Clinical assessment of aortic valve stenosis: Comparison between 4D flow MRI and transthoracic echocardiography.

BACKGROUND: The prevalence of valvular aortic stenosis (AS) increases as the population ages. Echocardiographic measurements of peak jet velocity (Vpeak ), mean pressure gradient (Pmean ), and aortic valve area (AVA) determine AS severity and play a pivotal role in the stratification towards valvular replacement. A multimodality imaging approach might be needed in cases of uncertainty about the actual severity of the stenosis. PURPOSE: To compare four-dimensional phase-contrast magnetic resonance (4D PC-MR), two-dimensional (2D) PC-MR, and transthoracic echocardiography (TTE) for quantification of AS. STUDY TYPE: Prospective. POPULATION: Twenty patients with various degrees of AS (69.3 ± 5.0 years). FIELD STRENGTH/SEQUENCES: 4D PC-MR and 2D PC-MR at 3T. ASSESSMENT: We compared Vpeak , Pmean , and AVA between TTE, 4D PC-MR, and 2D PC-MR. Flow eccentricity was quantified by means of normalized flow displacement, and its influence on the accuracy of TTE measurements was investigated. STATISTICAL TESTS: Pearson's correlation, Bland-Altman analysis, paired t-test, and intraclass correlation coefficient. RESULTS: 4D PC-MR measured higher Vpeak (r = 0.95, mean difference + 16.4 ± 10.7%, P <0.001), and Pmean (r = 0.92, mean difference + 14.9 ± 16.0%, P = 0.013), but a less critical AVA (r = 0.80, mean difference + 19.9 ± 20.6%, P = 0.002) than TTE. In contrast, unidirectional 2D PC-MR substantially underestimated AS severity when compared with TTE. Differences in Vpeak between 4D PC-MR and TTE showed to be strongly correlated with the eccentricity of the flow jet (r = 0.89, P <0.001). Use of 4D PC-MR improved the concordance between Vpeak and AVA (from 0.68 to 0.87), and between PGmean and AVA (from 0.68 to 0.86). DATA CONCLUSION: 4D PC-MR improves the concordance between the different AS parameters and could serve as an additional imaging technique next to TTE. Future studies should address the potential value of 4D PC-MR in patients with discordant echocardiographic parameters. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2020;51:472-480.

Adding Speckle-Tracking Echocardiography to Visual Assessment of Systolic Wall Motion Abnormalities Improves the Detection of Myocardial Infarction.

BACKGROUND: The aim of this study was to investigate whether speckle-tracking echocardiography (STE) improves the detection of myocardial infarction (MI) over visual assessment of systolic wall motion abnormalities (SWMAs) using delayed enhancement cardiac magnetic resonance imaging as a reference. METHODS: Transthoracic echocardiography was performed in 95 patients with first ST segment elevation MI 110 days (interquartile range, 97-171 days) after MI and in 48 healthy control subjects. Two experienced observers independently assessed SWMAs. Separately, longitudinal peak negative, peak systolic, end-systolic, global strain, and strain rate were measured and averaged for the American Heart Association-recommended coronary artery perfusion territories. Receiver operating characteristic analysis was used to determine a single optimal cutoff value for each strain parameter. The diagnostic accuracy of an algorithm combining visual assessment and STE was evaluated. RESULTS: Median infarct size and transmurality were 15% (interquartile range, 7%-24%) and 64% (interquartile range, 46%-78%), respectively. Sensitivity, specificity, and accuracy of visual assessment to detect MI were 74% (95% CI, 63%-82%), 85% (95% CI, 72%-93%), and 78% (95% CI, 70%-84%), respectively. Among the strain parameters, SR had the highest diagnostic accuracy (area under the curve, 0.88; 95% CI, 0.83-0.94; cutoff value, -0.97 sec-1). The combination with STE improved sensitivity compared with visual assessment alone (94%; 95% CI, 86%-97%; P < .001), minimally affecting specificity (79%; 95% CI, 65%-89%; P = .607). Overall accuracy improved to 89% (95% CI, 82%-93%; P = .011). Multivariate analysis accounting for age and sex demonstrated that SR was independently associated with MI (odds ratio, 2.0; 95% CI, 1.6-2.7). CONCLUSIONS: The sensitivity and diagnostic accuracy of visually detecting chronic MI by assessing SWMAs are moderate but substantially improve when adding STE.

Non-invasive assessment of microvascular dysfunction in patients with microvascular angina.

BACKGROUND: We aimed to evaluate the microvascular function in patients with microvascular angina (MVA) by assessing 1) the endothelial glycocalyx barrier properties using sublingual microscopy, and 2) the myocardial perfusion reserve using cardiovascular magnetic resonance (CMR) imaging. METHODS: Sublingual microscopy was performed in 13 MVA patients (angina pectoris, ST-depression on treadmill testing, normal coronary angiogram) and compared with 2 control groups of 13 volunteers and 14 patients with known obstructive coronary artery disease (CAD). To test the glycocalyx-mediated microvascular responsiveness, the erythrocyte perfused boundary region (PBR) was assessed at baseline and after nitroglycerin challenge. RESULTS: The baseline PBR of MVA patients was similar to controls with CAD (p=0.72), and larger than in volunteers (p=0.02). Only the volunteers demonstrated a significant increase in PBR after nitroglycerin (p=0.03). In the 13 MVA patients, adenosine stress CMR perfusion imaging was performed. Although a significant increase in myocardial perfusion was observed in both the subendocardium and subepicardium during stress, the subendocardial perfusion reserve was significantly lower (p=0.02). The PBR responsiveness of the sublingual microvasculature showed a strong correlation with the transmural myocardial perfusion reserve (r=0.86, p<0.001). CONCLUSIONS: Patients with MVA can be characterized by microvascular glycocalyx dysfunction using sublingual microscopy. The strong correlation between sublingual PBR responsiveness and myocardial perfusion reserve suggests that the glycocalyx may play an important role in the regulation of microvascular volume for myocardial perfusion and supports the concept of impaired glycocalyx barrier properties in MVA.

Balloon sizing and transcatheter closure of acute atrial septal defects guided by magnetic resonance fluoroscopy: assessment and validation in a large animal model.

PURPOSE: To quantitatively assess atrial septal defects (ASDs) with small shunts using MRI followed by transcatheter closure monitored by MR fluoroscopy. MATERIALS AND METHODS: Acute ASDs were created in 14 pigs under x-ray fluoroscopy. Six animals were studied in order to select MR-compatible delivery systems and imaging strategies. ASDs in eight animals were examined with balloon sizing under MR fluoroscopy, flow measurements, and contrast media injections, after which transcatheter closure was performed under MR fluoroscopy. The delivery system was assembled from commercially available materials. RESULTS: The ratio of pulmonary to systemic flow (Qp/Qs) was reduced from 1.23 +/- 0.15 before ASD closure to 1.07 +/- 0.11 after ASD closure (P < 0.001). In two out of eight animals Qp/Qs was close to 1.0 before closure despite the presence of defects >15 mm. The ASDs were measurable with MR balloon sizing in all of the animals. Balloon sizing was identical with MR (16.9 +/- 2.3 mm) and x-ray fluoroscopy (17.1 +/- 1.3 mm). The in-house-assembled delivery system allowed successful placement of closure devices under MR guidance. CONCLUSION: Assessment and closure of small shunts with MR fluoroscopy is feasible. A barrier to the rapid implementation of transcatheter closure in patients is uncertainty about the MR safety of guidewires and device delivery systems.

Accentuation of high susceptibility of hypertrophied myocardium to ischemia: complementary assessment of Gadophrin-enhancement and left ventricular function with MRI.

The aim of the study was to compare infarction size and left ventricular (LV) function in normal and hypertrophied hearts after brief ischemia using Gadophrin-enhancement and functional assessment by MRI. Rats (n = 20) were assigned to aortic banding to induce LV hypertrophy or control. Eight weeks later, rats were subjected to 25 min of regional myocardial ischemia followed by 3 hr of reperfusion. The necrosis-specific agent Gadophrin-3 was injected to delineate infarcted myocardium on MRI. Effects of aortic banding and ischemia on LV mass and function were determined. At postmortem, areas at risk and infarction were measured. Close correlation was found between LV mass measured with MRI and at postmortem (r = 0.98). LV mass measured with MRI was significantly greater (0.81 +/- 0.02 g) in animals with aortic banding compared to control (0.62 +/- 0.02 g; P < 0.001). Infarction size was larger in hypertrophied hearts (19.0 +/- 1.4% / 18.3 +/- 1.5%) than in control (9.8 +/- 1.7% / 9.2 +/- 2.0%) on Gadophrin-enhanced MRI and at postmortem, respectively. Similarly, greater impairment in ejection fraction was observed in hypertrophied hearts with MRI (39 +/- 4% vs. 49 +/- 2%; P = 0.02). Gadophrin-3 provides accurate estimation of infarct size in hypertrophied hearts. Hypertrophied hearts are more sensitive to ischemia than nonhypertrophied hearts. The complementary assessment of Gadophrin-enhancement and LV function with MRI provides unique information about myocardium sensitivity to ischemia.

Myocardial perfusion imaging using OMNISCAN: a dose finding study for visual assessment of stress-induced regional perfusion abnormalities.

BACKGROUND: Different doses of contrast agent are applied for magnetic resonance perfusion studies and mainly semiquantitative approaches have been reported for analysis. We aimed to determine the optimal dose for a visual detection of perfusion defects. METHODS: 49 patients (59+/-8 years; 33 male) scheduled for invasive angiography were examined at stress (0.14 mg adenosine/kg body weight/minute) and rest using a TFE-EPI hybrid sequence (Philips ACS NT; 1.5 T). Patients were assigned to three different dose groups of gadodiamide (0.05, 0.1, and 0.15 mmol/kg body weight) injected as a bolus via a peripheral vein. Visual assessment was used to detect a regional reduction of peak signal intensity or speed of contrast agent inflow at stress in comparison to rest. RESULTS: Prevalence for coronary artery disease was 67%. The highest diagnostic accuracy was reached for a dose of 0.1 mmol gadodiamide/kg body weight (86% p=nonsignificant vs. 0.15 and 0.05 mmol gadodiamide/kg). At this dose, no major artifacts related to the contrast agent were found. CONCLUSIONS: Visual assessment of myocardial perfusion using a high-flow rate contrast agent bolus injection and a TFE-EPI sequence can be best achieved with a dose of gadodiamide 0.1 mmol/kg bodyweight.