Longitudinal Changes in Left Ventricular Blood Flow Kinetic Energy After Myocardial Infarction: Predictive Relevance for Cardiac Remodeling.

BACKGROUND: Four-dimensional (4D) flow cardiac magnetic resonance (cardiac MR) imaging provides quantification of intracavity left ventricular (LV) flow kinetic energy (KE) parameters in three dimensions. ST-elevation myocardial infarction (STEMI) patients have been shown to have altered intracardiac blood flow compared to controls; however, how 4D flow parameters change over time has not been explored previously. PURPOSE: Measure longitudinal changes in intraventricular flow post-STEMI and ascertain its predictive relevance of long-term cardiac remodeling. STUDY TYPE: Prospective. POPULATION: Thirty-five STEMI patients (M:F = 26:9, aged 56 ± 9 years). FIELD STRENGTH/SEQUENCE: A 3 T/3D EPI-based, fast field echo (FFE) free-breathing 4D-flow sequence with retrospective cardiac gating. ASSESSMENT: Serial imaging at 3-7 days (V1), 3-months (V2), and 12-months (V3) post-STEMI, including the following protocol: functional imaging for measuring volumes and 4D-flow for calculating parameters including systolic and peakE-wave LVKE, normalized to end-diastolic volume (iEDV) and stroke volume (iSV). Data were analyzed by H.B. (3 years experience). Patients were categorized into two groups: preserved ejection fraction (pEF, if EF > 50%) and reduced EF (rEF, if EF < 50%). STATISTICAL TESTS: Independent sample t-tests were used to detect the statistical significance between any two cohorts. P < 0.05 was considered statistically significant. RESULTS: Across the cohort, systolic KEisv was highest at V1 (28.0 ± 4.4 µJ/mL). Patients with rEF retained significantly higher systolic KEisv than patients with pEF at V2 (18.2 ± 3.4 µJ/mL vs. 6.9 ± 0.6 µJ/mL, P < 0.001) and V3 (21.6 ± 5.1 µJ/mL vs. 7.4 ± 0.9 µJ/mL, P < 0.001). Patients with pEF had significantly higher peakE-wave KEiEDV than rEF patients throughout the study (V1: 25.4 ± 11.6 µJ/mL vs. 18.1 ± 9.9 µJ/mL, P < 0.03, V2: 24.0 ± 10.2 µJ/mL vs. 17.2 ± 12.2 µJ/mL, P < 0.05, V3: 27.7 ± 14.8 µJ/mL vs. 15.8 ± 7.6 µJ/mL, P < 0.04). DATA CONCLUSION: Systolic KE increased acutely following MI; in patients with pEF, this decreased over 12 months, while patients with rEF, this remained raised. Compared to patients with pEF, persistently lower peakE-wave KE in rEF patients is suggestive of early and fixed impairment in diastolic function. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY: Stage 3.

Comparison of fast acquisition strategies in whole-heart four-dimensional flow cardiac MR: Two-center, 1.5 Tesla, phantom and in vivo validation study.

PURPOSE: To validate three widely-used acceleration methods in four-dimensional (4D) flow cardiac MR; segmented 4D-spoiled-gradient-echo (4D-SPGR), 4D-echo-planar-imaging (4D-EPI), and 4D-k-t Broad-use Linear Acquisition Speed-up Technique (4D-k-t BLAST). MATERIALS AND METHODS: Acceleration methods were investigated in static/pulsatile phantoms and 25 volunteers on 1.5 Tesla MR systems. In phantoms, flow was quantified by 2D phase-contrast (PC), the three 4D flow methods and the time-beaker flow measurements. The later was used as the reference method. Peak velocity and flow assessment was done by means of all sequences. For peak velocity assessment 2D PC was used as the reference method. For flow assessment, consistency between mitral inflow and aortic outflow was investigated for all pulse-sequences. Visual grading of image quality/artifacts was performed on a four-point-scale (0 = no artifacts; 3 = nonevaluable). RESULTS: For the pulsatile phantom experiments, the mean error for 2D PC = 1.0 ± 1.1%, 4D-SPGR = 4.9 ± 1.3%, 4D-EPI = 7.6 ± 1.3% and 4D-k-t BLAST = 4.4 ± 1.9%. In vivo, acquisition time was shortest for 4D-EPI (4D-EPI = 8 ± 2 min versus 4D-SPGR = 9 ± 3 min, P < 0.05 and 4D-k-t BLAST = 9 ± 3 min, P = 0.29). 4D-EPI and 4D-k-t BLAST had minimal artifacts, while for 4D-SPGR, 40% of aortic valve/mitral valve (AV/MV) assessments scored 3 (nonevaluable). Peak velocity assessment using 4D-EPI demonstrated best correlation to 2D PC (AV:r = 0.78, P < 0.001; MV:r = 0.71, P < 0.001). Coefficient of variability (CV) for net forward flow (NFF) volume was least for 4D-EPI (7%) (2D PC:11%, 4D-SPGR: 29%, 4D-k-t BLAST: 30%, respectively). CONCLUSION: In phantom, all 4D flow techniques demonstrated mean error of less than 8%. 4D-EPI demonstrated the least susceptibility to artifacts, good image quality, modest agreement with the current reference standard for peak intra-cardiac velocities and the highest consistency of intra-cardiac flow quantifications. LEVEL OF EVIDENCE: 1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;47:272-281.

Four-dimensional flow cardiac magnetic resonance assessment of left ventricular diastolic function.

Left ventricular diastolic dysfunction is a major cause of heart failure and carries a poor prognosis. Assessment of left ventricular diastolic function however remains challenging for both echocardiography and conventional phase contrast cardiac magnetic resonance. Amongst other limitations, both are restricted to measuring velocity in a single direction or plane, thereby compromising their ability to capture complex diastolic hemodynamics in health and disease. Time-resolved three-dimensional phase contrast cardiac magnetic resonance imaging with three-directional velocity encoding known as '4D flow CMR' is an emerging technology which allows retrospective measurement of velocity and by extension flow at any point in the acquired 3D data volume. With 4D flow CMR, complex aspects of blood flow and ventricular function can be studied throughout the cardiac cycle. 4D flow CMR can facilitate the visualization of functional blood flow components and flow vortices as well as the quantification of novel hemodynamic and functional parameters such as kinetic energy, relative pressure, energy loss and vorticity. In this review, we examine key concepts and novel markers of diastolic function obtained by flow pattern analysis using 4D flow CMR. We consolidate the existing evidence base to highlight the strengths and limitations of 4D flow CMR techniques in the surveillance and diagnosis of left ventricular diastolic dysfunction.