Human Left Atrium Research Articles

Gene expression and genetic variation in human atria.

The human left and right atria have different susceptibilities to develop atrial fibrillation (AF). However, the molecular events related to structural and functional changes that enhance AF susceptibility are still poorly understood. The purpose of this study was to characterize gene expression and genetic variation in human atria. We studied the gene expression profiles and genetic variations in 53 left atrial and 52 right atrial tissue samples collected from the Myocardial Applied Genomics Network (MAGNet) repository. The tissues were collected from heart failure patients undergoing transplantation and from unused organ donor hearts with normal ventricular function. Gene expression was profiled using the Affymetrix GeneChip Human Genome U133A Array. Genetic variation was profiled using the Affymetrix Genome-Wide Human SNP Array 6.0. We found that 109 genes were differentially expressed between left and right atrial tissues. A total of 187 and 259 significant cis-associations between transcript levels and genetic variants were identified in left and right atrial tissues, respectively. We also found that a single nucleotide polymorphism at a known AF locus, rs3740293, was associated with the expression of MYOZ1 in both left and right atrial tissues. We found a distinct transcriptional profile between the right and left atrium and extensive cis-associations between atrial transcripts and common genetic variants. Our results implicate MYOZ1 as the causative gene at the chromosome 10q22 locus for AF.

High-order spectral/hp element discretisation for reaction–diffusion problems on surfaces: Application to cardiac electrophysiology

We present a numerical discretisation of an embedded two-dimensional manifold using high-order continuous Galerkin spectral/hp elements, which provide exponential convergence of the solution with increasing polynomial order, while retaining geometric flexibility in the representation of the domain. Our work is motivated by applications in cardiac electrophysiology where sharp gradients in the solution benefit from the high-order discretisation, while the computational cost of anatomically-realistic models can be significantly reduced through the surface representation and use of high-order methods. We describe and validate our discretisation and provide a demonstration of its application to modelling electrochemical propagation across a human left atrium.

An Immunohistochemical Analysis of Tissue Thrombin Expression in the Human Atria

ObjectiveThrombin, the final coagulation product of the coagulation cascade, has been demonstrated to have many physiological effects, including pro-fibrotic actions via protease-activated receptor (PAR)-1. Recent investigations have demonstrated that activation of the cardiac local coagulation system was associated with atrial fibrillation. However, the distribution of thrombin in the heart, especially difference between the atria and the ventricle, remains to be clarified. We herein investigated the expression of thrombin and other related proteins, as well as tissue fibrosis, in the human left atria and left ventricle.MethodsWe examined the expression of thrombin and other related molecules in the autopsied hearts of patients with and without atrial fibrillation. An immunohistochemical analysis was performed in the left atria and the left ventricle.ResultsThe thrombin was immunohistologically detected in both the left atria and the left ventricles. Other than in the myocardium, the expression of thrombin was observed in the endocardium and the subendocardium of the left atrium. Thrombin was more highly expressed in the left atrium compared to the left ventricle, which was concomitant with more tissue fibrosis and inflammation, as detected by CD68 expression, in the left atrium. We also confirmed the expression of prothrombin in the left atrium. The expression of PAR-1 was observed in the endocardium, subendocardium and myocardium in the left atrium. In patients with atrial fibrillation, strong thrombin expression was observed in the left atrium.ConclusionsThe strong expression levels of thrombin, prothrombin and PAR-1 were demonstrated in the atrial tissues of human autopsied hearts.

Novel Methods for Characterization of Paroxysmal Atrial Fibrillation in Human Left Atria

Introduction:More effective methods for characterizing 3D electrical activity in human left atrium (LA) are needed to identify substrates/triggers and microreentrant circuit for paroxysmal atrial fibrillation (PAF). We describe a novel wavelet-based approach and wave-front centroid tracking that have been used to reconstruct regional activation frequency and electrical activation pathways from non-contact multi-electrode array.Methods:Data from 13 patients acquired prior to ablation for PAF with a 64 electrode noncontact catheter positioned in the LA were analysed. Unipolar electrograms were reconstructed at 2048 locations across each LA endocardial surface. Weighted fine- and coarse-scale electrograms were constructed by wavelet decomposition and combined with peak detection to identify atrial fibrillation (AF) activation frequency and fractionated activity at each site. LA regions with upper quartile AF frequencies were identified for each patient. On the other hand, a wave-front centroid tracking approach was introduced for this first time to detect macro-reentrant circuit during PAF.Results:The results employing wavelet-based analysis on atrial unipolar electrograms are validated by the signals recorded simultaneously via the contacted ablation catheter and visually tracking the 3D spread of activation through the interest region. Multiple connected regions of high frequency electrical activity were seen; most often in left superior pulmonary vein (10/12), septum (9/12) and atrial roof (9/12), as well as the ridge (8/12). The wave-front centroid tracking approach detects a major macro circuit involving LPVs, PLA, atrial floor, MV, septum, atrial roof and ridge. The regions with high frequency by wave-front tracking are consistent with the results using wavelet approach and our clinical observations.Conclusions:The wavelet-based technique and wave-front centroid tracking approach provide a robust means of extracting spatio-temporal characteristics of PAF. The approach could facilitate accurate identification of pro-arrhythmic substrate and triggers, and therefore, to improve success rate of catheter ablation for AF.

Angiotensin Receptor Blockers and Statins Could Alleviate Atrial Fibrosis via Regulating Platelet-Derived Growth Factor/Rac1 /Nuclear Factor-Kappa B Axis

Aims: To investigate whether the administration of renin-angiotensin system (RAS) inhibitors and statins could alleviate atrial fibrosis via platelet-derived growth factor (PDGF)/Rac1 /nuclear factor-kappa B (NF-κB) axis.Methods and Results: In human left atrium, the degree of atrial fibrosis, as well as the expression levels of PDGF, Rac1 and NF-κB increased 1.5 to 2.9 folds in patients with atrial fibrillation compared to that with sinus rhythm, (P<0.0001). There were strongly positive correlations between angiotensin II (Ang II) or procollagen type III-alpha-1 (COL3A1) with PDGF, Rac1, NF-κB, and among PDGF, Rac1 and NF-κB (all P<0.05). At 3 weeks after the transverse aorta constriction (TAC) operation in rat model and with intervention of irbesartan or/and simvastatin, the collagen volume fraction (CVF) and atrial natriuretic peptide (ANP) values respectively increased 6-folds and 3.5-folds in the TAC group compared to SHAM group (P<0.0001), but these levels decreased by 16% to 63% with following drug intervention (all P<0.0001), the combined treatment was the lowest. Accordingly, the expression levels of PDGF (3-folds), Rac1 (1.6-folds), NF-κB (7-folds) and AngII (12-folds) significantly increased in the TAC group compared to the SHAM group, and these levels were also reduced by 25% to 64% with following drug intervention. The highest reduction could be seen after treatment with irbesartan and simvastatin in combination (all P<0.001).There were strongly positive correlations between AngII or CVF with PDGF, Rac1, NF-κB, and among PDGF, Rac1 and NF-κB (all P<0.05).Conclusions: Irbesartan or/and simvastatin can improve atrial fibrosis by regulating PDGF/Rac1/NF-κB axis.

Abstract 110: Noncoding RNAs: A Possible "Linc" to Atrial Fibrillation

Atrial fibrillation (AF), the most common cardiac arrhythmia, is associated with a 2-fold increased risk of mortality and a ~5- fold increased risk of stroke. Genome wide association studies have identified a locus on chromosome 4q25 that has the strongest association with AF. The SNPs in this locus most strongly associated with AF are located in an intergenic region that is 78 to 157 kb distal to the closest gene PITX2. PITX2 is a candidate gene for AF, due to its role in left/right patterning during heart development and expression found only in the left vs. right atrium. Our lab performed RNA-seq on human atria and identified a long intergenic non-coding RNA (linc-RNA) adjacent to PITX2 that is expressed with the same left/right atrial asymmetry as PITX2. We hypothesized that there may be functional genetic variants in the 4q25 region that directly affect expression of PITX2 or the linc-RNA adjacent to PITX2. Further, we hypothesized that the linc-RNA may control in trans the expression of genes that can alter cellular electrophysiology and lead to AF susceptibility. First we used qPCR to determine whether the expression of PITX2 and this linc-RNA were correlated in 199 human left atria samples. We found the expression of these genes to be highly and positively correlated with an r2 value of 0.47 (p &lt; .0001). We obtained genome-wide SNP information for each of these subjects using an Illumina SNP microarray. We determined the association of SNPs on chromosome 4 with the expression levels of PITX2 and the linc-RNA by performing expression QTL (eQTL) analysis. In the 4q25 region, common genetic variation was more strongly associated with expression of the linc-RNA than PITX2. Two of the strongest linc-RNA eQTL SNPs (p-value ~10-4) were associated with AF with a p-value of ~10 15. We are now starting functional studies to determine if this linc-RNA can modulate gene expression in trans by transfection of a linc-RNA expression plasmid into HEK-293 cells. We plan to determine the effects of over expression this linc-RNA on global gene expression profiles using expression arrays and RNA-seq

Spatiotemporal Behavior of High Dominant Frequency During Paroxysmal and Persistent Atrial Fibrillation in the Human Left Atrium

Sites of high dominant frequency (DF(peak)) are thought to indicate the location of drivers of atrial fibrillation (AF), but characterization of their spatiotemporal distribution and stability, critical to their relevance as targets for catheter ablation, requires simultaneous global mapping of the left atrium. Noncontact electrograms recorded simultaneously from 256 left atrial sites during spontaneous AF were analyzed. After subtraction of the ventricular component, fast Fourier transform identified the DF at each site. Focal areas of DF(peak) were defined as those having a DF >20% above all neighboring sites. Twenty-four patients with spontaneous AF (11 paroxysmal and 13 persistent) were studied. In paroxysmal AF, sites of DF(peak) (mean DF, 11.6±2.9 Hz) were observed in 100% of patients (present during 65% of the mapping period). In contrast, DF(peak) was detected in only 31% of patients with persistent AF (P<0.001) and for only 5% of the mapping period (P<0.001). In both groups, locations of DF(peak) varied widely in both consecutive and separated segments of AF (κ coefficient range, -0.07-0.22). Activation sequences around sites of DF(peak) did not demonstrate centrifugal activation that would be expected from focal drivers. Focal areas of high DF are more frequent in paroxysmal than persistent AF, are spatiotemporally unstable, are not the source of centrifugal activation, and are not, therefore, indicative of fixed drivers of AF. In the absence of spatiotemporal stability, the success of ablation at sites of DF(peak) cannot be explained by elimination of fixed drivers.

Chronic Histological Transmurality of High-Intensity Focused Ultrasound Ablation

We evaluated histologic results for surgical left maze with an high-intensity focused ultrasound (HIFU) energy source. Two patients came to our attention 6 and 48 months, respectively, after ablation concomitant to a valve procedure. Tissue specimens, obtained from the lesion site on the mitral isthmus and from the "box lesion" around the pulmonary veins were analyzed histologically. A complete transmural lesion was found in all specimens. Chronic lesions exhibited replacement of the muscular band with connective tissue. The atrial wall maintained normal thickness and vascularization. HIFU ablation represents an acceptable energy source to create transmural lesions on the beating human left atrium.

Rapid Atrial Rates and Atrio-Ventricular Dyssynchrony Predispose to Increased Thrombogenesis in the Human Left Atrium in Patients with Atrial Fibrillation

Rapid Atrial Rates and Atrio-Ventricular Dyssynchrony Predispose to Increased Thrombogenesis in the Human Left Atrium in Patients with Atrial Fibrillation

Abstract 8221: Cis Regulation of Genes in Human Atria Near SNPs Associated with Atrial Fibrillation and PR Interval

Genome-wide association studies have identified genetic variants in 3 regions associated with atrial fibrillation (AF) and in 9 regions associated with PR interval (PR), an AF-related endophenotype. The mechanisms linking these top variants to the AF phenotype remain unknown. Our study aimed to elucidate these mechanisms by associating SNP genotypes in the 12 implicated regions with proximal (cis) gene expression in human left atria (LA) and by examining differential expression of cis genes with atrial rhythm status at time of surgery. METHODS: Gene expression (Illumina HT12) and SNP genotypes (Illumina Hap550/610) were measured on LA appendages from 234 cardiac surgery patients. Expression and genotypes were preprocessed using best practices. Probes for the 15 genes closest to the top AF and PR-associated SNPs were adjusted for gender, age, genetic stratification and latent expression factors then regressed on their corresponding cis SNP dosage counts to obtain expression quantitative trait SNP (eSNP) p-values. Similar adjustments were done to obtain differential expression p-values. RESULTS: 7 significant eSNPs were found from 14 AF/PR SNPs: rs10033464 (p=0.033) and rs17570669 (9.9e-3) with PITX2 , rs13376333 with KCNN3 (0.046), rs3807989 with CAV1 (4.9e-9), rs11897119 with MEIS1 (2.2e-5), rs427684 with C5orf41 (4.6e-4), rs3825214 with TBX5 (5.0e-3), with rs7660702 marginal for ARHGAP24 (0.077). rs3807989 and rs11897119 were the strongest among all SNPs within 500 KB of their target gene. 8 out of 13 cis genes showed significant differential expression between the No AF (n=38) and AF Rhythm groups (n=100) or between the AF/In Sinus Rhythm (n=100) and AF Rhythm groups, respectively, with 3 showing both: CAV1 (2.1e-3,7.0e-11), TBX5 (0.015,NS), PITX2 (0.015,NS), BNIP1 (0.023,0.026), ARHGAP24 (0.029,2.4e-7), ZFHX3 (0.053,NS), CAV2 (NS,7.1e-3) and C5orf41 (NS,0.025). CONCLUSIONS: We have provided evidence that many of the SNPs associated with AF and PR also associate with expression levels of nearby genes in human left atria and that these genes are differentially expressed in AF.

The Effect of Acute Onset Atrial Fibrillation and Rapid Atrial Rates on Markers of Thrombogenesis in the Human Left Atrium

Background: Atrial fibrillation (AF) is associated with thromboembolic stroke. The precise mechanism of thrombogenesis in the human left atrium (LA) with acute AF remains unknown.Methods: 36 AF patients in sinus rhythm undergoing catheter ablation were studied. Blood samples were taken from the LA and femoral vein immediately after transseptal puncture and 15 minutes after AF induction (14 patients), atrial pacing at 150 bpm (14 patients) and in controls (8 patients). Platelet activation (P-selectin), thrombin generation [thrombin-antithrombin (TAT) complex], endothelial dysfunction [asymmetric dimethylarginine (ADMA)] and inflammation [soluble CD40-ligand (sCD40L)] were assessed by flow cytometry and ELISA.Results: P-selectin increased significantly with both AF (14.5±5.8 baseline vs. 22.9±12.9%+ve 15 min, p<0.01) and pacing (16.2±6.8 baseline vs. 19.5±5.6%+ve 15 min, p<0.01), but decreased in controls (p<0.05). TAT increased specifically in the LA with both AF (18.4±16.6 baseline vs. 32.1±25.2 µg/L 15 min, p<0.01) and pacing (16.5±13.8 baseline vs. 49.0±46.6 µg/L 15 min, p<0.01), but decreased peripherally (p<0.01), and decreased in controls (p<0.01). With acute AF, ADMA (p<0.05) and sCD40L (p<0.01) increased significantly, not seen with pacing (p=ns) or controls (p=ns).Conclusion: Acute onset human AF and rapid atrial rates both result in increased platelet activation and thrombin generation, more pronounced in the human LA. Acute AF also induces endothelial dysfunction and inflammation. These findings suggest that while rapid atrial rates increase the thrombogenic risk, abnormal rhythm further potentiates this risk.

First in Human Validation of Impedance‐Based Catheter Tip‐to‐Tissue Contact Assessment in the Left Atrium

In this study, a new method of contact assessment based on the measurement of the local electrical properties at the catheter tip-to-tissue interface was validated in a blinded fashion in vivo in the human left atrium. Using a 3-terminal circuit model, local resistance and reactance between catheter tip and tissue surface were measured and combined in an electrical coupling index (ECI). Twelve patients undergoing atrial fibrillation (AF) catheter ablation were included in this study. The catheter was placed in the left atrium at various levels of contact. Blinded to the physician, measurements of electrogram amplitudes, pacing thresholds, and impedances at the catheter tip-to-tissue interface were performed. As the catheter went from noncontact to contact, ECI increased from 118 +/- 15 to 145 +/- 24 (P < 0.0001), electrogram amplitudes increased from 0.14 +/- 0.16 to 2.0 +/- 1.9 mV (P < 0.0001), and pacing thresholds decreased from 13.9 +/- 3.1 to 3.1 +/- 2.0 mA (P < 0.0001). ECI was significantly higher in vascular tissue as compared with trabeculated and smooth myocardium. Patch orientation, operator, body mass index, or clinical type of AF had no influence on ECI values. On a patient-by-patient analysis, true contact/noncontact locations showed a mean ECI difference of 32.7 +/- 11.6 units (95% CI 25.8-39.6). A cut-off value of 5 ECI units was able to separate contact from noncontact with 97% sensitivity and 95% specificity. Measurement of local impedances between catheter tip and tissue is feasible to reproducibly describe electrical catheter contact within the left atrium in a clinical setting of AF catheter ablation.

Regulation of the 5-HT4 receptor protein in the human left atrium

Objectives: The involvement of the 5-HT4 receptor in atrial fibrillation is still unclear. Previous investigations in human right atria explored the expression of mRNA of the 5-HT4.

Long‐ and Short‐Term Temporal Stability of Complex Fractionated Atrial Electrograms in Human Left Atrium During Atrial Fibrillation

Complex fractionated atrial electrograms (CFAEs) have been reported as targets for catheter ablation of atrial fibrillation (AF). However, the temporal stability of CFAE sites remains poorly defined. The study consisted of two phases. In the initial phase, two automated software algorithms, namely the interval confidence level (ICL) and the average interpotential interval (AIPI) were assessed for their diagnostic accuracy for automated CFAE detection. The AIPI was found to be superior to the ICL, and an AIPI of <or=100 ms was associated with a sensitivity and specificity of both 92% for detection of CFAEs. In the second phase of the study, 12 patients (2 females, mean age 54 +/- 12 years) who underwent catheter ablation for persistent AF were studied to investigate the temporal stability of CFAEs. Two consecutive left atrial (LA) three-dimensional CFAE maps coded with AIPI readings were reconstructed during ongoing AF in each study patient, with a mean time difference of 34.3 +/- 8.7 minutes between the two maps. Among a total of 149 CFAE sites and 238 non-CFAE sites on the first CFAE map that were precisely revisited during the repeat mapping process, 135 (90.6%) and 225 (94.5%) remained as CFAE sites and non-CFAE sites, respectively. RF ablation at the selected stable CFAE sites significantly prolonged AF cycle length (181 +/- 26 ms to 199 +/- 29 ms, P < 0.0001). CFAEs recorded in the LA during AF display high temporal stability in patients with persistent AF. The clinical significance of our findings warrants further investigation.

Automated detection and characterization of complex fractionated atrial electrograms in human left atrium during atrial fibrillation

Complex fractionated atrial electrograms (CFAEs) have been reported as ablative targets for the treatment of atrial fibrillation (AF). However, the process of CFAE identification is highly dependent on the operator's judgment. It is the aim of the study to report our initial experience with a novel software algorithm designed to automatically detect CFAEs. Nineteen patients (6 female, 58 +/- 8 years) who underwent catheter ablation of paroxysmal (n = 11) or persistent (n = 8) AF were included in the study. During ongoing AF, 100 +/- 15 left atrial (LA) endocardial locations were sampled under the guidance of integrated electroanatomical mapping with computed tomographic images. Bipolar electrograms recorded throughout the LA were analyzed using custom software that allows for automated detection of CFAEs. Interval confidence level (ICL), defined as the number of intervals between consecutive CFAE complexes during 2.5-second recordings, was used to characterize CFAEs. The CFAE sites with an ICL >/=5 were considered as sites with highly repetitive CFAEs, which are thought to be potential ablation targets. For purposes of analysis, the LA was divided into 6 areas: pulmonary vein (PV) ostia, posterior wall, interatrial septum, roof, mitral annulus area, and appendage. Among a total of 1,904 LA locations sampled in 19 patients, 1,644 (86%) were categorized as CFAE sites, whereas 260 (14%) were categorized as as non-CFAE sites. Thirty-four percent of all CFAE sites were identified as sites with highly repetitive CFAEs. Of these, 24% were located at the interatrial septum, 22% on the posterior wall, 20% at the PV ostia, 18% at the mitral annulus area, 14% on the roof, and 2.7% at the LA appendage. In all patients, highly repetitive CFAE sites were distributed in 4 or more areas of the LA. Persistent AF patients had more highly repetitive CFAE sites on the posterior wall than paroxysmal AF patients (30% +/- 7.3% vs 14% +/- 8.2%, P < .001). There was a strong trend toward more highly repetitive CFAE sites located at the PV ostia in patients with paroxysmal AF compared with persistent AF patients (24% +/- 13% vs 13% +/- 7.7%, P = .05). With the use of custom software, CFAE complexes were identified in more than 80% of the LA endocardial locations. LA sites with highly repetitive CFAE sites were located predominately in the septum, posterior wall, and PV ostia. Patients with persistent AF had a different anatomical distribution pattern of highly repetitive CFAE sites from those with paroxysmal AF, with a greater prevalence of highly repetitive CFAEs located on the posterior wall. Further studies are warranted to determine the clinical significance of these findings.

Histopathology of intraoperatively induced linear radiofrequency ablation lesions in patients with chronic atrial fibrillation

Radiofrequency (RF) energy has been extensively used in ablation of arrhythmia but so far no analysis of morphological effects in human left atria has been conducted. We studied 59 ablation lesions from seven patients who died 2 to 22 days after open heart surgery plus intraoperative cooled-tip RF ablation to treat permanent atrial fibrillation (AF) (mean 4, 1-11 years). The ablation area was studied by macroscopy and histological analysis. RF ablation produced clearly delineated coagulation necrosis (up to a depth of 5.5 mm) bordered by an irregular zone of incomplete necrosis and fresh bleeding even 22 days post-operatively. No superficial charring, thrombotic deposition, or perforation was documented. Endocardium and subendocardium displayed oedematic loosening and microfragmentation of connective tissue fibres. Early after ablation (2-6 days), interfibrillar disseminated bleeding and necrosis without tissue removal response were found. Later after ablation (21, 22 days), mild inflammatory reaction and granulation tissue appeared. Twenty-five per cent of all studied lesions, especially in the thick region in between left pulmonary veins and mitral annulus (left atrial isthmus) (86%), were non-transmural. Nerve fibres with different degrees of thermal injury were detected in the pulmonary vein ostial region. Intraoperative cooled-tip ablation in AF resulted in coagulation necrosis of endocardium, subendocardium, and the atrial myocardial layer to a depth of 5.5 mm bordered by an irregular zone of incomplete thermal damage. Transmurality of the lesions could only be found in 75% of intraoperatively applied lesions.

Quantitative study of nerves of the human left atrium

To quantify and study the distribution of innervation of the left atrium and the pulmonary veins in humans. Damage to cardiac nerves has been hypothesized as the explanation for successful radiofrequency ablation of atrial fibrillation. From January 2003 to September 2003, histologic and quantitative studies of innervation of the left atrium and the pulmonary veins was performed in 43 consecutive necropsied adult hearts (30 men and 3 women; mean age 45.5 +/- 12.4 years). The left atrium was sectioned in 1-cm slices from left to right, with the plane of section perpendicular to the long axis of the heart. Sections of the pulmonary veins at their ostia and sections 1 cm away of this structure also were obtained. Nerve fiber density was counted manually for each case and expressed as the mean number per slice. Numerous epicardial nerve fibers and ganglia having distinct patterns of distribution in the left atrium were found. Nerve density was significantly higher at the ostia of the four pulmonary veins than in their distal part (7.1 +/- 2.1 vs 5.2 +/- 1.3 for left upper pulmonary vein; 6.3 +/- 1.5 vs 5.2 +/- 1.7 for right upper pulmonary vein; 7.4 +/- 2 vs 5.9 +/- 2 for left lower pulmonary vein; 6.7 +/- 1.8 vs 3.9 +/- 1.3 for right lower pulmonary vein). The left superior vein was significantly more innervated than the right inferior vein (12.3 +/- 3 vs 10.6 +/- 1.4). Gradients of innervation were found from right to left (9.8 +/- 4.6 vs 18.5 +/- 6.6, P < .05) and from the front to the rear of the atrium (17.2 +/- 6.4 vs 20.7 +/- 6.5, P < .05). The same heterogeneous distribution was observed at the myocardial level but with thinner nerve fibers, making quantification difficult. Only very thin nerve fibers were present in the endocardium. The human left atrium exhibits several gradients of innervation at discrete sites. These findings may have clinical implications for radiofrequency ablation of atrial fibrillation.

The role of angiotensin in electrophysiological gap junction remodeling in human atrial fibrillation

Objective: Atrial fibrillation (AF) is a progressive disease and associated with electrical remodeling in the atria. Because of positive clinical effects of ACE-inhibitors we wanted to elucidate, whether angiotensin and AT-receptors may be involved in the gap junction remodelling of the gap junction proteins (connexins) Cx43 and Cx40 in AF in the human left and right atria.

Alterations in the expression of P2X1 receptors in failing and nondiseased human atria.

This is the first report of the analysis of the ATP-specific P2X1 receptor subunit in human hearts. We have examined homogenate samples of human left atria for the presence of P2X1 receptors using Western blots. Anti-P2X1 immunoreactivity was detected in populations of nondiseased atria as well as in atria from explanted hearts from patients with terminally failing heart conditions such as dilated cardiomyopathy. At least three groups of P2X1 immunoreactive proteins were detected in the Western blots with approximate molecular mass values of 50, 70, and 160 kDa. We report changes in expression of their 50 and 70 kDa components. These changes may be related to the type of deficit in these hearts since the changes have been observed in hearts with decreased ejection fractions characteristic of dilated cardiomyopathy.

Characterization of endothelin isoforms in human heart: endothelin-2 demonstrated.

In humans, three endothelin (ET) isoforms are predicted to exist by analysis of genomic DNA. However, evidence for the presence of all three mature ET peptides and their precursors remains unclear. Our aim was to identify the ET isoforms present in human heart, using radioimmunoassay (RIA) and reverse-phase high-performance liquid chromatography (RP-HPLC). Antisera raised against the ET-1[15-21] terminal sequence were specific for mature ETs, showing no cross-reactivity with their precursor pro-ETs. Antisera raised against the pro-ET-1[31-38] terminal sequence was specific for pro-ET-1, showing no cross-reactivity with other ET peptides. In extracts of human cardiac tissues, the concentrations of immunoreactive (IR) mature ET and pro-ET-1 were found to be as follows: left atrium (n = 3): 282.3 +/- 113.0, 21.9 +/- 11.0, respectively; right atrium (n = 5): 308.3 +/- 95.4, 43.1 +/- 12.8, respectively; left ventricle (n = 6): 218.5 +/- 64.6, 47.9 +/- 11.9, respectively; right ventricle (n = 4): 215.1 +/- 79.8, 53.9 +/- 13.0, respectively (fmol/g wet weight, mean +/- SEM, for total IR mature ET and pro-ET-1, respectively). RP-HPLC showed peaks of immunoreactivity that coeluted with authentic ET-1 in all extracts of human left atria and ventricle tested. In addition, peaks were also present corresponding to ET-2, ET-3, and pro-ET-1. These results suggest that in addition to ET-1 and pro-ET-1, ET-2 and ET-3 are present in the human heart.