Angioarchitecture and hemodynamics of microvascular arterio-venous malformations

In vitro characterisation of the patient-specific haemodynamics of an extracranial peripheral arteriovenous malformation using PIV

Peripheral Arteriovenous Malformations (pAVMs) are congenital vascular anomalies characterised by abnormal connections between arteries and veins that bypass the capillary network. This bypass results on a high-flow and low resistance vascular structure termed nidus. The high-flow and complex angioarchitecture of pAVMs makes treatment challenging and often suboptimal, as evidenced by high recurrence rates. Current treatment strategies rely on qualitative imaging techniques. Quantitative haemodynamic information on pAVMs can provide insight into the pathology and potentially enhance intervention outcomes. We report an experimental study on pAVMs haemodynamics resolved using patient-specific 3D-printed phantoms and Particle Image Velocimetry. A 3D printable porous structure was implemented to reproduce the pressure drop the blood flow experiences as it passes through the nidus, derived from in vivo patient data. Velocity measurements past the nidus revealed complex flow patterns, due to the high flow nature of the pAVM and the vessel anatomy which could potentially serve as biomarkers to assess the efficacy of interventions and the disease severity and progression. To the best of our knowledge this is the first in vitro study to combine patient-specific phantoms and detailed velocity distributions in a pAVM. The in vitro approach reported herein can be used for in silico model validation, physical intervention testing and to inform data driven methodologies that could all optimise pAVM procedures and reduce recurrence rates.

One-Dimensional Blood Flow Modeling in the Cardiovascular System. From the Conventional Physiological Setting to Real-Life Hemodynamics

Research in the dynamics of blood flow is essential to the understanding of one of the major driving forces of human physiology. The hemodynamic conditions experienced within the cardiovascular system generate a highly variable mechanical environment that propels its function. Modeling this system is a challenging problem that must be addressed at the systemic scale to gain insight into the interplay between the different time and spatial scales of cardiovascular physiology processes. The vast majority of scientific contributions on systemic-scale distributed parameter-based blood flow modeling have approached the topic under relatively simple scenarios, defined by the resting state, the supine position, and, in some cases, by disease. However, the physiological states experienced by the cardiovascular system considerably deviate from such conditions throughout a significant part of our life. Moreover, these deviations are, in many cases, extremely beneficial for sustaining a healthy life. On top of this, inter-individual variability carries intrinsic complexities, requiring the modeling of patient-specific physiology. The impact of modeling hypotheses such as the effect of respiration, control mechanisms, and gravity, the consideration of other-than-resting physiological conditions, such as those encountered in exercise and sleeping, and the incorporation of organ-specific physiology and disease have been cursorily addressed in the specialized literature. In turn, patient-specific characterization of cardiovascular system models is in its early stages. As for models and methods, these conditions pose challenges regarding modeling the underlying phenomena and developing methodological tools to solve the associated equations. In fact, under certain conditions, the mathematical formulation becomes more intricate, model parameters suffer greater variability, and the overall uncertainty about the system's working point increases. This paper reviews current advances and opportunities to model and simulate blood flow in the cardiovascular system at the systemic scale in both the conventional resting setting and in situations experienced in everyday life.

Congestive colopathy in a patient with arteriovenous malformations and multiple mesenteric thromboses

Arteriovenous malformations (AVMs) in mesenteric vessels are exceptionally rare. These congenital vascular anomalies lead to direct vascular flow between the highly pressured arterial system and the low-pressure venous system. We describe the case of a patient with prior left colectomy for splenic flexure colonic adenocarcinoma presenting with persistent abdominal pain after developing multiple mesenteric thromboses. CT and colonoscopy showed left hemicolon congestion, anastomotic stenosis and mucosal oedema. Mesenteric angiogram revealed AVMs in the right colic and left colic arteries. Embolisation of the left colic AVM led to symptom resolution without recurrence at interval follow-up.

3D bioprinted multilayered cerebrovascular conduits to study cancer extravasation mechanism related with vascular geometry

Cerebral vessels are composed of highly complex structures that facilitate blood perfusion necessary for meeting the high energy demands of the brain. Their geometrical complexities alter the biophysical behavior of circulating tumor cells in the brain, thereby influencing brain metastasis. However, recapitulation of the native cerebrovascular microenvironment that shows continuities between vascular geometry and metastatic cancer development has not been accomplished. Here, we apply an in-bath 3D triaxial bioprinting technique and a brain-specific hybrid bioink containing an ionically crosslinkable hydrogel to generate a mature three-layered cerebrovascular conduit with varying curvatures to investigate the physical and molecular mechanisms of cancer extravasation in vitro. We show that more tumor cells adhere at larger vascular curvature regions, suggesting that prolongation of tumor residence time under low velocity and wall shear stress accelerates the molecular signatures of metastatic potential, including endothelial barrier disruption, epithelial-mesenchymal transition, inflammatory response, and tumorigenesis. These findings provide insights into the underlying mechanisms driving brain metastases and facilitate future advances in pharmaceutical and medical research.

Cardiac and Hemodynamic Manifestations of Hereditary Hemorrhagic Telangiectasia

The autosomal dominant trait hereditary hemorrhagic telangiectasia (HHT) causes multiorgan dysplastic lesions of the vasculature that can activate multiple physiological cascades leading to a broad array of cardiovascular diseases. Up to 78% of patients with HHT develop hepatic arteriovenous malformations (AVMs), which cause a hyperdynamic circulatory state secondary to hepatic/portal shunting. This condition can eventually progress to high-output cardiac failure (HOCF) with continued peripheral tissue hypoxemia. Treatment for HOCF is often limited to supportive measures (diuretics and treatment of anemia); however, recent studies using systemic bevacizumab have shown promise by substantially reducing the cardiac index. In the context of liver AVMs and high cardiac output, the pulmonary vasculature can also experience high flow. Without adequate dilation of pulmonary vessels, post-capillary pulmonary hypertension can develop. Another form of pulmonary hypertension observed in HHT, pulmonary arterial hypertension, is caused by HHT-related mutations in ENG and ACVRL1 causing congestive arteriopathy. Post-capillary pathogenesis is addressed by reducing the high-output state, whereas the pre-capillary state is treated with supportive mechanisms (diuretics, oxygen) and agents targeting pulmonary vasoreactivity: endothelin-1 receptor antagonists and phosphodiesterase-5 inhibitors. If either form of pulmonary hypertension is left untreated or proves refractory and progresses, the common hemodynamic complication is right heart failure. Targeted right heart therapies involve similar strategies to those of pulmonary arterial hypertension, with several experimental approaches under study. In this review, we describe in detail the mechanisms of pathogenesis, diagnosis, and treatment of the hemodynamic complications and associated cardiovascular diseases that may arise in patients with HHT.

A Computational Framework for Pre-Interventional Planning of Peripheral Arteriovenous Malformations

PURPOSE

Peripheral arteriovenous malformations (pAVMs) are congenital lesions characterised by abnormal high-flow, low-resistance vascular connections-the so-called nidus-between arteries and veins. The mainstay treatment typically involves the embolisation of the nidus, however the complexity of pAVMs often leads to uncertain outcomes. This study aims at developing a simple, yet effective computational framework to aid the clinical decision making around the treatment of pAVMs using routinely acquired clinical data.

METHODS

A computational model was developed to simulate the pre-, intra-, and post-intervention haemodynamics of a patient-specific pAVM. A porous medium of varying permeability was employed to simulate the sclerosant effect on the nidus haemodynamics. Results were compared against clinical data (digital subtraction angiography, DSA, images) and experimental flow-visualization results in a 3D-printed phantom of the same pAVM.

RESULTS

The computational model allowed the simulation of the pAVM haemodynamics and the sclerotherapy-induced changes at different interventional stages. The predicted inlet flow rates closely matched the DSA-derived data, although the post-intervention one was overestimated, probably due to vascular system adaptations not accounted for numerically. The nidus embolization was successfully captured by varying the nidus permeability and increasing its hydraulic resistance from 0.330 to 3970 mmHg s ml-1. The nidus flow rate decreased from 71% of the inlet flow rate pre-intervention to 1%: the flow completely bypassed the nidus post-intervention confirming the success of the procedure.

CONCLUSION

The study demonstrates that the haemodynamic effects of the embolisation procedure can be simulated from routinely acquired clinical data via a porous medium with varying permeability as evidenced by the good qualitative agreement between numerical predictions and both in vivo and in vitro data. It provides a fundamental building block towards a computational treatment-planning framework for AVM embolisation.

Preoperative embolization of high-flow peripheral AVMs using plug and push technique with low-density NBCA/Lipiodol

Arteriovenous malformations (AVMs) embolization is considered as a promising option either its single treatment or in combination with surgery, and the use of low-density N-butyl cyanoacrylate (NBCA)/Lipiodol is acceptable mixture agents but its application should be performed by experienced endovascular teams. We describe a successful case preoperative embolization of high-flow AVMs with low-density NBCA/Lipiodol. A 26-year-old male patient was hospitalized with a big pulsatile mass at the right thigh. Doppler ultrasound showed a mass with high systolic, and diastolic velocities coming from the right superficial femoral artery. Angiogram showed a large and high-flow AVM type IV, according to Yakes classification. Low-density NBCA/Lipiodol 12.5% were performed to obstruct all the nidus and feeding arteries. Extirpation surgery was implemented 4 days after the complete embolization procedure.

Capillary-venule malformation is a microfistulous variant of arteriovenous malformation

OBJECTIVE

To describe typical clinical presentation of patients with microfistular, capillary-venule (CV) malformation as a variant form of arteriovenous malformations (AVM).

METHODS

A retrospective clinical analysis of 15 patients with CV-AVM confirmed by a computational flow model enrolled in a prospective database of patients with congenital vascular malformation between January 2008 and May 2018.

RESULTS

The mean age of the patients at first time of presentation was 30 years with balanced sex ratio. Presentation was dominated by soft tissue hypertrophy (n = 12 [80.0%]) and atypical varicose veins (n = 11 [73.3%]). The anatomic location of enlarged varicose veins gave no uniform pattern and did not correspond with the typical picture of primary varicose vein disease. Most often, symptomatic CV-AVM was found at the lower extremities in this series of unselected patients. The most frequent compartment affected was the subcutis (n = 14 [93.3%]), involvement of muscle was recorded in one-third and cutis in one-fourth of patients.

CONCLUSIONS

A high grade of clinical suspicion is needed to recognize CV-AVM and to prevent inadequate therapy owing to missed diagnosis.