Persistent Microvascular Obstruction Research Articles

Microvascular recovery with ultrasound in myocardial infarction post-PCI trial.

Persistent microvascular obstruction (MVO) after successful percutaneous coronary intervention (PCI) in acute ST segment elevation myocardial infarction (STEMI) has been well-described. MVO predicts lack of recovery of left ventricular function and increased mortality. Sonothrombolysis utilizing diagnostic ultrasound induced cavitation of commercially available microbubble contrast has been effective at reducing infarct size and improving left ventricular ejection fraction (LVEF) when performed both pre- and post-PCI. However, the effectiveness of post-PCI sonothrombolysis alone after successful PCI has not been demonstrated. A prospective randomized controlled trial was performed in 50 consecutive consenting patients with anterior STEMI who underwent a continuous microbubble infusion immediately following successful PCI. Intermittent high mechanical index (MI) impulses were applied only in the sonthrombolysis group. Delayed enhancement magnetic resonance imaging (MRI) was performed at 48h and again at 6-8weeks to assess for differences in infarct size, LVEF, and MVO. There were no differences between groups in age, gender, and cardiovascular risk factors. Significant (>2 segments) MVO following successful PCI was observed in 66% of patients. Although sonothrombolysis reduced the extent of MVO acutely, there were no differences in infarct size, LVEF, or extent of MVO by MRI at 48h. Twenty-eight patients returned for a follow up MRI at 6-8weeks. LVEF improved only in the sonothrombolysis group (∆LVEF 7.81±4.57% with sonothrombolysis vs. 1.77±7.02% for low MI only, p=.011). Post-PCI sonothrombolysis had minimal effect on reducing myocardial infarct size but improved left ventricular systolic function in patients with acute anterior wall STEMI.

Deep learning myocardial infarction segmentation framework from cardiac magnetic resonance images

Segmentation of myocardial infarction (MI) is a crucial task in the field of heart disease theranostics. Cardiac magnetic resonance imaging (MRI) is a well-known non-invasive imaging technique that provides comprehensive insights into the structure and function of the heart. However, manually interpreting myocardial infarction from multiple MRI frames is time-consuming, labor-intensive, and prone to errors. This study aims to develop an end-to-end deep learning framework that can automatically segment myocardial infarction (MI) and persistent microvascular obstruction (MVO) among the normal tissues of left ventricle (LV), normal myocardium (Myo), and the remaining normal foreground (BG). The proposed framework includes various stages, such as cardiac MR image collection, preprocessing via three enhancement techniques, splitting and training set augmentation, selection of the most suitable artificial intelligence (AI) segmentation model, and performance evaluation and comparison. For the multi-class segmentation process, we adopt and develope four AI state-of-the-art models: U-Net, U-Net_VGG16, SegNet, and ResUnet, which are well-regarded for their effectiveness in image segmentation across different computer vision domains. The publicly available benchmark EMIDEC MRI dataset is utilized for training and evaluating the proposed segmentation framework. The ResU-Net achieved the top performance compared to other AI models, recording an overall accuracy (Acc) of 88.48%, recall (Re) of 85.24%, precision (Pre) of 85.46%, F1-score of 85.35, and MIoU of 84.23%. Comparing with the original dataset (without preprocessing), the CLAHE preprocessing improves the ResU-Net segmentation performance by 2.19% and 3.08% in terms of average F1-score and MIoU for all classes (LV, Myo, MI, and MVO). Therefore, the proposed AI segmentation framework demonstrates its potential for effectively performing multi-class segmentation of cardiac diseases from MRI images.

Impact of Persistent Microvascular Obstruction Late After STEMI on Adverse LV Remodeling: A CMR Study

BackgroundLittle is known about the occurrence and implications of persistent microvascular obstruction (MVO) after reperfused ST-segment elevation myocardial infarction (STEMI). ObjectivesThe authors used cardiac magnetic resonance (CMR) to characterize the impact of persistent MVO on adverse left ventricular remodeling (ALVR). MethodsA prospective registry of 471 STEMI patients underwent CMR 7 (IQR: 5-10) days and 198 (IQR: 167-231) days after infarction. MVO (≥1 segment) and ALVR (relative increase >15% at follow-up CMR) of left ventricular end-diastolic index (LVEDVI) and left ventricular end-systolic volume index (LVESVI) were determined. ResultsOne-week MVO occurred in 209 patients (44%) and persisted in 30 (6%). The extent of MVO (P = 0.026) and intramyocardial hemorrhage (P = 0.001) at 1 week were independently associated with the magnitude of MVO at follow-up CMR. Compared with patients without MVO (n = 262, 56%) or with MVO only at 1 week (n = 179, 38%), those with persistent MVO at follow-up (n = 30, 6%) showed higher rates of ALVR-LVEDVI (22%, 27%, and 50%; P = 0.003) and ALVR-LVESVI (20%, 21%, and 53%; P < 0.001). After adjustment, persistent MVO at follow-up (≥1 segment) was independently associated with ΔLVEDVI (relative increase, %) (P < 0.001) and ΔLVESVI (P < 0.001). Compared with a 1:1 propensity score–matched population on CMR variables made up of 30 patients with MVO only at 1 week, patients with persistent MVO more frequently displayed ALVR-LVEDVI (12% vs 50%; P = 0.003) and ALVR-LVESVI (12% vs 53%; P = 0.001). ConclusionsMVO persists in a small percentage of patients in chronic phase after STEMI and exerts deleterious effects in terms of LV remodeling. These findings fuel the need for further research on microvascular injury repair.

Impact of persistent MVO late after STEMI on adverse left ventricular remodelling: a CMR study

Abstract Background Despite successful revascularization at the epicardial level, microvascular obstruction (MVO) appears soon after reperfusion in up to 50% of cases. Early MVO has been solidly associated with adverse resulting cardiac structure and heightened risk of future cardiovascular events. Although clinical and experimental studies demostrated the spontaneous repair of MVO, little is known about the occurrence and implications of persistent MVO late after infarction. Purpose We used cardiovascular magnetic resonance (CMR) to characterize the impact of persistent MVO late after reperfused ST-segment elevation myocardial infarction (STEMI) on adverse left ventricular (LV) remodelling (ALVR). Methods A prospective registry of 471 STEMI patients underwent CMR 7 [5–10] and 198 [167–231] days post infarction, and MVO (&amp;gt;1 segment) and ALVR (relative increase &amp;gt;15% at follow-up CMR) of LV end-diastolic (LVEDVI) and end-systolic volume indices (LVESVI) were determined. Results One-week MVO occurred in 209 patients (44%) and persisted in 30 of these (6%). Most patients with persistent MVO (22/30, 73%) displayed extensive (&amp;gt;2.5% of LV mass) MVO at 1 week. Compared with patients without MVO (n=262, 56%) or with MVO only at 1 week (n=179, 38%), those with persistent MVO at follow-up (n=30, 6%) showed higher rates of ALVR-LVEDVI (22%, 27%, 50% p=0.003) and ALVR-LVESVI (20%, 21%, 53% p&amp;lt;0.001). After adjustment, the extent (% of LV mass) of MVO at follow-up was independently associated with ΔLVEDVI (relative increase, %) (p=0.01) and ΔLVESVI (p=0.03). Compared to a 1:1 matched population of 30 patients with MVO only at 1 week, patients with persistent MVO more frequently displayed ALVR-LVEDVI (12% vs. 50%, p=0.003) and ALVR-LVESVI (12% vs. 53%, p=0.001). Conclusion MVO persists in a small percentage of patients in chronic phase after STEMI and exerts deleterious effects in terms of LV remodelling. These findings fuel the need for further research on microvascular injury repair. Funding Acknowledgement Type of funding sources: Public grant(s) – National budget only. Main funding source(s): This work was supported by “Instituto de Salud Carlos III” and “Fondos Europeos de Desarrollo Regional FEDER” [grant numbers PI20/00637, PI15/00531, FI18/00320, and CIBERCV16/11/00486] and by Conselleria de Educaciόn – Generalitat Valenciana (PROMETEO/2021/008).

Prediction of Myocardial Infarction From Patient Features With Machine Learning.

This study proposes machine learning-based models to automatically evaluate the severity of myocardial infarction (MI) from physiological, clinical, and paraclinical features. Two types of machine learning models are investigated for the MI assessment: the classification models classify the presence of the infarct and the persistent microvascular obstruction (PMO), and the regression models quantify the Percentage of Infarcted Myocardium (PIM) of patients suspected of having an acute MI during their reception in the emergency department. The ground truth labels for these supervised models are derived from the corresponding Delayed Enhancement MRI (DE-MRI) exams and manual annotations of the myocardium and scar tissues. Experiments were conducted on 150 cases and evaluated with cross-validation. Results showed that for the MI (PMO inclusive) and the PMO (infarct exclusive), the best models obtained respectively a mean error of 0.056 and 0.012 for the quantification, and 88.67 and 77.33% for the classification accuracy of the state of the myocardium. The study of the features' importance also revealed that the troponin value had the strongest correlation to the severity of the MI among the 12 selected features. For the proposal's translational perspective, in cardiac emergencies, qualitative and quantitative analysis can be obtained prior to the achievement of MRI by relying only on conventional tests and patient features, thus, providing an objective reference for further treatment by physicians.

Association of myocardial edema, hemorrhage and persistent microvascular obstruction with circulating inflammatory biomarkers in acute myocardial infarction patient

Although early reperfusion, ST-elevation myocardial infarction (STEMI) remain a major cause of mortality and heart failure. Reperfusion is commonly associated with persistent micro-vascular obstruction (MVO), edema and intramyocardial hemorrhage (IMH) which are detected using cardiovascular magnetic resonance (CMR) imaging. Furthermore, STEMI is associated with an important inflammatory reaction. So far, the correlation between CMR parameters and inflammation remain unclear. This study aims at deciphering the correlation between adverse events and inflammatory biomarkers. This is a prospective study including 21 STEMI patients referred for a primary percutaneous coronary intervention. Seven blood samples were collected at admission, 4, 12, 24, 48 hours, 7 and 30 days after reperfusion. The presence of inflammatory markers including fibrinogen, inteleukin-10, interleukine-6, C reactive protein (CRP), interleukine-8, and neutrophils count was assessed by enzyme-linked immunosorbent assay (ELISA) technique. At day 7 after reperfusion, CMR was performed to determine infarct size, MVO, IMH and edema. The study compares the expression level of each biomarker with CMR measures. MVO was present in 55% of patients and IMH in 33.3%. We observed a correlation between IL-6, CRP, fibrinogen, neutrophil levels and IMH ( P = 0.033; P = 0.05; P = 0.0085; P = 0.0046 respectively). Patients with persistent MVO present a significantly higher rate of CRP ( P = 0.0125). No significant difference was found for other markers and edema was not significantly correlated with inflammation. Following acute myocardial infarction in human patient, IMH appears to be strongly correlated with inflammatory biomarkers. Targeting the couple IMH/inflammation could be a novel strategy in future adjunctive STEMI treatment.

TCT-133 Clinical Impact of Persistent Microvascular Obstruction Following Successful Percutaneous Coronary Intervention in Acute ST segment Elevation Myocardial Infarction

In the contemporary era of primary percutaneous coronary intervention (PPCI) to treat acute ST segment elevation myocardial infarction (STEMI), the frequency and predictors of persistent microvascular obstruction (MVO) have not been elucidated. Real time myocardial contrast echocardiography (RTMCE)

Persistent Microvascular Obstruction After Myocardial Infarction Culminates in the Confluence of Ferric Iron Oxide Crystals, Proinflammatory Burden, and Adverse Remodeling.

Emerging evidence indicates that persistent microvascular obstruction (PMO) is more predictive of major adverse cardiovascular events than myocardial infarct (MI) size. But it remains unclear how PMO, a phenomenon limited to the acute/subacute period of MI, drives adverse remodeling in chronic MI setting. We hypothesized that PMO resolves into chronic iron crystals within MI territories, which in turn are proinflammatory and favor adverse remodeling post-MI. Canines (n=40) were studied with cardiac magnetic resonance imaging to characterize the spatiotemporal relationships among PMO, iron deposition, infarct resorption, and left ventricular remodeling between day 7 (acute) and week 8 (chronic) post-MI. Histology was used to assess iron deposition and to examine relationships between iron content with macrophage infiltration, proinflammatory cytokine synthesis, and matrix metalloproteinase activation. Atomic resolution transmission electron microscopy was used to determine iron crystallinity, and energy-dispersive X-ray spectroscopy was used to identify the chemical composition of the iron composite. PMO with or without reperfusion hemorrhage led to chronic iron deposition, and the extent of this deposition was strongly related to PMO volume (r>0.8). Iron deposits were found within macrophages as aggregates of nanocrystals (≈2.5 nm diameter) in the ferric state. Extent of iron deposits was strongly correlated with proinflammatory burden, collagen-degrading enzyme activity, infarct resorption, and adverse structural remodeling (r>0.5). Crystallized iron deposition from PMO is directly related to proinflammatory burden, infarct resorption, and adverse left ventricular remodeling in the chronic phase of MI in canines. Therapeutic strategies to combat adverse remodeling could potentially benefit from taking into account the chronic iron-driven inflammatory process.

Abstract 15170: Persistent Microvascular Obstruction Leads to Localized Iron Deposition and Active Inflammation Within Chronic Myocardial Infarctions

Introduction: The mechanism by which persistent microvascular obstruction (PMO) post myocardial infarction (MI) exerts adverse long-term effects is not well understood. Hypothesis: We hypothesized that PMO, with or without reperfusion hemorrhage, can resolve into iron deposition within chronic MI (CMI) territories, and is associated with prolonged inflammation and adverse LV remodeling. Methods: Canines subjected to reperfused (n=17) and non-reperfused (n=16) MI underwent Cardiovascular Magnetic Resonance (CMR) at 7 (acute) and 56 days (chronic) post-MI. Cine, T2*-weighted and Late Gadolinium Enhancement images were used to characterize LV remodeling (End-Diastolic Sphericity Index (EDSI)), iron and PMO respectively. Histological analysis was used to examine chronic inflammation. Results: In the reperfused group, 9 canines had PMO and hemorrhage with subsequent chronic iron deposition (PMO+/T2*+), while 4 canines had no PMO, hemorrhage, or chronic iron deposition (PMO-/T2*-). The remaining 4 canines had PMO without hemorrhage (PMO+/T2*-), but all subsequently had chronic iron deposition. In the non-reperfused group, 15 canines had PMO, and acute and subsequent chronic iron deposition (NR-PMO+/T2*+); 1 canine had no PMO, acute or chronic iron deposition (NR-PMO-/T2*-). In both groups, PMO volume was significantly associated with both acute and chronic iron volumes (p&lt;0.001 all cases). In both groups, infarct and iron volumes measured in both acute and chronic phases were significant predictors of change in EDSI between acute and chronic phases (p&lt;0.01 all cases). Histological sections of the harvested hearts post day 56 CMR showed extensive newly recruited macrophage, IL-1β, TNF-α and MMP-9 activities highly localized with iron in CMI regions (p&lt;0.001 all cases). Conclusions: PMO, with or without reperfusion hemorrhage, can lead to iron deposition within CMIs, and is associated with active inflammation and adverse LV remodeling in canines.

Multi-detector CT and MRI of microembolized myocardial infarct: monitoring of left ventricular function, perfusion, and myocardial viability in a swine model.

Patients with acute myocardial infarct (MI) show additional damage after coronary interventions. To longitudinally quantify structural and functional changes in the left ventricle (LV) subjected to microembolized MI using multidisciplinary computed tomography (MDCT) and independent reference methods. Swine (n = 20) served as controls (group I) or were subjected to a combination of coronary occlusion, microembolization, and reperfusion and imaged at 3 days (group II) or 3 days and 5 weeks (group III). LV volumes, perfusion, and MI mass were quantified on cine, perfusion, and delayed contrast enhancement (DE) MDCT. MRI, cardiac injury biomarkers, histochemical and histopathologic stains were used as independent references. MDCT showed a reduction in ejection fraction and increased end systolic volume (31 ± 2% and 82 ± 3 mL, respectively) of group III compared with I (48 ± 2% and 57 ± 1 mL, respectively). It also demonstrated perfusion deficits in microembolized MI and peri-infarcts. DE-MDCT delineated microvascular obstruction (MVO) zones embedded in acute microembolized MI and microinfarct specks resulting from persistent MVO by deposited microemboli in microvessels of peri-infarct zone. Bland-Altman test showed close agreements between the extents of microembolized MI measured on DE-MDCT, DE-MRI, and histochemical TTC staining, but not between these modalities and microscopy. MI resorption was evident between 3 days and 5 weeks (13.4 ± 0.5 g and 9.8 ± 0.5 g, P < 0.017) and histologic examination revealed incomplete healing. Injury biomarkers were increased after intervention. MDCT can longitudinally quantify regional perfusion deficits, LV dysfunction, and resorption of microembolized MI. MDCT or MRI can be used alternatively after coronary interventions in cases of contraindications for one modality or the other.

T2 values of the acutely infarcted myocardium following primary PCI: the relationship with infarct characteristics and gadolinium extracellular volume of distribution

Background T2 mapping has been shown to detect myocardial oedema as assessed by histology in animals, and is a promising sequence to detect the area at risk in STEMI. The specific cut off value to identify abnormal myocardium in STEMI has not been identified nor have the effects of infarct characteristics on T2 valves. The extra cellular volume fraction (ECV) has been validated against histology in humans. The aims of this study were to identify a cut-off T2 for prediction of myocardial oedema following acute reperfused myocardial infarction and determine if infarct characteristics affect T2 values. In addition, this study aims to determine if T2 values are associated with the ECV following STEMI. Methods 50 consecutive patients presenting with STEMI to the Bristol Heart Institute Primary PCI service were approached for inclusion in the study. Patients had a CMR scan day 2 following STEMI. T2 values were assessed by T2 mapping. The myocardium was divided according to the AHA segments. Regional wall motion, LGE transmurality, presence of persistent microvascular obstruction (PMVO) and T2 values were assessed per segment. Segments were deemed affected if they did not have normal wall motion. In addition, a further 30 patients had a CMR day 2 following STEMI. Pre-contrast T1, T2 valves were assessed. Post contrast T1 was measured at 25 minutes following contrast administration. ECV was calculated as:

MRI demonstrates a decrease in myocardial infarct healing and increase in compensatory ventricular hypertrophy following mechanical microvascular obstruction

To provide direct evidence that mechanical obstruction of microvessels inhibits infarct resorption (healing) and enhances left ventricular (LV) remodeling using MRI. Animals (n = 20 pigs) served as controls (group I) or were subjected to either 90 min left anterior descending (LAD) coronary artery occlusion/reperfusion (group II) or 90 min LAD occlusion/ microemboli delivery/reperfusion (group III). MRI (cine and delayed contrast enhanced MRI, DE-MRI) was performed at 3 days and 5 weeks after interventions and used for assessing LV function, mass, and extent of myocardial damage and microvascular obstruction (MVO) using semi-automated threshold method. Persistent MVO in the core of contiguous infarct was larger and more frequent (n = 8/8) in group III than group II (4/8) on DE-MRI at 3 days. Furthermore, patchy microinfarct, as a result of microembolization, was visible as hyperenhanced zone at the borders of the contiguous infarct. The reduction in ejection fraction and increase in LV volumes on cine MRI were greater in group III than group II at 3 days and 5 weeks, which may be attributed to the slow infarct resorption, MVO extents and patchy microinfarct at the borders. This MRI study illustrates the recently raised conjecture that MVO delays/inhibits infarct resorption (healing), accentuates LV hypertrophy and pathological remodeling.

Early vs. persistent microvascular obstruction following primary PCI- two pathologies or one? A cardiovascular magnetic resonance study

Background 20-40% of reperfused ST-elevation acute myocardial infarction (STEMI) features microvascular obstruction (MO), which confers adverse prognosis. Different CMR sequences are commonly used to detect MO: first pass perfusion (FPP), early gadolinium enhancement (EGE), and late gadolinium enhancement (LGE). FPP and EGE are more sensitive than LGE for the detection of MO. However, only MO by LGE has been shown to confer prognostic information. It is unclear whether these three

Assessment of microembolization associated with revascularization in acute myocardial infarction: MDCT cardiac perfusion and function study

To use multi-detector computed tomography (MDCT) for assessing the effects of coronary microemboli on pre-existing acute myocardial infarct (AMI) and to compare this pathology to LAD microembolization and occlusion/reperfusion. An angioplasty balloon catheter was placed in the LAD coronary artery of pigs under X-ray guidance. Four animals served as controls without intervention (group A) and an additional 24 animals (8/group) were subjected to microembolization (group B), occlusion/reperfusion (group C) or combination of the two insults (group D). MDCT was used to assess perfusion, LV function and viability. At postmortem, the LV sections were stained with hematoxylin/eosin and triphenyltetrazolium chloride (TTC). Dynamic perfusion and helical cine MDCT demonstrated decline in regional LV perfusion and function, respectively, after all interventions. MDCT showed significant differences in ejection fraction between groups: A = 57.5 ± 4.7%, B = 40.3 ± 0.5% P < 0.05, C = 34.9 ± 1.3% P < 0.05 and D = 30.7 ± 1.2% P < 0.05, while viability MDCT demonstrated differences in enhancement patterns and extents of damage between the groups (B = 9.1 ± 0.4% LV mass, C = 11.9 ± 0.7% and D = 16.2 ± 1.2%, P < 0.05) and extent of microvascular obstruction (MVO) (group C = 3.2 ± 1.0% LV mass versus D = 5.2 ± 0.7%, P < 0.01). DE-MDCT overestimated all types of myocardial damage compared with TTC, but showed a close correlation (r > 0.7). Microscopic examination confirmed the presence of patchy and contiguous necrosis, MVO, edema and calcium deposits. Dynamic and helical cine MDCT imaging can grade LV dysfunction and perfusion deficit, respectively. DE-MDCT demonstrated a large and persistent MVO zone after microembolization of pre-existing AMI. Furthermore, it has the potential to visualize patchy microinfarct, detect perfusion deficits and dysfunction at the border zone after microembolization of pre-existing AMI.

Low-dose dobutamine adds incremental value to late gadolinium enhancement cardiac magnetic resonance in the prediction of adverse remodelling following acute myocardial infarction.

To examine the relative and combined value of late gadolinium enhancement (LGE) and low-dose dobutamine (LDD) cardiac magnetic resonance (CMR) to predict 'adverse remodelling' (AR) following acute myocardial infarction (AMI). Forty-five patients with AMI were recruited. CMR was performed 2-4 days after presentation and at 6 months. Ventricular wall motion and volume were recorded at rest and following dobutamine infusion. Measures of first pass perfusion, persistent microvascular obstruction (PMO), and LGE were obtained following contrast administration. Quantitation was performed using the MEDIS 6.2 software. Regression analysis was employed to determine the univariables and multivariate models most predictive of AR at 6 months. The incremental and relative value of LDD over LGE was investigated. The most predictive univariable was 'volume of PMO' (r = 0.51, r2 = 0.26, P < 0.001). The optimal 'combined' multivariate model, utilizing data from all components, was highly predictive of AR (r = 0.82, r2 = 0.67, P < 0.001). The optimal model using parameters only from the LGE component also predicted remodelling (r = 0.65, r2 = 42.0, P = 0.001) but with less accuracy. In contrast, the optimal model using variables from the LDD component alone predicted remodelling with a similar accuracy to the optimal combined model (r = 0.82, r2 = 0.67, P < 0.001). A comprehensive CMR examination accurately predicts AR following AMI. LDD is superior to LGE CMR in this respect. These data suggest that LDD not only adds incremental value to LGE in the prediction of remodelling post-AMI but also may be utilized alone with the same predictive power.

MRI manifestations of persistent microvascular obstruction and acute left ventricular remodeling in an experimental reperfused myocardial infarction.

To investigate varied manifestations of persistent microvascular obstruction (PMO) and acute left ventricular (LV) remodeling in an experimental reperfused myocardial infarction (MI) using MRI. In eleven Yorkshire pigs an acute MI was produced through a 90-minute balloon occlusion of the middle left anterior descending coronary artery, followed by reperfusion. All animals underwent MRI examinations on a 1.5T system including a SSFP functional study, first pass myocardial perfusion (FPMP), T1 preparation Look-Locker and delayed contrast-enhanced MRI (DE-MRI). Imaging was performed immediately post-intervention (day 0) and at days 7-9. In four animals a repeat MRI examination was performed at day 2 as well. Upon study completion, animals underwent histological analysis including infarct assessment with triphenyltetrazolium chloride (TTC). Following reperfusion, Thrombolysis In Myocardial Infarction (TIMI) Flow grade 3 was achieved in all animals, demonstrated by repeat angiography following balloon deflation (day 0). Various MR appearances of PMO were noticed including predominance in the subendocardial region, a central core within the infarcted tissue and also multiple separate clusters. In ten of eleven animals PMO was demonstrated as a persistent hypo-enhanced area in FPMP and DE-MRI, and identified as bright regions in later T1 difference images. In one animal PMO was identified only at day 2. At day 7-9 PMO could be identified on early DE-MRI at 5-15 minutes post Gd injection but not on late DE-MRI and T1 difference images after 45-60 minutes post-contrast. A larger volume of PMO and MI at day 2 was noted in comparison to data from day 0 but the difference was not statistically significant. An increased end-diastolic LV volume (EDV) without changes in end-systolic LV volume (ESV) and LV mass at end-diastolic phase (LVM) was observed at day 7-9 in comparison to data from day 0. There was good correlation between the relative extent of persistent MO in the infarcted myocardium (% MO/MI) and EDV at day 7-9 (r=0.83, n=10, P=0.003). MI was confirmed in all animals by TTC staining and/or histology. A variable MR appearance of persistent microvascular obstruction is observed during a short time course MRI study of reperfused acute MI. Acute negative LV remodeling was closely related to the relative extent of persistent microvascular obstruction within the infarct myocardium.

Prognostic Value of Microvascular Damage Determined by Cardiac Magnetic Resonance in Non ST-Segment Elevation Myocardial Infarction

To compare 2 cardiac magnetic resonance (CMR) techniques for the evaluation of the prognostic significance of microvascular damage after non ST-segment elevation myocardial infarction (NSTEMI). CMR was performed at 3T in 61 patients within the week following their first NSTEMI. A first-pass saturation-recovery gradient-echo perfusion sequence was started during the infusion of contrast material to evaluate the extent of microvascular obstruction (MO) during the first 2 minutes after injection (MO(<2 min)) and between 3 and 5 minutes thereafter (MO(3 min), MO(4 min), MO(5 min)). Ten minutes after injection, late gadolinium-enhanced images were obtained using a phase sensitive inversion recovery sequence to assess persistent MO (PMO) and infarct size. Major adverse cardiac events (MACE) were collected at 1-year follow-up. MO(<2 min) and PMO were found in 28 of 61 and 17 of 61 patients, respectively. About 15 patients had MACE at 1 year, including 4 cardiac deaths. In univariate logistic regression analysis, age (odds ratio [OR], 1.07, P = 0.020), infarct size (OR, 1.08, P = 0.020), multivessel disease (OR, 5.08, P = 0.011), end diastolic volume (OR, 1.04, P = 0.003), end systolic volume (OR, 1.03, P = 0.010), MO from < 2 to 5 minutes postinjection (P < 0.05) and PMO (OR, 18.33, P < 0.001) were significantly associated with the outcome. In multivariate analysis, only PMO remained an independent predictor of MACE. Microvascular damage assessed by CMR is associated with a dramatically higher risk of cardiovascular events in NSTEMI patients. Moreover, our data suggest that PMO as assessed on late gadolinium-enhanced images might have a higher prognostic value than MO evaluated on first-pass images.

121 Patients with persistent microvascular obstruction following acute myocardial infarction remain at high risk of adverse remodelling despite optimal medical therapy and may benefit from aldosterone antagonism

Introduction Microvascular obstruction (MVO) is associated with large acute myocardial infarction (AMI) and lower left ventricular (LV) ejection fraction, and predicts greater remodelling, but whether this effect is abolished by contemporary anti-remodelling therapies is subject to debate. We examined the influence of several infarct characteristics, including MVO, on LV remodelling in an optimally-treated post-AMI cohort enrolled in a clinical trial investigating the potential anti-remodelling effects of eplerenone, using contrast-enhanced cardiac magnetic resonance (ceCMR). Methods Hundred patients (mean age 58.9±12 years, 77% male) admitted with AMI in the previous 1-14 days underwent ceCMR at baseline (∼4 days), 12 and 24 weeks. The effects on LV remodelling (ie, change in LV end-systolic volume index (▵LVESVI)) of infarct site, transmurality, endocardial extent, and the presence of early and late MVO were analysed. Tests for interaction between MVO persistence and eplerenone therapy were also performed. Results Mean baseline infarct volume index decreased from 34.0 (21.2) ml/m2 to 20.9 (12.9) ml/m2 at 24 weeks (p Conclusions Late MVO on pre-discharge ceCMR remains an ominous predictor of adverse LV remodelling despite powerful anti-remodelling therapy, and may be useful in the risk-stratification of survivors of AMI. Eplerenone may attenuate remodelling more powerfully in patients at the highest risk of remodelling, that is, those with persistent MVO.

Major prognostic impact of persistent microvascular obstruction as assessed by contrast-enhanced cardiac magnetic resonance in reperfused acute myocardial infarction

The aim of this study was to compare the prognostic significance of microvascular obstruction (MO) and persistent microvascular obstruction (PMO) as assessed by cardiac magnetic resonance (CMR) in patients with acute myocardial infarction (AMI). CMR was performed in 184 patients within the week following successfully reperfused first AMI. First-pass images were performed to evaluate extent of MO and late gadolinium-enhanced images to assess PMO and infarct size (IS). Major adverse cardiac events (MACE) were collected at 1-year follow-up. MO and PMO were found in 127 (69%) and 87 (47%) patients, respectively. By using univariate logistic regression analysis, high Global Registry of Acute Coronary Events (GRACE) risk score (odds ratio [OR] 95% confidence interval [CI]: 3.6 [1.8-7.4], p < 0.001), IS greater than 10% (OR [95% CI]: 2.7 [1.1-6.9], p = 0.036), left ventricular ejection fraction less than 40% (OR [95% CI]: 2.4 [1.1-5.2], p = 0.027), presence of MO (OR [95% CI]: 3.1 [1.3-7.3], p = 0.004) and presence of PMO (OR [95% CI]:10 [4.1-23.9], p < 0.001) were shown to be significantly associated with the outcome. By using multivariate analysis, presence of MO (OR [95% CI]: 2.5 [1.0-6.2], p = 0.045) or of PMO (OR [95% CI]: 8.7 [3.6-21.1], p < 0.001), associated with GRACE score, were predictors of MACE. Presence of microvascular obstruction and persistent microvascular obstruction is very common in AMI patients even after successful reperfusion and is associated with a dramatically higher risk of subsequent cardiovascular events, beyond established prognostic markers. Moreover, our data suggest that the prognostic impact of PMO might be superior to MO.

Magnetic resonance imaging of persistent myocardial obstruction after myocardial infarction. A tool becoming increasingly important in clinical cardiology?

Aggressive reperfusion therapy using percutaneous coronary intervention (PCI) techniques has contributed significantly with the decrease of cardiac mortality after myocardial infarction in the last decade. This by limiting myocardial necrosis and infarct size [1]. Despite complete restoration of flow in the epicardial coronary artery after PCI, myocardial perfusion is not restored in up to 30% of patients due to microvascular obstruction [2]. Microvascular obstruction is known to be associated with a higher incidence of left ventricular remodeling, post infarct complications, congestive heart failure and death [3]. Imaging of the extent of microvascular obstruction is important because local delivery of pluripotent cells, having cardiomyogenic potential, in viable infarct borders might regenerate heart tissue [4]. The preferred way to detect microvascular obstruction with MRI is using gadolinium enhanced magnetic resonance imaging. This can be done using first-pass perfusion and with late gadolinium enhancement [5, 6]. After contrast injection, initially hypoenhanced regions, corresponding to areas with microvascular obstruction, are seen surrounded by a larger region of hyperenhancement. The hypoenhancement is due to substantially reduced perfusion at the microcirculatory level, which prevents penetration of contrast into the core of the infarct. Because the flow in these regions is low, they become dark initially but become hyperenhanced later, as soon as contrast accumulates. Acute myocardial infarction is also accompanied by myocardial edema [7]. T2-weighted (T2w) MRI is a noninvasive method to visualize myocardial edema after myocardial infarction [8]. In T2w images, there is a high signal intensity in the area of the infarction, corresponding with the amount of myocardial water [9, 10]. Because the area of edema is larger than the true infarction size, the hyperintense area on T2w images corresponds to a viable area, which is at risk [10]. The peri-infarct zone can be calculated as the size of edema on T2w MRI and the infarct size on delayed contrast enhanced MRI [8]. The current study of Choi et al. [11] in the International Journal of Cardiac Imaging shows, that in a pig pig model the extent of persistent microvascular obstruction was nearly half in a group without high signal intensity on T2w imaging compared to the group with high intensity signals. The contrast ratio of T2w images showed a significant inverse correlation with the extent of persistent microvascular obstruction observed in delayed enhancement images. The contrast ratio of T2-weighted image showed also a significant inverse correlation with the extent of intramyocardial hemorrhage seen in postmortem histochemical staining. In clinical practice, these findings could be used for risk stratification of patients after myocardial infarction or L. H. B. Baur (&) Department of Cardiology, Atrium medical centre parkstad, University of Maastricht, Henri Dunantstreet 5, 6401CX Heerlen, the Netherlands e-mail: l.baur@atriummc.nl