Lowie M Van Assche

LV Thrombus Detection by Routine Echocardiography : Insights Into Performance Characteristics Using Delayed Enhancement CMR

OBJECTIVES This study sought to evaluate performance characteristics of routine echo for left ventricular thrombus (LVT). BACKGROUND Although the utility of dedicated echocardiography (echo) for LVT is established, echo is widely used as a general test for which LVT is rarely the primary indication. We used delayed-enhancement cardiac magnetic resonance (DE-CMR) as a reference to evaluate LVT detection by routine echo. METHODS Dedicated LVT assessment using DE-CMR was prospectively performed in patients with left ventricular systolic dysfunction. Echoes were done as part of routine clinical care. Echo and CMR were independently read for LVT and related indexes of LVT size, shape, and image quality/diagnostic confidence. Follow-up was done for embolic events and pathology validation of LVT. RESULTS In this study, 243 patients had routine clinical echo and dedicated CMR within 1 week without intervening events. Follow-up supported DE-CMR as a reference standard, with >5-fold difference in endpoints between patients with versus without LVT by DE-CMR (p = 0.02). LVT prevalence was 10% by DE-CMR. Echo contrast was used in 4% of patients. Echo sensitivity and specificity were 33% and 91%, with positive and negative predictive values of 29% and 93%. Among patients with possible LVT as the clinical indication for echo, sensitivity and positive predictive value were markedly higher (60%, 75%). Regarding sensitivity, echo performance related to LVT morphology and mirrored cine-CMR, with protuberant thrombus typically missed when small (p ≤ 0.02). There was also a strong trend to miss mural thrombus irrespective of size (p = 0.06). Concerning positive predictive value, echo performance related to image quality, with lower diagnostic confidence scores for echoes read positive for LVT in discordance with DE-CMR compared with echoes concordant with DE-CMR (p < 0.02). CONCLUSIONS Routine echo with rare contrast use can yield misleading results concerning LVT. Echo performance is improved when large protuberant thrombus is present and when the clinical indication is specifically for LVT assessment.

Relationship of T2-Weighted MRI Myocardial Hyperintensity and the Ischemic Area-At-Risk

RATIONALE After acute myocardial infarction (MI), delineating the area-at-risk (AAR) is crucial for measuring how much, if any, ischemic myocardium has been salvaged. T2-weighted MRI is promoted as an excellent method to delineate the AAR. However, the evidence supporting the validity of this method to measure the AAR is indirect, and it has never been validated with direct anatomic measurements. OBJECTIVE To determine whether T2-weighted MRI delineates the AAR. METHODS AND RESULTS Twenty-one canines and 24 patients with acute MI were studied. We compared bright-blood and black-blood T2-weighted MRI with images of the AAR and MI by histopathology in canines and with MI by in vivo delayed-enhancement MRI in canines and patients. Abnormal regions on MRI and pathology were compared by (a) quantitative measurement of the transmural-extent of the abnormality and (b) picture matching of contours. We found no relationship between the transmural-extent of T2-hyperintense regions and that of the AAR (bright-blood-T2: r=0.06, P=0.69; black-blood-T2: r=0.01, P=0.97). Instead, there was a strong correlation with that of infarction (bright-blood-T2: r=0.94, P<0.0001; black-blood-T2: r=0.95, P<0.0001). Additionally, contour analysis demonstrated a fingerprint match of T2-hyperintense regions with the intricate contour of infarcted regions by delayed-enhancement MRI. Similarly, in patients there was a close correspondence between contours of T2-hyperintense and infarcted regions, and the transmural-extent of these regions were highly correlated (bright-blood-T2: r=0.82, P<0.0001; black-blood-T2: r=0.83, P<0.0001). CONCLUSION T2-weighted MRI does not depict the AAR. Accordingly, T2-weighted MRI should not be used to measure myocardial salvage, either to inform patient management decisions or to evaluate novel therapies for acute MI.

Stress Cardiac MR Imaging Compared with Stress Echocardiography in the Early Evaluation of Patients Who Present to the Emergency Department with Intermediate-Risk Chest Pain

PURPOSE To compare the utility and efficacy of stress cardiac magnetic resonance (MR) imaging and stress echocardiography in an emergency setting in patients with acute chest pain (CP) and intermediate risk of coronary artery disease (CAD). MATERIALS AND METHODS Written informed consent was obtained from all patients. This HIPAA-compliant study was approved by the institutional review board for research ethics. Sixty patients without history of CAD presented to the emergency department with intermediate-risk acute CP and were prospectively enrolled. Patients underwent both stress cardiac MR imaging and stress echocardiography in random order within 12 hours of presentation. Stress imaging results were interpreted clinically immediately (blinded interpretation was performed months later), and coronary angiography was performed if either result was abnormal. CAD was considered significant if it was identified at angiography (narrowing >50% ) or if a cardiac event (death or myocardial infarction) occurred during follow-up (mean, 14 months ± 5 [standard deviation]). McNemar test was used to compare the diagnostic accuracy of techniques. RESULTS Stress cardiac MR imaging and stress echocardiography had similar specificity, accuracy, and positive and negative predictive values (92% vs 96%, 93% vs 88%, 67% vs 60%, and 100% vs 91%, respectively, for clinical interpretation; 90% vs 92%, 90% vs 88%, 58% vs 56%, and 98% vs 94%, respectively, for blinded interpretation). Stress cardiac MR imaging had higher sensitivity at clinical interpretation (100% vs 38%, P = .025), which did not reach significance at blinded interpretation (88% vs 63%, P = .31). However, multivariable logistic regression analysis showed stress cardiac MR imaging to be the strongest independent predictor of significant CAD (P = .002). CONCLUSION In patients presenting to the emergency department with intermediate-risk CP, adenosine stress cardiac MR imaging performed within 12 hours of presentation is safe and potentially has improved performance characteristics compared with stress echocardiography. Online supplemental material is available for this article.

Flow-Independent Dark-blood DeLayed Enhancement (FIDDLE): validation of a novel black blood technique for the diagnosis of myocardial infarction

Background A fundamental component of the CMR exam is contrast enhanced imaging, which is crucial for delineating diseased from normal tissue. Unfortunately, diseased tissue adjacent to vasculature often remains hidden since there is poor contrast between hyperenhanced tissue and bright blood-pool. Conventional black-blood double-IR methods are not a solution; these were not designed to function after contrast administration since they rely on the long native T1 of blood (~2s at 3T) and adequate blood flow within this time period. We introduce a novel Flow-Independent Dark-blood DeLayed Enhancement technique (FIDDLE) that allows visualization of tissue contrast-enhancement while suppressing blood-pool signal. We validate FIDDLE in an animal model of myocardial infarction (MI) and demonstrate feasibility in patients.

Performance of CMR Methods for Differentiating Acute From Chronic MI

OBJECTIVES The purpose of this study was to assess the performance of cardiac magnetic resonance (CMR) methods for discriminating acute from chronic myocardial infarction (MI). BACKGROUND Although T2-weighted CMR is thought to be accurate in differentiating acute from chronic MI, few studies have reported on diagnostic accuracy, and these generally compared extremes in infarct age (e.g., <1 week old vs. more than 6 months old) and did not evaluate other CMR methods that could be informative. METHODS A total of 221 CMR studies were performed at various time points after ST-segment elevation myocardial infarction in 117 consecutive patients without a history of MI or revascularization enrolled prospectively at 2 centers. Imaging markers of acute MI (<1 month) were T2 hyperintensity on double inversion recovery turbo spin echo (DIR-TSE) images, microvascular obstruction (MO) on delayed-enhancement CMR, and focally increased end-diastolic wall thickness (EDWT) on cine-CMR. RESULTS The prevalence of T2-DIR-TSE hyperintensity decreased with infarct age but remained substantial up to 6 months post-MI. In contrast, the prevalence of both MO and increased EDWT dropped sharply after 1 month. T2-DIR-TSE sensitivity, specificity, and accuracy for identifying acute MI were 88%, 66%, and 77% compared with 73%, 97%, and 85%, respectively, for the combination of MO or increased EDWT. On multivariable analysis, persistence of T2-hyperintensity in intermediate-age infarcts (1 to 6 months old) was predicted by larger infarct size, diabetes, and better T2-DIR-TSE image quality score. For infarct size ≥ 10% of the left ventricle, a simple algorithm incorporating all CMR components allowed classification of infarct age into 3 categories (<1 month old, 1 to 6 months old, and ≥ 6 months old) with 80% (95% confidence interval: 73% to 87%) accuracy. CONCLUSIONS T2-DIR-TSE hyperintensity is specific for infarcts <6 months old, whereas MO and increased EDWT are specific for infarcts <1 month old. Incorporating multiple CMR markers of acute MI and their varied longevity leads to a more precise assessment of infarct age.

Left Ventricular Thrombus Detection by Routine Echocardiography – Insights into Performance Characteristics using Delayed Enhancement CMR

OBJECTIVES This study sought to evaluate performance characteristics of routine echo for left ventricular thrombus (LVT). BACKGROUND Although the utility of dedicated echocardiography (echo) for LVT is established, echo is widely used as a general test for which LVT is rarely the primary indication. We used delayed-enhancement cardiac magnetic resonance (DE-CMR) as a reference to evaluate LVT detection by routine echo. METHODS Dedicated LVT assessment using DE-CMR was prospectively performed in patients with left ventricular systolic dysfunction. Echoes were done as part of routine clinical care. Echo and CMR were independently read for LVT and related indexes of LVT size, shape, and image quality/diagnostic confidence. Follow-up was done for embolic events and pathology validation of LVT. RESULTS In this study, 243 patients had routine clinical echo and dedicated CMR within 1 week without intervening events. Follow-up supported DE-CMR as a reference standard, with >5-fold difference in endpoints between patients with versus without LVT by DE-CMR (p = 0.02). LVT prevalence was 10% by DE-CMR. Echo contrast was used in 4% of patients. Echo sensitivity and specificity were 33% and 91%, with positive and negative predictive values of 29% and 93%. Among patients with possible LVT as the clinical indication for echo, sensitivity and positive predictive value were markedly higher (60%, 75%). Regarding sensitivity, echo performance related to LVT morphology and mirrored cine-CMR, with protuberant thrombus typically missed when small (p ≤ 0.02). There was also a strong trend to miss mural thrombus irrespective of size (p = 0.06). Concerning positive predictive value, echo performance related to image quality, with lower diagnostic confidence scores for echoes read positive for LVT in discordance with DE-CMR compared with echoes concordant with DE-CMR (p < 0.02). CONCLUSIONS Routine echo with rare contrast use can yield misleading results concerning LVT. Echo performance is improved when large protuberant thrombus is present and when the clinical indication is specifically for LVT assessment.

The prevalence of microvascular obstruction in acute myocardial infarction: importance of ST elevation, infarct size, transmurality and infarct age.

Results The population consisted of 147 (56%) patients with STEMI, 2 (0.8%) with left bundle branch block, and the remaining 117 (44%) with non-STEMI. The mean age was 59±13 years and 68% were male. The overall observed prevalence of MO was 53%. IS and transmurality were significantly larger in patients with MO than without (24% vs 7%, p 25%) or transmural extent was high (upper tertile, >80%) the prevalence of MO was similar (93% vs 92%, p=0.9; and 90% vs 85%, p=0.5, respectively). The prevalence of MO was dependent on both IS and

Assessment and improvement of image homogeneity in black-blood T2-weighted turbo spin-echo CMR

Background Double inversion recovery (DIR) and triple inversion recovery (TIR) prepared Turbo-Spin-Echo (TSE) are the most commonly used sequences for black-blood T2weighted (T2W) cardiac magnetic resonance. For both, cardiac motion often leads to signal loss and image inhomogeneity, which can affect diagnosis. Signal loss artifacts are thought to be due to misalignment of the black-blood preparation with readout. However, the TSE readout itself is also motion sensitive and could lead to signal loss. We examined image homogeneity in routine Black-Blood T2W-TSE and investigated potential improvement by reducing interecho-spacing of the TSE readout.

A simple visual algorithm incorporating the components of a routine CMR study improves the determination of infarct age compared with T2-CMR alone.

≥1- month-old-MI as (a) individual components, (b) basic combinations, and (c) using new algorithm. T2CMR-alone was sensitive (88%) but not specific (66%) for <1-month-old-MI resulting in only moderate accuracy (77%). Using a later cutpoint for ‘acute’ MI (2-months or 3-months) did not improve accuracy since sensitivity decreased with increasing specificity. MO and increased-EDWT were very specific but not sensitive for acute MI. The basic combination of MO-or-increasedEDWT improved sensitivity (73%) while retaining specificity (97%). Basic algebraic combinations including T2-CMR did not improve overall accuracy since ‘OR’ function led to low specificity while ‘AND’ function led to low sensitivity. The new algorithm resulted in high sensitivity (92%) and specificity (90%). Accuracy (91%) was improved compared with T2-CMR alone (p<0.001) and compared with basic algebraic combinations involving T2-CMR (p<0.05). An additional benefit of the algorithm was the ability to identify intermediate-aged-MI (1-6-month-old). This was based on finding T2-hyperintensity-size < DE-infarct-size, and when present, patients had median infarct age of 110 days (IQR: 96, 115) (Figure 1). Conclusions A novel algorithm incorporating components of a routine CMR scan improves the determination of infarct age compared with T2-CMR alone. Certain CMR findings may be specific for intermediate-aged MI. Funding None.

Direct in vivo myocardial infarct visualization using 3D ultrasound and passive strain contrast

An approach for myocardial elastography is presented for infarct visualization. Infarcts are visualized using passive strain in the ventricles induced by atrial contraction. Results are compared against ARFI and delay-enhanced contrast MR.