Personne :
Garcia, Julio

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Structures organisationnelles
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Université Laval. Faculté de médecine
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Voici les éléments 1 - 10 sur 12
  • Publication
    Evaluation of aortic stenosis severity using 4D flow jet shear layer detection for the measurement of valve effective orifice area.
    (Pergamon Press, 2014-09-01) Garcia, Julio; Markl, Michael; Pibarot, Philippe; Schnell, Susanne; Allen, Bradley; Entezari, Pegah; Mahadevia, Riti; Malaisrie, S. Chris; Carr, J. C. (James C.); Barker, Alex J.
    Aims: The objective of this study was to evaluate the potential of 4D flow MRI to assess valve effective orifice area (EOA) in patients with aortic stenosis as determined by the jet shear layer detection (JSLD) method. Methods and Results: An in-vitro stenosis phantom was used for validation and in-vivo imaging was performed in 10 healthy controls and 40 patients with aortic stenosis. EOA was calculated by the JSLD method using standard 2D phase contrast MRI (PC-MRI) and 4D flow MRI measurements (EOAJSLD-2D and EOAJSLD-4D, respectively). As a reference standard, the continuity equation was used to calculate EOA (EOACE) with the 2D PC-MRI velocity field and compared to the EOAJSLD measurements. The in-vitro results exhibited excellent agreement between flow theory (EOA = 0.78 cm2) and experimental measurement (EOAJSLD-4D = 0.78 ±0.01 cm2) for peak velocities ranging from 0.9 to 3.7 m/s. In-vivo results showed good correlation and agreement between EOAJSLD-2D and EOACE (r = 0.91, p b 0.001; bias: -0.01 ± 0.38 cm2; agreement limits: 0.75 to -0.77 cm2), and between EOAJSLD-4D and EOACE (r = 0.95, p b 0.001; bias: -0.09 ± 0.26 cm2; limits: 0.43 to -0.62 cm2). Conclusion: This study demonstrates the feasibility of measuring EOAJSLD using 4D flow MRI. The technique allows for optimization of the EOA measurement position by visualizing the 3D vena contracta, and avoids potential sources of EOACE measurement variability.
  • Publication
    Accès libre
    On the evaluation of vorticity using cardiovascular magnetic resonance velocity measurements.
    (2013-10-24) Garcia, Julio; Larose, Éric; Kadem, Lyes; Pibarot, Philippe
    Vorticity and vortical structures play a fundamental role affect- ing the evaluation of energetic aspects (mainly left ventricle work) of cardiovascular function. Vorticity can be derived from cardiovascular magnetic resonance (CMR) imaging velocity measurements. However, several numerical schemes can be used to evaluate the vorticity field. The main objective of this work is to assess different numerical schemes used to evaluate the vor- ticity field derived from CMR velocity measurements. We com- pared the vorticity field obtained using direct differentiation schemes (eight-point circulation and Chapra) and derivate dif- ferentiation schemes (Richardson 4* and compact Richardson 4*) from a theoretical velocity field and in vivo CMR velocity measurements. In all cases, the effect of artificial spatial resolu- tion up-sampling and signal-to-noise ratio (SNR) on vorticity computation was evaluated. Theoretical and in vivo results showed that the eight-point circulation method underestimated vorticity. Up-sampling evaluation showed that the artificial improvement of spatial resolution had no effect on mean abso- lute vorticity estimation but it affected SNR for all methods. The Richardson 4* method and its compact version were the most accurate and stable methods for vorticity magnitude evaluation. Vorticity field determination using the eight-point circulation method, the most common method used in CMR, has reduced ac- curacy compared to other vorticity schemes. Richardson 4* and its compact version showed stable SNR using both theoretical and in vivo data.
  • Publication
    Accuracy of Doppler-echocardiographic parameters for the detection of aortic bileaflet mechanical prothetic valve dysfunction
    (Oxford University Press, 2014-02-01) Smadi, Othman; Garcia, Julio; Kadem, Lyes; Pibarot, Philippe; Gaillard, Emmanuel; Hassan, Ibrahim
    Aims : In vitro and in vivo studies were performed to evaluate the diagnostic accuracy of the different Doppler-echocardiographic parameters proposed in the American Society of Echocardiography guidelines to identify dysfunction of bileaflet mechanical valves (BMV) in the aortic position. Methods and results : Two models of BMV (St Jude HP, MCRI On-X) of different sizes (21;23;25;27 mm) were tested in vitro under a wide range of cardiac outputs (3–7 L/min). The motion of one or both leaflets was restricted to induce a mild (25% restriction in total valve orifice area) and moderate-to-severe (50% restriction in total valve area). Doppler-echocardiographic parameters of valve function were also measured in 17 patients with BMV of whom 4 had valve dysfunction confirmed by cinefluoroscopy. The specificity of all the parameters was high (in vitro: 83–100%; in vivo: 69–100%), but the sensitivity was low (range: 0–83% and 25–100%, respectively). A higher cut-off value for the ratio of peak left ventricular outflow tract velocity to peak aortic velocity or Doppler velocity index (DVI) (<0.35 instead of 0.3 or 0.25) improved the sensitivity (>90%) for the detection of moderate-to-severe dysfunction but remained low for mild dysfunction (50%). Furthermore, a difference of normal reference effective orifice area (EOA) minus measured EOA (EOA-D) >1 standard deviation identified mild and moderate-to-severe dysfunction with sensitivity of 61 and 100%, respectively. Conclusion : The Doppler-echocardiographic parameters and criteria proposed in the guidelines lack sensitivity for the detection of BMV dysfunction. The utilization of a DVI < 0.35 or an EOA-D > 1 SD improved the sensitivity (>90%) for the detection of moderate-to-severe dysfunction, but the sensitivity remained suboptimal (<65%) for detection of mild dysfunction.
  • Publication
    Normalized left ventricular workload using phase-contrast magnetic resonance imaging in patients with aortic stenosis.
    (Institute of Electrical and Electronics Engineers, 2014-08-31) Garcia, Julio; Keshavarz-Motamed, Zahra; Larose, Éric; Kadem, Lyes; Le Ven, Florent; Capoulade, Romain; Pibarot, Philippe
    Aortic stenosis (AS) severity contributes to the left ventricle (LV) deterioration due to the aortic valve narrowing and the alteration of systemic hemodynamic load. This load increment may also increase the LV stroke work (SW) which represent the required energy to deliver the blood at ejection. In this study, SW was derived from in-vivo cardiovascular magnetic resonance (CMR) velocity measurements (n=57) using a lumped-parametric model. Furthermore, normalized SW (N-SW) was evaluated as AS severity parameter. SW differentiated from normal flow (>35 mL/m2 ) and low flow (<35 mL/m2 ) states (p<0.05). N-SW showed a good association with valve effective orifice area (EOA, r=-0.5, p<0.001) and valvuloarterial impedance (ZVA, r=0.65, p<0.001). A severity threshold for N-SW (1.5 cJ/mL) was found using an EOA=1 cm2 as AS severity marker. CMR-derived SW and N-SW may be useful to the assessment and grading of AS patients.
  • Publication
    Accès libre
    Non-invasive determination of left ventricular workload in patients with aortic stenosis using magnetic resonance imaging and Doppler echocardiographye
    (Public Library of Science, 2014-01-28) Keshavarz-Motamed, Zahra; Garcia, Julio; Le Ven, Florent; Gaillard, Emmanuel; Capoulade, Romain; Pibarot, Philippe; Cloutier, Guy; Kadem, Lyes
    Early detection and accurate estimation of aortic stenosis (AS) severity are the most important predictors of successful longterm outcomes in patients. Current clinical parameters used for evaluation of the AS severity have several limitations including flow dependency. Estimation of AS severity is specifically challenging in patients with low-flow and low transvalvular pressure gradient conditions. A proper diagnosis in these patients needs a comprehensive evaluation of the left ventricle (LV) hemodynamic loads. This study has two objectives: (1) developing a lumped-parameter model to describe the ventricular-valvular-arterial interaction and to estimate the LV stroke work (SW); (2) introducing and validating a new index, the normalized stroke work (N-SW), to assess the global hemodynamic load imposed on the LV. N-SW represents the global hemodynamic load that the LV faces for each unit volume of blood ejected. The model uses a limited number of parameters which all can be measured non-invasively using current clinical imaging modalities. The model was first validated by comparing its calculated flow waveforms with the ones measured using Cardiovascular Magnetic Resonance (CMR) in 49 patients and 8 controls. A very good correlation and concordance were found throughout the cycle (median root mean square: 12.21 mL/s) and between the peak values (r = 0.98; SEE = 0.001, p,0.001). The model was then used to determine SW using the parameters measured with transthoracic Doppler-echocardiography (TTE) and CMR. N-SW showed very good correlations with a previously-validated index of global hemodynamic load, the valvular arterial impedance (ZVA), using data from both imaging modalities (TTE: r = 0.82, SEE = 0.01, p,0.001; CMR: r = 0.74, SEE = 0.01, p,0.001). Furthermore, unlike , N-SW was almost independent from variations in the flow rate. This study suggests that considering N-SW may provide incremental diagnostic and prognostic information, beyond what standard indices of stenosis severity and provide, particularly in patients with low LV outflow.
  • Publication
    Accès libre
    Comparison between cardiovascular magnetic resonance and transthoracic doppler echocardiography for the estimation of effective orifice area in aortic stenosis
    (2011-04-28) Garcia, Julio; Larose, Éric; Kadem, Lyes; Pibarot, Philippe; Clavel, Marie-Annick
    Background : The effective orifice area (EOA) estimated by transthoracic Doppler echocardiography (TTE) via the continuity equation is commonly used to determine the severity of aortic stenosis (AS). However, there are often discrepancies between TTE-derived EOA and invasive indices of stenosis, thus raising uncertainty about actual definite severity. Cardiovascular magnetic resonance (CMR) has emerged as an alternative method for non-invasive estimation of valve EOA. The objective of this study was to assess the concordance between TTE and CMR for the estimation of valve EOA. Methods and results : 31 patients with mild to severe AS (EOA range: 0.72 to 1.73 cm2) and seven (7) healthy control subjects with normal transvalvular flow rate underwent TTE and velocity-encoded CMR. Valve EOA was calculated by the continuity equation. CMR revealed that the left ventricular outflow tract (LVOT) cross-section is typically oval and not circular. As a consequence, TTE underestimated the LVOT cross-sectional area (ALVOT, 3.84 ± 0.80 cm2) compared to CMR (4.78 ± 1.05 cm2). On the other hand, TTE overestimated the LVOT velocity-time integral (VTILVOT: 21 ± 4 vs. 15 ± 4 cm). Good concordance was observed between TTE and CMR for estimation of aortic jet VTI (61 ± 22 vs. 57 ± 20 cm). Overall, there was a good correlation and concordance between TTE-derived and CMR-derived EOAs (1.53 ± 0.67 vs. 1.59 ± 0.73 cm2, r = 0.92, bias = 0.06 ± 0.29 cm2). The intra- and inter- observer variability of TTE-derived EOA was 5 ± 5% and 9 ± 5%, respectively, compared to 2 ± 1% and 7 ± 5% for CMR-derived EOA. Conclusion : Underestimation of ALVOT by TTE is compensated by overestimation of VTILVOT, thereby resulting in a good concordance between TTE and CMR for estimation of aortic valve EOA. CMR was associated with less intra- and inter- observer measurement variability compared to TTE. CMR provides a non-invasive and reliable alternative to Doppler-echocardiography for the quantification of AS severity.
  • Publication
    Discrepancies between cardiovascular magnetic resonance and Doppler echocardiography in the measurement of transvalvular gradient in aortic stenosis : the effect of flow vorticity.
    (M. Dekker, 2013-09-20) Garcia, Julio; Larose, Éric; Le Ven, Florent; Gaillard, Emmanuel; Kadem, Lyes; Capoulade, Romain; Pibarot, Philippe
    BACKGROUND: Valve effective orifice area EOA and transvalvular mean pressure gradient (MPG) are the most frequently used parameters to assess aortic stenosis (AS) severity. However, MPG measured by cardiovascular magnetic resonance (CMR) may differ from the one measured by transthoracic Doppler-echocardiography (TTE). The objectives of this study were: 1) to identify the factors responsible for the MPG measurement discrepancies by CMR versus TTE in AS patients; 2) to investigate the effect of flow vorticity on AS severity assessment by CMR; and 3) to evaluate two models reconciling MPG discrepancies between CMR/TTE measurements. METHODS: Eight healthy subjects and 60 patients with AS underwent TTE and CMR. Strouhal number (St), energy loss (EL), and vorticity were computed from CMR. Two correction models were evaluated: 1) based on the Gorlin equation (MPG(CMR-Gorlin)); 2) based on a multivariate regression model (MPG(CMR-Predicted)). RESULTS: MPGCMR underestimated MPGTTE (bias = -6.5 mmHg, limits of agreement from -18.3 to 5.2 mmHg). On multivariate regression analysis, St (p = 0.002), EL (p = 0.001), and mean systolic vorticity (p < 0.001) were independently associated with larger MPG discrepancies between CMR and TTE. MPG(CMR-Gorlin) and MPGTTE correlation and agreement were r = 0.7; bias = -2.8 mmHg, limits of agreement from -18.4 to 12.9 mmHg. MPG(CMR-Predicted) model showed better correlation and agreement with MPGTTE (r = 0.82; bias = 0.5 mmHg, limits of agreement from -9.1 to 10.2 mmHg) than measured MPGCMR and MPG(CMR-Gorlin). CONCLUSION: Flow vorticity is one of the main factors responsible for MPG discrepancies between CMR and TTE.
  • Publication
    Usefulness of cardiovascular magnetic resonance imaging for the evaluation of valve opening and closing kinetics in aortic stenosis
    (Oxford University Press, 2013-08-01) Garcia, Julio; Larose, Éric; Le Ven, Florent; Kadem, Lyes; Capoulade, Romain; Pibarot, Philippe
    Aims : The aims of this study were : (i) to determine the feasibility and reproducibility of the measurement of valve kinetic parameters by cardiovascular magnetic resonance (CMR) and (ii) to examine the association between these parameters and markers of a poor prognosis in patients with aortic stenosis (AS). Methods and results : Eight healthy control subjects and 71 patients with AS (0.60 cm2 = EOA = 1.90 cm2) underwent transthoracic echocardiography (TTE) and CMR. The valve opening slope (OS) and closing slope (CS) were calculated from instantaneous effective orifice area (EOA) curves obtained by CMR. Intra- and inter-observer variability were 4.8 ± 3.9 and 5.0 ± 4.1%, respectively, for OS, 3.8 ± 2.9 and 4.0 ± 3.1% for CS. OS was significantly related to the plasma level of NT-pro-brain natriuretic peptide (BNP) (r = -0.36, P = 0.002), whereas the EOA or gradient were not. Conclusion : This study demonstrates the excellent feasibility and reproducibility of CMR for the measurement of valve kinetic parameters in patients with AS. Larger studies are needed to confirm the incremental prognostic value of these new CMR parameters of aortic valve kinetics in patients with severe AS.
  • Publication
    Accès libre
    Cardiovascular magnetic resonance evaluation of aortic stenosis severity using single plane measurement of effective orifice area
    (M. Dekker, 2012-04-06) Garcia, Julio; Marrufo, Oscar R.; Larose, Éric; Rodriguez, Alfredo O.; Kadem, Lyes; Pibarot, Philippe
    BACKGROUND: Transthoracic echocardiography (TTE) is the standard method for the evaluation of the severity of aortic stenosis (AS). Valve effective orifice area (EOA) measured by the continuity equation is one of the most frequently used stenotic indices. However, TTE measurement of aortic valve EOA is not feasible or not reliable in a significant proportion of patients. Cardiovascular magnetic resonance (CMR) has emerged as a non-invasive alternative to evaluate EOA using velocity measurements. The objectives of this study were: 1) to validate a new CMR method using jet shear layer detection (JSLD) based on acoustical source term (AST) concept to estimate the valve EOA; 2) to introduce a simplified JSLD method not requiring vorticity field derivation. METHODS AND RESULTS: We performed an in vitro study where EOA was measured by CMR in 4 fixed stenoses (EOA = 0.48, 1.00, 1.38 and 2.11 cm²) under the same steady flow conditions (4-20 L/min). The in vivo study included eight (8) healthy subjects and 37 patients with mild to severe AS (0.72 cm² = EOA = 1.71 cm²). All subjects underwent TTE and CMR examinations. EOA was determinated by TTE with the use of continuity equation method (TTE(CONT)). For CMR estimation of EOA, we used 3 methods: 1) Continuity equation (CMR(CONT)); 2) Shear layer detection (CMR(JSLD)), which was computed from the velocity field of a single CMR velocity profile at the peak systolic phase; 3) Single plane velocity truncation (CMR(SPVT)), which is a simplified version of CMR(JSLD) method. There was a good agreement between the EOAs obtained in vitro by the different CMR methods and the EOA predicted from the potential flow theory. In the in vivo study, there was good correlation and concordance between the EOA measured by the TTE(CONT) method versus those measured by each of the CMR methods: CMR(CONT) (r = 0.88), CMR(JSLD) (r = 0.93) and CMR(SPVT) (r = 0.93). The intra- and inter- observer variability of EOA measurements was 5 ± 5% and 9 ± 5% for TTE(CONT), 2 ± 1% and 7 ± 5% for CMR(CONT), 7 ± 5% and 8 ± 7% for CMR(JSLD), 1 ± 2% and 3 ± 2% for CMR(SPVT). When repeating image acquisition, reproducibility of measurements was 10 ± 8% and 12 ± 5% for TTE(CONT), 9 ± 9% and 8 ± 8% for CMR(CONT), 6 ± 5% and 7 ± 4% for CMR(JSLD) and 3 ± 2% and 2 ± 2% for CMR(SPVT). CONCLUSION: There was an excellent agreement between the EOA estimated by the CMR(JSLD) or CMR(SPVT) methods and: 1) the theoretical EOA in vitro, and 2) the TTE(CONT) EOA in vivo. The CMR(SPVT) method was superior to the TTE and other CMR methods in terms of measurement variability. The novel CMR-based methods proposed in this study may be helpful to corroborate stenosis severity in patients for whom Doppler-echocardiography exam is inconclusive.
  • Publication
    Estimation of stroke volume and aortic valve area in patients with aortic stenosis : a comparison of echocardiography versus cardiovascular magnetic resonance
    (Elsevier, 2020-06-21) Guzzetti, Ezequiel; Garcia, Julio; Larose, Éric; Le Ven, Florent; Capoulade, Romain; Pibarot, Philippe; Bédard, Élisabeth; Clavel, Marie-Annick; Tastet, Lionel; Arsenault, Marie
    Background: In aortic stenosis, accurate measurement of left ventricular stroke volume (SV) is essential for the calculation of aortic valve area (AVA) and the assessment of flow status. Current American Society of Echocardiography and European Association of Cardiovascular Imaging guidelines suggest that measurements of left ventricular outflow tract diameter (LVOTd) at different levels (at the annulus vs 5 or 10 mm below) yield similar measures of SV and AVA. The aim of this study was to assess the effect of the location of LVOTd measurement on the accuracy of SV and AVA measured on transthoracic echocardiography (TTE) compared with cardiovascular magnetic resonance (CMR). Methods: One hundred six patients with aortic stenosis underwent both TTE and CMR. SV was estimated on TTE using the continuity equation with LVOTd measurements at four locations: at the annulus and 2, 5, and 10 mm below annulus. SV was also determined on CMR using phase contrast acquired in the aorta (SVCMR-PC), and a hybrid AVACMR-PC was calculated by diving SVCMR-PC by the transthoracic echocardiographic Doppler aortic velocity-time integral. Comparison between methods was made using Bland-Altman analysis. Results: Compared with the referent method of phase-contrast CMR for the estimation of SVCMR-PC and AVACMR-PC (SVCMR-PC 83 6 16 mL, AVACMR-PC 1.27 6 0.35 cm2 ), the best agreement was obtained by measuring LVOTd at the annulus or 2 mm below (P = NS), whereas measuring 5 and 10 mm below the annulus resulted in significant underestimation of SV and AVA by up to 15.9 6 17.3 mL and 0.24 6 0.28 cm2 , respectively (P < .01 for all). Accuracy for classification of low flow was best at the annulus (86%) and 2 mm below (82%), whereas measuring 5 and 10 mm below the annulus significantly underperformed (69% and 61%, respectively, P < .001). Conclusions: Measuring LVOTd at the annulus or very close to it provides the most accurate measures of SV and AVA, whereas measuring LVOTd 5 or 10 mm below significantly underestimates these parameters and leads to significant overestimation of the severity of aortic stenosis and prevalence of low-flow status.