms and 519 ± 27 ms, respectively, both p<0.01). The APD was also prolonged accordingly. Both rapidly and slowly activating delayed rectifier potassium channel (IKr and IKs) blockers E4031 and chromanol 293B, respectively, also prolonged QTc interval in a dose-dependent manner (523 ± 25 ms and 529 ± 27 ms, respectively, both p<0.01). Quinidine, E4031 and chromanol 293B also decreased HR. CONCLUSIONS Direct in-vitro recording of adult zebrafish heart is an efficient platform for test of drugs which exert electrophysiological effects on cardiomyocytes, and perturbation of ionic channels that are responsible for human long QT syndrome also modulates QT interval in adult zebrafish heart.

Preclinical Systolic and Diastolic Dysfunctions in Metabolically Healthy and Unhealthy Obese Individuals

Background—Despite the substantial overlap of obesity and metabolic disease, there is heterogeneity with respect to cardiovascular risk. We sought to investigate preclinical differences in systolic and diastolic function in obesity, and specifically compare obese individuals with and without metabolic syndrome (MS). Methods and Results—Obese individuals without cardiac disease with (OB/MS+, n=124) and without (OB/MS−, n=37) MS were compared with nonobese controls (n=29). Diastolic function was assessed by transmitral and tissue Doppler. Global longitudinal strain (LS) and time-based dyssynchrony were assessed by speckle tracking. Both OB/MS− and OB/MS+ groups had similar ejection fraction but worse systolic mechanics as assessed by LS and dyssynchrony when compared with nonobese controls. Specifically, OB/MS− had 2.5% lower LS (SE, 0.7%; P=0.001 in multivariable-adjusted analyses) and 10.8 ms greater dyssynchrony (SE, 3.3 ms; P=0.002), and OB/MS+ had 1.0% lower LS (SE, 0.3%; P<0.001) and 7.8 ms greater dyssynchrony (SE, 1.5 ms; P<0.001) when compared with controls. Obesity was associated with impaired diastolic function regardless of MS status, as evidenced by greater left atrial diameter and left ventricular mass although diastolic dysfunction was more pronounced in OB/MS+ than in OB/MS− individuals. Conclusions—Obesity is associated with subclinical differences in both systolic and diastolic function regardless of the presence or absence of MS although MS seems to be associated with worse diastolic dysfunction. When compared with controls, metabolically healthy obese had lower LS, greater dyssynchrony, and early diastolic dysfunction, supporting the notion that obesity per se may have adverse cardiovascular effects regardless of metabolic disease.

Interaction of gender, hypertension, and the angiotensinogen gene haplotypes on the risk of coronary artery disease in a large angiographic cohort.

There is increasing evidence suggesting the importance of evaluating gene-environment interactions in the genetic study of coronary artery disease (CAD). We investigated the association of multiple single nucleotide polymorphisms in the angiotensinogen (AGT) gene with CAD, considering the interaction between the genetic and non-genetic factors, using a larger and ethnically homogeneous angiographic cohort. A total of 1254 consecutive patients who underwent cardiac catheterization (735 with CAD and 519 without) were recruited. T174M (rs4762), M235T (rs699), G-6A, A-20C, G-152A, and G-217A polymorphisms of the AGT gene were genotyped. We used a regression approach based on a generalized linear model to evaluate haplotype effects defined by the multilocus data and detection of gene-environment interaction by incorporating interaction terms in the model. We found significant differences in global AGT gene haplotype profile between patients with and without CAD (the global score statistic=25.411, P=0.008). Significant interactions between AGT gene haplotypes, gender and hypertension were detected. We also used haplotype counting to directly estimate the odds ratio of each AGT gene haplotype, and found that the effects of haplotypes were markedly different in subgroups defined by gender and hypertension, providing strong evidence of gene-environment interaction. Female gender synergistically enhances (or male gender reverses) the effects of AGT gene haplotypes on the risk of CAD in the presence of hypertension. In conclusion, the effect of AGT gene haplotypes on the risk of CAD was significantly increased in women with hypertension, which highlights the importance of evaluating gene-environment interactions in the genetic study of CAD.

Renin-Angiotensin System Gene Polymorphisms and Atrial Fibrillation: A Regression Approach for the Detection of Gene-Gene Interactions in a Large Hospitalized Population

Objectives: To test the association between renin-angiotensin system gene variants and atrial fibrillation (AF) using a regression approach. Methods: A total of 1,236 consecutive patients (227 with AF and 1,009 with normal sinus rhythm as controls) were recruited. Angiotensin-converting enzyme (ACE) gene I/D polymorphism; T174M, M235T, G–6A, A–20C, G–152A and G–217A polymorphisms of the angiotensinogen (AGT) gene, and A1166C polymorphism of the angiotensin II type I receptor (AT1R) gene were genotyped. We used a regression approach based on a generalized linear model to evaluate haplotype effects and to detect gene-gene interactions by incorporating interaction terms in the model. Results: In single-locus analyses, no locus was associated with AF. After adjustment for AF risk factors, we found significant differences in the global AGT gene haplotype profile (the global score statistic = 30.364, p = 0.001) and individual haplotype frequencies between AF patients and controls. Furthermore, significant 2-way gene-gene interactions between ACE I/D polymorphism and AGT gene haplotypes and between AT1R A1166C polymorphism and AGT gene haplotypes, and 3-way interaction between ACE I/D, AT1R A1166C and AGT gene haplotypes were detected. Conclusions: These results are compatible with the concept of multilocus and multigene effects in determining the risk of complex diseases such as AF, which would be missed with conventional single-locus approaches.

TNF-α down-regulates sarcoplasmic reticulum Ca2+ ATPase expression and leads to left ventricular diastolic dysfunction through binding of NF-κB to promoter response element

AIMS TNF-alpha (TNF-α) causes left ventricular diastolic dysfunction. Down-regulation of sarcoplasmic reticulum Ca(2+)-ATPase 2a protein (SERCA2a) expression is one of the major mechanisms underlying diastolic dysfunction. We investigated whether TNF-α modulates SERCA2a expression and alters cardiac diastolic function, and its detailed signalling pathway. METHODS AND RESULTS We used both in vitro cellular cardiomyocyte model and in vivo rat model to address this issue. We found that TNF-α decreased the levels of both SERCA2a mRNA and protein in the cardiomyocytes, with corresponding impairment of diastolic calcium reuptake, a cellular phenotype of cardiac diastolic function. An ∼2 kb promoter of the SERCA2a gene (atp2a2) along with its serial deletions was cloned into the luciferase reporter system. TNF-α significantly decreased the promoter activity, and truncation of the SERCA2a gene promoter with the putative nuclear factor kappa-B (NF-κB) response element abolished TNF-α-induced SERCA2a gene suppression. Chromatin immunoprecipitation and gel retardation also confirmed the binding of NF-κB to this putative-binding site. TNF-α increased the phosphorylation of IKK and the degradation of IκB, resulted in NF-κB nuclear translocation, and decreased SERCA2a gene promoter activity. This process was attenuated by NF-κB blockers and simvastatin. In the in vivo rat model, lipopolysaccharide treatment significantly elevated the serum TNF-α level, as well as phosphorylation of IKK, resulting in a decrease in myocardial SERCA2a expression, diastolic calcium reuptake, and diastolic dysfunction. Oral treatment with simvastatin led to an increase in SERCA2a expression, alleviation, and prevention of the diastolic dysfunction. CONCLUSIONS TNF-α suppresses SERCA2a gene expression via the IKK/IκB/NF-κB pathway and binding of NF-κB to the SERCA2a gene promoter, and its effect is blocked by simvastatin, demonstrating the potential therapeutic effect of statins in treating inflammation-related diastolic dysfunction.

Outcome of primary percutaneous coronary intervention in octogenarians with acute myocardial infarction

BACKGROUND/PURPOSE Acute myocardial infarction (AMI) results in more complications and increased mortality in octogenarians compared to patients in younger age groups. This study investigated the short- and long-term outcomes in octogenarians after primary percutaneous coronary intervention (PCI). METHODS During the study period from May 1997 to August 2004, 54 patients > or = 80 years old with ST-elevation myocardial infarction (STEMI) were eligible for primary PCI. Data collected included baseline clinical characteristics and usage of cardiovascular medications. Diagnostic coronary angiography and revascularization procedures were performed using standard practices. During hospitalization, the clinical course including serial changes in cardiac enzymes, adverse events associated with myocardial infarction or treatment, and inhospital or long-term mortality of patients were recorded. RESULTS The mean age of the 54 patients (35 men, 19 women) was 82.8 +/- 2.5 years (range, 80-89 years). Among them, 27 (50%) had anterior infarction, six (11%) had anterolateral infarction, and 21 (39%) had inferior infarction, inclusive of three patients with accompanying right ventricular infarction. Among them, 20 (37%) patients were in Killip class I, nine (17%) were in class II, two (4%) in class III, and 23 (43%) in class IV. The mean delay from onset of symptoms to arrival in hospital was 220 +/- 167 minutes, and 189 +/- 169 minutes from hospital arrival to reperfusion. Diagnostic coronary angiography revealed that 48 (89%) patients had multivessel disease. Inhospital death occurred in 23 (43%) patients, with the leading causes of death being profound cardiogenic shock (61%), and free wall rupture (26%). CONCLUSION Octogenarian patients who developed STEMI tended to have multivessel disease. These patients had a high inhospital mortality rate that was most likely to be due to cardiogenic shock.

Left Atrial Dysfunction in Patients With Atrial Fibrillation After Successful Rhythm Control for > 3 Months*

BACKGROUND Large-scale clinical trials have demonstrated that patients with atrial fibrillation (AF), when treated with a rhythm-control strategy, are still at risk for embolic events. We hypothesized that left atrial (LA) dysfunction persisted even after successful maintenance of sinus rhythm for > 3 months. METHODS A total of 93 patients with AF and satisfactory rhythm control for > 3 months were included. Satisfactory rhythm control was defined as being free of AF based on patient-reported symptoms, monthly ECG follow-up, and ambulatory Holter ECG if needed. Among the 93 patients, 25 patients had sustained AF that was terminated by electrical or pharmacologic cardioversion, while 68 patients had paroxysmal AF under good medical control. Clinical data were obtained, and transthoracic and transesophageal echocardiography were performed after satisfactory rhythm control for > 3 months. RESULTS Among the 93 patients, 34 patients (37%) had LA dysfunction, defined as LA appendage (LAA) peak emptying velocity < 40 cm/s or spontaneous echo contrast and/or thrombus in the LA or LAA. When compared to the other 59 patients without LA dysfunction, they had larger LA dimension (40 +/- 6 mm vs 36 +/- 8 mm [+/- SD], p = 0.018) but did not differ significantly regarding the left ventricular (LV) chamber size, LV ejection fraction, mitral or tricuspid inflow, and ratio of the amplitude of the waves created by early diastolic filling and atrial contraction. We also analyzed the relationship between LA function and clinical risk factors for stroke, including hypertension, diabetes mellitus, coronary artery disease, age > 65 years, and prior cerebral vascular accident. LA dysfunction was found in 10 of 17 patients (59%) with three or more risk factors. The odds ratio for having LA dysfunction was 3.1 (p = 0.04; 95% confidence interval, 1.1 to 9.1) when compared with patients with less than three risk factors. CONCLUSIONS LA dysfunction was present in more than one third of AF patients after satisfactory rhythm control for > 3 months. Patients with higher burden (three or more) of clinical risk factors were more likely to have impaired LA function.