Late Gadolinium Enhancement Cardiac Magnetic Resonance Imaging: From Basic Concepts to Emerging Methods

Imaging of Cardiac Fibrosis: An Update, From the AJR Special Series on Imaging of Fibrosis

Myocardial fibrosis (MF) is defined as excessive production and deposition of extra-cellular matrix (ECM) proteins that result in pathologic myocardial remodeling. Three types of MF have been identified: replacement fibrosis from tissue necrosis, reactive fibrosis from myocardial stress, and infiltrative interstitial fibrosis from progressive deposition of nondegradable material such as amyloid. Although echocardiography, nuclear medicine, and CT play important roles in the assessment of MF, MRI is pivotal in the evaluation of MF, with the late gadolinium enhancement (LGE) technique used as a primary end point. The LGE technique focuses on the pattern and distribution of gadolinium accumulation in the myocardium and assists in the diagnosis and establishment of the cause of both ischemic and nonischemic cardiomyopathy. LGE MRI also aids prognostication and risk stratification. In addition, LGE MRI is used to guide the management of patients considered for ablation for arrhythmias. Parametric mapping techniques, including T1 mapping and extracellular volume measurement, allow detection and quantification of diffuse fibrosis, which may not be detected by LGE MRI. These techniques also allow monitoring of disease progression and therapy response. This review provides an update on the imaging of MF, including prognostication and risk stratification tools, electrophysiologic considerations, and disease monitoring.

Late/delayed gadolinium enhancement in MRI after intravenous administration of extracellular gadolinium-based contrast agents: is it worth waiting?

The acquisition of images minutes or even hours after intravenous extracellular gadolinium-based contrast agents (GBCA) administration ("Late/Delayed Gadolinium Enhancement" imaging; in this review, further termed LGE) has gained significant prominence in recent years in magnetic resonance imaging. The major limitation of LGE is the long examination time; thus, it becomes necessary to understand when it is worth waiting time after the intravenous injection of GBCA and which additional information comes from LGE. LGE can potentially be applied to various anatomical sites, such as heart, arterial vessels, lung, brain, abdomen, breast, and the musculoskeletal system, with different pathophysiological mechanisms. One of the most popular clinical applications of LGE regards the assessment of myocardial tissue thanks to its ability to highlight areas of acute myocardial damage and fibrotic tissues. Other frequently applied clinical contexts involve the study of the urinary tract with magnetic resonance urography and identifying pathological abdominal processes characterized by high fibrous stroma, such as biliary tract tumors, autoimmune pancreatitis, or intestinal fibrosis in Crohn's disease. One of the current areas of heightened research interest revolves around the possibility of non-invasively studying the dynamics of neurofluids in the brain (the glymphatic system), the disruption of which could underlie many neurological disorders.

Dark-Blood Late Gadolinium Enhancement MRI Is Noninferior to Bright-Blood LGE in Non-Ischemic Cardiomyopathies

(1) Background and Objectives: Dark-blood late gadolinium enhancement has been shown to be a reliable cardiac magnetic resonance (CMR) method for assessing viability and depicting myocardial scarring in ischemic cardiomyopathy. The aim of this study was to evaluate dark-blood LGE imaging compared with conventional bright-blood LGE for the detection of myocardial scarring in non-ischemic cardiomyopathies. (2) Materials and Methods: Patients with suspected non-ischemic cardiomyopathy were prospectively enrolled in this single-centre study from January 2020 to March 2023. All patients underwent 1.5 T CMR with both dark-blood and conventional bright-blood LGE imaging. Corresponding short-axis stacks of both techniques were analysed for the presence, distribution, pattern, and localisation of LGE, as well as the quantitative scar size (%). (3) Results: 343 patients (age 44 ± 17 years; 124 women) with suspected non-ischemic cardiomyopathy were examined. LGE was detected in 123 of 343 cases (36%) with excellent inter-reader agreement (κ 0.97-0.99) for both LGE techniques. Dark-blood LGE showed a sensitivity of 99% (CI 98-100), specificity of 99% (CI 98-100), and an accuracy of 99% (CI 99-100) for the detection of non-ischemic scarring. No significant difference in total scar size (%) was observed. Dark-blood imaging with mean 5.35 ± 4.32% enhanced volume of total myocardial volume, bright-blood with 5.24 ± 4.28%, p = 0.84. (4) Conclusions: Dark-blood LGE imaging is non-inferior to conventional bright-blood LGE imaging in detecting non-ischemic scarring. Therefore, dark-blood LGE imaging may become an equivalent method for the detection of both ischemic and non-ischemic scars.

Post-myocardial infarction fibrosis: Pathophysiology, examination, and intervention

Cardiac fibrosis plays an indispensable role in cardiac tissue homeostasis and repair after myocardial infarction (MI). The cardiac fibroblast-to-myofibroblast differentiation and extracellular matrix collagen deposition are the hallmarks of cardiac fibrosis, which are modulated by multiple signaling pathways and various types of cells in time-dependent manners. Our understanding of the development of cardiac fibrosis after MI has evolved in basic and clinical researches, and the regulation of fibrotic remodeling may facilitate novel diagnostic and therapeutic strategies, and finally improve outcomes. Here, we aim to elaborate pathophysiology, examination and intervention of cardiac fibrosis after MI.

High-resolution structural-functional substrate-trigger characterization: Future roadmap for catheter ablation of ventricular tachycardia

Introduction

Patients with ventricular tachyarrhythmias (VT) are at high risk of sudden cardiac death. When appropriate, catheter ablation is modestly effective, with relatively high VT recurrence and complication rates. Personalized models that incorporate imaging and computational approaches have advanced VT management. However, 3D patient-specific functional electrical information is typically not considered. We hypothesize that incorporating non-invasive 3D electrical and structural characterization in a patient-specific model improves VT-substrate recognition and ablation targeting.

Materials and methods

In a 53-year-old male with ischemic cardiomyopathy and recurrent monomorphic VT, we built a structural-functional model based on high-resolution 3D late-gadolinium enhancement (LGE) cardiac magnetic resonance imaging (3D-LGE CMR), multi-detector computed tomography (CT), and electrocardiographic imaging (ECGI). Invasive data from high-density contact and pace mapping obtained during endocardial VT-substrate modification were also incorporated. The integrated 3D electro-anatomic model was analyzed off-line.

Results

Merging the invasive voltage maps and 3D-LGE CMR endocardial geometry led to a mean Euclidean node-to-node distance of 5 ± 2 mm. Inferolateral and apical areas of low bipolar voltage (<1.5 mV) were associated with high 3D-LGE CMR signal intensity (>0.4) and with higher transmurality of fibrosis. Areas of functional conduction delay or block (evoked delayed potentials, EDPs) were in close proximity to 3D-LGE CMR-derived heterogeneous tissue corridors. ECGI pinpointed the epicardial VT exit at ∼10 mm from the endocardial site of origin, both juxtaposed to the distal ends of two heterogeneous tissue corridors in the inferobasal left ventricle. Radiofrequency ablation at the entrances of these corridors, eliminating all EDPs, and at the VT site of origin rendered the patient non-inducible and arrhythmia-free until the present day (20 months follow-up). Off-line analysis in our model uncovered dynamic electrical instability of the LV inferolateral heterogeneous scar region which set the stage for an evolving VT circuit.

Discussion and conclusion

We developed a personalized 3D model that integrates high-resolution structural and electrical information and allows the investigation of their dynamic interaction during arrhythmia formation. This model enhances our mechanistic understanding of scar-related VT and provides an advanced, non-invasive roadmap for catheter ablation.

Retrospective, observational analysis of cardiac function associated with global preoperative myocardial scar in patients with ischemic cardiomyopathy after coronary artery bypass grafting

BACKGROUND

Drawing on accumulated patient data from a hospital database, the goal of this retrospective study was to analyze cardiac function associated with global preoperative myocardial scarring assessed by cardiac magnetic resonance with late gadolinium enhancement (CMR-LGE) in patients with ischemic cardiomyopathy (ICM) after coronary artery bypass grafting (CABG).

METHODS

A total of 57 patients diagnosed with ICM who underwent isolated CABG at Beijing Anzhen Hospital between September 2017 and September 2019 were enrolled in this retrospective study. All these patients underwent a preoperative CMR-LGE examination. Based on postoperative echocardiography results at 6 months, cases were divided into the following 2 groups: improved cardiac function [a difference of left ventricular ejection fraction (LVEF) greater than or equal to 5%] and unimproved cardiac function. The factors contributing to these patients' unimproved cardiac function were investigated.

RESULTS

At 6 months after surgery, 64.9% (37/57) of cases had improved cardiac function, and 35.1% (20/57) had no improvement. There was no statistical difference between the 2 groups in the Synergy Between Percutaneous Coronary Intervention With Taxus and Cardiac Surgery (SYNTAX) score (41.7±7.6 vs. 42.8±8.3; P=0.603), but compared to the improved group, preoperative myocardial scarring was significantly enlarged in the unimproved group (41.9%±6.4% vs. 27.8%±8.5%; P<0.001). In regression analysis, only preoperative myocardial scarring [odds ratio (OR) =1.44; 95% confidence interval (CI): 1.13-1.83; P=0.003] was associated with no change in cardiac function evaluated by echocardiography after CABG. The median follow-up of 1.6 years (range, 0.6-4.1 years) found that the unimproved group had a higher incidence of major adverse cardiovascular and cerebrovascular events (MACCEs) (8.1% vs. 25.0%; P=0.044), and that the New York Heart Association (NYHA) classification of the unimproved group was higher than that of the improved group (P=0.018).

CONCLUSIONS

In ICM patients, a greater amount of preoperative myocardial scarring is associated with unimproved cardiac function after CABG. The measurement of preoperative myocardial scarring may aid clinicians in identifying patients who would benefit from CABG.

TRoponin of Unknown origin in STroke evaluated by multi-component cardiac Magnetic resonance Imaging – The TRUST-MI study

Aims

Increased high-sensitive cardiac troponin I (hs-cTnI) levels are common in patients with acute ischemic stroke. However, only a minority demonstrates culprit lesions on coronary angiography, suggesting other mechanisms, e.g., inflammation, as underlying cause of myocardial damage. Late Gadolinium Enhancement (LGE)-cardiac magnetic resonance (CMR) with mapping techniques [T1, T2, extracellular volume (ECV)] allow the detection of both focal and diffuse myocardial abnormalities. We investigated the prevalence of culprit lesions by coronary angiography and myocardial tissue abnormalities by a comprehensive CMR protocol in troponin-positive stroke patients.

Methods and results

Patients with troponin-positive acute ischemic stroke and no history of coronary artery disease were prospectively enrolled. Coronary angiography and CMR (LGE, T1 + T2 mapping, ECV) were performed within the first days of the acute stroke. Twenty-five troponin-positive patients (mean age 62 years, 44% females) were included. 2 patients (8%) had culprit lesions on coronary angiography and underwent percutaneous coronary intervention. 13 patients (52%) demonstrated LGE: (i) n = 4 ischemic, (ii) n = 4 non-ischemic, and (iii) n = 5 ischemic AND non-ischemic. In the 12 LGE-negative patients, mapping revealed diffuse myocardial damage in additional 9 (75%) patients, with a high prevalence of increased T2 values.

Conclusions

Our data show a low prevalence of culprit lesions in troponin-positive stroke patients. However, &gt; 50% of the patients demonstrated myocardial scars (ischemic + non-ischemic) by LGE-CMR. Mapping revealed additional myocardial abnormalities (mostly inflammatory) in the majority of LGE-negative patients. Therefore, a comprehensive CMR protocol gives important insights in the etiology of troponin which might have implications for the further work-up of troponin-positive stroke patients.

[Cardiac magnetic resonance imaging and the myocardium : Differentiation between vital and nonvital tissue]

Cardiac magnetic resonance (cMR), a well-established imaging tool, is indispensable in the diagnosis and management of cardiovascular disease. Given its high spatial resolution and ability to characterize tissue, cMR represents the gold standard in determining myocardial viability. Gadolinium-based contrast-enhanced cMR can accurately identify myocardial scars and fibrosis in the ventricle and the atria, and differentiate it from normal myocardium. Gadolinium is an extracellular molecule which has been shown to be safe and beneficial in magnetic resonance imaging (MRI). Due to the larger extracellular space in myocardial scars, there is more uptake (wash-in) and slower elimination (wash-out) of gadolinium in those areas as opposed to normal myocardium. When imaged several minutes after intravenous administration of gadolinium, nonviable myocardial areas appear brighter than viable myocardium. The use of late-gadolinium enhancement (LGE) technique in assessing myocardial viability has been shown to highly correlate with histological examinations. Furthermore, this technique is highly reproducible and has very high intra- and interobserver agreement. Extent of LGE after myocardial infarction predicts the occurrence of adverse cardiovascular events. Moreover, LGE is highly accurate in predicting functional recovery of dysfunctional myocardial segments in patients undergoing revascularization and consequently has a key role in guiding revascularization procedures. In addition, use of LGE in the identification of myocardial fibrosis or myocardial damage in inflammatory myocardial disease helps to differentiate the type of cardiomyopathy and to predict sudden cardiac death among patients with heart failure. The role of LGE-MRI in the field of electrophysiology through recognition of different substrate for arrythmias and guiding the ablation therapy is steadily increasing and has fundamentally changed our understanding of atrial myopathy.