4D Flow MR Imaging of the Left Atrium: What is Non-physiological Blood Flow in the Cardiac System?

Integrating soft robotics and computational models to study left atrial hemodynamics and device testing in sinus rhythm and atrial fibrillation

Atrial fibrillation (AF) poses significant clinical challenges due to the complex and variable geometry of the left atrial appendage (LAA), whose structure complicates the development of personalized interventions like LAA occlusion (LAAO) for stroke prevention Current reliance on animal models and cadavers for the assessment of left atrium (LA) and LAA to study AF-related disease and interventions raises reproducibility concerns, necessitating the development of high fidelity, physiologically relevant tools. To address this, we present a multimodal framework combining a soft robotic benchtop simulator, a lumped parameter model (LPM), and finite element analysis (FEA) to replicate LA function in sinus rhythm, atrial flutter, and AF. The system integrates 3D-printed, patient-specific LA geometries with soft robotic actuators to reproduce realistic wall motion and hemodynamics. A compact, magnetic resonance imaging (MRI)-compatible flow loop, driven by a soft robotic left ventricle (LV), eliminates bulky and non-physiological pulsatile pumps, allowing precise flow measurements and LAAO device testing under clinically relevant conditions. Complementary LPM and FEA models provide mechanistic insights, quantifying systemic hemodynamic changes and LA wall stress during disease and interventions. The models effectively replicate the clinical markers of atrial dysfunction and arrhythmia disorders, and their physiological accuracy is demonstrated through validation against human imaging and porcine models. The soft robotic LV's ability to drive the mock flow loop is validated in a hybrid synthetic-biological configuration within a swine circulatory system, where the soft robotic ventricle replaces native ventricular contraction to sustain systemic circulation. This scalable and versatile framework integrates experimental and computational techniques to advance cardiovascular biomechanics, supporting device development, clinical research/training, and personalized AF treatment to improve patient outcomes.

Intracardiac flow dynamics in mitral regurgitation: state of the art

Intracardiac flow dynamics is a complex phenomenon interrelated with cardiac mechanics. Today, it can be evaluated non-invasively using various imaging modalities, including echocardiography, magnetic resonance imaging, and computed tomography. This review explores the effects of mitral regurgitation on blood flow dynamics inside the left ventricular and atrial cavities and emphasizes the disruption of normal flow dynamics caused by mitral regurgitation, leading to turbulent flow and increased energy dissipation. It further examines the consequences of mitral valve repair and replacement, noting that, while repair generally improves intracardiac flow dynamics compared with replacement, residual flow disturbances may persist. Finally, the implications of abnormal intracardiac vorticity on left ventricular wall stress, myocardial remodelling, and thromboembolic risk are discussed.

Do blood flow patterns in the left atriums differ between left upper lobectomy and other lobectomies? A computational study

Background

Left atrial (LA) hemodynamics after lung lobectomies with pulmonary vein (PV) resection is widely understood to be a risk factor for LA thrombosis. A recent magnetic resonance imaging study showed that left upper lobectomy (LUL) with left superior pulmonary vein resection tended to cause LA flow patterns distinct from those of other lobectomies, with flow disturbances seen near the PV stump. However, little is known about this flow pattern because of severe image resolution limitations. The present study compared flow patterns in the LA after LUL with the flow patterns of other lobectomies using computational simulations.

Methods

The computational simulations of LA blood flow were conducted on the basis of four-dimensional computed tomography images of four lung cancer patients prior to lobectomies. Four kinds of PV resection cases were constructed by cutting each one of the PVs from the LA of each patient. We performed a total of five cases (pre-resection case and four PV resection cases) in each patient and evaluated global flow patterns formed by the remaining PV inflow, especially in the upper LA region.

Results

LUL tended to enhance the remaining left inferior PV inflow, with impingements seen in the right PV inflows in the upper LA region near the PV stump. These flow alterations induced viscous dissipation and the LUL cases had the highest values compared to other PV resection cases, especially in the LV systole in three patients, and reached three to four times higher than those in pre-resection cases. However, in another patient, these tendencies were weaker when PV inflow was stronger from the right side than from the left side, and the degree of flow dissipation was lower than those in other PV resection cases.

Conclusion

These findings suggest marked variations in LA flow patterns among patients after lobectomies and highlights the importance of patient-specific assessment of LA hemodynamics after lobectomies.

Computational study on hemodynamic effects of left superior pulmonary vein resection and associated physiological changes in the left atrium after left upper lobectomy

Left upper lobectomy (LUL) with left superior pulmonary vein (LSPV) resection alters the left atrium (LA) physiological states and LA hemodynamics associated with thrombosis, although this underlying mechanism is poorly understood. Therefore, we investigated the effects of LSPV resection and associated LA physiological changes on LA hemodynamics using four-dimensional computed tomography image-based computational simulations. Three cases were considered: the LA before and after LUL extracted from computed tomography images and artificial LSPV resection without physiological changes. Comparisons among the three cases demonstrated that physiological changes associated with LSPV resection are the possible factors that affect the LA hemodynamics after LUL.

Why 4D Flow MRI? Real Advantages

This special issue of Magnetic Resonance in Medical Sciences features the most recent reviews on 4D Flow MRI. These reviews deal with the current status of the emerging technique of 4D Flow MRI facilitated in various areas that are difficult to obtain with conventional flowmetry. MR signals inherently contain flow velocity information. In previous decades, in vivo blood flow measurement was traditionally performed by 2D methods, such as Doppler ultrasonography and 2D phase-contrast MRI, which have long been regarded as mature techniques in hemodynamic flowmetry. Although 2D velocimetries have many advantages over 4D Flow MRI in terms of cost and accessibility, and provide excellent temporal and in-plane spatial resolutions, they also have some disadvantages. The emerging technology of 4D Flow MRI can overcome the shortcomings of conventional 2D imaging. In recent years, hemodynamic analysis has witnessed significant progress that is primarily attributable to advances in 4D Flow MRI.