Fibrosis in Hypertrophic Cardiomyopathy Patients With and Without Sarcomere Gene Mutations

Detection of late gadolinium enhancement in patients with hypertrophic cardiomyopathy using machine learning

BACKGROUND

Late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR) in hypertrophic cardiomyopathy (HCM) typically represents myocardial fibrosis and may lead to fatal ventricular arrhythmias. However, CMR is resource-intensive and sometimes contraindicated. Thus, in patients with HCM, we aimed to detect LGE on CMR by applying machine learning (ML) algorithm to clinical parameters.

METHODS AND RESULTS

In this trans-Pacific multicenter study of HCM, a ML model was developed to distinguish the presence or absence of LGE on CMR by ridge classification method using 22 clinical parameters including 9 echocardiographic data. Among 742 patients in this cohort, the ML model was constructed in 2 institutions in the United States (training set, n = 554) and tested using data from an institution in Japan (test set, n = 188). LGE was detected in 299 patients (54%) in the training set and 76 patients (40%) in the test set. In the test set, the area under the receiver-operating-characteristic curve (AUC) of the ML model derived from the training set was 0.77 (95% confidence interval [CI] 0.70-0.84). When compared with a reference model constructed with 3 conventional risk factors for LGE on CMR (AUC 0.69 [95% CI 0.61-0.77]), the ML model outperformed the reference model (DeLong's test P = 0.01).

CONCLUSIONS

This trans-Pacific study demonstrates that ML analysis of clinical parameters can distinguish the presence of LGE on CMR in patients with HCM. Our ML model would help physicians identify patients with HCM in whom the pre-test probability of LGE is high, and therefore CMR will have higher utility.

The Role of Signalling Pathways in Myocardial Fibrosis in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most prevalent hereditary cardiovascular disorder, characterised by left ventricular hypertrophy and cardiac fibrosis. Cardiac fibroblasts, transformed into myofibroblasts, play a crucial role in the development of fibrosis. However, interactions between fibroblasts, cardiomyocytes, and immune cells are considered major mechanisms driving fibrosis progression. While the disease has a strong genetic background, its pathogenetic mechanisms remain complex and not fully understood. Several signalling pathways are implicated in fibrosis development. Among these, transforming growth factor-beta and angiotensin II are frequently studied in the context of cardiac fibrosis. In this review, we summarise the most current evidence on the involvement of signalling pathways in the pathogenesis of HCM. Additionally, we discuss the potential role of monitoring pro-fibrotic molecules in predicting clinical outcomes in patients with HCM.

Cardiovascular Magnetic Resonance-Based Tissue Characterization in Patients With Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a common hereditable cardiomyopathy that affects between 1:200 to 1:500 of the general population. The role of cardiovascular magnetic resonance (CMR) imaging in the management of HCM has expanded over the past 2 decades to become a key informant of risk in this patient population, delivering unique insights into tissue health and its influence on future outcomes. Numerous mature CMR-based techniques are clinically available for the interrogation of tissue health in patients with HCM, inclusive of contrast and noncontrast methods. Late gadolinium enhancement imaging remains a cornerstone technique for the identification and quantification of myocardial fibrosis with large cumulative evidence supporting value for the prediction of arrhythmic outcomes. T1 mapping delivers improved fidelity for fibrosis quantification through direct estimations of extracellular volume fraction but also offers potential for noncontrast surrogate assessments of tissue health. Water-sensitive imaging, inclusive of T2-weighted dark blood imaging and T2 mapping, have also shown preliminary potential for assisting in risk discrimination. Finally, emerging techniques, inclusive of innovative multiparametric methods, are expanding the utility of CMR to assist in the delivery of comprehensive tissue characterization toward the delivery of personalized HCM care. In this narrative review we summarize the contemporary landscape of CMR techniques aimed at characterizing tissue health in patients with HCM. The value of these respective techniques to identify patients at elevated risk of future cardiovascular outcomes are highlighted.

Novel Magnetic Resonance Imaging Tools for Hypertrophic Cardiomyopathy Risk Stratification

Hypertrophic cardiomyopathy (HCM) is a common genetic disorder with a well described risk of sudden cardiac death; however, risk stratification has remained a challenge. Recently, novel parameters in cardiac magnetic resonance imaging (CMR) have shown promise in helping to improve upon current risk stratification paradigms. In this manuscript, we have reviewed novel CMR risk markers and their utility in HCM. The results of the review showed that T1, extracellular volume, CMR feature tracking, and other miscellaneous novel CMR variables have the potential to improve sudden death risk stratification and may have additional roles in diagnosis and prognosis. The strengths and weaknesses of these imaging techniques, and their potential utility and implementation in HCM risk stratification are discussed.

Myocardial Fibrosis in Hypertrophic Cardiomyopathy: A Perspective from Fibroblasts

Hypertrophic cardiomyopathy (HCM) is the most common inherited heart disease and the leading cause of sudden cardiac death in young people. Mutations in genes that encode structural proteins of the cardiac sarcomere are the more frequent genetic cause of HCM. The disease is characterized by cardiomyocyte hypertrophy and myocardial fibrosis, which is defined as the excessive deposition of extracellular matrix proteins, mainly collagen I and III, in the myocardium. The development of fibrotic tissue in the heart adversely affects cardiac function. In this review, we discuss the latest evidence on how cardiac fibrosis is promoted, the role of cardiac fibroblasts, their interaction with cardiomyocytes, and their activation via the TGF-β pathway, the primary intracellular signalling pathway regulating extracellular matrix turnover. Finally, we summarize new findings on profibrotic genes as well as genetic and non-genetic factors involved in the pathophysiology of HCM.

Multimodality Imaging in Patients with Hypertrophic Cardiomyopathy and Atrial Fibrillation

Ventricular hypertrophy is associated with diastolic dysfunction, resulting in increased left atrial (LA) pressure, enlargement, fibrosis, and decreased LA function. Hypertrophic cardiomyopathy (HCM) is characterized by myocyte disarray, myocardial fibrosis, and hypertrophy. Notably, a thickened and noncompliant LV results in the impairment of diastolic function. These conditions promote LA remodeling and enlargement, which contribute to developing and maintaining atrial fibrillation (AF). AF is an atrial arrhythmia that occurs frequently in HCM, and evaluating the morphology and physiology of the atrium and ventricle is important for treatment and prognosis determination in HCM patients with AF. In addition, it provides a clue that can predict the possibility of new AF, even in patients not previously diagnosed with AF. Cardiac magnetic resonance (CMR), which can overcome the limitations of transthoracic echocardiography (TTE), has been widely used traditionally and even enables tissue characterization; moreover, it has emerged as an essential imaging modality for patients with HCM. Here, we review the role of multimodal imaging in patients with HCM and AF.

Hypertrophic Cardiomyopathy versus Storage Diseases with Myocardial Involvement

One of the main causes of heart failure is cardiomyopathies. Among them, the most common is hypertrophic cardiomyopathy (HCM), characterized by thickening of the left ventricular muscle. This article focuses on HCM and other cardiomyopathies with myocardial hypertrophy, including Fabry disease, Pompe disease, and Danon disease. The genetics and pathogenesis of these diseases are described, as well as current and experimental treatment options, such as pharmacological intervention and the potential of gene therapies. Although genetic approaches are promising and have the potential to become the best treatments for these diseases, further research is needed to evaluate their efficacy and safety. This article describes current knowledge and advances in the treatment of the aforementioned cardiomyopathies.

SARC Gene Mutation Is Associated With Myocardial Fibrosis Measured by Histopathology and Cardiac Magnetic Resonance in Patients With Hypertrophic Cardiomyopathy

Background Sarcomere gene mutation and myocardial fibrosis are both associated with poorer clinical outcomes in patients with hypertrophic cardiomyopathy (HCM). The aim of this study was to determine the relationship between sarcomere gene mutation and myocardial fibrosis measured by both histopathology and cardiac magnetic resonance (CMR). Methods and Results Two hundred twenty-seven patients with HCM who underwent surgical treatment, genetic testing, and CMR were enrolled. We retrospectively analyzed basic characteristics, sarcomere gene mutation, and myocardial fibrosis measured by CMR and histopathology. In our study, the mean age was 43 years, and 152 patients (67.0%) were men. A total of 107 patients (47.1%) carried a positive sarcomere gene mutation. The myocardial fibrosis ratio was significantly higher in the late gadolinium enhancement (LGE)+ group (LGE+ 14.3±7.5% versus LGE- 9.0±4.3%; P=0.001). Patients with HCM with SARC+ showed a high probability of fibrosis both in histopathology (myocardial fibrosis ratio 15.3±8.0% versus 12.4±6.5%; P=0.003) and CMR examination (LGE+ 98.1% versus 84.2%; P<0.001; LGE quantification 8.3% versus 5.8%; P<0.001). Linear regression analysis showed that sarcomere gene mutation (B=2.661; P=0.005) and left atrial diameter (B=0.240; P=0.001) were related factors for histopathological myocardial fibrosis. Also, the myocardial fibrosis ratio was significantly higher in the MYH7 (myosin heavy chain) group (MYH7 18.1±9.6% versus MYBPC3 [myosin binding protein C] 13.1±5.2%; P=0.019). Conclusions Patients with HCM with positive sarcomere gene mutation had a higher myocardial fibrosis extent than patients without mutation, and a significant difference in myocardial fibrosis was also observed between the MYBPC3 and MYH7 groups. In addition, a high consistency was found between CMR-LGE and histopathological myocardial fibrosis in patients with HCM.

Efficient in vivo genome editing prevents hypertrophic cardiomyopathy in mice

Dominant missense pathogenic variants in cardiac myosin heavy chain cause hypertrophic cardiomyopathy (HCM), a currently incurable disorder that increases risk for stroke, heart failure and sudden cardiac death. In this study, we assessed two different genetic therapies-an adenine base editor (ABE8e) and a potent Cas9 nuclease delivered by AAV9-to prevent disease in mice carrying the heterozygous HCM pathogenic variant myosin R403Q. One dose of dual-AAV9 vectors, each carrying one half of RNA-guided ABE8e, corrected the pathogenic variant in ≥70% of ventricular cardiomyocytes and maintained durable, normal cardiac structure and function. An additional dose provided more editing in the atria but also increased bystander editing. AAV9 delivery of RNA-guided Cas9 nuclease effectively inactivated the pathogenic allele, albeit with dose-dependent toxicities, necessitating a narrow therapeutic window to maintain health. These preclinical studies demonstrate considerable potential for single-dose genetic therapies to correct or silence pathogenic variants and prevent the development of HCM.

A Case of Severe Left-Ventricular Noncompaction Associated with Splicing Altering Variant in the FHOD3 Gene

Left ventricular noncompaction (LVNC) is a highly heterogeneous primary disorder of the myocardium. Its clinical features and genetic spectrum strongly overlap with other types of primary cardiomyopathies, in particular, hypertrophic cardiomyopathy. Study and the accumulation of genotype–phenotype correlations are the way to improve the precision of our diagnostics. We present a familial case of LVNC with arrhythmic and thrombotic complications, myocardial fibrosis and heart failure, cosegregating with the splicing variant in the FHOD3 gene. This is the first description of FHOD3-dependent LVNC to our knowledge. We also revise the assumed mechanism of pathogenesis in the case of FHOD3 splicing alterations.