Morphology of the left atrial appendage

Understanding the role of the left atrial appendage on the flow in the atrium

BACKGROUND

The exclusion/occlusion of the left atrial appendage (LAA) is a treatment option for atrial fibrillation (AF) patients who are at high risk of stroke and high risk of bleeding. As the role of the LAA is not well understood or explored, this study aims to assess its role on flow dynamics in the left atrium.

METHODS

Computational fluid dynamics (CFD) simulations were carried out for nine AF patients before and after LAA exclusion. The flow parameters investigated included the LA velocities, Time Averaged Wall Shear Stress (TAWSS), Oscillatory Shear Index (OSI), Relative Residence Time (RRT), and Pressure in the LA.

RESULTS

This study shows that, on average, a decrease in TAWSS (1.82 ± 1.85 Pa to 1.27 ± 0.96 Pa, p < 0.05) and a slight increase in OSI (0.16 ± 0.10 to 0.17 ± 0.10, p < 0.05), RRT (1.87 ± 1.84 Pa-1 to 2.11 ± 1.78 Pa-1, p < 0.05), and pressure (-19.2 ± 6.8 mmHg to -15.3 ± 8.3 mmHg, p < 0.05) were observed in the LA after the exclusion of the LAA, with a decrease in low-magnitude velocities.

CONCLUSION

The exclusion of the LAA seems to be associated with changes in LA flow dynamics. Further studies are needed to elucidate the clinical implications of these changes.

Left Atrial Appendage Pseudothrombus Is Associated With Stroke History in Patients With Atrial Fibrillation Undergoing Cardiac Computed Tomography

BACKGROUND

In nonvalvular atrial fibrillation (NVAF), the left atrial appendage (LAA) is the source of thrombus in up to 90% of patients. LAA pseudothrombus (LAAPT), defined as a filling defect on the initial but not the 60-second delayed acquisition on cardiovascular computed tomography scan (CCT), is a recognized phenomenon in NVAF, with unknown clinical relevance. We aimed to determine the relationship between LAAPT and history of stroke in patients with NVAF.

METHODS AND RESULTS

The study included 213 consecutive patients with NVAF undergoing CCT who were assessed for LAAPT. LA and LAA dimensions and LAA morphology correlated with clinical demographics including cardiovascular risk factors, history of stroke, thromboembolic stroke, and transient ischemic attack. Mean age (±SD) was 65.1±10.5 years (range 31-89) and 150 of 213 (70.4%) were men. LAAPT was present in 59 of 213 (27.7%) patients. Greater mean LAA ostium area (5.7 versus 4.5, P<0.001), greater mean LAA ostium area:curved length (0.11 versus 0.08, P<0.001), increased LAA volume (14.0 versus 10.2, P<0.001), and lower mean LAA tortuosity index (1.17 versus 1.38, P<0.001) were all associated with the presence of LAAPT. On multivariable analysis, LAAPT on CCT (odds ratio [OR], 3.20 [95% CI, 1.40-7.20]; P<0.006) and higher CHA2DS2-VASc score (OR, 1.65 [95% CI, 1.16-2.35]; P=0.01) were associated with all strokes, with LAAPT remaining a statistically significant risk factor even after adjustment for CHA2DS2-VASc score.

CONCLUSIONS

LAAPT on CCT is common in patients with NVAF. It has a strong positive association with stroke prevalence, even after adjustment for CHA2DS2-VASc score. LAAPT on CCT may potentially allow further stratification for stroke risk, additive to the CHA2DS2-VASc score.

Left Atrial Appendage Closure: A Narrative Review

Atrial fibrillation (AF) is the most common cardiac arrhythmia and the cause of thromboembolic events in elderly patients worldwide. AF is associated with a significantly increased risk of morbidity and mortality due to cardiac emboli, primarily from left atrial appendage (LAA) thrombus. Oral anticoagulation therapy is the standard treatment to effectively reduce the risk of thromboembolic events in patients with AF. However, anticoagulation treatment increases bleeding risk. LAA closure (LAAC) has recently been introduced as a feasible mechanical preventive intervention for thromboembolic events while minimizing the risk of bleeding. Transcatheter LAAC devices have evolved in the past decade, and several ongoing trials have demonstrated the improvements of safety and outcomes in newer generation devices. This review summarizes the current perspectives and outcomes regarding LAAC as an alternative to pharmacologic therapy.

Mechanisms and Prediction of Ischemic Stroke in Atrial Fibrillation Patients

Atrial fibrillation (AF) is the most common arrhythmia in adults worldwide and represents an important burden for patients, physicians, and healthcare systems. AF is associated with substantial mortality and morbidity, due to the disease itself and its specific complications, such as the increased risk of stroke and thromboembolic events associated with AF. The temporal relation between AF episodes and stroke is nonetheless incompletely understood. The factors associated with an increased thromboembolic risk remain unclear, as well as the stroke risk stratification. Therefore, in this review, we intend to expose the mechanisms and physiopathology leading to intracardiac thrombus formation and stroke in AF patients, together with the evidence supporting the causal hypothesis. We also expose the risk factors associated with increased risk of stroke, the current different risk stratification tools as well as future prospects for improving this risk stratification.

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.

Left Atrial Thrombus-Are All Atria and Appendages Equal?

Although the left atrial appendage (LAA) seems useless, it has several critical functions that are not fully known yet, such as the causes for being the main origin of cardioembolic stroke. Difficulties arise due to the extreme range of LAA morphologic variability, making the definition of normality challenging and hampering the stratification of thrombotic risk. Furthermore, obtaining quantitative metrics of its anatomy and function from patient data is not straightforward. A multimodality imaging approach, using advanced computational tools for their analysis, allows a complete characterization of the LAA to individualize medical decisions related to left atrial thrombosis patients.

Morphological changes in the orifices of the left atrial appendage and left atrium in patients with atrial fibrillation

BACKGROUND

As an integral part of the left atrium (LA), the left atrial appendage (LAA) plays an important role in atrial fibrillation (AF). However, the relationship between LAA remodeling and AF has not been clearly defined. This retrospective case-control study aimed to assess the morphological and functional features of the LA and the LAA in AF patients using images obtained by computed tomography angiography (CTA).

METHODS

A total of 140 AF patients and 64 patients without AF or other cardiovascular diseases who underwent CTA scans between September 2016 and August 2017 were enrolled in this observational study as the experimental and the control groups, respectively. The major and minor axes, area, and perimeter of the LAA orifice, the LAA depth, and the volume of both the LAA and LA were analyzed. The data of the AF group and the control group were compared. The t-test was used to analyze the normally distributed data, and the Wilcoxon rank-sum test was used for abnormally distributed data. The best critical value of predictors of AF was calculated using receiver operating characteristic (ROC) curve analysis. The correlation of the LAA volume change with the major and minor axes, area, and perimeter of the LAA orifice, and the LAA depth were analyzed using the Pearson correlation coefficient.

RESULTS

The LAA orifice's minor axis, LAA volume, and LA volume were significantly greater (P=0.004, P=0.010, and P<0.001, respectively) in patients with AF than in those without AF. The LAA volume [95% confidence interval (CI): 1.01 to 1.30; P=0.038] and LA volume (95% CI: 1.03 to 1.07; P<0.001) were significantly independent predictors of AF. An LAA volume of 8.75 mL had the highest predictive value for AF [area under the curve (AUC), 0.612], with a sensitivity of 76.6% and a specificity of 48.6%. In contrast, an LA volume of 97.15 mL had the highest predictive value for AF (AUC, 0.771), with a sensitivity of 90.6% and a specificity of 53.6%. The change of LAA volume was positively weakly correlated with the area and perimeter of the LAA orifice (r=0.1703 and r=0.1378, respectively). The LAA emptying fraction was negatively correlated with the major axis and the area of the LAA orifice. The major and minor axes, area, and perimeter of the LAA orifice, and LAA depth were significantly greater in female than in male patients (P=0.003, P=0.003, P=0.001, P=0.019, and P<0.001, respectively).

CONCLUSIONS

The AF patients had a longer minor axis of the LAA orifice than that of the control group, resulting in a more circular LAA orifice. The LAA orifice area and perimeter were positively correlated with LAA volume change. The LAA orifice major and minor axes, area, and perimeter, and the LAA depth of the female patients were significantly greater than those of their male counterparts in AF patients.

Long-term safety and efficacy of left atrial appendage closure in patients with small appendage orifices measured with transesophageal echocardiography

BACKGROUND

The Watchman device is the most widely used occluder but is indicated in atrial fibrillation (AF) patients with a maximal left atrial appendage (LAA) orifice diameter between 17 and 31 mm. We aimed to compare the long-term safety and efficacy of left atrial appendage closure (LAAC) between patients with a small LAA (<17 mm) and those with an indicated LAA (17-31 mm) measured by transesophageal echocardiography (TEE).

METHODS

A total of 369 AF patients treated with LAAC between March 2015 and February 2019 were included and divided into two groups based on the maximal LAA orifice diameter measured by TEE: small LAA group (n = 22) and indicated LAA group (n = 347). Periprocedural complications and long-term clinical outcomes were compared.

RESULTS

The Watchman device was successfully implanted in all patients. Mean device compression was higher in the small LAA group. Four patients (1.2%) in the indicated LAA group experienced pericardial effusion, and none experienced pericardial effusion in the small LAA group. Device-related thrombus was detected in one (4.5%) patient in the small LAA group and five (1.4%) in the indicated LAA group (p = .310). After a mean follow-up period of 4.1 ± 1.6 years, one patient in the small LAA group (4.5%; 1.1/100 person-years) and four in the indicated LAA group (1.2%; 0.3/100 person-years) suffered an ischemic stroke (p = .266).

CONCLUSIONS

The safety and efficacy of LAAC with the Watchman device were comparable between patients with small and indicated LAA orifice diameters measured by TEE.

Impact of atrial fibrillation on left atrium haemodynamics: A computational fluid dynamics study

We analyse the haemodynamics of the left atrium, highlighting differences between healthy individuals and patients affected by atrial fibrillation. The computational study is based on patient-specific geometries of the left atria to simulate blood flow dynamics. We design a novel procedure to compute the boundary data for the 3D haemodynamic simulations, which are particularly useful in absence of data from clinical measurements. With this aim, we introduce a parametric definition of atrial displacement, and we use a closed-loop lumped parameter model of the whole cardiovascular circulation conveniently tuned on the basis of the patient's characteristics. We evaluate several fluid dynamics indicators for atrial haemodynamics, validating our numerical results in terms of clinical measurements; we investigate the impact of geometric and clinical characteristics on the risk of thrombosis. To highlight the correlation of thrombus formation with atrial fibrillation, according to medical evidence, we propose a novel indicator: age stasis. It arises from the combination of Eulerian and Lagrangian quantities. This indicator identifies regions where slow flow cannot properly rinse the chamber, accumulating stale blood particles, and creating optimal conditions for clots formation.

In Vitro Pressure Measurements Across an Interatrial Shunt for HFpEF Treatment

PURPOSE

Preserved ejection fraction heart failure (HFpEF) can be treated by installing a shunt in the interatrial septum, which relieves excess pressure in the left atrium by allowing blood to flow from left to right. This technique has proven effective in clinical trials, but the details of the flow through the shunted heart are not well understood. The current study aims to collect quantitative data on the relationship between pressure and flow rate in such shunts.

METHODS

An in vitro, shunted double atrium flow phantom was fabricated and used to investigate the relationship between pressure drop and flow across an interatrial shunt. Flow rate was controlled and the resulting pressure drop across the shunt was measured for a variety of flow cases, including steady and pulsatile flow, flow rate waveforms typical of healthy and failing hearts, and low and high heart rates.

RESULTS

The results show a positive relationship between shunt flow rate and pressure drop which is more pronounced in steady flow than in pulsatile flow. Increasing heart rate increases the time-averaged pressure drop across the shunt but not the maximum pressure drop. For steady-flow cases, large changes in pressure drop resulting from moderate changes in flow rate suggest a flow regime transition during parts of the cardiac cycle. Comparison of time-averaged pulsatile flow pressure measurements with steady-flow measurements and two analytical plate-orifice models suggests that none approximate pulsatile flow accurately.

CONCLUSIONS

The flow rate/pressure drop relationship across an in vitro model of an interatrial shunt has been measured for a variety of physiologically relevant cases. Among other things, the results suggest that steady flow approximations to the heart's pulsatile flow should be used with caution and simplified theoretical models do not approximate the flow rate/pressure drop relationship accurately.

Left Atrial Appendage Occlusion: Current Stroke Prevention Strategies and a Shift Toward Data-Driven, Patient-Specific Approaches

The left atrial appendage (LAA) is a complex structure with unknown physiologic function protruding from the main body of the left atrium. In patients with atrial fibrillation, the left atrium does not contract effectively. Insufficient atrial and LAA contractility predisposes the LAA morphology to hemostasis and thrombus formation, leading to an increased risk of cardioembolic events. Oral anticoagulation therapies are the mainstay of stroke prevention options for patients; however, not all patients are candidates for long-term oral anticoagulation. Percutaneous occlusion devices are an attractive alternative to long-term anticoagulation therapy, although they are not without limitations, such as peri-implant leakage and device-related thrombosis. Although efforts have been made to reduce these risks, significant interpatient heterogeneity inevitably yields some degree of device-anatomy mismatch that is difficult to resolve using current devices and can ultimately lead to insufficient occlusion and poor patient outcomes. In this state-of-the-art review, we evaluated the anatomy of the LAA as well as the current pathophysiologic understanding and stroke prevention strategies used in the management of the risk of stroke associated with atrial fibrillation. We highlighted recent advances in computed tomography imaging, preprocedural planning, computational modeling, and novel additive manufacturing techniques, which represent the tools needed for a paradigm shift toward patient-centric LAA occlusion. Together, we envisage that these techniques will facilitate a pipeline from the imaging of patient anatomy to patient-specific computational and bench-top models that enable customized, data-driven approaches for LAA occlusion that are engineered specifically to meet each patient's unique needs.

Clinical Characteristics of Non-Valvular Atrial Fibrillation Patients With a Large Left Atrial Appendage Ostium-Limiting Percutaneous Closure

BACKGROUND

The left atrial appendage (LAA) is a therapeutic target for preventing cardioembolic stroke in patients with non-valvular atrial fibrillation (NVAF). A large LAA ostium limits percutaneous LAA closure. This study investigated the characteristics and factors associated with a large LAA ostium in Japanese patients with NVAF.Methods and Results: In 1,102 NVAF patients, the maximum LAA diameter was measured using transesophageal echocardiography (TEE). A large LAA ostium was defined by a maximum diameter of >30 mm. Forty-four participants underwent repeated TEEs, and changes in LAA size under lasting AF were assessed. A large LAA ostium was observed in 3.1% of all participants and 8.9% of patients with long-standing persistent AF (LSAF). The large LAA group had greater CHA₂DS₂-VASc (P=0.024) and HAS-BLED scores (P=0.046) and a higher prevalence of LAA thrombus (P=0.004) than did the normal LAA group. LSAF, moderate or severe mitral regurgitation, left atrial volume ≥42 mL/m², E/E' ratio ≥9.5, and left ventricular mass ≥85 mg/m²were independently associated with a large LAA ostium (P<0.001, P<0.001, P=0.009, P=0.009, and P=0.032, respectively). In 44 patients with lasting AF, the LAA ostial diameter increased over time (P<0.001).

CONCLUSIONS

NVAF patients with a large LAA ostium may have a higher risk of stroke and bleeding. LSAF and factors leading to LA overload may be closely associated with LAA ostial dilatation and can promote it.

Evaluation of Stroke Risk in Patients With Atrial Fibrillation Using Morphological and Hemodynamic Characteristics

Background

It is well known that the thrombus triggering stroke in patients with atrial fibrillation (AF) mainly comes from the left atrial appendage (LAA). This study aims to characterize the morphological and hemodynamic parameters and evaluate their differences between AF patients with and without a stroke history.

Methods

Cardiac CT images were obtained from AF patients with (n = 10) and without a history of stroke (n = 10). 3D models of the left atrium (LA) were reconstructed by processing the CT image, and the LA/LAA morphological parameters were measured. Computational fluid dynamics (CFD) simulations were performed to calculate the hemodynamic parameters in LA. The species-transport model and discrete phase model (DPM) were applied to analyze blood residual ratio and particle residual ratio, two qualitative parameters for thrombus formation and flow-out potential, respectively.

Results

There were significant differences in LAA actual depth (p = 0.002), and direct length (p = 0.049) between the non-stroke and stroke groups. Significant differences were also found in certain hemodynamic parameters. The blood residual ratio in LAA was significantly smaller in the stroke group than in the non-stroke group (p < 0.05). Moreover, the particle residual ratio within LAA was significantly smaller in the stroke groups than in the non-stroke group (p < 0.05).

Conclusion

There are significant differences in both morphological and hemodynamic parameters between AF patients with and without a stroke history. A high blood residual ratio in LAA confirms that thrombus is more likely to form in AF patients. A significantly smaller particle residual ratio in the stroke group may suggest the thrombus formed with LAA is more likely to flow out of LAA, leading to a higher risk of stroke. The proposed morphological and hemodynamic parameters may be additional risk factors that can be used to better risk stratify AF patients.

Left Atrial Thrombus-Are All Atria and Appendages Equal?

Although the left atrial appendage (LAA) seems useless, it has several critical functions that are not fully known yet, such as the causes for being the main origin of cardioembolic stroke. Difficulties arise due to the extreme range of LAA morphologic variability, making the definition of normality challenging and hampering the stratification of thrombotic risk. Furthermore, obtaining quantitative metrics of its anatomy and function from patient data is not straightforward. A multimodality imaging approach, using advanced computational tools for their analysis, allows a complete characterization of the LAA to individualize medical decisions related to left atrial thrombosis patients.

Clinical application of percutaneous left atrial appendage occlusion guided only by transesophageal echocardiography without fluoroscopy and angiography in the patients with nonvalvular atrial fibrillation

BACKGROUND AND AIM

The objective of this study was to understand the clinical efficacy and application of the percutaneous left atrial appendage occlusion (PLAAO) guided only by the transesophageal echocardiography (TEE) in patients with nonvalvular atrial fibrillation (NVAF), without using the fluoroscopy and angiography.

METHODS

During the time period of this study from June 2020 to June 2021, 32 patients underwent PLAAO and all underwent a TEE guided approach. The anatomical features of the left atrial appendage (LAA) were evaluated and observed by TEE before and during the procedure. LAA occluder device was selected for the appropriate size. Intraoperative TEE guided and monitored the process of PLAAO in real-time, and also evaluated the stability and tightness of the occluder device, following monitored postoperative complications.

RESULTS

The PLAAO procedure was successful in all the patients. No serious complications like dislocation of the occluder and embolism were seen. Postoperative TEE demonstrated that the PLAAO occluder devices were in a good position without residual shunting.

CONCLUSIONS

PLAAO only guided by TEE may become a safe and reliable surgical procedure, which can protect surgeons and patients from radiation, and can gradually become a novel surgical method of PLAAO with the practical application value.

Improving Left Atrial Appendage Occlusion Device Size Determination by Three-Dimensional Printing-Based Preprocedural Simulation

Background

The two-dimensional (2D)-based left atrial appendage (LAA) occluder (LAAO) size determination by using transesophageal echocardiography (TEE) is limited by the structural complexity and wide anatomical variation of the LAA.

Objective

This study aimed to assess the accuracy of the LAAO size determination by implantation simulation by using a three-dimensional (3D)-printed model compared with the conventional method based on TEE.

Methods

We retrospectively reviewed patients with anatomically and physiologically properly implanted the Amplatzer Cardiac Plug and Amulet LAAO devices between January 2014 and December 2018 by using the final size of the implanted devices as a standard for size prediction accuracy. The use of 3D-printed model simulations in device sizing was compared with the conventional TEE-based method.

Results

A total of 28 cases with the percutaneous LAA occlusion were reviewed. There was a minimal difference [−0.11 mm; 95% CI (−0.93, 0.72 mm); P = 0.359] between CT-based reconstructed 3D images and 3D-printed left atrium (LA) models. Device size prediction based on TEE measurements showed poor agreement (32.1%), with a mean difference of 2.3 ± 3.2 mm [95% CI (−4.4, 9.0)]. The LAAO sizing by implantation simulation with 3D-printed models showed excellent correlation with the actually implanted LAAO size (r = 0.927; bias = 0.7 ± 2.5). The agreement between the 3D-printed and the implanted size was 67.9%, with a mean difference of 0.6 mm [95% CI (−1.9, 3.2)].

Conclusion

The use of 3D-printed LA models in the LAAO size determination showed improvement in comparison with conventional 2D TEE method.

Pre-procedural determination of device size in left atrial appendage occlusion using three-dimensional cardiac computed tomography

The complex structure of the left atrial appendage (LAA) brings limitations to the two-dimensional-based LAA occlusion (LAAO) size prediction system using transesophageal echocardiography. The LAA anatomy can be evaluated more precisely using three-dimensional images from cardiac computed tomography (CT); however, there is lack of data regarding which parameter to choose from CT-based images during pre-procedural planning of LAAO. We aimed to assess the accuracy of measurements derived from cardiac CT images for selecting LAAO devices. We retrospectively reviewed 62 patients with Amplatzer Cardiac Plug and Amulet LAAO devices who underwent implantation from 2017 to 2020. The minimal, maximal, average, area-derived, and perimeter-derived diameters of the LAA landing zone were measured using CT-based images. Predicted device sizes using sizing charts were compared with actual successfully implanted device sizes. The mean size of implanted devices was 27.1 ± 3.7 mm. The perimeter-derived diameter predicted device size most accurately (mean error = − 0.8 ± 2.4 mm). All other parameters showed significantly larger error (mean error; minimal diameter = − 4.9 ± 3.3 mm, maximal diameter = 1.0 ± 2.9 mm, average diameter = − 1.6 ± 2.6 mm, area-derived diameter = − 2.0 ± 2.6 mm) than the perimeter-derived diameter (all p for difference < 0.05). The error for other parameters were larger in cases with more eccentrically-shaped landing zones, while the perimeter-derived diameter had minor error regardless of eccentricity. When oversizing was used, all parameters showed significant disagreement. The perimeter-derived diameter on cardiac CT images provided the most accurate estimation of LAAO device size regardless of landing zone eccentricity. Oversizing was unnecessary when using cardiac CT to predict an accurate LAAO size.

Effectiveness and safety of transcatheter left atrial appendage closure

Atrial fibrillation (AF) is responsible for cardiogenic stroke. Since left atrial appendage (LAA) is a cause of most of cardiac thrombus, LAA closure is an emerging novel stroke prevention procedure for patients with AF alternative to anticoagulation. WATCHMAN LAA Closure device (Boston Scientific, Marlborough, MA, USA) is the only approved device in the USA and Japan. The device is indicated in high bleeding risk and high stroke risk non-valvular AF patients. Cardiac tamponade, stroke, and device embolization are typical procedural complications. Procedural complication rate is reduced with implanters' experience and matured procedure steps. Several randomized trials demonstrated procedure safety and efficacy of the device. The device resulted in similar thromboembolic event rates but significantly reduced bleeding events compared to anticoagulants. After the procedure, optimal post procedural antithrombotic drug regimen has not been fully investigated. Also, device-related thrombosis can be a new issue. Modification of the device can improve issues, but not fully solve it. Tailor made treatment based on the individual risk by heart team communication with neurologists is essential to treat patients.

Surgical clip closure of the left atrial appendage

Atrial fibrillation (AF) is the most common atrial arrhythmia, but it is not a benign disease. AF is an important risk factor for thromboembolic events, causing significant morbidity and mortality. The left atrial appendage (LAA) plays an important role in thrombus formation, but the ideal management of the LAA remains a topic of debate. The increasing popularity of surgical epicardial ablation and hybrid endoepicardial ablation approaches, especially in patients with a more advanced diseased substrate, has increased interest in epicardial LAA management. Minimally invasive treatment options for the LAA offer a unique opportunity to close the LAA with a clip device. This review highlights morphologic, electrophysiologic, and surgical aspects of the LAA with regard to AF surgery, and aims to illustrate the importance of surgical clip closure of the LAA.

Anatomical Characteristics of the Left Atrium and Left Atrial Appendage in Relation to the Risk of Stroke in Patients With Versus Without Atrial Fibrillation

[Figure: see text].

Subject-Specific Calculation of Left Atrial Appendage Blood-Borne Particle Residence Time Distribution in Atrial Fibrillation

Atrial fibrillation (AF) is the most common arrhythmia that leads to thrombus formation, mostly in the left atrial appendage (LAA). The current standard of stratifying stroke risk, based on the CHA2DS2-VASc score, does not consider LAA morphology, and the clinically accepted LAA morphology-based classification is highly subjective. The aim of this study was to determine whether LAA blood-borne particle residence time distribution and the proposed quantitative index of LAA 3D geometry can add independent information to the CHA2DS2-VASc score. Data were collected from 16 AF subjects. Subject-specific measurements included left atrial (LA) and LAA 3D geometry obtained by cardiac computed tomography, cardiac output, and heart rate. We quantified 3D LAA appearance in terms of a novel LAA appearance complexity index (LAA-ACI). We employed computational fluid dynamics analysis and a systems-based approach to quantify residence time distribution and associated calculated variable (LAA mean residence time, t m) in each subject. The LAA-ACI captured the subject-specific LAA 3D geometry in terms of a single number. LAA t m varied significantly within a given LAA morphology as defined by the current subjective method and it was not simply a reflection of LAA geometry/appearance. In addition, LAA-ACI and LAA t m varied significantly for a given CHA2DS2-VASc score, indicating that these two indices of stasis are not simply a reflection of the subjects' clinical status. We conclude that LAA-ACI and LAA t m add independent information to the CHA2DS2-VASc score about stasis risk and thereby can potentially enhance its ability to stratify stroke risk in AF patients.

Incidence and clinical relevance of left atrial appendage membranes: a new congenital heart disease?

AIMS

Left atrial appendage (LAA) membranes are rare congenital anomalies. Those involving the appendage orifice may obstruct its emptying flows, thus promoting blood stasis and clot formation. However, the epidemiology of LAA membranes has never been studied and a correlation with appendage thrombosis has never been proved. Very few case reports described LAA membranes, therefore, their frequency and clinical significance are not known. Moreover, their presence and degree are of crucial importance in planning LAA percutaneous closure, a procedure whose indication is evolving, and whether their presence can represent technical issues during the device implantation is not known. This study aimed to evaluate the incidence and the clinical significance of LAA membranes.

METHODS AND RESULTS

A population of 6030 consecutive transoesophageal echo (TOE) studies has been retrospectively reviewed in order to find those patients in whom an LAA membrane has been found. A literature research has been performed to review previous described cases. Among 6030 TOE cases, an LAA membrane has been described in 6 (prevalence of 1/1000). In one case, the membrane was associated to a severe LAA hypoplasia and in another case to an LAA thrombus (these represent the first cases ever described). All patients had an atrial fibrillation (AF) history and two were in AF during the TOE exam.

CONCLUSION

LAA membranes are rare congenital abnormalities occasionally discovered during a TOE exam, frequently in patients affected by AF. In half of the cases, they obstruct the LAA flow, thus theoretically pre-disposing to clot formation. They may be rarely associated to an appendage hypoplasia. During a TOE exam, cardiac imagers should always rule out their presence.

Modification of the left atrial appendage and its role in stroke risk reduction with non-valvular atrial fibrillation

Atrial fibrillation is one of the most common cardiovascular disorders encountered by clinicians in clinical practice. Patients with atrial fibrillation are at risk of cerebrovascular and systemic embolic events, which may be attenuated by commencement of anticoagulation therapy. Even so, due to extremely high bleeding risk certain patients may not be suitable for long-term anticoagulation therapy. The left atrial appendage is a common site for thrombus formation in patients with atrial fibrillation. Left atrial appendage exclusion, either surgical or percutaneous, has been performed to ostensibly reduce the risk of cerebrovascular events and potentially minimise or omit anticoagulation therapy in select patients. This review summarises the role of the left atrial appendage in cerebrovascular events, current evidence with modification of the left atrial appendage and future trials that may change practice with these procedures.

Left atrial appendage morphology predicts the formation of left atrial appendage thrombus

BACKGROUND

Nonchicken wing left atrial appendage (LAA) morphology is associated with higher risk for stroke in patients with atrial fibrillation (AF) than chicken wing (CW) morphology.

OBJECTIVE

Assess whether LAA morphology predicts the formation of LAA thrombus independent of age, sex, presenting rhythm, left ventricular ejection fraction (LVEF), or anticoagulant use.

METHODS

A cross-sectional analysis was performed on patients prospectively enrolled in the Vanderbilt LAA Registry or presenting for transesophageal echocardiogram (TEE) between January 1, 2015, and November 1, 2017 (n = 306). Two physicians independently reviewed TEEs interpreted as having LAA thrombus. Determination of LAA morphology, ejection velocity, and presence of thrombus (n = 102) were based on 0°, 45°, 90°, and 135° TEE views. The control cohort (n = 204) included consecutive AF patients undergoing TEE without LAA thrombus.

RESULTS

LAA morphology in patients with LAA thrombus was: 35% windsock, 47% broccoli, and 12% CW. Windsock (odds ratio [OR], 4.0; 95% confidence interval [CI]: 1.7-9.3, p = .001) and broccoli (OR, 6.6; 95% CI: 2.6-16.6; p < .001) morphology were higher risk for thrombus compared to CW. Female sex predicted higher-odds for LAA thrombus (OR, 2.6; 95% CI: 1.4-4.8; p = .002) as did LAA-EV < 20 cm/s (OR, 11.12; 95% CI: 5.6-22.1). Anticoagulation use (OR, 0.5; 95% CI: 0.3-0.9; p = .03) and higher LVEF (OR, 0.95; 95% CI: 0.93-0.98; p < .001) were associated with lower risk. In patients with a CW morphology who had LAA thrombus, 4 of the 7 had an LAA-EV < 20 cm/s and acute systolic heart failure with LVEF < 30% or active malignancy. In multivariable linear regression analysis controlling for presenting rhythm, anticoagulant use, age, sex, and LVEF, CW morphology appears relatively protective from LAA thrombus (p = .001).

CONCLUSION

CW LAA morphology appears relatively protective against the formation of LAA thrombus.

The left atrial appendage in humans: structure, physiology, and pathogenesis

For many years, the left atrial appendage (LAA) was considered a dormant embryological remnant; however, it is a structurally complex and functional organ that contributes to cardiac haemodynamic changes and volume homeostasis through both its contractile properties and neurohormonal peptide secretion. When dysfunctional, the LAA contributes to thrombogenesis and subsequent increased predisposition to cardioembolic events. Consequently, the LAA has gained much attention as a therapeutic target to lower this risk. In addition, attention has focused on the LAA in its role as an electrical trigger for atrial tachycardia and atrial fibrillation with ablation of the LAA to achieve electrical isolation showing promising results in the maintenance of sinus rhythm. This in-depth review explores the structure, physiology and pathophysiology of the LAA, as well as LAA intervention and their sequelae.

Anatomy and Physiologic Roles of the Left Atrial Appendage: Implications for Endocardial and Epicardial Device Closure

The left atrial appendage has been implicated as a major nidus for thrombus formation, particularly in atrial fibrillation. This discovery has prompted substantial interest in the development of left atrial appendage exclusion devices aimed at decreasing systemic thromboembolism risk. Its deceptively simple appearance belies the remarkable complexity that characterizes its anatomy and physiology. We highlight the key anatomic features and variations of the left atrial appendage as well as its relationships with surrounding structures. We also summarize crucial anatomic factors that should be taken into account by the interventional cardiologist when planning for or performing left atrial appendage exclusion procedures.

Relation of Left Atrial Appendage Morphology Determined by Computed Tomography to Prior Stroke or to Increased Risk of Stroke in Patients With Atrial Fibrillation

Left atrial appendage (LAA) morphology is considered to be associated with ischemic stroke, non-Chicken Wing LAA morphology increases the risk of thromboembolic events. However, existing classification of LAA morphology remains not well quantifiable and therefore may leave room for substantial subjective interpretation. This study aimed to assess interobserver and intraobserver agreements in LAA morphology and its real value in stroke prediction. A total of 2,264 atrial fibrillation patients who underwent computed tomography to explore the LAA anatomy were enrolled. All computed tomography images were given to 3 reviewers to judge the LAA morphology independently. A consensus between all 3 reviewers was only reached in 655 cases (28.9%). In which, 86 patients had previous stroke. Poor intraobserver consistency was observed between 2 times of reading in all the 3 reviewers (Kappa = 0.368, p = 0.014; Kappa = 0.350, p = 0.014; Kappa = 0.333, p = 0.015). Multivariate analysis showed that persistent atrial fibrillation (odds ratio [OR] 1.679; 95% confidence interval [CI] 1.031 to 2.736; p = 0.037), female gender (OR 1.761; 95% CI 1.037 to 2.994; p = 0.036) and age (OR 1.029; 95% CI 1.004 to 1.056; p = 0.025) were associated with previous stroke. LAA morphology was not associated with previous stroke and non-Chicken Wing LAA morphology did not increase the risk of stroke (OR 1.392; 95% CI 0.847 to 2.288; p = 0.192). In conclusion, high interobserver and intraobserver variabilities suggested that existing classification of LAA morphology was unreliable, the interpretation of the relation between LAA morphology and stroke needs caution.

Image-Based Flow Simulations of Pre- and Post-left Atrial Appendage Closure in the Left Atrium

PURPOSE

For patients with atrial fibrillation, the left atrial appendage (LAA) is often the site of thrombus formation due to low atrial ejection fraction that triggers strokes and other thromboembolic events. Recently introduced percutaneous LAA occlusion procedure is known to reduce LAA-induced strokes. Despite having the procedure, there are still 11% of the patients who continue to suffer from future strokes or transient ischemic attacks, not accounting for the procedural related complications. The high failure rate is largely due to the variabilities in LAA's shape, size, and contractility which may result in ineffectiveness of this procedure. To correctly identify the candidates and evaluate the effectiveness of the procedure, we rely on patient-specific CT scans which provides the exact LA and LAA geometries and predictive hemodynamic analysis to assist in evaluating quantitative flow parameters pre- and post-LAA occlusion procedures. Hemodynamic parameters are critical to predict adverse hemodynamic flow patterns in LAA as well as the effectiveness of LAA closure in individual patient. The aim of this paper is to establish an image-based patient-specific computational fluid dynamic (CFD) simulation framework specific to the prediction of treatment outcomes of LAA closure with atrial fibrillation. This framework utilizes automated LA/LAA image segmentation which yields significant reduction in image processing. One set of patient data with successful procedure outcome is used to illustrate the potential of the proposed framework.

METHODS

The proposed LAA occlusion simulation framework is composed of several components: (1) a novel image segmentation procedure, which is fully-automated to identify LA/LAA geometries from CT images, (2) a finite-element mesh generation procedure which transforms the surface geometry into a 3-D volume mesh and properly identified boundary planes, (3) performing CFD simulations with atrial fibrillation flow boundary conditions, and (4) analyzing flow characteristics (velocity, flow patterns, streamlines, vortices) within the LA for before and after LAA closure.

RESULTS

Based on the LA/LAA segmentation of a 65 year old female patient with chronic atrial fibrillation, a CFD analysis was pursued to examine flow characteristics upon LAA closure. The results showed that the flow velocity magnitudes were significantly reduced by a maximum factor of 2.21, flow streamlines were greatly stabilized, and mitral outflow appeared to be more organized. Vortices were dramatically reduced in size, number, intensity, as well as duration. During diastole, the peak vortex diameter was reduced from 2.8 to 1.5 cm, while the vortex duration was reduced from 0.210 to 0.135 s. These flow characteristics all indicated a reduced risk in future thrombus formation and strokes based on the established relationship between flow and thrombus formation. For the patient case under study, the effectiveness of the procedure is predicted and found to be consistent with the actual procedural outcome.

CONCLUSIONS

This framework successfully predicted patient-specific outcome of a LAA closure procedure for one patient with atrial fibrillation. It can be further developed into a useful tool for pre-procedural planning and candidate selection. More patient data are necessary for further validation studies.

Electrical isolation of the left atrial appendage increases the risk of ischemic stroke and transient ischemic attack regardless of postisolation flow velocity

BACKGROUND

Electrical isolation of the left atrial appendage (LAA) is associated with a lower rate of atrial fibrillation (AF) recurrence in patients undergoing radiofrequency catheter ablation. However, LAA isolation can significantly impair LAA contractility.

OBJECTIVE

This study was performed to evaluate whether electrical isolation of the LAA is associated with an increased risk of ischemic stroke or transient ischemic attack (TIA).

METHODS

Consecutive patients with AF undergoing radiofrequency catheter ablation at Korea University Medical Center Anam Hospital were analyzed.

RESULTS

Of 2352 patients, 39 (1.7%) had LAA isolation. Patients with LAA isolation had a significantly higher rate of ischemic stroke or TIA than did those without LAA isolation (log-rank, P < .001; hazard ratio 23.6; P < .001). There were significant differences in the baseline characteristics of the 2 groups, including type of AF (34 [87.2%] and 911 [39.4%] patients with and without LAA isolation had nonparoxysmal AF, respectively). After multivariate adjustment, LAA isolation was found to be a significant risk factor for ischemic stroke or TIA (adjusted hazard ratio 11.3; P < .001). Propensity score-matched analysis also revealed an increased risk of ischemic stroke or TIA in patients with LAA isolation compared with those without LAA isolation (log-rank, P = .001). The LAA flow velocity of post-LAA isolation status was not significantly different between patients who did and did not experience ischemic stroke or TIA (30.3 ± 17.7 cm/s vs 33.9 ± 17.9 cm/s; P = .608).

CONCLUSION

A significantly increased risk of ischemic stroke or TIA was observed in patients with electrical isolation of the LAA. In addition, postisolation LAA flow velocity is not a reliable marker to predict future ischemic events.

Hemodynamic impact of percutaneous left atrial appendage closure in patients with paroxysmal atrial fibrillation

PURPOSE

Percutaneous left atrial appendage (LAA) closure has become a valid alternative to anticoagulation therapy for the prevention of thromboembolic events in patients with atrial fibrillation (AF). However, scarce data exist on the impact of LAA closure on left atrial and ventricular function. We sought to assess the acute hemodynamic changes associated with percutaneous LAA closure in patients with paroxysmal AF.

METHODS

The study population consisted of 31 patients (mean age 73 ± 10 years; 49% women) with paroxysmal AF who underwent successful percutaneous LAA closure. All patients were in sinus rhythm and underwent 2D transthoracic echocardiography at baseline and the day after the procedure. A subset of 14 patients underwent preprocedural cardiac computed tomography (CT) with 3D LA and LAA reconstruction.

RESULTS

Left ventricular systolic function parameters and LA volumetric indexes remained unchanged after the procedure. No significant changes in left ventricular stroke volume (72.4 ± 16.0 vs. 73.3 ± 15.7 mL, p = 0.55) or LA stroke volume (total 15.6 ± 4.2 vs. 14.6 ± 4.2 mL, p = 0.21; passive 9.0 ± 2.8 vs. 8.3 ± 2.6 mL, p = 0.31; active 10.3 ± 5.6 vs. 10.0 ± 6.4 mL, p = 0.72) occurred following LAA closure. Mean ratio of LAA to LA volume by 3D CT was 10.2 ± 2.3%. No correlation was found between LAA/LA ratio and changes in LA stroke volume (r = 0.35, p = 0.22) or left ventricular stroke volume (r = 0.28, p = 0.33).

CONCLUSIONS

The LAA accounts for about 10% of the total LA volume, but percutaneous LAA closure did not translate into any significant changes in LA and left ventricular function.

Sensitivity analysis of geometrical parameters to study haemodynamics and thrombus formation in the left atrial appendage

The left atrial appendage (LAA) is a complex and heterogeneous protruding structure of the left atrium (LA). In atrial fibrillation patients, it is the location where 90% of the thrombi are formed. However, the role of the LAA in thrombus formation is not fully known yet. The main goal of this work is to perform a sensitivity analysis to identify the most relevant LA and LAA morphological parameters in atrial blood flow dynamics. Simulations were run on synthetic ellipsoidal left atria models where different parameters were individually studied: pulmonary veins and mitral valve dimensions; LAA shape; and LA volume. Our computational analysis confirmed the relation between large LAA ostia, low blood flow velocities and thrombus formation. Additionally, we found that pulmonary vein configuration exerted a critical influence on LAA blood flow patterns. These findings contribute to a better understanding of the LAA and to support clinical decisions for atrial fibrillation patients.

Evaluation of the left atrial appendage by real time three-dimensional transesophageal echocardiography online

OBJECTIVE

The objective of this study was to evaluate the feasibility of online real time three-dimensional transesophageal echocardiography (RT3DTEE) in the measurement of left atrial appendage (LAA) orifice size. We also analyzed the correlation between LAA ejection fraction (EF) and its peak empty velocity (PEV).

METHODS

There were 91 subjects enrolled in this study, with 46 patients with AF and 45 individuals with sinus rhythm (SR). RT3DTEE was performed by four methods including iSlice and iCrop online and QLAB software 3DQ and GI-3DQ off-line which were used to measure LAA orifice area, long diameter, short diameter, depth in the largest LAA, and number of LAA lobes. These LAA parameters achieved by the four methods were compared, respectively. GI-3DQ off-line was used to measure LAA end-diastolic and end-systolic volumes to calculate EF of LAA. Two-dimensional (2D) TEE was applied to measure PEV of LAA. The correlation between EF and PEV was analyzed.

RESULTS

There were no significant differences in all LAA parameters between any two RT3DTEE methods (All P > .05). There was a significant and positive correlation between PEV and EF (r = .423, P = .000). There were statistical differences in LAA EF and PEV between patients with AF and SR individuals (0.38 ± 0.12 vs 0.61 ± 0.07, 35.7 ± 12.1 vs 49.5 ± 10.0 cm/s, P = .000).

CONCLUSION

Using online RT3DTEE for measuring LAA orifice size is feasible, and online RT3DTEE is more convenient than offline RT3DTEE. EF is positively correlated with PEV. LAA function is significantly decreased in patients with AF.

Echocardiographic Imaging for Left Atrial Appendage Occlusion: Transesophageal Echocardiography and Intracardiac Echocardiographic Imaging

Left atrial appendage occlusion (LAAO) is a rapidly evolving technology. Multi-modality imaging and understanding of left atrial appendage anatomy are sure to advance. Two-dimensional and 3-dimensional transesophageal echocardiography with fluoroscopy are the mainstay for LAAO image-guided therapy. Key to successful LAAO is an understanding of the transseptal puncture, LAAO size selection for the device-specific landing zone, and postdeployment evaluation for leak and complications. With advancements in computed tomography, there may be a greater role for intracardiac echocardiographic imaging in specific types of LAAO anatomy and devices.

Left atrial enlargement and clinical considerations in patients with or without a residual interatrial shunt after closure of the left atrial appendage with the WATCHMAN™-device

BACKGROUND

Interventional closure of the left atrial appendage (LAA) in patients with non-valvular atrial fibrillation, high thromboembolic and bleeding risk or bleeding history is an alternative therapeutic strategy to oral anticoagulation. It is not known if the exclusion of the LAA from the blood circulation affects the left atrial volume (LAV) and consequently its prognostic value or the circulatory performance of the heart in humans.

METHODS

We aimed to prospectively assess potential changes in baseline LAV, left ventricular ejection fraction (LVEF), NT-proBNP-level and the covered distance in the 6-min walk-test 6 weeks and 6 months after LAA closure with the WATCHMAN™ device. We used serial 3-dimensional transthoracic and transesophageal echocardiography to assess LAV, residual interatrial shunt and device performance in 58 consecutive patients with successful LAA closure.

RESULTS

Accurate 3D-echocardiographic data for LAV measurements were evaluable for 51 (91%) patients. Maximum LAV (LAVmax) at baseline was 102.8 ± 30.8 ml and increased significantly to 107.7 ± 32.8 ml after 6 weeks (p < 0.01) and 113.5 ± 34.2 ml after 6 months (p < 0.01). Minimal LAV (LAVmin) increased from 76.9 ± 29.5 ml at baseline to 81.8 ± 30.2 ml after 45 days (p < 0.01) and 82.1 ± 33.3 ml after 6 months (p < 0.01). Similarly, their indexes to BSA (LAVImax and LAVImin) increased significantly, as well. Patients without a residual left-to-right interatrial shunt showed a significantly higher increase in LAVmax or LAVmin. Baseline LVEF, NT-proBNP-level or the distance covered at the 6-min walk test did not significantly change 6 weeks or 6 months after LAA closure.

CONCLUSIONS

LAVmax and LAVmin increase significantly after interventional LAA closure. LA enlargement does not correlate with clinical progression of heart failure. Persistent left-to-right interatrial shunt counteracts the LA enlargement. A reduced LA compliance after exclusion of the LAA from the blood circulation with consecutive increase in LA pressure may be a potential cause of LA enlargement and warrants further investigation.

TRIAL REGISTRATION

German Clinical Trials Register ID: DRKS00010768 ; Registration Date 07.07.2016.

ANMCO/AIAC/SICI-GISE/SIC/SICCH Consensus Document: percutaneous occlusion of the left atrial appendage in non-valvular atrial fibrillation patients: indications, patient selection, staff skills, organisation, and training

Atrial fibrillation (AF) is the most common arrhythmia and its prevalence is increasing due to the progressive aging of the population. About 20% of strokes are attributable to AF and AF patients are at five-fold increased risk of stroke. The mainstay of treatment of AF is the prevention of thromboembolic complications with oral anticoagulation therapy. Drug treatment for many years has been based on the use of vitamin K antagonists, but recently newer and safer molecules have been introduced (dabigatran etexilate, rivaroxaban, apixaban, and edoxaban). Despite these advances, many patients still do not receive adequate anticoagulation therapy because of contraindications (relative and absolute) to this treatment. Over the last decade, percutaneous closure of left atrial appendage, main site of thrombus formation during AF, proved effective in reducing thromboembolic complications, thus offering a valid medical treatment especially in patients at increased bleeding risk. The aim of this consensus document is to review the main aspects of left atrial appendage occlusion (selection and multidisciplinary assessment of patients, currently available methods and devices, requirements for centres and operators, associated therapies and follow-up modalities) having as a ground the significant evolution of techniques and the available relevant clinical data.

Assessment of the left atrial appendage structure and morphology: comparison of real-time three-dimensional transesophageal echocardiography and computed tomography

In this study, the left atrial appendage (LAA) structure and morphology were assessed using real-time three-dimensional transesophageal echocardiography (RT3D-TEE) and enhanced cardiac computed tomography (CT) scanning, and the two measurements obtained using these different techniques were compared. Two hundred nonvalvular atrial fibrillation (NVAF) patients who were prepared to undergo radiofrequency ablation were enrolled, and 62 controls were enrolled prospectively. RT3D-TEE and CT were performed, and the following parameters were measured: LAA orifice diameter, area, depth, maximum volume, and emptying velocity. The differences between the NVAF patients and controls were compared, and the differences and correlations in the LAA parameters between the two imaging techniques were assessed. The NVAF patients had significantly bigger orifice sizes, orifice areas, and maximum volumes, and lower emptying rates. The AF cohort had roughly equal proportions of the four morphological types, whereas the controls predominantly had the windsock type. A Bland-Altman analysis demonstrated that the LAA measurements obtained using RT3D-TEE were lower than those obtained with the CT. However, linear regression analysis showed the good correlations between the RT3D-TEE and CT measurements of the LAA orifice area, depth and volume (r = 0.86, 0.63, and 0.75, respectively). The use of RT3D-TEE for the visualization and quantitative analysis of LAA parameters is feasible, and the obtained measurements correlate well with those obtained with cardiac CT. This technique may be an ideal tool for guiding LAA occlusion procedures, and combining these two methods may enhance the accuracy of LAA measurements.

Structural Comparison between the Right and Left Atrial Appendages Using Multidetector Computed Tomography

The three-dimensional (3D) structures of the right atrial appendage (RAA) and left atrial appendage (LAA) were compared to clarify why thrombus formation less frequently occurs in RAA than in LAA. Morphological differences between RAA and LAA of 34 formalin-preserved cadaver hearts were investigated. Molds of RAA and LAA specimens were made and the neck areas, volumes of the atrial appendages (AA), and amount of pectinate muscles (PMs) were analyzed using multidetector computed tomography. In RAA, most PMs were connected to one another and formed a “dendritic” appearance and the inner surface area was smaller than in LAA. RAA had smaller volumes and larger neck areas than LAA. The ratios of the neck area/volume were larger and the amounts of PMs were smaller in RAA than in LAA. The volumes, neck areas, and amount of PMs of RAA were significantly correlated with those of LAA. According to the 3D structure, RAA appears to be suited for a more favorable blood flow, which may explain why the thrombus formation is less common in RAA than in LAA. Examining not only LAA but also RAA by transesophageal echocardiography may be useful in high-risk patients of thrombus formation in LAA because the volume, neck area, and amount of PMs of LAA reflect the shape of RAA.

Morphological changes evaluation of left atrial appendage in patients with ischaemic heart disease

BACKGROUND

Since the majority of morphological changes evaluation of myocardium in ischaemic heart disease was in animal model, we detected the importance to evaluate such changes in human patients to gain insights into the targets of cellular damage and to reconcile or refine those experiments.

METHODS

Tissue sections from left atrial appendage of the heart were carefully dissected from seventy five patients underwent conventional coronary artery bypass grafting at the cardiothoracic surgical department, Manchester Royal Infirmary. Tissue was fixed, sectioned, stained and six random sections were photographed and the images were assessed and quantified using Image Analyser Pro-Plus software, version 4.1. Arterioles, venules, intermediate sized vessels, and capillaries were directly counted within the highlighted area of myocardium under LM. Ultra-thin sections were imaged in a Tecnai 12 Biotwin transmission electron microscope at a magnification of ×4200 and photographed by a camera with a black and white film to quantify different structures of myocardium.

RESULTS

The arteriole wall to lumen ratio was significantly increased in ischaemic heart disease patients 18.57 ± 2.89 compared to controls 8.3 ± 1.57, (P < 0.01). The regression analysis between vascular density and cardiomyocyte size demonstrated a significant inverse correlation between transverse cardiomyocyte diameter and arteriole, capillary and total vessel density (P < 0.01, 0.04, 0.02), respectively. Lumen area of the distal myocardial capillary was significantly reduced in IHD patients compared to controls (P < 0.01).

CONCLUSION

These results elucidate the morphological changes in the myocardial microvasculature of patients with ischaemic heart disease and its pathological magnitudes.