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.

Acute intra-cavity 4D flow cardiovascular magnetic resonance predicts long-term adverse remodelling following ST-elevation myocardial infarction.

BACKGROUND: Despite advancements in percutaneous coronary intervention, a significant proportion of ST-elevation myocardial infarction (STEMI) survivors develop long-term adverse left ventricular (LV) remodelling, which is associated with poor prognosis. Adverse remodelling is difficult to predict, however four-dimensional (4D) flow cardiovascular magnetic resonance (CMR) can measure various aspects of LV intra-cavity flow beyond LV ejection fraction and is well equipped for exploring the underlying mechanical processes driving remodelling. The aim for this study was to compare acute 4D flow CMR parameters between patients who develop adverse remodelling with patients who do not. METHODS: Fifty prospective 'first-event' STEMI patients underwent CMR 5 days post-reperfusion, which included cine-imaging, and 4D flow for assessing in-plane kinetic energy (KE), residual volume, peak-E and peak-A wave KE (indexed for LV end-diastolic volume [LVEDV]). All subjects underwent follow-up cine CMR imaging at 12 months to identify adverse remodelling (defined as 20% increase in LVEDV from baseline). Quantitative variables were compared using unpaired student's t-test. Tests were deemed statistically significant when p < 0.05. RESULTS: Patients who developed adverse LV remodelling by 12 months had significantly higher in-plane KE (54 ± 12 vs 42 ± 10%, p = 0.02), decreased proportion of direct flow (27 ± 9% vs 11 ± 4%, p < 0.01), increased proportion of delayed ejection flow (22 ± 9% vs 12 ± 2, p < 0.01) and increased proportion of residual volume after 2 consecutive cardiac cycles (64 ± 14 vs 34 ± 14%, p < 0.01), in their acute scan. CONCLUSION: Following STEMI, increased in-plane KE, reduced direct flow and increased residual volume in the acute scan were all associated with adverse LV remodelling at 12 months. Our results highlight the clinical utility of acute 4D flow in prognostic stratification in patients following myocardial infarction.

Insight Into Myocardial Microstructure of Athletes and Hypertrophic Cardiomyopathy Patients Using Diffusion Tensor Imaging.

BACKGROUND: Hypertrophic cardiomyopathy (HCM) remains the commonest cause of sudden cardiac death among young athletes. Differentiating between physiologically adaptive left ventricular (LV) hypertrophy observed in athletes' hearts and pathological HCM remains challenging. By quantifying the diffusion of water molecules, diffusion tensor imaging (DTI) MRI allows voxelwise characterization of myocardial microstructure. PURPOSE: To explore microstructural differences between healthy volunteers, athletes, and HCM patients using DTI. STUDY TYPE: Prospective cohort. POPULATION: Twenty healthy volunteers, 20 athletes, and 20 HCM patients. FIELD STRENGTH/SEQUENCE: 3T/DTI spin echo. ASSESSMENT: In-house MatLab software was used to derive mean diffusivity (MD) and fractional anisotropy (FA) as markers of amplitude and anisotropy of the diffusion of water molecules, and secondary eigenvector angles (E2A)-reflecting the orientations of laminar sheetlets. STATISTICAL TESTS: Independent samples t-tests were used to detect statistical significance between any two cohorts. Analysis of variance was utilized for detecting the statistical difference between the three cohorts. Statistical tests were two-tailed. A result was considered statistically significant at P ≤ 0.05. RESULTS: DTI markers were significantly different between HCM, athletes, and volunteers. HCM patients had significantly higher global MD and E2A, and significantly lower FA than athletes and volunteers. (MDHCM = 1.52 ± 0.06 × 10-3 mm2 /s, MDAthletes = 1.49 ± 0.03 × 10-3 mm2 /s, MDvolunteers = 1.47 ± 0.02 × 10-3 mm2 /s, P < 0.05; E2AHCM = 58.8 ± 4°, E2Aathletes = 47 ± 5°, E2Avolunteers = 38.5 ± 7°, P < 0.05; FAHCM = 0.30 ± 0.02, FAAthletes = 0.35 ± 0.02, FAvolunteers = 0.36 ± 0.03, P < 0.05). HCM patients had significantly higher E2A in their thickest segments compared to the remote (E2Athickest = 66.8 ± 7, E2Aremote = 51.2 ± 9, P < 0.05). DATA CONCLUSION: DTI depicts an increase in amplitude and isotropy of diffusion in the myocardium of HCM compared to athletes and volunteers as reflected by increased MD and decreased FA values. While significantly higher E2A values in HCM and athletes reflect steeper configurations of the myocardial sheetlets than in volunteers, HCM patients demonstrated an eccentric rise in E2A in their thickest segments, while athletes demonstrated a concentric rise. Further studies are required to determine the diagnostic capabilities of DTI. EVIDENCE LEVEL: 1 TECHNICAL EFFICACY STAGE: 2.