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Alcohol consumption is associated with a higher increased risk of atrial fibrillation (AF), but the acute effects on cardiac electrophysiology in humans remain poorly understood. The HOw ALcohol InDuces Atrial TachYarrhythmias (HOLIDAY) Trial revealed that alcohol shortened pulmonary vein atrial effective refractory periods, but more global electrophysiologic changes gleaned from the surface ECG have not yet been reported. This was a secondary analysis of the HOLIDAY Trial. During AF ablation procedures, 100 adults were randomized to intravenous alcohol titrated to 0.08% blood alcohol concentration versus a volume and osmolarity-matched, masked, placebo. Intervals measured from 12‑lead ECGs were compared between pre infusion and at infusion steady state (20 min). The average age was 60 years and 11% were female. No significant differences in the P-wave duration, PR, QRS or QT intervals, were present between alcohol and placebo arms. However, infusion of alcohol was associated with a statistically significant relative shortening of the JT interval (r: −14.73, p = 0.048) after multivariable adjustment. Acute exposure to alcohol was associated with a relative reduction in the JT interval, reflecting shortening of ventricular repolarization. These acute changes may reflect a more global shortening of refractoriness, suggesting immediate proarrhythmic effects pertinent to the atria and ventricles. [ABSTRACT FROM AUTHOR]

Left atrial appendage (LAA) epicardial exclusion has been associated with addressing 2 potential deleterious consequences attributed to the LAA, namely, thrombus formation and an arrhythmogenic contributor in advanced forms of atrial fibrillation. With more than 60 years of history, the surgical exclusion of the LAA has been firmly established. Numerous approaches have been used for surgical LAA exclusion including surgical resections, suture ligation, cutting and non-cutting staples, and surgical clips. Additionally, a percutaneous epicardial LAA ligation approach has been developed. A discussion of the various epicardial LAA exclusion approaches and their efficacy will be discussed, along with the salient beneficial affects on LAA thrombus formation, LAA electrical isolation and neuroendocrine homeostasis. [ABSTRACT FROM AUTHOR]

Left atrial appendage (LAA) epicardial exclusion has been associated with addressing 2 potential deleterious consequences attributed to the LAA, namely, thrombus formation and an arrhythmogenic contributor in advanced forms of atrial fibrillation. With more than 60 years of history, the surgical exclusion of the LAA has been firmly established. Numerous approaches have been used for surgical LAA exclusion including surgical resections, suture ligation, cutting and non-cutting staples, and surgical clips. Additionally, a percutaneous epicardial LAA ligation approach has been developed. A discussion of the various epicardial LAA exclusion approaches and their efficacy will be discussed, along with the salient beneficial affects on LAA thrombus formation, LAA electrical isolation and neuroendocrine homeostasis. [ABSTRACT FROM AUTHOR]

Left atrial appendage closure is an increasingly used means of achieving thromboprophylaxis in atrial fibrillation, particularly in patients with contraindications to anticoagulation. Left atrial appendage anatomy is highly variable, and preprocedural imaging is critical to choosing the correct device and approach for left atrial appendage closure. This article reviews the common endocardial and epicardial closure systems, including anatomic considerations, advantages and disadvantages, as well as complications to be avoided. [ABSTRACT FROM AUTHOR]

Background: Published studies of epicardial ligation of left atrial appendage (LAA) have reported discordant results.Objective: The purpose of this study was to delineate the safety and efficacy of LAA closure with the LARIAT device.Methods: This is a multicenter registry of 712 consecutive patients undergoing LAA ligation with LARIAT at 18 US hospitals. The primary end point was successful suture deployment, no leak by intraprocedural transesophageal echocardiography (TEE), and no major complication (death, stroke, cardiac perforation, and bleeding requiring transfusion) at discharge. A leak of 2-5 mm on follow-up TEE was the secondary end point.Results: LARIAT was successfully deployed in 682 patients (95.5%). A complete closure was achieved in 669 patients (98%), while 13 patients (1.8%) had a trace leak (<2 mm). There was 1 death related to the procedure. Ten patients (1.44%) had cardiac perforation necessitating open heart surgery, while another 14 (2.01%) did not need surgery. The risk of cardiac perforation decreased significantly after the introduction of a micropuncture (MP) needle for pericardial access. Delayed complications (pericarditis requiring >2 weeks of treatment with nonsteroidal anti-inflammatory drugs/colchicine and pericardial and pleural effusion after discharge) occurred in 34 (4.78%) patients, and the risk decreased significantly with the periprocedural use of colchicine. Follow-up TEE (n = 480) showed a leak of 2-5 mm in 6.5% and a thrombus in 2.5%. One patient had a leak of >5 mm.Conclusion: LARIAT effectively closes the LAA and has acceptable procedural risks with the evolution of the use of the micropuncture needle for pericardial access and the use of colchicine for mitigating the postinflammatory response associated with LAA ligation and pericardial access. [ABSTRACT FROM AUTHOR]

Background: Pulmonary vein antrum isolation (PVI) as a treatment of paroxysmal atrial fibrillation (AF) is associated with a high rate of success; however, outcomes for treating persistent and long-standing persistent AF with PVI alone are substantially lower and often require multiple procedures to maintain long-term freedom from atrial arrhythmias. Foci and/or substrate outside the pulmonary veins, particularly in the left atrial appendage (LAA), has been identified as a key mechanism in the maintenance of persistent AF and long-standing persistent AF.Objective: The goals of the study are to evaluate the safety and effectiveness of the LARIAT System to percutaneously isolate and ligate the LAA and to determine if LAA ligation as adjunctive therapy to PVI improves maintenance of sinus rhythm in patients with persistent and long-standing persistent AF.Study Design: The trial is a prospective, multicenter, randomized controlled study. The trial design incorporates a Bayesian adaptive design that will randomize a maximum of 600 patients with persistent or long-standing persistent AF to LAA ligation and PVI vs PVI alone in a 2:1 randomization. The primary end points include 30-day safety of the LARIAT procedure and freedom from documented AF, atrial flutter, or atrial tachycardia of more than 30 seconds at 12 months after the PVI off antiarrhythmic drugs. Key secondary outcomes include a composite of cardiovascular death and stroke, as well as quality of life.Conclusion: The aMAZE trial will determine if LAA ligation as adjunctive therapy to PVI increases the efficacy of maintaining sinus rhythm in patients with persistent and long-standing persistent AF. [ABSTRACT FROM AUTHOR]

Catheter ablation of atrial fibrillation (AF) has been shown to be effective for paroxysmal AF. However, for patients with persistent or longstanding persistent AF, the success rates for catheter ablation is low. The Cox-Maze procedure is the most effective non-pharmacological treatment of AF. However, due to the need for open-heart surgery and the morbidity associated with the surgical Cox-Maze procedure, minimally invasive and epicardial-endocardial (hybrid) ablation procedures have been developed. This article will review the main surgical and hybrid approaches used for the treatment of persistent and long-standing persistent AF. [ABSTRACT FROM AUTHOR]

Background The left atrial appendage (LAA) is a well-known source of atrial arrhythmia and atrial fibrillation (AF). Objective The purpose of this study was to determine whether LAA exclusion using the LARIAT device would decrease AF burden. Methods A total of 50 patients with AF and cardiac implantable electronic devices who underwent successful LAA exclusion were enrolled in this prospective observational study. AF burden before LAA exclusion (baseline) and 3 and 12 months after exclusion was assessed by device interrogation. Results AF burden at 3-month follow-up (42% ± 34%) was significantly lower compared to baseline (76% ± 33%, P < .0001). The reduction in AF burden was sustained at 12 months (59% ± 26%, P < .001). Subgroup analysis revealed that AF burden at 3-month follow-up was similarly reduced in both paroxysmal AF (n = 19) and nonparoxysmal AF (n = 31). However, there was no reduction in AF burden in patients with paroxysmal AF at 12 months. AF burden in patients with known AF triggers in the LAA (n = 9) was significantly reduced at 3 months (52% ± 35%) and 12 months (42% ± 19%) compared to respective baseline (84 ± 31%, P < .0001). Conclusion LAA exclusion appears to reduce AF burden. The presence of AF triggers in the LAA appears to be the strongest predictor of AF reduction. The study underscores the role of the LAA in arrhythmogenesis for AF and highlights the complementary role of LAA exclusion in restoration of normal sinus rhythm. [ABSTRACT FROM AUTHOR]

Background Because the His bundle is intrinsic to the circuit in orthodromic reciprocating tachycardia and remote from that of atrioventricular nodal reentrant tachycardia (AVNRT), pacing the His bundle during supraventricular tachycardia (SVT) may be useful to distinguish these arrhythmias. Objective The purpose of this study was to test the hypothesis that His overdrive pacing (HOP) would affect SVT immediately for orthodromic reciprocating tachycardia and in a delayed manner for AVNRT. Methods Once SVT was induced, HOP was performed by pacing the His bundle 10-30 ms faster than the SVT cycle length. The maneuver was determined to have entered the tachycardia circuit when a nonfused His-capture beat advanced or delayed the subsequent atrial electrogram by ≥10 ms or when the tachycardia was terminated. The number of beats required to enter each tachycardia with HOP was recorded. Results HOP was performed during 66 SVTs (26 atrioventricular reciprocating tachycardia [AVRT] and 40 AVNRT). Entry into the tachycardia within 1 beat had sensitivity of 92%, specificity of 92%, positive predictive value (PPV) of 89% and negative predictive value (NPV) of 95% to confirm the diagnosis of AVRT. A cutoff ≥3 beats to enter the circuit had sensitivity of 90%, specificity of 92%, PPV of 95% and NPV of 86% to confirm the diagnosis of AVNRT. HOP had sensitivity, specificity, PPV, and NPV of 100% for distinguishing septal AVRT from atypical AVNRT. Conclusion HOP during SVT is a novel technique for distinguishing orthodromic reciprocating tachycardia from AVNRT. It can reliably distinguish between these arrhythmias with high sensitivity and specificity. [ABSTRACT FROM AUTHOR]

Background: The arrhythmic role of the left atrial appendage (LAA) has been implicated in the maintenance of persistent atrial fibrillation. LAA isolation with catheter ablation has been successful but is limited by the risk of tamponade and electromechanical dissociation with the potential for LAA thrombus formation. Objective: To assess whether LAA ligation results in LAA electrical isolation. Methods: A total of 68 patients with contraindication or intolerance to oral anticoagulation therapy underwent LAA ligation with the LARIAT suture delivery device. Patients had unipolar [n = 30(44%)] or bipolar [n = 38(56%)] voltage measurements pre- and post-LAA ligation. Results: All 68 patients underwent successful LAA ligation. There was a statistically significant reduction in the mean LAA voltage from pre-ligation (unipolar pre-ligation voltage 1.1 ± 0.53 mV; bipolar pre-ligation voltage 4.7 ± 2.83 mV) to post-ligation (unipolar post-ligation voltage 0.3 ± 0.38 mV; bipolar post-ligation voltage 0.6 ± 0.27 mV). Ninety-four percent of the patients had a reduction in the LAA voltage after the closure of the snare, with 10 of 30 (33%) of the patients having complete elimination of LAA voltage with the initial tightening of the suture. Pacing from the LAA after the closure of the snare resulted in lack of capture of the left atrium in 28 of 31 patients. Conclusions: The snare closure of the LAA using the LARIAT device produces an acute reduction in the LAA voltage and inhibits the capture of the left atrium during LAA pacing. Future studies are needed to determine whether LAA ligation affects atrial fibrillation burden. [Copyright &y& Elsevier]

Background: Focal atrial tachycardia (AT) originates from preferential sites, including the tricuspid and mitral annuli. AT arising from the atrioventricular annuli is initiated and terminated with programmed stimulation and is, in general, adenosine and verapamil sensitive. Para-Hisian AT arising from the apex of the triangle of Koch has been considered to be a distinct entity, characterized by unique electrophysiological properties. Objective: We sought to more fully delineate the electrophysiological and electrocardiographic properties of para-Hisian AT in a large series of patients. Methods: The study population consisted of 38 patients (63 ± 15 years; 23 female) with AT from the para-Hisian region. The ATs were focal and originated from the anteroseptal tricuspid annulus, in close proximity to the His bundle recording. Proximity to the His bundle was confirmed by electrogram recordings, fluoroscopy, and centrifugal activation during three-dimensional mapping. Results: The mean AT cycle length was 421 ± 69 ms. AT was associated with a distinct P-wave morphology that was significantly narrower than the P wave during sinus rhythm. Adenosine (5.0 ± 1.5 mg) terminated AT in 34/35 patients. Intravenous verapamil terminated AT in three of three patients. Catheter ablation was attempted in 30 patients and was successful in 26 (87%). Conclusion: The para-Hisian region is a source of focal AT, with properties consistent with AT arising circumferentially along the tricuspid and mitral annuli, and should be considered a subset of this broader group of “annular” ATs. The electropharmacologic findings in para-Hisian AT are mechanistically consistent with cyclic AMP-mediated triggered activity. [Copyright &y& Elsevier]

Background: Atrial fibrillation is associated with an increased risk of embolic events. The left atrial appendage (LAA) is believed to be an incubator for thrombus formation. LAA exclusion has been advocated to potentially reduce embolic events arising from the LAA. Objective: The aim of the study was to determine the feasibility of a closed-chest surgical suture ligation of the LAA in man. Methods: Thirteen patients undergoing either mitral valve surgery (n = 2) or electrophysiological study and radiofrequency catheter ablation for atrial fibrillation (n = 11) underwent ligation of the LAA with the LARIAT snare device. In patients having an ablation procedure, pericardial access was obtained prior to the patients undergoing radiofrequency catheter ablation. After transseptal catheterization, endocardial and epicaridal magnet-tipped guide wires were positioned under fluoroscopic guidance to stabilize the LAA. Transesophageal echocardiography (TEE) was used as guidance for positioning a marker balloon at the ostium of the LAA. An over-the-wire approach was used to guide the LARIAT snare device over the LAA to allow closure and suture ligation of the LAA. TEE and contrast fluoroscopy were used to confirm acute closure of the LAA. Results: Both mitral valve replacement (MVR) patients had complete closure of the LAA determined by visual inspection. Ten of 11 patients having ablation underwent a successful closed-chest LAA ligation procedure with TEE and contrast fluoroscopy verification of closure of the LAA. Only one of 11 procedures was terminated owing to the lack of echocardiography guidance of the snare over the marker balloon. One patient with pectus excavatum did have ligation of his LAA; however, a thorascopic procedure was required to remove the snare from the LAA owing to compression of the LARIAT by the concave sternum. There were no other significant complications. Conclusions: Catheter-based surgical suture ligation of the LAA is feasible in humans. This novel catheter approach may be appropriate for patients with atrial fibrillation who are ineligible for anticoagulation therapy. Further investigation is needed to demonstrate the long-term safety and efficacy of LAA closure. [Copyright &y& Elsevier]

Abstract: Mesenchymal stromal cells (MSCs) are multipotent cells that have high expansion yields and fibrin is a native extracellular matrix (ECM) material widely used for cell delivery and surgery. MSCs and fibrin have tremendous potential for tissue engineering applications, but the effect of fibrin on MSCs is not well characterized. The purpose of this study was to analyze the role of fibrin in modulating MSC phenotype by gene expression analysis. The results demonstrate that fibrin up-regulated MSC gene expression of vasculogenic (FLK1, ACTA2, VECAD, SM22 and CNN1), myogenic (MYF5 and MYH13), neurogenic (TH and GFAP) and chondrogenic (COL2A1) markers after 5days incubation. These gene expression results were supported by induction of expression on the protein level for early lineage-specific markers such as ACTA2, FLK1 and MYF5. The ability of fibrin to modulate MSC gene expression was not affected by matrix pore size (80–110μm diameter) or Young’s modulus (5–25kPa) and the differential expression of some phenotypic markers could be partially mimicked by other ECM proteins, such as fibronectin and collagen I. In some cases the inductive effect of fibrin on gene expression could be further augmented by the treatment with growth factors such as nerve growth factor. However, the effect of fibrin appeared to be limited, as MSCs did not differentiate into fully mature cells based on immunofluorescence staining after 12days. This body of work provides a rational approach for studying the interactions of MSC with fibrin, which has important therapeutic implications for the delivery of stem cells. [ABSTRACT FROM AUTHOR]

The article focuses on a study which examined the safety and effectiveness of catheter-based left atrial appendage (LAA) in a canine model. The study included 26 healthy mongrel dogs that underwent ligation of the LAA through a catheter-based approach. It concluded that the catheter-based snare delivery device can be a safe and reliable ligation of the entire LAA.

Background: A decrease in inflammation after cure of atrial arrhythmias suggests that such arrhythmias are proinflammatory, and lower inflammatory marker levels in the coronary sinus suggest that atrial arrhythmias result in intracardiac appropriation of inflammatory cytokines. Objective: The purpose of this study was to investigate the effect of atrial fibrillation on inflammatory markers drawn from intracardiac and extracardiac chambers. Methods: We performed a case-control study of 167 AF patients and 207 controls. Blood from intracardiac and extracardiac sites was obtained from a subset of patients undergoing curative AF ablation (n = 46). Results: No significant differences in C-reactive protein (CRP) or interleukin-6 (IL-6) levels were seen between patients with and those without a history of AF. Both levels were significantly higher when blood was drawn during AF than during sinus rhythm: median CRP 3.1 mg/dL (interquartile range [IQR] 1.0–6.0) versus 1.7 mg/dL (IQR 0.7–3.9, P = .0005); median IL-6 2.3 ng/mL (IQR 1.5–3.9) versus 1.5 ng/mL (IQR 0.7–2.5, P = .007). This finding persisted after adjusting for potential confounders. AF ablation patients in AF exhibited a positive median left atrial minus coronary sinus gradient CRP (0.3 mg/dL, IQR −0.03–1.1), whereas those in sinus rhythm had a negative median left atrial minus coronary sinus gradient CRP (−0.2, IQR −0.8–[−0.02], P = .01). Femoral artery minus femoral vein gradients in AF versus sinus rhythm did not show any differences. Conclusion: AF at the time of the blood draw, rather than a history of AF, was independently associated with inflammation. Differences in transcardiac gradients suggest that AF results in sequestration of inflammatory cytokines in the heart. [Copyright &y& Elsevier]

Background: The etiology of accessory pathway (AP) formation is generally unknown. Objective: The purpose of this study was to test the hypothesis that AP formation is genetically mediated by examining whether AP location differs by sex and/or race, using sex and race as proxies to distinguish genetically different individuals. Methods: This was a single-center, retrospective cohort study of 282 consecutive patients undergoing their first electrophysiology study that revealed at least one AP between 2004 and 2008. Sex and race were compared with AP location determined by invasive electrophysiology study. Results: Eighty-nine (52%) males and 40 (36%) females had a left posterior AP (P = .006). Sixty-four (57%) females had a right annular AP, compared with 55 (32%) males (P <.001). After adjusting for age and race, females had 2.8-fold greater odds of having a right annular AP compared with males (95% confidence interval [CI] 1.70–4.65 greater odds; P <.001). While right anterior (free-wall) pathways were rare in all other races (12%), a significantly larger proportion of Asians (n = 10, 26%) had a right anterior AP (P = .017). After adjusting for sex and age, Asians had 3.8-fold greater odds of having a right anterior AP compared with other races (95% CI 1.5–9.4 greater odds; P = .004). Conclusions: Females more commonly had right annular APs, and Asians had right anterior APs substantially more frequently than other races. These findings suggest that the pathogenesis of AP formation may have a genetic component. [Copyright &y& Elsevier]

Objectives: Various approaches to myocardial reconstruction have been developed for the treatment of congestive heart failure resulting from ischemic cardiomyopathy. Methods: In this study we determined whether in situ application of polymers could reshape left ventricular geometry in a chronic rodent model of ischemic cardiomyopathy. Results: We demonstrate that alginate and fibrin can augment left ventricular wall thickness, resulting in reconstruction of left ventricular geometry and improvement of cardiac function. Echocardiographic results at 5 weeks after injection of alginate demonstrated persistent improvement of left ventricular fractional shortening and prevention of a continued enlargement of left ventricular dimensions, whereas fibrin glue demonstrated no progression of left ventricular negative remodeling. There was increased arteriogenesis in both the alginate and fibrin glue groups compared with that seen in the phosphate-buffered saline control group. Infarct size was significantly reduced in the fibrin group (P < .05), and there was a trend toward a smaller myocardial infarction in the alginate group. Conclusion: Intramyocardially injected polymers can be used to reshape the aneurysmal left ventricle and might therefore be an approach for myocardial reconstruction and a potential option in treating chronic heart failure in human subjects. [Copyright &y& Elsevier]

Background: Atrial fibrillation (AF) may be due to an inherited trait, particularly in lone AF patients. A family history of AF in lone AF patients has not previously been compared with a family history of patients with AF and established risk factors (non-lone AF).Objective: The purpose of this study was to compare the frequency of having a first-degree relative with AF in lone and non-lone AF patients.Methods: We performed a case-control study of consecutive subjects presenting to a single electrophysiology laboratory. A convenience sample of subjects with no known arrhythmias was also enrolled.Results: Four hundred twenty-nine subjects were enrolled: 136 had AF (54 with lone AF), 84 had atrial flutter, 158 had other supraventricular arrhythmias, and 51 had no known arrhythmias. Significantly more subjects with AF reported a first-degree family history of AF compared with the remainder of the cohort (25% vs. 5%; P <.001). In multivariable analysis adjusting for potential confounders, AF patients had a 6-fold greater odds of having a family member with AF (95% confidence interval [CI] 2.93-12.7; P <.001). Lone AF patients had a first-degree family member with AF substantially more often than those with non-lone AF (41% vs. 14%; P <.001). After adjusting for potential confounders, lone AF patients remained significantly more likely than other AF patients to have a first-degree relative with AF (OR 7.2; 95% CI 2.1-24.7; P = .002).Conclusion: Lone AF patients have a first-degree family member with AF substantially more often than other AF patients. This suggests that an inherited trait may be particularly important in this subgroup of patients. [ABSTRACT FROM AUTHOR]

Background: Atrial arrhythmias are associated with inflammation. The cause and effect of the association are unknown. Objective: The purpose of this study was to test the hypothesis that atrial tachyarrhythmias contribute to inflammation. Methods: We performed a prospective observational study wherein C-reactive protein (CRP) and interleukin-6 (IL-6) levels from the femoral vein and coronary sinus (CS) were compared before curative ablation for atrial flutter (AFL; n = 59) and paroxysmal supraventricular tachycardia (SVT; n = 110). Follow-up levels were obtained at 1 and 6 months. Results: Peripheral levels of both biomarkers were significantly higher in the AFL group. After multivariate adjustment, only those in the AFL group who presented in AFL or atrial fibrillation (AF) had significantly elevated CRP levels (odds ratio 1.26; P = .033). Levels of each marker were similar in the CS and peripheral blood in the SVT group; in the AFL group, both CRP and IL-6 were significantly lower in the CS than in the periphery (P = .0076 and P = .0021, respectively). CRP was significantly lower a median of 47 days after AFL ablation (from a median of 6.28 mg/L to a median of 2.92 mg/L; P = .028) and remained reduced at second follow-up. IL-6 decreased across three time points after AFL ablation (P = .002). No reduction in inflammatory biomarkers was observed after SVT ablation. Conclusions: CRP and IL-6 levels are elevated in patients presenting in AFL. Given the lower CS values in these patients, their origin appears to be systemic rather than cardiac. Because these levels significantly fall after ablation of AFL, the atrial tachyarrhythmia appears to be the cause (not the effect) of the inflammation. [Copyright &y& Elsevier]

Background: Regional differences in fibrosis, particularly related to the posterior wall and septum, may be important in atrial fibrillation (AF). Using electroanatomic mapping, voltage can be used as a measure of fibrosis.Objectives: The purpose of this study was to determine if patients with AF have disproportionately lower voltage in the septal and posterior walls of the left atrium.Methods: Sinus rhythm left atrial electroanatomic maps were used in serial patients presenting for left atrial ablation of AF (8-mm tip). Patients undergoing left atrial mapping for focal atrial tachycardia (AT) were used as a comparison group (4-mm tip). Animal experiments were performed to assess the influence of ablation catheter tip size on voltage amplitude.Results: The posterior and septal walls exhibited the lowest voltages in both groups. Compared with the anterior wall, there was a 3.78-fold greater odds of finding a low-voltage point (<0.5 mV) in the septum (P <.001) and a 3.37-fold greater odds of finding a low-voltage point in the posterior wall (P <.001) in the AF patients; the proportion of low-voltage points by region were not significantly different in the AT group. In the animal model, the mean voltage obtained from an 8-mm ablation catheter was significantly higher (0.30 +/- 0.17 mV) than that obtained from the same points using a 4-mm catheter (0.22 +/- 0.17, P = .05).Conclusion: Regional differences in voltage are present in patients with atrial arrhythmias, with AF patients exhibiting significantly more low-voltage areas in the septum and posterior walls. [ABSTRACT FROM AUTHOR]