Mohamad Ghosn

An in vitro validation of cardiac magnetic resonance 4D flow measurements with bioprosthetic mitral valve flow volumes quantification

Background Four dimensional flow MRI is a new methodology for evaluating the morphology of the heart using phase contrast cardiac magnetic resonance imaging not only in the usual three dimensions (x, y and z), but also across time. The full breadth of this new form of imaging has yet to be fully established. In order to evaluate this modality and its accuracy, we decided to use 4D flow MRI to quantify diastolic flow volumes across a bioprosthetic valve (BPV) in a controlled and reproducible in vitro system. Methods Three different sizes of BMV’s (27, 29, and 31 mm) were consecutively mounted in an MRI compatible flow loop where the flow conditions could be controlled using software that programmed a pump to generate pulsatile, physiologic ventricular ejection and filling simulations. The generated pulses were generated using each valve and mimicked diastolic flow volumes of about 70, 90 and 110 ml/beat at a rate of 70 bpm. An in-series ultrasonic flow transducer (UFT) was used to measure flow (L/min) by which diastolic flow volumes were determined. The acquisition of 3D cine (4D flow) phase contrast velocity data was acquired in a 1.5 Tesla MRI scanner (Avanto, Siemens Medical Solutions, Inc., Erlangen, Germany). The typical imaging parameters were: repetition time 45-48 ms, echo time 2.75 ms, flip angle 15°, slice thickness 1.5 mm, field of view 350 × 260 mm2, voxel size 1.5 × 1 × 1.25 mm3. The flow measurements were determined at 3 locations within the valve in post-imaging examination including at the valve base, leaflet tips, and midway between the base and the tips. Results

Four-dimensional flow cardiovascular magnetic resonance in aortic dissection: Assessment in an ex vivo model and preliminary clinical experience

Objective Four‐dimensional flow cardiovascular magnetic resonance may improve assessment of hemodynamics in patients with aortic dissection. The purpose of this study was to evaluate the feasibility and accuracy of 4‐dimensional flow cardiovascular magnetic resonance assessment of true and false lumens flow. Methods Thirteen ex vivo porcine aortic dissection models were mounted to a flow loop. Four‐dimensional flow cardiovascular magnetic resonance and 2‐dimensional phase‐contrast cardiovascular magnetic resonance measurements were performed, assessed for intraobserver and interobserver variability, and compared with a reference standard of sonotransducer flow volume measurements. Intraobserver and interobserver variability of 4‐dimensional flow cardiovascular magnetic resonance were also assessed in 14 patients with aortic dissection and compared with 2‐dimensional phase‐contrast cardiovascular magnetic resonance. Results In the ex vivo model, the intraobserver and interobserver measurements had Lins correlation coefficients of 0.98 and 0.96 and mean differences of 0.17 (±3.65) mL/beat and −0.59 (±5.33) mL/beat, respectively; 4‐dimensional and sonotransducer measurements had a Lins concordance correlation coefficient of 0.95 with a mean difference of 0.35 (±4.92) mL/beat, respectively. In patients with aortic dissection, the intraobserver and interobserver measurements had Lins concordance correlation coefficients of 0.98 and 0.97 and mean differences of −0.95 (±8.24) mL/beat and 0.62 (±10.05) mL/beat, respectively; 4‐dimensional and 2‐dimensional flow had a Lins concordance correlation coefficient of 0.91 with a mean difference of −9.27 (±17.79) mL/beat because of consistently higher flow measured with 4‐dimensional flow cardiovascular magnetic resonance in the ascending aorta. Conclusions Four‐dimensional flow cardiovascular magnetic resonance is feasible in patients with aortic dissection and can reliably assess flow in the true and false lumens of the aorta. This promotes potential future work on functional assessment of aortic dissection hemodynamics.

Left ventricular function in patients with hypertrophic cardiomyopathy and its relation to myocardial fibrosis and exercise tolerance

We sought to determine the relation between myocardial extracellular volume (ECV), left ventricular (LV) diastolic function, and exercise tolerance in patients with hypertrophic cardiomyopathy (HCM). Forty five HCM patients with an ejection fraction >50% and no previous septal reduction therapy underwent imaging by CMR and transthoracic echocardiography. CMR was used to quantify LV volumes, mass, EF, LA volumes, scar burden, pre and post contrast T1 relaxation times and ECV. Echocardiography was used to measure outflow tract gradients, mitral inflow and annular velocities, circumferential strain, systolic, early and late diastolic strain rates. Exercise duration and peak oxygen consumption were noted. HCM patients had increased native T1 relaxation time and ECV vs. controls [ECV controls: 24.7 (23.2–26.4) vs. HCM: 26.8 (24.6–31.3)%, P = 0.014]. Both parameters were significantly associated with LV diastolic dysfunction, circumferential strain, diastolic strain rate and peak oxygen consumption (r = −0.73, P < 0.001). Compared to controls, HCM patients have significantly longer native T1 relaxation time and higher ECV. These structural changes lead to worse LV global and segmental diastolic function and in turn reduced exercise tolerance.

Unmodified, autologous adipose-derived regenerative cells improve cardiac function, structure and revascularization in a porcine model of chronic myocardial infarction

Numerous studies have investigated cell-based therapies for myocardial infarction (MI), with mixed results. In the present study the left anterior descending (LAD) artery of pigs was occluded for 180 min. Four weeks later, the mean left ventricular ejection fraction (LVEF) was shown to have been reduced to approximately 35%. At that time, 18×106 unmodified, autologous adipose-derived regenerative cells (UA-ADRCs) were delivered into the LAD vein (control: delivery of saline). Six weeks following UA-ADRCs/saline delivery, the mean LVEF had increased by 18% (p<0.01) after delivery of UA-ADRCs, but was unchanged after delivery of saline. This is among the best outcome ever reported in studies on porcine animal models of cell-based therapies for MI in which functional outcome was assessed with cardiac magnetic resonance imaging. The unique combination of the procedure used for isolating UA-ADRCs, the late cell delivery time and the uncommon cell delivery route applied in the present study may open new horizons for cell-based therapies for MI.

Using transfer function approach to develop MRI visible and low RF heating sleeve for cardiac applicaion

A method is developed to evaluate the design of MRI visible and low heating catheter coating layer for cardiac and neuromodulation applications. The procedure consists of both experimental characterization of the coating layer as well as detailed electromagnetic simulation of human subject models during MRI procedure. Practical examples are used to demonstrate the effectiveness of this procedure.

DETECTION OF LEFT ATRIAL AND LEFT ATRIAL APPENDAGE THROMBUS BY CARDIAC MAGNETIC RESONANCE IN PATIENTS UNDERGOING PULMONARY VEIN ISOLATION

Evaluation of left atrial (LA)/left atrial appendage (LAA) thrombus and determination of pulmonary vein (PV) anatomy are important steps prior to PV isolation procedure. Transesophageal echocardiography (TEE) is a semi-invasive procedure that is currently a routine study for assessing LA/LAA

REPLACEMENT AND INTERSTITIAL FIBROSIS BY CARDIAC MR AND DIASTOLIC DYSFUNCTION IN PATIENTS WITH DILATED CARDIOMYOPATHY

Cardiac MR can be used to determine the extent of both replacement and interstitial fibrosis in patients with cardiomyopathies. We hypothesized that myocardial extracellular volume fraction (ECV) and scar burden by CMR are related to LV diastolic function in patients with dilated cardiomyopathy (DCM

Bioprosthetic Mitral Valve Effective Orifice Area Using 4D Flow Cardiac Magnetic Resonance Derived Time Velocity Integral. An In-Vitro Comparison with Doppler Echocardiography

\Background 4D Flow Cardiac Magnetic Resonance (CMR) is a novel imaging modality to assess bioprosthetic mitral valve (BMV) function. We describe a new, 4D Flow derived velocity time integral (TVI) based method to assess effective orifice area (EOA) for BMVs. Methods In our MRI-compatible circulatory loop 4 stented porcine BMVs (27, 29, 31, 33mm) underwent CMR with a 1.5T Siemens scanner. The valves were evaluated at forward stroke volumes of 70, 90 and 110ml at a beat rate of 70bpm. We plotted instantaneous peak velocities and calculated TVI for each scenario. 4D CMR-EOA was

Evaluating change of function after revascularization in patients with multi vessel coronary artery disease, severely reduced left ventricular systolic function and no scar on CMR imaging

Evaluating change of function after revascularization in patients with multi vessel coronary artery disease, severely reduced left ventricular systolic function and no scar on CMR imaging Alexander Ivanov, James Yossef, Ambreen Mohamed, Joshua Socolow, Iossif Gulkarov, Berhane Worku, Pairoj Chattranukulchai, Anthony Tortolani, Terrence Sacchi, Mohamad G Ghosn, Dipan J Shah, John D Grizzard, Robert W Biederman, Igor Klem, John Heitner

Examining the relationship between cardiac troponin T and cardiac morphology, function, and fibrosis - a cardiac magnetic resonance study

Background Elevated high sensitivity cardiac troponin (cTnT) levels, LVEF, and the degree of myocardial replacement fibrosis (RF) have been shown to be significantly associated with cardiovascular outcomes. However, the relationship amongst them has yet to be studied. Cardiac magnetic resonance (CMR) has become the gold standard for viability imaging and accurately characterizing RF. Recently, a new technique has been employed to quantify diffuse myocardial fibrosis via assessment of myocardial extracellular volume (ECV). The current study sought to investigate the association between ECV, RF, LVEF, LV mass (LVM) and cTnT levels.