Remodeling after acute myocardial infarction: mapping ventricular dilatation using three dimensional CMR image registration

Using LDDMM and a kinematic cardiac growth model to quantify growth and remodelling in rat hearts under PAH

Pulmonary arterial hypertension (PAH) is a rapidly progressive and fatal disease, with right ventricular failure being the primary cause of death in patients with PAH. This study aims to determine the mechanical stimuli that may initiate heart growth and remodelling (G&R). To achieve this, two bi-ventricular models were constructed: one for a control rat heart and another for a rat heart with PAH. The growth of the diseased heart was estimated by warping it to the control heart using an improved large deformation diffeomorphic metric mapping (LDDMM) framework. Correlation analysis was then performed between mechanical cues (stress and strain) and growth tensors, which revealed that principal strains may serve as a triggering stimulus for myocardial growth and remodelling under PAH. The growth tensors, estimated from in vivo images, could explain 84.3% of the observed geometrical changes in the diseased heart with PAH by using a kinematic cardiac growth model. Our approach has the potential to quantify G&R using sparse in vivo images and to provide insights into the underlying mechanism of triggering right heart failure from a biomechanical perspective.

An updated Lagrangian constrained mixture model of pathological cardiac growth and remodelling

Progressive left ventricular (LV) growth and remodelling (G&R) is often induced by volume and pressure overload, characterized by structural and functional adaptation through myocyte hypertrophy and extracellular matrix remodelling, which are dynamically regulated by biomechanical factors, inflammation, neurohormonal pathways, etc. When prolonged, it can eventually lead to irreversible heart failure. In this study, we have developed a new framework for modelling pathological cardiac G&R based on constrained mixture theory using an updated reference configuration, which is triggered by altered biomechanical factors to restore biomechanical homeostasis. Eccentric and concentric growth, and their combination have been explored in a patient-specific human LV model under volume and pressure overload. Eccentric growth is triggered by overstretching of myofibres due to volume overload, i.e. mitral regurgitation, whilst concentric growth is driven by excessive contractile stress due to pressure overload, i.e. aortic stenosis. Different biological constituent's adaptations under pathological conditions are integrated together, which are the ground matrix, myofibres and collagen network. We have shown that this constrained mixture-motivated G&R model can capture different phenotypes of maladaptive LV G&R, such as chamber dilation and wall thinning under volume overload, wall thickening under pressure overload, and more complex patterns under both pressure and volume overload. We have further demonstrated how collagen G&R would affect LV structural and functional adaption by providing mechanistic insight on anti-fibrotic interventions. This updated Lagrangian constrained mixture based myocardial G&R model has the potential to understand the turnover processes of myocytes and collagen due to altered local mechanical stimuli in heart diseases, and in providing mechanistic links between biomechanical factors and biological adaption at both the organ and cellular levels. Once calibrated with patient data, it can be used for assessing heart failure risk and designing optimal treatment therapies. STATEMENT OF SIGNIFICANCE: Computational modelling of cardiac G&R has shown high promise to provide insight into heart disease management when mechanistic understandings are quantified between biomechanical factors and underlying cellular adaptation processes. The kinematic growth theory has been dominantly used to phenomenologically describe the biological G&R process but neglecting underlying cellular mechanisms. We have developed a constrained mixture based G&R model with updated reference by taking into account different mechanobiological processes in the ground matrix, myocytes and collagen fibres. This G&R model can serve as a basis for developing more advanced myocardial G&R models further informed by patient data to assess heart failure risk, predict disease progression, select the optimal treatment by hypothesis testing, and eventually towards a truly precision cardiology using in-silico models.

Normative healthy reference values for global and segmental 3D principal and geometry dependent strain from cine cardiac magnetic resonance imaging

3-Dimensional (3D) myocardial deformation analysis (3D-MDA) enables novel descriptions of geometry-independent principal strain (PS). Applied to routine 2D cine cardiovascular magnetic resonance (CMR), this provides unique measures of myocardial biomechanics for disease diagnosis and prognostication. However, healthy reference values remain undefined. This study describes age- and sex-stratified reference values from CMR-based 3D-MDA, including 3D PS. One hundred healthy volunteers were prospectively recruited following institutional ethics approval and underwent CMR imaging. 3D-MDA was performed using validated software. Age- and sex-stratified global and segmental strain measures were derived for conventional geometry-dependent [circumferential (CS), longitudinal (LS), and radial (RS)] and geometry-independent [minimum (minPS) and maximum principal (maxPS)] directions of deformation. Layer-specific contraction angle interactions were determined using local minPS vectors. The average age was 43 ± 15 years and 55% were women. Strain measures were higher in women versus men. 3D PS-based assessment of maximum tissue shortening (minPS) and maximum tissue thickening (maxPS) were greater than corresponding geometry-dependent markers of LS and RS, consistent with improved representation of local tissue deformations. Global maxPS amplitude best discriminated both age and sex. Segmental analyses showed greater strain amplitudes in apical segments. Transmural PS contraction angles were higher in females and showed a heterogeneous distribution across segments. In this study we provided age and sex-based reference values for 3D strain from CMR imaging, demonstrating improved capacity for 3D PS to document maximal local tissue deformations and to discriminate age and sex phenotypes. Novel markers of layer-specific strain angles from 3D PS were also described.

Left Ventricular Adverse Remodeling in Ischemic Heart Disease: Emerging Cardiac Magnetic Resonance Imaging Biomarkers

Post-ischemic left ventricular (LV) remodeling is a biologically complex process involving myocardial structure, LV shape, and function, beginning early after myocardial infarction (MI) and lasting until 1 year. Adverse remodeling is a post-MI maladaptive process that has been associated with long-term poor clinical outcomes. Cardiac Magnetic Resonance (CMR) is the best tool to define adverse remodeling because of its ability to accurately measure LV end-diastolic and end-systolic volumes and their variation over time and to characterize the underlying myocardial changes. Therefore, CMR is the gold standard method to assess in vivo myocardial infarction extension and to detect the presence of microvascular obstruction and intramyocardial hemorrhage, both associated with adverse remodeling. In recent times, new CMR quantitative biomarkers emerged as predictive of post-ischemic adverse remodeling, such as T1 mapping, myocardial strain, and 4D flow. Additionally, CMR T1 mapping imaging may depict infarcted tissue and assess diffuse myocardial fibrosis by using surrogate markers such as extracellular volume fraction, which may predict functional recovery or risk stratification of remodeling. Finally, there is emerging evidence supporting the utility of intracavitary blood flow kinetic energy and hemodynamic features assessed by the 4D flow CMR technique as early predictors of remodeling.

Three-dimensional quantitative assessment of myocardial infarction via multimodality fusion imaging: methodology, validation, and preliminary clinical application

BACKGROUND

The precise assessment of myocardial infarction (MI) is crucial both for therapeutic interventions in old MI and the development of new and effective techniques to repair injured myocardium. A novel method was developed to assess left ventricular (LV) quantitatively infarction through three-dimensional (3D) multimodality fusion based on computed tomography angiography (CTA) and technetium-99m methoxyisobutylisonitrile (99mTc-MIBI) single-photon emission computed tomography (SPECT) images. This study sought to develop a 3D quantitative method for MI for pre-clinical study and clinical application.

METHODS

Three months after the MI models were established in 20 minipigs, CTA and SPECT images were acquired separately, which were then aligned automatically with the constraints of the shape and the whole heart and LV myocardium position. Infarct ratios were quantified based on the 3D fusion images. The quantitative assessment was then experimentally validated via an ex vivo histology analysis using triphenyl-tetrazolium-chloride staining and subsequently applied to post-MI patients (n=8).

RESULTS

The location of an infarct identified by the SPECT was consistent with that identified by an ex vivo heart in a 3D space. Infarct size determined by CTA-SPECT was correlated with infarct size assessed by triphenyl-tetrazolium-chloride pathology {27.6% [interquartile range (IQR) 17.1-34.7%] vs. 24.1% (IQR 14.7-32.5%), r2=0.99, P<0.01}. In clinical cases, the CTA-SPECT 3D fusion quantitative results were significantly correlated with the quantitative perfusion SPECT results (r=0.976, P<0.01).

CONCLUSIONS

The proposed 3D fusion quantitative assessment method provides reliable and intuitive evaluations of infarction. This novel quantification technique enables whole heart quantification for the pre-operation evaluation and post-diagnosis management of old MI patients. It could also be applied to the design of 3D-printed cardiac patches.

Surgery for heart failure: Treatment options and implications

Heart failure is considered one of the leading causes of death worldwide. Over the years, etiological risk factors, diagnostic criteria, and classifications have been revised to create guide management needed to alleviate the global health burden caused by heart failure. Pharmacological treatments have progressed over time but are insufficient in reducing mortality. This leads to many patients developing advanced heart failure who will require surgical intervention often in the form of the gold standard, a heart transplant. However, the number of patients requiring a transplant far exceeds the number of donors. Other surgical inventions have been utilized, yet the rate of patients being diagnosed with heart failure is still increasing. Future developments in the surgical field of heart failure include the 77SyncCardia and atrial shunting but long-term clinical trials involving larger cohorts of patients have not yet taken place to view how effective these approaches can be.

Neural-Network-Based Diagnosis Using 3-Dimensional Myocardial Architecture and Deformation: Demonstration for the Differentiation of Hypertrophic Cardiomyopathy

The diagnosis of cardiomyopathy states may benefit from machine-learning (ML) based approaches, particularly to distinguish those states with similar phenotypic characteristics. Three-dimensional myocardial deformation analysis (3D-MDA) has been validated to provide standardized descriptors of myocardial architecture and deformation, and may therefore offer appropriate features for the training of ML-based diagnostic tools. We aimed to assess the feasibility of automated disease diagnosis using a neural network trained using 3D-MDA to discriminate hypertrophic cardiomyopathy (HCM) from its mimic states: cardiac amyloidosis (CA), Anderson–Fabry disease (AFD), and hypertensive cardiomyopathy (HTNcm). 3D-MDA data from 163 patients (mean age 53.1 ± 14.8 years; 68 females) with left ventricular hypertrophy (LVH) of known etiology was provided. Source imaging data was from cardiac magnetic resonance (CMR). Clinical diagnoses were as follows: 85 HCM, 30 HTNcm, 30 AFD, and 18 CA. A fully-connected-layer feed-forward neural was trained to distinguish HCM vs. other mimic states. Diagnostic performance was compared to threshold-based assessments of volumetric and strain-based CMR markers, in addition to baseline clinical patient characteristics. Threshold-based measures provided modest performance, the greatest area under the curve (AUC) being 0.70. Global strain parameters exhibited reduced performance, with AUC under 0.64. A neural network trained exclusively from 3D-MDA data achieved an AUC of 0.94 (sensitivity 0.92, specificity 0.90) when performing the same task. This study demonstrates that ML-based diagnosis of cardiomyopathy states performed exclusively from 3D-MDA is feasible and can distinguish HCM from mimic disease states. These findings suggest strong potential for computer-assisted diagnosis in clinical practice.

Coexistence of transmural and lateral wavefront progression of myocardial infarction in the human heart

INTRODUCTION AND OBJECTIVES

According to the wavefront phenomenon described in the late 1970s, myocardial infarction triggered by acute coronary occlusion progresses with increasing duration of ischemia as a transmural wavefront from the subendocardium toward the subepicardium. However, whether wavefront progression of necrosis also occurs laterally has been disputed. We aimed to assess the transmural and lateral spread of myocardial damage after acute myocardial infarction in humans and to evaluate the impact of metoprolol on these.

METHODS

We assessed myocardial infarction in the transmural and lateral dimensions in a cohort of 220 acute ST-segment elevation myocardial infarction (STEMI) patients from the METOCARD-CNIC trial (Effect of Metoprolol in Cardioprotection During an Acute Myocardial Infarction). The patients underwent cardiac magnetic resonance imaging at 5 to 7 days and 6 months post-STEMI.

RESULTS

On day 5 to 7 post-STEMI cardiac magnetic resonance, there was a strong linear correlation between the transmural and lateral extent of infarction (delayed gadolinium enhancement) (r=-0.88; P<.001). Six months after STEMI, myocardial scarring (delayed gadolinium enhancement) was significantly less extensive in the transmural and lateral dimensions, suggesting that infarct resorption occurs in both. Furthermore, progression in both directions occurred both in patients receiving metoprolol and control patients, implying that myocardial salvage occurs both in the transmural and the lateral direction.

CONCLUSIONS

Our findings challenge the assumption that irreversible injury does not spread laterally. A "circumferential" or multidirectional wavefront would imply that cardioprotective therapies might produce meaningful salvage at lateral borders of the infarct. This trial was registered at ClinicalTrial.gov (Identifier: NCT01311700).

Biomechanics of infarcted left Ventricle-A review of experiments

Myocardial infarction (MI) is one of leading diseases to contribute to annual death rate of 5% in the world. In the past decades, significant work has been devoted to this subject. Biomechanics of infarcted left ventricle (LV) is associated with MI diagnosis, understanding of remodelling, MI micro-structure and biomechanical property characterizations as well as MI therapy design and optimization, but the subject has not been reviewed presently. In the article, biomechanics of infarcted LV was reviewed in terms of experiments achieved in the subject so far. The concerned content includes experimental remodelling, kinematics and kinetics of infarcted LVs. A few important issues were discussed and several essential topics that need to be investigated further were summarized. Microstructure of MI tissue should be observed even carefully and compared between different methods for producing MI scar in the same animal model, and eventually correlated to passive biomechanical property by establishing innovative constitutive laws. More uniaxial or biaxial tensile tests are desirable on MI, border and remote tissues, and viscoelastic property identification should be performed in various time scales. Active contraction experiments on LV wall with MI should be conducted to clarify impaired LV pumping function and supply necessary data to the function modelling. Pressure-volume curves of LV with MI during diastole and systole for the human are also desirable to propose and validate constitutive laws for LV walls with MI.

Assessing regional left ventricular thickening dysfunction and dyssynchrony via personalized modeling and 3D wall thickness measurements for acute myocardial infarction

BACKGROUND

Existing clinical diagnostic and assessment methods could be improved to facilitate early detection and treatment of cardiac dysfunction associated with acute myocardial infarction (AMI) to reduce morbidity and mortality.

PURPOSE

To develop 3D personalized left ventricular (LV) models and thickening assessment framework for assessing regional wall thickening dysfunction and dyssynchrony in AMI patients.

STUDY TYPE

Retrospective study, diagnostic accuracy.

SUBJECTS

Forty-four subjects consisting of 15 healthy subjects and 29 AMI patients.

FIELD STRENGTH/SEQUENCE

1.5T/steady-state free precession cine MRI scans; LGE MRI scans.

ASSESSMENT

Quantitative thickening measurements across all cardiac phases were correlated and validated against clinical evaluation of infarct transmurality by an experienced cardiac radiologist based on the American Heart Association (AHA) 17-segment model.

STATISTICAL TEST

Nonparametric 2-k related sample-based Kruskal-Wallis test; Mann-Whitney U-test; Pearson's correlation coefficient.

RESULTS

Healthy LV wall segments undergo significant wall thickening (P < 0.05) during ejection and have on average a thicker wall (8.73 ± 1.01 mm) compared with infarcted wall segments (2.86 ± 1.11 mm). Myocardium with thick infarct (ie, >50% transmurality) underwent remarkable wall thinning during contraction (thickening index [TI] = 1.46 ± 0.26 mm) as opposed to healthy myocardium (TI = 4.01 ± 1.04 mm). For AMI patients, LV that showed signs of thinning were found to be associated with a significantly higher percentage of dyssynchrony as compared with healthy subjects (dyssynchrony index [DI] = 15.0 ± 5.0% vs. 7.5 ± 2.0%, P < 0.01). Also, a strong correlation was found between our TI and left ventricular ejection fraction (LVEF) (r = 0.892, P < 0.01), and moderate correlation between DI and LVEF (r = 0.494, P < 0.01).

DATA CONCLUSION

The extracted regional wall thickening and DIs are shown to be strongly correlated with infarct severity, therefore suggestive of possible practical clinical utility.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:1006-1019.

TIME Trial: Effect of Timing of Stem Cell Delivery Following ST-Elevation Myocardial Infarction on the Recovery of Global and Regional Left Ventricular Function: Final 2-Year Analysis

RATIONALE

The TIME trial (Timing in Myocardial Infarction Evaluation) was the first cell therapy trial sufficiently powered to determine if timing of cell delivery after ST-segment-elevation myocardial infarction affects recovery of left ventricular (LV) function.

OBJECTIVE

To report the 2-year clinical and cardiac magnetic resonance imaging results and their modification by microvascular obstruction.

METHODS AND RESULTS

TIME was a randomized, double-blind, placebo-controlled trial comparing 150 million bone marrow mononuclear cells versus placebo in 120 patients with anterior ST-segment-elevation myocardial infarctions resulting in LV dysfunction. Primary end points included changes in global (LV ejection fraction) and regional (infarct and border zone) function. Secondary end points included changes in LV volumes, infarct size, and major adverse cardiac events. Here, we analyzed the continued trajectory of these measures out to 2 years and the influence of microvascular obstruction present at baseline on these long-term outcomes. At 2 years (n=85), LV ejection fraction was similar in the bone marrow mononuclear cells (48.7%) and placebo groups (51.6%) with no difference in regional LV function. Infarct size and LV mass decreased ≥30% in each group at 6 months and declined gradually to 2 years. LV volumes increased ≈10% at 6 months and remained stable to 2 years. Microvascular obstruction was present in 48 patients at baseline and was associated with significantly larger infarct size (56.5 versus 36.2 g), greater adverse LV remodeling, and marked reduction in LV ejection fraction recovery (0.2% versus 6.2%).

CONCLUSIONS

In one of the longest serial cardiac magnetic resonance imaging analyses of patients with large anterior ST-segment-elevation myocardial infarctions, bone marrow mononuclear cells administration did not improve recovery of LV function over 2 years. Microvascular obstruction was associated with reduced recovery of LV function, greater adverse LV remodeling, and more device implantations. The use of cardiac magnetic resonance imaging leads to greater dropout of patients over time because of device implantation in patients with more severe LV dysfunction resulting in overestimation of clinical stability of the cohort.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT00684021.

Electromechanics modeling of the effects of myocardial infarction on left ventricular function

Ventricular remodeling may occur following myocardial infarction of the left ventricle (LV) and such remodeling has been shown to be correlated with increased patient morbidity and mortality. It is thus important to estimate the likelihood of remodeling from the state of the infarcted LV. In this paper, we present simulations from an actively-contracting truncated ellipsoid LV model, incorporating realistic fiber orientation and electromechanical properties, to investigate the effects of infarct size and transmural extent (TME) on myofiber regional mechanics. Results showed that transmural infarcts greatly elevated both the myofiber stress and strain at the border zone during end systole, making the LV more susceptible to structural remodeling. It was found that TME rather than infarct size was more predictive of LV remodeling.

Soluble interleukin 6 receptor levels are associated with reduced myocardial reperfusion after percutaneous coronary intervention for acute myocardial infarction

AIMS

Interleukin-6 receptor (IL-6R) signalling has been suggested to play a causal role in the development and outcome of coronary heart disease (CHD). The aim of this study was to investigate the association of sIL-6R levels with myocardial reperfusion after percutaneous coronary intervention (PCI) for acute ST-elevated myocardial infarction (STEMI).

METHODS

Blood was sampled from 70 patients presenting with STEMI at 6 different time-points (baseline, post-PCI, t=1h, t=6h, t=24h, t=2w). Coronary angiograms post-PCI were analysed for myocardial blush grade (MBG) as indicator of myocardial reperfusion. Serum IL-6 and sIL-6R were measured using IL-6 and sIL-6R enzyme-linked immunosorbent assays (ELISA).

RESULTS

sIL-6R levels fluctuated biphasic during the two weeks after STEMI. Reduced MBG was associated with a larger change in sIL-6R levels between baseline and post-PCI compared to optimal MBG (-13.40; SEM 2.78ng/ml vs -1.99; SEM 2.35ng/ml, respectively; p<0.001). Patients with reduced MBG also showed a larger increase in sIL-6R levels after PCI and 1h after myocardial infarction (MI) compared to optimal MBG (respectively 11.56; SEM 2.68ng/ml vs 3.02; SEM 2.39ng/ml; p=0.018). IL-6/sIL-6R ratio was also more increased in patients with reduced MBG at 24h after myocardial infarction (0.23; SEM 0.08-0.51 vs 0.10; SEM 0.05-0.21; p=0.024). An optimal MBG was associated with a 10ng increase in sIL-6R level between baseline and post-PCI (OR 1.687, CI 1.095-2.598; p=0.018).

CONCLUSIONS

sIL-6R levels fluctuate biphasic during the two weeks after MI with larger changes and increased IL-6/sIL-6R ratio in patients with reduced MBG. Further research is needed to increase our understanding of the possible causality of these associations.

Review of Journal of Cardiovascular Magnetic Resonance 2013

There were 109 articles published in the Journal of Cardiovascular Magnetic Resonance (JCMR) in 2013, which is a 21% increase on the 90 articles published in 2012. The quality of the submissions continues to increase. The editors are delighted to report that the 2012 JCMR Impact Factor (which is published in June 2013) has risen to 5.11, up from 4.44 for 2011 (as published in June 2012), a 15% increase and taking us through the 5 threshold for the first time. The 2012 impact factor means that the JCMR papers that were published in 2010 and 2011 were cited on average 5.11 times in 2012. The impact factor undergoes natural variation according to citation rates of papers in the 2 years following publication, and is significantly influenced by highly cited papers such as official reports. However, the progress of the journal's impact over the last 5 years has been impressive. Our acceptance rate is <25% and has been falling because the number of articles being submitted has been increasing. In accordance with Open-Access publishing, the JCMR articles go on-line as they are accepted with no collating of the articles into sections or special thematic issues. For this reason, the Editors have felt that it is useful once per calendar year to summarize the papers for the readership into broad areas of interest or theme, so that areas of interest can be reviewed in a single article in relation to each other and other recent JCMR articles. The papers are presented in broad themes and set in context with related literature and previously published JCMR papers to guide continuity of thought in the journal. We hope that you find the open-access system increases wider reading and citation of your papers, and that you will continue to send your quality manuscripts to JCMR for publication.

Atlas-based Anatomical Modeling and Analysis of Heart Disease

Heart shape and function are major determinants of disease severity and predictors of future morbidity and mortality. Many studies now rely on non-invasive cardiac imaging techniques to quantify structural and functional changes. Statistical anatomical modeling of heart shape and motion provides a new tool for the quantification and evaluation of heart disease. This review surveys recent progress in the evaluation of statistical shape measures across populations and sub-cohorts, and highlights collaborative efforts to facilitate data sharing and atlas-based shape analysis.

Review of Journal of Cardiovascular Magnetic Resonance 2012

There were 90 articles published in the Journal of Cardiovascular Magnetic Resonance (JCMR) in 2012, which is an 8% increase in the number of articles since 2011. The quality of the submissions continues to increase. The editors are delighted to report that the 2011 JCMR Impact Factor (which is published in June 2012) has risen to 4.44, up from 3.72 for 2010 (as published in June 2011), a 20% increase. The 2011 impact factor means that the JCMR papers that were published in 2009 and 2010 were cited on average 4.44 times in 2011. The impact factor undergoes natural variation according to citation rates of papers in the 2 years following publication, and is significantly influenced by highly cited papers such as official reports. However, the progress of the journal's impact over the last 5 years has been impressive. Our acceptance rate is approximately 25%, and has been falling as the number of articles being submitted has been increasing. In accordance with Open-Access publishing, the JCMR articles go on-line as they are accepted with no collating of the articles into sections or special thematic issues. For this reason, the Editors have felt that it is useful once per calendar year to summarize the papers for the readership into broad areas of interest or theme, so that areas of interest can be reviewed in a single article in relation to each other and other recent JCMR articles. The papers are presented in broad themes and set in context with related literature and previously published JCMR papers to guide continuity of thought in the journal. We hope that you find the open-access system increases wider reading and citation of your papers, and that you will continue to send your quality manuscripts to JCMR for publication.