Andrea Guala

Politecnico di Torino, DIATI - Dipartimento di Ingegneria dell'Ambiente, dei Trasporti e delle Infrastrutture, Graduate Student

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Andrea Guala completed a Ph.D. at the Politecnico of Turin, designing a multi-scale model of the heart-arterial interaction and a subject-specific setting procedure based on non-invasive measurements. This model has been validated in real population and used to study arterial ageing and atrial fibrillation. His research interests cover the field of hemodynamics and large artery mechanics with a strong focus on the physical processes involved. Since May 2016 he started working on on MRI at VHIR.

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Papers by Andrea Guala

Raphe in bicuspid aortic valve without significant aortic valve disease is unrelated to aortic hemodynamics and stiffness

Revista Española de Cardiología (English Edition)

Simulating myocardial oxygen balance changes due to anti-hypertensive drugs

Artery Research

Influence of Aortic Dilation on the Regional Aortic Stiffness of Bicuspid Aortic Valve Assessed by 4-Dimensional Flow Cardiac Magnetic Resonance: Comparison With Marfan Syndrome and Degenerative Aortic Aneurysm

JACC. Cardiovascular imaging, Jan 11, 2018

This study sought to ascertain whether patients with a bicuspid aortic valve (BAV) have an intrin... more This study sought to ascertain whether patients with a bicuspid aortic valve (BAV) have an intrinsic alteration in regional aortic stiffness compared with patients with tricuspid aortic valve (TAV) and Marfan syndrome (MFS) patients with similar aortic sizes, as well as to assess the influence of ascending aorta (AAo) dilation on regional stiffness parameters in BAV patients. Imaging biomarkers as predictors of BAV, MFS, and degenerative AAo aneurysms in TAV patients (DA-TAV) are lacking. Biomechanical characterization has been proposed as a possible tool for further aneurysm stratification. Two hundred thirty-four subjects (136 BAV, 44 MFS, and 18 DA-TAV patients and 36 healthy control subjects) were included. The cardiac magnetic resonance protocol comprised 4-dimensional flow to assess AAo and descending aorta (DAo) pulse wave velocities (PWVs) and double-oblique, 2-dimensional, steady-state free-precession cine cardiac magnetic resonance to compute aortic distensibility (AD). On...

3D axial and circumferential wall shear stress from 4D flow MRI data using a finite element method and a laplacian approach

Magnetic resonance in medicine, 2018

To decompose the 3D wall shear stress (WSS) vector field into its axial (WSS) and circumferential... more To decompose the 3D wall shear stress (WSS) vector field into its axial (WSS) and circumferential (WSS) components using a Laplacian finite element approach. We validated our method with in silico experiments involving different geometries and a modified Poiseuille flow. We computed 3D maps of the WSS, WSS, and WSSusing 4D flow MRI data obtained from 10 volunteers and 10 patients with bicuspid aortic valve (BAV). We compared our method with the centerline method. The mean value, standard deviation, root mean-squared error, and Wilcoxon signed rank test are reported. We obtained an error <0.05% processing analytical geometries. We found good agreement between our method and the modified Poiseuille flow for the WSS, WSS, and WSS. We found statistically significance differences between our method and a 3D centerline method. In BAV patients, we found a 220% significant increase in the WSSin the ascending aorta with respect to volunteers. We developed a novel methodology to decompose ...

Mathematical modelling of cardiovascular fluid mechanics: physiology, pathology and clinical practice

Characterizing the Cardiovascular Functions During Atrial Fibrillation Through Lumped-Parameter Modeling

Fluid mechanics-based processes in the arterial ageing

Coronary fluid mechanics in an ageing cardiovascular system

Meccanica, 2015

Modelling and Subject-Specific Validation of the Heart-Arterial Tree System

Annals of Biomedical Engineering, 2014

Modelling and Subject-Specific Validation of the Heart-Arterial Tree System

Annals of Biomedical Engineering, 2014

Modelling and Subject-Specific Validation of the Heart-Arterial Tree System

Annals of Biomedical Engineering, 2014

Tridimensional Axial and Circumferential WSS from 4D flow data using a finite element method and a Laplacian approach

Magnetic resonance in medicine, 2017

Aortic Arch Tortuosity, a Novel Biomarker for Thoracic Aortic Disease, is increased in Adults with Bicuspid Aortic Valve

International Journal of Cardiology , 2019

Introduction: Arterial tortuosity has emerged as a predictor ofadverse outcomes in congenital aor... more Introduction: Arterial tortuosity has emerged as a predictor ofadverse outcomes in congenital aortopathies using 3D reconstructed images. We validated a new method to estimate aortic arch tortuosity on 2D CT. We hypothe- size that arch tortuosity may identify bicuspid aortic valve (BAV) patients at high risk to develop thoracic aortic aneurysms or aortic dissections (TAD). Methods: BAV subjects with chest CT scans were retrospectively identified in our clinical records and matched to tricuspid aortic valve (TAV) controls by age, gender, and presentation with TAD. Subjects with prior ascending aortic intervention were excluded. Measurements included aortic arch tortuosity, length, angle, width and height. Total aortic tortuosity was estimated in subjects with available abdominal images. Results: 120 BAV and 234 TAV subjects were included. Our 2D measurements were highly correlated with 3D midline arch measurements and had high inter- and intra-observer reliability. Compared to TAV, BAV subjects had increased arch tortuosity (median 1.76 [Q1-Q3: 1.62–1.95] vs. 1.63 [1.53–1.78], P b 0.01), length (149 [136–160] vs. 135 [122–152] mm, P b 0.01), height (46 [41–53] vs. 39 [34–47] mm, P b 0.01), and vertex acuity (70 [61–77] vs. 75 [68–81] degree, P b 0.01). In a multivariable analysis, arch tortuosity remained independently associated with BAV after adjusting for aortic diameter and other clinical characteristics. Conclusions: We found that aortic arch tortuosity is significantly increased in BAV and may identify BAV patients who are at increased risk for TAD. Further studies to evaluate the association between tortuosity and clinical out- comes are in progress.

Implications of asymmetry and valvular morphotype on echocardiographic measurements of aortic root in bicuspid aortic valve

J Am Soc Echocardiogr, 2018

Background: Transthoracic echocardiography (TTE) and magnetic resonance imaging (MRI) have yielde... more Background: Transthoracic echocardiography (TTE) and magnetic resonance imaging (MRI) have yielded excellent results in aortic root diameter measurement in patients with tricuspid aortic valve. However, accu- racy in bicuspid aortic valve (BAV), often associated with aortic root asymmetry, is not fully defined. The aim of this study was to determine the agreement between TTE and MRI in proximal ascending aortic diam- eters in patients with BAVs.
Methods: Seventy-six consecutive patients with BAVs (mean age, 53 6 15 years; 65% men) who underwent both TTE and MRI for ascending aortic assessment in a follow-up protocol were included in the study. Maximum aortic root and ascending aortic diameters were compared.
Results: For the whole population, TTE slightly underestimated aortic root diameter (difference, ?0.8 6 2.9 mm; P = .02). However, agreement was significantly better in BAV with fusion of the left and right coronary cusps than with fusion of the right coronary and noncoronary cusps, both with (type 1) and without (type 0) raphe (mean difference, 0.1 6 2.5 vs ?2.8 6 2.8 mm, P < .001, respec- tively). In raphe BAV, mean absolute differences of maximum diameters between both techniques were significantly greater in asymmetric versus symmetric aortic roots (3.3 6 2.2 vs 1.6 6 1.9 mm, P = .002). BAV type and root asymmetry were independent related to measurement disagreement be- tween both modalities.
Conclusions: Although TTE is the technique of choice in the follow-up of patients with BAVs, aortic root diam- eter measurements may be inaccurate in the presence of root asymmetry and in BAV with fusion of the right coronary and noncoronary cusps. In these cases, cross-sectional imaging, with MRI or computed tomogra- phy, to confirm aortic diameters may be advisable

Familial clustering of biscupid aortic valve and its relationship with aortic dilation in first-degree relatives

Heart, 2018

Objective Bicuspid aortic valve (BaV) is the most common congenital heart disease. this study aim... more Objective Bicuspid aortic valve (BaV) is the most common congenital heart disease. this study aimed to determine the prevalence rate of BaV in first-degree relatives (FDr) and the inheritance pattern according to different morphotypes and aortic dilation. Methods BaV probands were consecutively studied at eight tertiary referral centres. after sequential screening, FDr were included in the study. the BaV morphotype, aortic dilation and aortic phenotype were assessed by transthoracic echocardiography. results seven hundred and twenty-four FDr of 256 BaV probands agreed to undergo family screening. the prevalence of BaV was 6.4% in FDr (9.2% in men, 3.5% in women, p=0.002). aortic dilation was diagnosed in 9.6% of FrD with tricuspid aortic valves (taV), with a root phenotype in 2.7% and tubular in 6.9% and more frequently in the presence of arterial hypertension (Or 4.48; ci 95% 2.51 to 7.99; p=0.0001) and valvular regurgitation (Or 5.87, ci 95% 1.37 to 25.16; p=0.025). the heritability (h2) of BaV was highly significant (0.47; p=0.002); however, no concordance was observed among valve morphotypes. aortic dilation heritability was not significant. Conclusions the BaV prevalence rate in FDr was low (6.4%) but aortic dilation was observed in 9.6% of FDr with taV. the heritability of BaV was high without concordance in valve morphotypes, and aortic dilation heritability was not observed. Patients with BaV should be made aware of its familial pattern

Multiscale mathematical modelling vs. generalized transfer function approach for aortic pressure estimation: a comparison with invasive data

Hypertension Research, 2019

We aimed to evaluate the performance of a mathematical model and currently available non-invasive... more We aimed to evaluate the performance of a mathematical model and currently available non-invasive techniques (generalized transfer function (GTF) method and brachial pressure) in the estimation of aortic pressure. We also aimed to investigate error dependence on brachial pressure errors, aorta-to-brachial pressure changes and demographic/clinical conditions. Sixty-two patients referred for invasive hemodynamic evaluation were consecutively recruited. Simultaneously, the registration of the aortic pressure using a fluid-filled catheter, brachial pressure and radial tonometric waveform was recorded. Accordingly, the GTF device and mathematical model were set. Radial invasive pressure was recorded soon after aortic measurement. The average invasive aortic pressure was 141.3 ± 20.2/76 ± 12.2 mm Hg. The simultaneous brachial pressure was 144 ± 17.8/ 81.5 ± 11.7 mm Hg. The GTF-based and model-based aortic pressure estimates were 133.1 ± 17.3/82.4 ± 12 and 137 ± 21.6/ 72.2 ± 16.7 mm Hg, respectively. The Bland-Altman plots showed a marked tendency to pressure overestimation for increasing absolute values, with the exclusion of mathematical model diastolic estimations. The systolic pressure was increased from the aortic to radial locations (7.5 ± 19 mm Hg), while the diastolic pressure was decreased (3.8 ± 9.8 mm Hg). The brachial pressure underestimated the systolic and overestimated diastolic intra-arterial radial pressure. GTF errors were independently correlated with the variability in pulse pressure amplification and with the brachial error. Errors of the mathematical model were related to only demographic and clinical conditions. Neither a multiscale mathematical model nor a generalized transfer function device substantially outperformed the oscillometric brachial pressure in the estimation of aortic pressure. Mathematical modeling should be improved by including further patient-specific conditions, while the variability in pulse pressure amplification may hamper the performance of the GTF method in patients at the risk of coronary artery disease.

Aortic flow patterns and wall shear stress maps by 4D-flow MRI in the assessment of aortic dilatation in bicuspid aortic valve

Journal of Cardiovascular Magnetic Resonance, 2018

Abstract Background: In patients with bicuspid valve (BAV), ascending aorta (AAo) dilatation may ... more Abstract
Background: In patients with bicuspid valve (BAV), ascending aorta (AAo) dilatation may be caused by altered flow patterns and wall shear stress (WSS). These differences may explain different aortic dilatation morphotypes. Using 4D- flow cardiovascular magnetic resonance (CMR), we aimed to analyze differences in flow patterns and regional axial and circumferential WSS maps between BAV phenotypes and their correlation with ascending aorta dilatation morphotype. Methods: One hundred and one BAV patients (aortic diameter ≤ 45 mm, no severe valvular disease) and 20 healthy subjects were studied by 4D-flow CMR. Peak velocity, flow jet angle, flow displacement, in-plane rotational flow (IRF) and systolic flow reversal ratio (SFRR) were assessed at different levels of the AAo. Peak-systolic axial and circumferential regional WSS maps were also estimated. Unadjusted and multivariable adjusted linear regression analyses were used to identify independent correlates of aortic root or ascending dilatation. Age, sex, valve morphotype, body surface area, flow derived variables and WSS components were included in the multivariable models. Results: The AAo was non-dilated in 24 BAV patients and dilated in 77 (root morphotype in 11 and ascending in 66). BAV phenotype was right-left (RL-) in 78 patients and right-non-coronary (RN-) in 23. Both BAV phenotypes presented different outflow jet direction and velocity profiles that matched the location of maximum systolic axial WSS. RL-BAV velocity profiles and maximum axial WSS were homogeneously distributed right-anteriorly, however, RN-BAV showed higher variable profiles with a main proximal-posterior distribution shifting anteriorly at mid-distal AAo. Compared to controls, BAV patients presented similar WSS magnitude at proximal, mid and distal AAo (p = 0.764, 0.516 and 0.053, respectively) but lower axial and higher circumferential WSS components (p < 0.001 for both, at all aortic levels). Among BAV patients, RN-BAV presented higher IRF at all levels (p = 0.024 proximal, 0.046 mid and 0.002 distal AAo) and higher circumferential WSS at mid and distal AAo (p = 0.038 and 0.046, respectively) than RL-BAV. However, axial WSS was higher in RL-BAV compared to RN-BAV at proximal and mid AAo (p = 0.046, 0.019, respectively). Displacement and axial WSS were independently associated with the root-morphotype, and circumferential WSS and SFRR with the ascending-morphotype
Conclusions: Different BAV-phenotypes present different flow patternswithananteriordistributioninRL-BAV, whereas, RN-BAV patients present a predominant posterior outflow jet at the sinotubular junction that shifts to anterior or right anterior in mid and distal AAo. Thus, RL-BAV patients present a higher axial WSS at the aortic root while RN-BAV present a higher circumferential WSS in mid and distal AAo. These results may explain different AAo dilatation morphotypes in the BAV population

InfluenceofAorticDilationonthe Regional Aortic Stiffness of Bicuspid Aortic Valve Assessed by 4-Dimensional Flow Cardiac Magnetic Resonance. Comparison With Marfan Syndrome and Degenerative Aortic Aneurysm

JACC cardiovascular imaging, 2019

OBJECTIVES This study sought to ascertain whether patients with a bicuspid aortic valve (BAV) hav... more OBJECTIVES This study sought to ascertain whether patients with a bicuspid aortic valve (BAV) have an intrinsic alteration in regional aortic stiffness compared with patients with tricuspid aortic valve (TAV) and Marfan syndrome (MFS) patients with similar aortic sizes, as well as to assess the influence of ascending aorta (AAo) dilation on regional stiffness parameters in BAV patients.
BACKGROUND Imaging biomarkers as predictors of BAV, MFS, and degenerative AAo aneurysms in TAV patients (DA-TAV) are lacking. Biomechanical characterization has been proposed as a possible tool for further aneurysm stratification.
METHODS Two hundred thirty-four subjects (136 BAV, 44 MFS, and 18 DA-TAV patients and 36 healthy control subjects) were included. The cardiac magnetic resonance protocol comprised 4-dimensional flow to assess AAo and descending aorta (DAo) pulse wave velocities (PWVs) and double-oblique, 2-dimensional, steady-state free-precession cine cardiac magnetic resonance to compute aortic distensibility (AD).
RESULTS On adjusted analysis, nondilated BAV patients had similar PWV and AD as healthy control subjects in both AAo and DAo, whereas dilated BAV did not differ from DA-TAV. In contrast, AAo and DAo stiffness in MFS patients was markedly greater than in BAV patients, increasing slightly with dilation severity. AAo PWV showed a biphasic pattern in BAV patients: it first decreased and then increased throughout AAo dilation, with a clear turning point at 50 mm, whereas distensibility did not discern mildly dilated aorta. In multivariate analysis adjusted for clinical and demographic characteristics, only PWV was related to AAo dilation in BAV patients.
CONCLUSIONS The mechanical properties of AAo aneurysms are similar in BAV and TAV patients, whereas MFS patients have a stiffer aorta. Aortic stiffness strongly depends on dilation severity. AAo PWV resulted in a potentially clinically useful biphasic trend with respect to aneurysm diameter, whereas distensibility did not discern mildly dilated aorta. Beyond clinical risk factors, PWV but not AD was independently related to AAo dilation in BAV patients

Measuring the interaction between the macro- and micro-vasculature

Frontiers in cardiovascular medicine, 2019

Structural and functional dysfunction in both the macro- and microvasculature are a feature of es... more Structural and functional dysfunction in both the macro- and microvasculature are a feature of essential hypertension. In a healthy cardiovascular system, the elastic properties of the large arteries ensure that pulsations in pressure and flow generated by cyclic left ventricular contraction are dampened, so that less pulsatile pressure and flow are delivered at the microvascular level. However, in response to aging, hypertension, and other disease states, arterial stiffening limits the buffering capacity of the elastic arteries, thus exposing the microvasculature to increased pulsatile stress. This is thought to be particularly pertinent to high flow/low resistance organs such as the brain and kidney, which may be sensitive to excess pressure and flow pulsatility, damaging capillary networks, and resulting in target organ damage. In this review, we describe the clinical relevance of the pulsatile interaction between the macro- and microvasculature and summarize current methods for measuring the transmission of pulsatility between the two sites

Increased rotational flow in the proximal aortic arch contributes to its dilation in bicuspid aortic valve disease

European Heart Journal cardiovascular imaging, 2019

Aims Aortic dilation in bicuspid aortic valve (BAV) might extend to the proximal arch. Arch flow ... more Aims
Aortic dilation in bicuspid aortic valve (BAV) might extend to the proximal arch. Arch flow dynamics and their re- lationship with this segment dilation are still unexplored. Using 4D-flow cardiovascular magnetic resonance, we analysed flow dynamics in the arch for each BAV morphotype and their association with this segment dilation.

Methods
One hundred and eleven BAV patients (aortic diameters <_55mm, non-severe valvular disease), 21 age-matched tri-
and results
cuspid aortic valve (TAV) patients with dilated arch and 24 healthy volunteers (HV) underwent 4D-flow. BAV were classified per fusion morphotype: 75% right-left (RL-BAV), and per arch dilation: 57% dilated, mainly affecting the right-noncoronary (RN) BAV (86% dilated vs. 47% in RL-BAV). Peak velocity, jet angle, normalized displacement, in- plane rotational flow (IRF), wall shear stress, and systolic flow reversal ratio (SFRR) were calculated along the thor- acic aorta. ANCOVA and multivariate linear regression analyses were used to identify correlates of arch dilation. BAV had higher rotational flow and eccentricity than TAV in the proximal arch. Dilated compared with non-dilated BAV had higher IRF being more pronounced in the RN-morphotype. RN-BAV, IRF, and SFRR were independently associated with arch dilation. Aortic stenosis and male sex were independently associated with arch dilation in RL- BAV. Flow parameters associated with dilation converged to the values found in HV in the distal arch.

Conclusions
Increased rotational flow could explain dilation of the proximal arch in RN-BAV and in RL-BAV patients of male sex and with valvular stenosis. These patients may benefit from a closer follow-up with cardiac magnetic resonance or computed tomography

Andrea Guala

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