Alterations in electrophysiology and tissue structure of the left atrial posterior wall in a canine model of atrial fibrillation caused by chronic atrial dilatation

A Review on Atrial Fibrillation (Computer Simulation and Clinical Perspectives)

Atrial fibrillation (AF), a heart condition, has been a well-researched topic for the past few decades. This multidisciplinary field of study deals with signal processing, finite element analysis, mathematical modeling, optimization, and clinical procedure. This article is focused on a comprehensive review of journal articles published in the field of AF. Topics from the age-old fundamental concepts to specialized modern techniques involved in today’s AF research are discussed. It was found that a lot of research articles have already been published in modeling and simulation of AF. In comparison to that, the diagnosis and post-operative procedures for AF patients have not yet been totally understood or explored by the researchers. The simulation and modeling of AF have been investigated by many researchers in this field. Cellular model, tissue model, and geometric model among others have been used to simulate AF. Due to a very complex nature, the causes of AF have not been fully perceived to date, but the simulated results are validated with real-life patient data. Many algorithms have been proposed to detect the source of AF in human atria. There are many ablation strategies for AF patients, but the search for more efficient ablation strategies is still going on. AF management for patients with different stages of AF has been discussed in the literature as well but is somehow limited mostly to the patients with persistent AF. The authors hope that this study helps to find existing research gaps in the analysis and the diagnosis of AF.

The hemodynamic and atrial electrophysiologic consequences of chronic left atrial volume overload in a controllable canine model

OBJECTIVE

The purpose of this study was to determine the effects of chronic left atrial volume overload on atrial anatomy, hemodynamics, and electrophysiology using a titratable left ventriculoatrial shunt in a canine model.

METHODS

Canines (n = 16) underwent implantation of a shunt between the left ventricle and the left atrium. Sham animals (n = 8) underwent a median sternotomy without a shunt. Atrial activation times and effective refractory periods were determined using 250-bipolar epicardial electrodes. Biatrial pressures, systemic pressures, left atrial and left ventricle diameters and volumes, atrial fibrillation inducibility, and durations were recorded at the initial and at 6-month terminal study.

RESULTS

Baseline shunt fraction was 46% ± 8%. The left atrial pressure increased from 9.7 ± 3.5 mm Hg to 13.8 ± 4 mm Hg (P < .001). At the terminal study, the left atrial diameter increased from a baseline of 2.9 ± 0.05 cm to 4.1 ± 0.6 cm (P < .001) and left ventricular ejection fraction decreased from 64% ± 1.5% to 54% ± 2.7% (P < .001). Induced atrial fibrillation duration (median, range) was 95 seconds (0-7200) compared with 0 seconds (0-40) in the sham group (P = .02). The total activation time was longer in the shunt group compared with the sham group (72 ± 11 ms vs 62 ± 3 ms, P = .003). The right atrial and not left atrial effective refractory periods were shorter in the shunt compared with the sham group (right atrial effective refractory period: 156 ± 11 ms vs 141 ± 11 ms, P = .005; left atrial effective refractory period: 142 ± 23 ms vs 133 ± 11 ms, P = .35).

CONCLUSIONS

This canine model of mitral regurgitation reproduced the mechanical and electrical remodeling seen in clinical mitral regurgitation. Left atrial size increased, with a corresponding decrease in left ventricle systolic function, and an increased atrial activation times, lower effective refractory periods, and increased atrial fibrillation inducibility. This model provides a means to understand the remodeling by which mitral regurgitation causes atrial fibrillation.

Cardiac structural remodeling in hypertensive cardiomyopathy

Heart failure with preserved ejection fraction (HFpEF), which is a primary driver of morbidity and mortality, accounts for approximately half of all heart failure cases. Therefore, it is essential to develop preclinical animal models for HFpEF pharmacological treatment strategies. We created a porcine model of severe hypertension and hyperlipidemia by using a combination of deoxycorticosterone acetate (DOCA, 100 mg kg^-1), Western diet (WD) and angiotensin II infusion. Systolic blood pressure, echocardiography and invasive pressure-volume loop were assessed at baseline, 12 weeks and 18 weeks. A detailed histological assessment was also performed to determine the cardiac structural remodeling. Compared with controls (n=10), hypertensive animals (n=10) showed markedly higher systolic blood pressure (181 vs. 86 mm Hg) at 18 weeks. Concentric remodeling, characterized by a normal chamber size with a thicker wall, was observed in hypertensive animals. Left ventricle diastolic function showed a tendency toward decline, according to the echocardiographic data. Hemodynamic data showed that the end-diastolic pressure-volume relationship was elevated without changes in the end-systolic pressure-volume relationship. Histological results revealed that the fibrotic area in hypertensive animals (P<0.05 vs. controls) and the fibrotic area in the posterior wall of hypertensive animals' left atria were larger than other sites of the left atria (P<0.05 vs. other sites). This model can mimic clinical HFpEF to some degree. We found that the posterior wall of the left atrium is more susceptible to atrial remodeling associated with hypertension compared with other regions of the left atrium.

Evaluation of Atrial Conduction Times, Epicardial Fat Thickness and Carotid Intima-Media Thickness in Patients With Ankylosing Spondylitis

Objectives

This study aims to determine the relationship between atrial electromechanical delay (EMD), carotid intima-media thickness (CIMT), and epicardial fat thickness (EFT) in ankylosing spondylitis (AS), which has a complicated inflammatory nature.

Patients and methods

The study population included 42 consecutive patients with AS (28 males, 14 females; mean age 39.3±8.5 years; range 22 to 60 years) and 40 healthy subjects as controls (24 males, 16 females; mean age 37.2±8.7 years; range 22 to 60 years) (p>0.05). All patients underwent a standard tissue Doppler echocardiography to assess the left ventricular diastolic dysfunction, atrial EMD, CIMT, and EFT. All values were compared between the groups.

Results

Interatrial (29.5±5.8 ms vs. 17.9±5.3 ms) left and right intraatrial EMD (18.2±4.6 ms and 11.7±3.5 ms vs. 11.9±3.2 ms and 7.1±3.2 ms, respectively) intervals were longer in AS patients than in healthy controls (all p<0.001). Left and right CIMT (0.50±0.11 mm and 0.44±0.06 mm vs. 0.51±0.11 mm and 0.43±0.04 mm, respectively) and EFT (0.73±0.15 cm and 0.63±0.07 cm) values were higher in AS patients than in healthy controls (all p<0.01).

Conclusion

To our best knowledge, this is the first report evaluating the atrial EMD, CIMT, and EFT values together in AS patients. As indicators of cardiovascular involvement, all parameters were higher in AS patients.

Atrial electromechanical coupling intervals in pregnant subjects

OBJECTIVE

The aim of this study was to evaluate atrial conduction abnormalities obtained by tissue Doppler imaging (TDI) and electrocardiogram analysis in pregnant subjects.

METHODS

A total of 30 pregnant subjects (28 ± 4 years) and 30 controls (28 ± 3 years) were included. Systolic and diastolic left ventricular (LV) function was measured using conventional echocardiography and TDI. Inter-atrial, intraatrial and intra-left atrial electromechanical coupling (PA) intervals were measured with TDI. P-wave dispersion (PD) was calculated from a 12-lead electrocardiogram.

RESULTS

Atrial electromechanical coupling at the septal and left lateral mitral annulus (PA septal, PA lateral) was significantly prolonged in pregnant subjects (62.1 ± 2.7 vs 55.3 ±3.2 ms, p < 0.001; 45.7 ± 2.5 vs 43.1 ± 2.7 ms, p < 0.001, respectively). Inter-atrial (PA lateral - PA tricuspid), intra-atrial (PA septum - PA tricuspid) and intra-left atrial (PA lateral - PA septum) electromechanical coupling intervals, maximum P-wave (Pmax) duration and PD were significantly longer in the pregnant subjects (26.4 ± 4.0 vs 20.2 ± 3.6 ms, p < 0.001; 10.0 ± 2.0 vs 8.0 ± 2.6 ms, p = 0.002; 16.4 ± 3.3 vs 12.2 ± 3.0 ms, p < 0.001; 103.1 ± 5.4 vs 96.8 ± 7.4 ms, p ± 0.001; 50.7 ± 6.8 vs 41.6 ± 5.5 ms, p < 0.001, respectively). We found a significant positive correlation between inter-atrial and intraleft atrial electromechanical coupling intervals and Pmax (r = 0.282, p = 0.029, r = 0.378, p = 0.003, respectively).

CONCLUSION

This study showed that atrial electromechanical coupling intervals and PD, which are predictors of AF, were longer in pregnant subjects and this may cause an increased risk of AF in pregnancy.

Improved understanding of the pathophysiology of atrial fibrillation through the lens of discrete pathological pathways

Atrial fibrillation (AF) is a common disorder with a complex and incompletely understood pathophysiology. Genetic approaches to understanding the pathophysiology of AF have led to the identification of several biological pathways important in the pathogenesis of the arrhythmia. These include pathways important for cardiac development, generation and propagation of atrial electrical impulses, and atrial remodeling and fibrosis. While common and rare genetic variants in these pathways are associated with increased susceptibility to AF, they differ substantially among patients with lone versus typical AF. Furthermore, how these pathways converge to a final common clinical phenotype of AF is unclear and might also vary among different patient populations. Here, we review the contemporary knowledge of AF pathogenesis and discuss how derangement in cardiac development, ion channel dysfunction, and promotion of atrial fibrosis may contribute to this common and important clinical disorder.

Atrial fibrillation ablation outcome is predicted by left atrial remodeling on MRI

BACKGROUND

Although catheter ablation therapy for atrial fibrillation (AF) is becoming more common, results vary widely, and patient selection criteria remain poorly defined. We hypothesized that late gadolinium enhancement MRI (LGE-MRI) can identify left atrial (LA) wall structural remodeling (SRM) and stratify patients who are likely or not to benefit from ablation therapy.

METHODS AND RESULTS

LGE-MRI was performed on 426 consecutive patients with AF without contraindications to MRI before undergoing their first ablation procedure and on 21 non-AF control subjects. Patients were categorized by SRM stage (I-IV) based on the percentage of LA wall enhancement for correlation with procedure outcomes. Histological validation of SRM was performed comparing LGE-MRI with surgical biopsy. A total of 386 patients (91%) with adequate LGE-MRI scans were included in the study. After ablation, 123 patients (31.9%) experienced recurrent atrial arrhythmias during the 1-year follow-up. Recurrent arrhythmias (failed ablations) occurred at higher SRM stages with 28 of 133 (21.0%) in stage I, 40 of 140 (29.3%) in stage II, 24 of 71 (33.8%) in stage III, and 30 of 42 (71.4%) in stage IV. In multivariate analysis, ablation outcome was best predicted by advanced SRM stage (hazard ratio, 4.89; P<0.0001) and diabetes mellitus (hazard ratio, 1.64; P=0.036), whereas increased LA volume and persistent AF were not significant predictors. LA wall enhancement was significantly greater in patients with AF versus non-AF controls (16.6±11.2% versus 3.1±1.9%; P<0.0001). Histological evidence of remodeling from surgical biopsy specimens correlated with SRM on LGE-MRI.

CONCLUSIONS

Atrial SRM is identified on LGE-MRI, and extensive LGE (≥30% LA wall enhancement) predicts poor response to catheter ablation therapy for AF.

The effects of a single dialysis session on atrial electromechanical conduction times and functions

BACKGROUND/AIMS

Abnormalities in atrial electromechanical delay (EMD) times and mechanical functions are considered as independent predictors of atrial fibrillation. However, to date, effects of a single hemodialysis (HD) session and acute volume-preload changes on atrial-EMD functions have not been investigated by Tissue Doppler Echocardiography (TDE). The aim of the present study was to evaluate atrial-EMD times and mechanical functions in HD patients.

METHODS

Thirty-five non-diabetic, normotensive HD patients and 35 healthy control subjects were enrolled in the study. Standard and TDE performed before mid-week dialysis session for hemodialysis group and on admission for control group.

RESULTS

Interatrial and left-right intraatrial-EMD intervals and left atrial mechanical volumes were significantly longer in hemodialysis group compared to controls (all p<0.01) and were reduced after HD session. Furthermore, removed ultrafiltration volume was associated with reduction in atrial-EMD intervals and functional volumes. LA-passive emptying volume, ultrafiltration volume, LV-E/E' ratio, and Vp were independent predictors of interatrial-EMD.

CONCLUSIONS

The present study confirms negative effects in HD patients of structural remodeling and reveals negative effects of electrical remodeling. Prolonged inter and intraatrial-EMD intervals should be the underlying pathophysiological factors of increased rate of atrial fibrillation in the HD population.

Detection and quantification of left atrial structural remodeling with delayed-enhancement magnetic resonance imaging in patients with atrial fibrillation

BACKGROUND

Atrial fibrillation (AF) is associated with diffuse left atrial fibrosis and a reduction in endocardial voltage. These changes are indicators of AF severity and appear to be predictors of treatment outcome. In this study, we report the utility of delayed-enhancement magnetic resonance imaging (DE-MRI) in detecting abnormal atrial tissue before radiofrequency ablation and in predicting procedural outcome.

METHODS AND RESULTS

Eighty-one patients presenting for pulmonary vein antrum isolation for treatment of AF underwent 3-dimensional DE-MRI of the left atrium before the ablation. Six healthy volunteers also were scanned. DE-MRI images were manually segmented to isolate the left atrium, and custom software was implemented to quantify the spatial extent of delayed enhancement, which was then compared with the regions of low voltage from electroanatomic maps from the pulmonary vein antrum isolation procedure. Patients were assessed for AF recurrence at least 6 months after pulmonary vein antrum isolation, with an average follow-up of 9.6+/-3.7 months (range, 6 to 19 months). On the basis of the extent of preablation enhancement, 43 patients were classified as having minimal enhancement (average enhancement, 8.0+/-4.2%), 30 as having moderate enhancement (21.3+/-5.8%), and 8 as having extensive enhancement (50.1+/-15.4%). The rate of AF recurrence was 6 patients (14.0%) with minimal enhancement, 13 (43.3%) with moderate enhancement, and 6 (75%) with extensive enhancement (P<0.001).

CONCLUSIONS

DE-MRI provides a noninvasive means of assessing left atrial myocardial tissue in patients suffering from AF and might provide insight into the progress of the disease. Preablation DE-MRI holds promise for predicting responders to AF ablation and may provide a metric of overall disease progression.

Impact of obstructive sleep apnea on the atrial electromechanical activation time

BACKGROUND

Obstructive sleep apnea (OSA) is closely associated with atrial fibrillation, which is provoked by electrical and structural remodeling. However, the association between OSA and atrial remodeling has not been fully elucidated.

METHODS AND RESULTS

Atrial electromechanical activation time (EMAT) was investigated using tissue Doppler imaging (TDI) in men with severe OSA (n=24) and control subjects (n=24). The EMAT was determined as the time interval from the initiation of P-wave deflection until the peak of local lateral left atrial (LA) TDI signal. The early diastolic velocity of the mitral annulus (E(a)) and the EMAT were significantly lower and longer in OSA cases than in controls (E(a): 6.1+/-0.9 cm/s vs 7.3+/-1.5 cm/s, P=0.001; EMAT: 129.7+/-11.5 ms vs 118.5+/-12.3 ms, P=0.002). Among OSA cases, the apnea - hypopnea index (AHI) was significantly correlated with EMAT (r=0.660, P<0.001), E(a) (r=-0.609, P=0.002), LA dimension (r=0.486, P=0.016), and early diastolic velocity of mitral flow (E)/E(a) ratio (r=0.418, P=0.042). In multivariate stepwise linear regression analysis, EMAT was independently associated with AHI (P=0.025) and E(a) (P=0.028) in OSA cases.

CONCLUSION

EMAT measured by TDI could be a useful parameter for identifying atrial remodeling in patients with severe OSA.