Is the left atrial appendage more than a simple appendage?

A highly-detailed anatomical study of left atrial auricle as revealed by in-vivo computed tomography

The left atrial auricle (LAA) is the main source of intracardiac thrombi, which contribute significantly to the total number of stroke cases. It is also considered a major site of origin for atrial fibrillation in patients undergoing ablation procedures. The LAA is known to have a high degree of morphological variability, with shape and structure identified as important contributors to thrombus formation. A detailed understanding of LAA form, dimension, and function is crucial for radiologists, cardiologists, and cardiac surgeons. This review describes the normal anatomy of the LAA as visualized through multiple imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI), and echocardiography. Special emphasis is devoted to a discussion on how the morphological characteristics of the LAA are closely related to the likelihood of developing LAA thrombi, including insights into LAA embryology.

Organ Dynamics and Hemodynamic of the Whole HH25 Avian Embryonic Heart, Revealed by Ultrasound Biomicroscopy, Boundary Tracking, and Flow Simulations

Congenital heart malformations occur to substantial number of pregnancies. Studies showed that abnormal flow biomechanical environments could lead to malformations, making it important to understand the biomechanical environment of the developing heart. We performed 4D high-frequency ultrasound scans of chick embryonic hearts at HH25 to study the biomechanics of the whole heart (atria and ventricle). A novel and high-fidelity motion estimation technique, based on temporal motion model and non-rigid image registration algorithm, allowed automatic tracking of fluid-structure boundaries from scan images, and supported flow simulations. Results demonstrated that atrial appendages were the most contractile portion of the atria, having disproportionately high contribution to atrial blood pumping for its volume in the atria. However, the atria played a small role in blood pumping compared to the ventricle, as it had much lower ejection energy expenditure, and as the ventricle appeared to be able to draw inflow from the veins directly during late diastole. Spatially and temporally averaged wall shear stresses (WSS) for various cardiac structures were 0.062–0.068 Pa, but spatial-averaged WSS could be as high as 0.54 Pa in the RV. WSS was especially elevated at the atrial inlet, atrioventricular junction, regions near to the outflow tract, and at dividing lines between the left and right atrium and left and right side of the ventricle, where septation had begun and the lumen had narrowed. Elevated WSS could serve as biomechanics stimulation for proper growth and development.

Impact of Pulmonary Venous Inflow on Cardiac Flow Simulations: Comparison with In Vivo 4D Flow MRI

Blood flow simulations are making their way into the clinic, and much attention is given to estimation of fractional flow reserve in coronary arteries. Intracardiac blood flow simulations also show promising results, and here the flow field is expected to depend on the pulmonary venous (PV) flow rates. In the absence of in vivo measurements, the distribution of the flow from the individual PVs is often unknown and typically assumed. Here, we performed intracardiac blood flow simulations based on time-resolved computed tomography on three patients, and investigated the effect of the distribution of PV flow rate on the flow field in the left atrium and ventricle. A design-of-experiment approach was used, where PV flow rates were varied in a systematic manner. In total 20 different simulations were performed per patient, and compared to in vivo 4D flow MRI measurements. Results were quantified by kinetic energy, mitral valve velocity profiles and root-mean-square errors of velocity. While large differences in atrial flow were found for varying PV inflow distributions, the effect on ventricular flow was negligible, due to a regularizing effect by mitral valve. Equal flow rate through all PVs most closely resembled in vivo measurements and is recommended in the absence of a priori knowledge.

Impact of left atrial appendage closure on cardiac functional and structural remodeling: A difference-in-difference analysis of propensity score matched samples

BACKGROUND

Although the safety and efficacy of left atrial (LA) appendage (LAA) closure (LAAC) in nonvalvular atrial fibrillation (NVAF) patients have been well documented in randomized controlled trials and real-world experience, there are limited data in the literature about the impact of LAAC on cardiac remodeling. The aim of the study was to examine the impact of LAAC on cardiac functional and structural remodeling in NVAF patients.

METHODS

Between March 2014 and November 2016, 47 NVAF patients who underwent LAAC were included in this study (LAAC group). A control group (non-LAAC group) was formed from 141 NVAF patients without LAAC using propensity score matching. The difference-in-difference analysis was used to evaluate the difference in cardiac remodeling between the two groups at baseline and follow-up evaluations.

RESULTS

The LAAC group had a larger increase in LA dimension, volume and volume index than the non-LAAC group (+3.9 mm, p = 0.001; +9.7 mL, p = 0.006 and +5.9 mL/m2, p = 0.011, respectively). Besides, a significant increase in E and E/e' ratio was also observed in the LAAC group (+14.6 cm/s, p = 0.002 and +2.3, p = 0.028, respectively). Compared with the non-LAAC group, left ventricular (LV) ejection fraction and fractional shortening decreased in LAAC patients, but were statistically insignificant (-3.5%, p = 0.109 and -2.0%, p = 0.167, respectively).

CONCLUSIONS

There were significant increases in LA size and LV filling pressure among NVAF patients after LAAC. These impacts of LAAC on cardiac functional and structural remodeling may have some clinical implications that need to be addressed in future studies.

The Left Atrial Appendage Revised

Nonvalvular atrial fibrillation is associated with a 4- to 5-fold strokes increase and may be responsible for 15% to 20% of all strokes in the elderly. In this scenario, the left atrial appendage thrombus would be the associated with 90% of cases. The use of anticoagulants, percutaneous devices, and the left atrial appendage surgical exclusion is still an open discussion. For left atrial appendage procedures, relevant anatomic spatial relationships have to be emphasized, besides the chance of the normal physiological functioning would be eliminated with the proceedings. There are evidences that the left atrial appendage closure during routine cardiac surgery is significantly associated with an increased risk of early postoperative atrial fibrillation. Therefore, the purpose of this review is to focus basic aspects for continuous medical education. In summary, the rationale of this text is to emphasize anatomical and pharmacological aspects involved in the simple surgical exclusion of left atrial appendage under cardiopulmonary bypass. There are several operative techniques, but to conclude this revision it will present one of them based on the discussed basic sciences.

Occlusion of left atrial appendage affects metabolomic profile: focus on glycolysis, tricarboxylic acid and urea metabolism

BACKGROUND

Left atrial appendage (LAA) closure (LAAC) by implantation of an occlusion device is an established cardiac intervention to reduce risk of stroke while avoiding intake of oral anticoagulation medication during atrial fibrillation. Cardiac interventions can alter local or systemic gene and protein expression. Effects of LAAC on systemic metabolism have not been studied yet.

OBJECTIVES

We aimed to study the effects of interventional LAAC on systemic metabolism.

METHODS

Products of glycolysis, tricarboxylic acid and urea metabolism were analyzed by ESI-LC-MS/MS and MS/MS using the AbsoluteIDQ™ p180 Kit in plasma of 44 patients undergoing successful interventional LAAC at baseline (T0) and after 6 months (T1).

RESULTS

During follow up, plasma concentrations of several parameters of glycolysis and tricarboxylic acid cycle (TCA) and urea metabolism increased (alanine, hexose, proline, sarcosine), while others decreased (aspartate, glycine, SDMA, serine). Multivariate linear regression analysis showed that time after interventional LAAC was an independent predictor for metabolite changes, including the decrease of SDMA (beta -0.19, p < 0.01) and the increase of sarcosine (beta 0.16, p < 0.01).

CONCLUSIONS

Successful interventional LAAC affects different pathways of the metabolome, which are probably related to cardiac remodeling. The underlying mechanisms as well as the long term effects have to be studied in the future.

A Review Of The Relevant Embryology, Pathohistology, And Anatomy Of The Left Atrial Appendage For The Invasive Cardiac Electrophysiologist

The three-dimensional morphology of the left atrial appendage provides the substrate for thrombus generation, and is a harbinger for embolic material due to its direct connection to the left-sided circulation. Appreciating the development of the appendage from mesodermal layer to its adult form provides the basis to improve exclusion from the atrial circulation, and thereby can lead to a significant reduction in stroke risk. This process also provides insight into the role of the left atrial appendage as an endocrine organ, its involvement in fluid homeostasis, and its connection to the autonomic nervous system. Knowledge of the surrounding structural arrangement is critical to identify landmarks from both an endocardial and epicardial perspective to improve targeted device placement. Furthermore, correlation of the left atrial appendage body, neck, and ostium to the surrounding anatomy can also improve both procedural efficacy and safety. In addition, a working knowledge of the regional anatomy adds a prudent degree of awareness for procedural complications, and allows for early identification and timely intervention as these situations arise. A detailed understanding of the left atrial appendage embryology, histology, and gross anatomy is imperative to identify the correct device and approach for each individual patient. In addition, this increased awareness can identify areas that are in need of further innovation, and thus provide the ability to adapt and refine existing technologies to overcome pitfalls currently facing catheter-based approaches.

The three integrated phases of left atrial macrophysiology and their interactions

Our understanding of the left atrium is growing, although there are many aspects that are still poorly understood. The left atrium size as an imaging biomarker has been consistently shown to be a powerful predictor of outcomes and of different cardiovascular disorders, such as, but not limited to, atrial fibrillation, congestive heart failure, mitral regurgitation and stroke. Left atrial function has been conventionally divided into three integrated phases: reservoir, conduit and booster-pump. The highly dynamic left atrium and its response to the stretch and secretion of atrial neuropeptides leaves the left atrium far from being a simple transport chamber. The aim of this review is to provide an understanding of the left atrial physiology and its relation to disorders within the heart.

Left atrial appendage exclusion-Where do we stand?

Atrial fibrillation (AF) is consider to be the most common cardiac arrhythmia with an increasingly prevalence. It is postulated that the source of thromboembolism in 90% of patients with non-valvular AF arises from the left atrial appendage (LAA). Stroke is the most feared and life threatening consequence of thromboembolism. Oral anticoagulation (OAC) with vitamin-K-antagonists is the standard medical therapy for stroke prevention in patients with AF. Unfortunately, chronic therapy with vitamin-K-antagonists is contraindicated in 14% to 44% of patients with AF who are at risk for stroke, and its benefits are limited by underutilization, narrow therapeutic window and increased risk for bleeding, making it often undesired. Therefore, mechanical LAA exclusion is a means of preventing thrombus formation in the appendage and subsequent thromboembolic events in these patients. The LAA can be excluded from the systemic circulation via surgical, percutaneous, or thoracoscopic approaches. Several studies of percutaneous transcatheter delivery of dedicated LAA exclusion devices, such as the percutaneous left atrial appendage transcatheter occlusion (PLAATO) device, Watchman device and the Amplatzer cardiac plug, have shown encouraging results as an alternative to vitamin-K-antagonists therapy for selected patients, good feasibility and efficacy, with a high rate of successful implantation. We discuss the current evidence for LAA exclusion in patients and review their results.

Atrial Fibrillation and the Role of LAA in Pathophysiology and Clinical Outcomes?

Left atrial appendage (LAA) is a source of thromboembolism especially in patients with non valvular atrial fibrillation (AF). It is reasonable to accept LAA as a distinct part of left atrium (LA) with unique anatomical and physiological properties. Advances in imaging modalities increased the knowledge about anatomical and physiological characteristics of LAA. It is important to prevent the AF patients from systemic thromboembolic events, and new pharmacological and non pharmacological management approaches demonstrate encouraging results. Also pulmonary vein isolation which has been accepted as a curative and useful treatment option for the treatment of drug resistant AF has been helpful in understanding the electrophysiological properties of LAA. Accumulating data revealed that LAA continues to be the one of the most important structure of heart during AF because of its distinctive anatomical, mechanical, and electrophysiological properties.

Percutaneous treatment of patients with heart diseases: selection, guidance and follow-up. A review

Aortic stenosis and mitral regurgitation, patent foramen ovale, interatrial septal defect, atrial fibrillation and perivalvular leak, are now amenable to percutaneous treatment. These percutaneous procedures require the use of Transthoracic (TTE), Transesophageal (TEE) and/or Intracardiac echocardiography (ICE). This paper provides an overview of the different percutaneous interventions, trying to provide a systematic and comprehensive approach for selection, guidance and follow-up of patients undergoing these procedures, illustrating the key role of 2D echocardiography.

Left atrial appendage closure

Stroke prevention is the primary goal in atrial fibrillation (AF) given its clinical and socioeconomic impact. With AF, the prevalence of thromboembolic stroke continues to rise and there is an urgent need to develop better strategies of stroke prevention. Warfarin, although effective when used appropriately, is burdened by underutilization, narrow therapeutic windows, and life-threatening bleeding complications. Novel pharmacologic agents have been plagued by off-target toxicity and only modest improvement in bleeding complications over warfarin. Because most thromboemboli arise from the left atrial appendage (LAA), surgical exclusion of the LAA is often used in AF patients undergoing cardiac surgery. Percutaneous device LAA closure has now been developed as an adjunct and as an alternative to pharmacotherapy in patients with AF. Promising randomized data are available with the WATCHMAN device, while several other devices are in various stages of clinical and preclinical development.

A practical approach to the management of patients with atrial fibrillation

Atrial fibrillation is the most commonly encountered clinical arrhythmia and continues to grow in incidence. Current management involves highly individualised therapies based on underlying concomitant disease processes and symptoms. Moreover, there are numerous therapeutic permutations involving anticoagulation, rate-limitation and antiarrhythmic strategies. This review serves to update the clinician with a practical approach to each patient population and on current advances in management.