Elena Di Martino | University of Calgary (original) (raw)

Papers by Elena Di Martino

Frontiers in Cardiovascular Medicine

Bicuspid aortic valve (BAV), which affects up to 2% of the general population, results from the a... more Bicuspid aortic valve (BAV), which affects up to 2% of the general population, results from the abnormal fusion of the cusps of the aortic valve. Patients with BAV are at a higher risk for developing aortic dilatation, a condition known as bicuspid aortopathy, which is associated with potentially life-threatening sequelae such as aortic dissection and aortic rupture. Although BAV biomechanics have been shown to contribute to aortopathy, their precise impact is yet to be delineated. Herein, we present the latest literature related to BAV biomechanics. We present the most recent definitions and classifications for BAV. We also summarize the current evidence pertaining to the mechanisms that drive bicuspid aortopathy. We highlight how aberrant flow patterns can contribute to the development of aortic dilatation. Finally, we discuss the role cardiac magnetic resonance imaging can have in assessing and managing patient with BAV and bicuspid aortopathy.

Frontiers in Mechanical Engineering

Collagen has an essential role in aortic biomechanics, and collagen remodeling has been associate... more Collagen has an essential role in aortic biomechanics, and collagen remodeling has been associated with the development and progression of aortic aneurysm. However, the exact mechanisms behind collagen remodeling and the biomechanical implications are not well understood. This study presents an investigation of the relationship between collagen remodeling in the aortic wall and biomechanics, by means of collagen assays, smooth muscle cell gene expression, and mechanical testing on human aortic specimens collected from patients with bicuspid aortic valve. Collagen assay analysis was employed to determine collagen-I and total collagen content; quantitative real-time PCR was used to determine amounts COL1A1 and COL3A1 expression in the tissue. These parameters were compared with the local biomechanical properties determined from biaxial and uniaxial tensile testing. Collagen-I content was found to relate to improved mechanical properties, while total collagen content did not exhibit a ...

Figure S1. Mesh and Corresponding CTA view throughout the cardiac cycle, for two separate subject... more Figure S1. Mesh and Corresponding CTA view throughout the cardiac cycle, for two separate subjects. For each patient, the upper panels depict the progression of the maximum principal strain distribution throughout the cardiac cycle. The lower panes depict the evolution of the aorta as seen in a CTA plane. (PNG 891 kb)

Frontiers in Cardiovascular Medicine, 2021

Background: Current clinical practice for the assessment of abdominal aortic aneurysms (AAA) is b... more Background: Current clinical practice for the assessment of abdominal aortic aneurysms (AAA) is based on vessel diameter and does not account for the multifactorial, heterogeneous remodeling that results in the regional weakening of the aortic wall leading to aortic growth and rupture. The present study was conducted to determine correlations between a novel non-invasive surrogate measure of regional aortic weakening and the results from invasive analyses performed on corresponding ex vivo aortic samples. Tissue samples were evaluated to classify local wall weakening and the likelihood of further degeneration based on non-invasive indices.Methods: A combined, image-based fluid dynamic and in-vivo strain analysis approach was used to estimate the Regional Aortic Weakness (RAW) index and assess individual aortas of AAA patients prior to elective surgery. Nine patients were treated with complete aortic resection allowing the systematic collection of tissue samples that were used to det...

Computers in biology and medicine, 2018

Mechanical stretch plays a major role in modulating atrial function, being responsible for beat-b... more Mechanical stretch plays a major role in modulating atrial function, being responsible for beat-by-beat responses to changes in chamber preload, enabling a prompt regulation of cardiac function. Mechano-electric coupling (MEC) operates through many mechanisms and has many targets, making it experimentally difficult to isolate causes and effects especially under sinus conditions where effects are more transient and subtle. Therefore, modelling is a powerful tool to help understand the role of MEC with respect to the atrial electromechanical interaction. We propose a cellular-based computational model of the left atrium that includes a strongly coupled MEC component and mitral flow component to account for correct pressure generation in the atrial chamber as a consequence of blood volume and contraction. The method was applied to a healthy porcine left atrium. Results of the strongly coupled simulation show that strains are higher in the areas adjacent to the mitral annulus, the rim o...

The Journal of thoracic and cardiovascular surgery, Jan 12, 2018

The objectives of this study were to investigate an association between the magnitude of flow-med... more The objectives of this study were to investigate an association between the magnitude of flow-mediated aortic wall shear stress (WSS) and medial wall histopathology in patients with bicuspid aortic valve (BAV) with aortopathy. Patients with BAV (n = 27; 52 ± 15 years; 3 women; proximal thoracic aorta diameter = 4.4 ± 0.7 and 4.6 ± 0.5 cm) who underwent prophylactic aortic resection received preoperative 3-dimensional time-resolved phase-contrast magnetic resonance imaging with 3-dimensional velocity encoding to quantify WSS relative to a population of healthy age- and sex-matched tricuspid aortic valve control participants (n = 20). Quantitative histopathology was conducted on BAV aorta tissue samples resected at surgery (n = 93), and correlation was performed between elastic fiber thickness and in vivo aortic WSS as continuous variables. Validation of elastic fiber thickness was achieved by correlation relative to tissue stiffness determined using biaxial biomechanical testing (n =...

The opening angle method is a popular choice in biomechanics to estimate residual stresses in art... more The opening angle method is a popular choice in biomechanics to estimate residual stresses in arteries. Experimentally, it means that an artery is cut into rings; then the rings are cut axially or radially allowing them to open into sectors; then the corresponding opening angles are measured to give residual stress levels by solving an inverse problem. However, for many tissues, for example in pathological tissues, the ring does not open according to the theory into a neat single circular sector, but rather creates an asymmetric geometry, often with abruptly changing curvature(s). This phenomenon may be due to a number of reasons including variation in thickness, microstructure, varying mechanical properties, etc. As a result, these samples are often eliminated from studies relying on the opening angle method, which limits progress in understanding and evaluating residual stresses in real arteries. With this work we propose an effective approach to deal with these non-trivial openings of rings. First, we digitize pictures of opened rings to split them into multiple, connected circular sectors. Then we measure the corresponding opening angles for each sub-sector. Finally, we can determine the non-homogeneous distribution of residual stresses for individual sectors in a closed ring configuration.

Applied Sciences

The current clinical guidelines for the management of aortic abdominal aneurysms (AAAs) overlook ... more The current clinical guidelines for the management of aortic abdominal aneurysms (AAAs) overlook the structural and mechanical heterogeneity of the aortic tissue and its role in the regional weakening that drives disease progression. This study is a comprehensive investigation of the structural and biomechanical heterogeneity of AAA tissue along the length and circumference of the aorta, by means of regional ex vivo and in vivo properties. Biaxial testing and histological analysis were performed on ex vivo human aortic specimens systematically collected during open repair surgery. Wall-shear stress and three-dimensional principal strain analysis were performed to allow for in vivo regional characterization of individual aortas. A marked effect of position along the aortic length was observed in both ex vivo and in vivo properties, with the central regions corresponding to the aneurysmal sac being significantly different from the adjacent regions. The heterogeneity along the circumfe...

Proceedings of the Canadian Engineering Education Association (CEEA), 2020

Diversity in engineering is a key goal, however a barrier for students from diverse backgrounds i... more Diversity in engineering is a key goal, however a barrier for students from diverse backgrounds is the physics requirements in engineering. Often, they will have to choose between the three sciences, and don’t realize that without physics, their options are limited. We launched a pilot program in 2019 to expand access into engineering. Students without high school physics can take a summer bridge program to teach them the fundamentals and prepare them for first year engineering. Physics is taught through bioengineering to leverage their biology background knowledge. This paper presents a thematic analysis of student reflections in the program, using student identity development as a framework.

The Journal of thoracic and cardiovascular surgery, 2018

Speckle tracking software and circumferential strain analysis of the ascending aorta. Central Mes... more Speckle tracking software and circumferential strain analysis of the ascending aorta. Central Message Advances in imaging-based analysis with biomechanical models have opened a path toward new and more effective clinical tools for risk assessment of aortic aneurysms.

Frontiers in cardiovascular medicine, 2018

Current recommendations for surgical treatment of abdominal aortic aneurysms (AAAs) rely on the a... more Current recommendations for surgical treatment of abdominal aortic aneurysms (AAAs) rely on the assessment of aortic diameter as a marker for risk of rupture. The use of aortic size alone may overlook the role that vessel heterogeneity plays in aneurysmal progression and rupture risk. The aim of the current study was to investigate intra-patient heterogeneity of mechanical and fluid mechanical stresses on the aortic wall and wall tissue histopathology from tissue collected at the time of surgical repair. Finite element analysis (FEA) and computational fluid dynamics (CFD) simulations were used to predict the mechanical wall stress and the wall shear stress fields for a non-ruptured aneurysm 2 weeks prior to scheduled surgery. During open repair surgery one specimen partitioned into different regions was collected from the patient's diseased aorta according to a pre-operative map. Histological analysis and mechanical testing were performed on the aortic samples and the results we...

BMC cardiovascular disorders, Jan 2, 2018

Functional impairment of the aorta is a recognized complication of aortic and aortic valve diseas... more Functional impairment of the aorta is a recognized complication of aortic and aortic valve disease. Aortic strain measurement provides effective quantification of mechanical aortic function, and 3-dimenional (3D) approaches may be desirable for serial evaluation. Computerized tomographic angiography (CTA) is routinely performed for various clinical indications, and offers the unique potential to study 3D aortic deformation. We sought to investigate the feasibility of performing 3D aortic strain analysis in a candidate population of patients undergoing transcatheter aortic valve replacement (TAVR). Twenty-one patients with severe aortic valve stenosis (AS) referred for TAVR underwent ECG-gated CTA and echocardiography. CTA images were analyzed using a 3D feature-tracking based technique to construct a dynamic aortic mesh model to perform peak principal strain amplitude (PPSA) analysis. Segmental strain values were correlated against clinical, hemodynamic and echocardiographic variabl...

The Annals of thoracic surgery, 2018

Aortic regurgitation is a prevalent, detrimental complication of left ventricular assist devices ... more Aortic regurgitation is a prevalent, detrimental complication of left ventricular assist devices (LVADs). The altered hemodynamics of LVADs results in aortic valves (AVs) having distinct mechanical stimulation. Our hypothesis was that the altered AV hemodynamics modulates the valve cells and matrix, resulting in changes in valvular mechanical properties that then can lead to regurgitation. AVs were collected from 16 LVAD and 6 non-LVAD patients at time of heart transplant. Standard demographic and preoperative data were collected and comparisons between the two groups were calculated using standard statistical methods. Samples were analyzed using biaxial mechanical tensile testing, mass spectrometry-based proteomics, and transmission electron microscopy to assess ultrastructure. The maximum circumferential leaflet strain in LVAD patients was less than in non-LVAD patients (0.35 ± 0.10MPa versus 0.52 ± 0.18 MPa, p = 0.03) with a trend of reduced radial strain (p = 0.06) and a tendenc...

Journal of Vascular Surgery, 2017

Objective: The objective of this study was to compare clinical outcomes of cyanoacrylate (CA) and... more Objective: The objective of this study was to compare clinical outcomes of cyanoacrylate (CA) and radiofrequency ablation (RFA) in the treatment of varicose veins at our institution. Methods: Between January 2014 and December 2016, there were 335 patients with 476 venous segments who were treated with either CA (n ¼ 148) or RFA (n ¼ 328) for varicose veins at the Vancouver General Hospital vascular clinic. Charts were reviewed to assess demographics of the patients, location and severity of disease, treatment details, and outcome at short-term and midterm follow-ups. Outcome parameters included treatment success and presence of short-term and midterm complications. Results: The average age of patients was 57 6 1 years, with the majority being female (78%) and with an average body mass index of 24.8 6 0.5. Clinical, Etiology, Anatomy, and Pathophysiology classes were 2 (49%), 3 (26%), 4a (22%), and >4b (3%). Of the 148 segments treated with CA, the vein types were as follows: 112 great saphenous veins (GSVs), 24 small saphenous veins, 2 accessory GSVs, and 8 perforator veins. The average amount of CA delivered for GSV treatment was 1.8 6 0.1 mL, with a treatment length of 43 6 1 cm. Subgroup comparison was done for GSV segments. Treatment success was 100% in CA and 99% in RFA. Superficial phlebitis was the most common complication noted at midterm follow-up in 5% of CA and 16% of RFA treatments. There was one patient in each group who had asymptomatic proximal thrombus extension treated with anticoagulation for 2 weeks. Three superficial glue protrusions requiring minor incision and drainage were noted in the CA group. Five patients in the RFA group had persistent numbness and two had nonhealing wounds at the access site. Conclusions: CA is a minimally invasive endovenous technique for treating varicose veins without the need of tumescent analgesia. In our experience, CA offers success rates equivalent to RFA with lower midterm complication rates.

Wound repair and regeneration : official publication of the Wound Healing Society [and] the European Tissue Repair Society, Mar 7, 2016

The gold standard treatment for full thickness injuries of the skin is autologous split-thickness... more The gold standard treatment for full thickness injuries of the skin is autologous split-thickness skin grafting. This involves harvesting the epidermis and superficial dermis from healthy skin and transplanting it onto the prepared wound bed. The donor site regenerates spontaneously, but the appendages and cellular components from the dermal layer are excluded from the graft. As a result, the new tissue is inferior; the healed graft site is dry/itchy, has decreased elasticity, increased fragility and altered sensory function. Because this dermal layer is composed of collagen and other extracellular matrix proteins, our aim was to characterize the changes in the dermal collagen after split thickness grafting that could contribute to a deficit in functionality. This will serve as a baseline for future studies designed to improve skin function using pharmacological or cell-based therapies for skin repair. We used a xenograft model whereby human split-thickness grafts were implanted int...

Advances in Bioengineering, 2002

The early benefits of an endovascular approach to abdominal aortic aneurysm (AAA) treatment has b... more The early benefits of an endovascular approach to abdominal aortic aneurysm (AAA) treatment has been reported by many authors [1,2]. One of the major advantages is that endovascular repair of AAA (EVAR) as opposed to traditional open surgery, is not a major abdominal surgery. EVAR has been shown to be associated with a death rate comparable to that of surgical repair [3]. In short term follow-up, EVAR is associated with fewer complications and a more rapid recovery [2]. On the contrary very limited data is available on long term follow-up of EVAR patients. Graft-related secondary interventions affect a consistent percentage of the treated cases. The EUROSTAR study [4] recently reported 13% of reintervention in 15.4 months. Our surgical unit reported 20.6% across 48 months in a recent review of 242 cases [3]. The frequence and type of reintervention, whose principal cause is endoleak or perigraft flow, requires careful consideration.Copyright © 2002 by ASME

Advances in Bioengineering, 2004

Abdominal aortic aneurysm (AAA), a localized dilation of the infrarenal aorta, represents a signi... more Abdominal aortic aneurysm (AAA), a localized dilation of the infrarenal aorta, represents a significant disease in the western population. There are approximately 200,000 patients in the US and 500,000 patients worldwide diagnosed with AAAs every year (Bosch, et al. 2001), and rupture of AAAs currently ranks as the 13th leading cause of death in the US. (Silverberg and Lubera 1987) In the past 30 years, the diagnosis of AAA has tripled in the Western world, and this will likely increase in the coming years as the average age of the population is increasing. (Bosch, et al. 2001)

ASME 2007 Summer Bioengineering Conference, 2007

Computational models, developed to study abdominal aortic aneurysm (AAA) biomechanics, demonstrat... more Computational models, developed to study abdominal aortic aneurysm (AAA) biomechanics, demonstrated that the presence of an intraluminal thrombus (ILT) can significantly alter the wall stress distribution in the degenerated vessel wall [1,2]. ILT is a soft hydrated tissue constituted of 90% of water. The solid porous matrix is made of a fibrin lattice entrapping solid aggregates, mostly platelets [3].. Although the ILT is subjected to compression in vivo, up to now ILT constitutive models have been based on parameters derived from tensile testing of ILT specimens [1]. The aim of this study was to define the biomechanical properties of ILT under compressive loads, using a combined experimental-numerical approach. ILT samples were tested for unconfined compression and permeation. A poroviscoelastic model was implemented to interpret the experimental data.

Medical Physics, 2010

Quantitative measurements of wall thickness in human abdominal aortic aneurysms ͑AAAs͒ may lead t... more Quantitative measurements of wall thickness in human abdominal aortic aneurysms ͑AAAs͒ may lead to more accurate methods for the evaluation of their biomechanical environment. Methods: The authors describe an algorithm for estimating wall thickness in AAAs based on intensity histograms and neural networks involving segmentation of contrast enhanced abdominal computed tomography images. The algorithm was applied to ten ruptured and ten unruptured AAA image data sets. Two vascular surgeons manually segmented the lumen, inner wall, and outer wall of each data set and a reference standard was defined as the average of their segmentations. Reproducibility was determined by comparing the reference standard to lumen contours generated automatically by the algorithm and a commercially available software package. Repeatability was assessed by comparing the lumen, outer wall, and inner wall contours, as well as wall thickness, made by the two surgeons using the algorithm. Results: There was high correspondence between automatic and manual measurements for the lumen area ͑r = 0.978 and r = 0.996 for ruptured and unruptured aneurysms, respectively͒ and between vascular surgeons ͑r = 0.987 and r = 0.992 for ruptured and unruptured aneurysms, respec-tively͒. The authors' automatic algorithm showed better results when compared to the reference with an average lumen error of 3.69%, which is less than half the error between the commercially available application Simpleware and the reference ͑7.53%͒. Wall thickness measurements also showed good agreement between vascular surgeons with average coefficients of variation of 10.59% ͑ruptured aneurysms͒ and 13.02% ͑unruptured aneurysms͒. Ruptured aneurysms exhibit significantly thicker walls ͑1.78Ϯ 0.39 mm͒ than unruptured ones ͑1.48Ϯ 0.22 mm͒, p = 0.044. Conclusions: While further refinement is needed to fully automate the outer wall segmentation algorithm, these preliminary results demonstrate the method's adequate reproducibility and low interobserver variability.

The Journal of Thoracic and Cardiovascular Surgery, 2003

A completely endoscopic approach has been achieved clinically in highly selected cases of coronar... more A completely endoscopic approach has been achieved clinically in highly selected cases of coronary revascularization, mitral valve repair, and closure of atrial septal defect using telerobotic manipulation systems. 1 However, a major drawback of endoscopic surgery is the lack of sensory feedback and the complete reliance on visual information. Computer-assisted techniques and tools are needed to supply the lacking tactile information. For example, tissue hardness may be transformed into a numerical value that could be interpreted as an index of what the surgeon would have felt with his fingers in open surgery. Highly sensitive and accurate sensors that replace human discrimination capabilities and that can be introduced inside the chest through small ports may improve the safety and reproducibility of endoscopic procedures. Microelectromechanical systems (MEMS) represent a recent technological advancement, sharing a fabrication process that enables the design and construction of integrated mechanical and electrical components that have dimensions in the range of micrometers. 2 The same concept that made microelectronics possible with the invention of the silicone-based integrated circuit can be adapted to produce small mechanical structures integrated with electrical components. The micromechanical component represents the interface for receiving information and for interacting with the physical world. MEMS technology might provide new opportunities for minimally invasive surgery because it enables the creation of miniaturized devices able to acquire and digitize information that can be integrated into endoscopic instruments. Moreover, MEMS have excellent mechanical resonance properties for manufacturing highly sensitive devices in which the measured quantity (eg, pressure, hardness, flow) is represented by a change in the resonant frequency of the sensor. 2,3 Current MEMS applications include pressure, chemical, and flow sensors; accelerometers; optical micromirrors; and fluid pumps that can be employed in strategic fields such as defense, environmental control, and the health sciences. 2 Although medical applications of MEMS technology are at an early stage, it is expected that the integration of sensors, actuators, and other microstructures with electronics will transform medicine and surgery. 3,4 A MEMS sensor for differentiating between different levels of rigidity in tissues has been recently developed (H-Probe; Verimetra Inc, Pittsburgh, Pa). The H-Probe consists of 4 components: (1) the outer support tube, (2) miniature bellows, (3) the sensing rod, and (4) a piezoresistive MEMS pressure sensor (Figure 1). By applying a controlled displacement of the outer support tube, the sensing rod is brought into contact with the tissue to be characterized. Further displacement of the outer support creates a reaction force with a magnitude representative of the hardness of the anatomical matter. The reaction force causes the sense rod to compress the miniature bellows, thus creating a pressure change within the bellows that is detected by the MEMS pressure sensor as a voltage output representative of the hardness of the tissue. We experimentally evaluated the H-Probe for its ability to discriminate different degrees of coronary arterial hardness. Six fresh porcine hearts were retrieved from 40-to 50-kg healthy adult pigs. The left anterior descending (LAD) coronary artery was left within its myocardial bed, removing a strip of ventricular tissue approximately 2 cm ϫ 4 cm ϫ wall thickness. Collateral vessels were ligated. Only the proximal and distal ends of the coronary artery were dissected free from the myocardium to allow cannulation and placement into a vessel loop system. A closed loop perfusion circuit was used to circulate sterile, oxygenated,