The Current and Emerging Role of Cardiovascular Magnetic Resonance Imaging in Hypertrophic Cardiomyopathy

Ion Channel Impairment and Myofilament Ca2+ Sensitization: Two Parallel Mechanisms Underlying Arrhythmogenesis in Hypertrophic Cardiomyopathy

Life-threatening ventricular arrhythmias are the main clinical burden in patients with hypertrophic cardiomyopathy (HCM), and frequently occur in young patients with mild structural disease. While massive hypertrophy, fibrosis and microvascular ischemia are the main mechanisms underlying sustained reentry-based ventricular arrhythmias in advanced HCM, cardiomyocyte-based functional arrhythmogenic mechanisms are likely prevalent at earlier stages of the disease. In this review, we will describe studies conducted in human surgical samples from HCM patients, transgenic animal models and human cultured cell lines derived from induced pluripotent stem cells. Current pieces of evidence concur to attribute the increased risk of ventricular arrhythmias in early HCM to different cellular mechanisms. The increase of late sodium current and L-type calcium current is an early observation in HCM, which follows post-translation channel modifications and increases the occurrence of early and delayed afterdepolarizations. Increased myofilament Ca²⁺ sensitivity, commonly observed in HCM, may promote afterdepolarizations and reentry arrhythmias with direct mechanisms. Decrease of K⁺-currents due to transcriptional regulation occurs in the advanced disease and contributes to reducing the repolarization-reserve and increasing the early afterdepolarizations (EADs). The presented evidence supports the idea that patients with early-stage HCM should be considered and managed as subjects with an acquired channelopathy rather than with a structural cardiac disease.

Defining genotype-phenotype relationships in patients with hypertrophic cardiomyopathy using cardiovascular magnetic resonance imaging

PURPOSE

HCM is the most common inherited cardiomyopathy. Historically, there has been poor correlation between genotype and phenotype. However, CMR has the potential to more accurately assess disease phenotype. We characterized phenotype with CMR in a cohort of patients with confirmed HCM and high prevalence of genetic testing.

METHODS

Patients with a diagnosis of HCM, who had undergone contrast-enhanced CMR were identified. Left ventricular mass index (LVMI) and volumes were measured from steady-state free precession sequences. Late gadolinium enhancement (LGE) was quantified using the full width, half maximum method. All patients were prospectively followed for the development of septal reduction therapy, arrhythmia or death.

RESULTS

We included 273 patients, mean age 51.2 ± 15.5, 62.9% male. Of those patients 202 (74.0%) underwent genetic testing with 90 pathogenic, likely pathogenic, or rare variants and 13 variants of uncertain significance identified. Median follow-up was 1138 days. Mean LVMI was 82.7 ± 30.6 and 145 patients had late gadolinium enhancement (LGE). Patients with beta-myosin heavy chain (MYH7) mutations had higher LV ejection fraction (68.8 vs 59.1, p<0.001) than those with cardiac myosin binding protein C (MYBPC3) mutations. Patients with MYBPC3 mutations were more likely to have LVEF < 55% (29.7% vs 4.9%, p = 0.005) or receive a defibrillator than those with MYH7 mutations (54.1% vs 26.8%, p = 0.020).

CONCLUSIONS

We found that patients with MYBPC3 mutations were more likely to have impaired ventricular function and may be more prone to arrhythmic events. Larger studies using CMR phenotyping may be capable of identifying additional characteristics associated with less frequent genetic causes of HCM.

Myocardial contraction fraction derived from cardiovascular magnetic resonance cine images-reference values and performance in patients with heart failure and left ventricular hypertrophy

Aims

Left ventricular hypertrophy (LVH) has strong prognostic implications and is associated with heart failure. Recently, myocardial contraction fraction (MCF) was identified as a useful marker for specifically identifying cardiac amyloidosis (CA). The purpose of this study was to evaluate the diagnostic accuracy of MCF for the discrimination of different forms of LVH.

Methods and results

We analysed cardiovascular magnetic resonance (CMR) scans of patients with CA (n = 132), hypertrophic cardiomyopathy (HCM, n = 60), hypertensive heart disease (HHD, n = 38) and in 100 age- and gender-matched healthy controls. MCF was calculated by dividing left ventricular (LV) stroke volume by LV myocardial volume. The diagnostic accuracy of MCF was compared to that of LV ejection fraction (EF) and the mass index (MI). Compared with controls (136.3 ± 24.4%, P < 0.05), mean values for MCF were significantly reduced in LVH (HHD:92.6 ± 20%, HCM:80 ± 20.3%, transthyretin CA:74.9 ± 32.2% and light-chain (AL) CA:50.5 ± 21.4%). MCF performed better than LVEF (AUC = 0.96 vs. AUC = 0.6, P < 0.001) and was comparable to LVMI (AUC = 0.95, P = 0.4) in discriminating LVH from controls. There was a significant yet weak correlation between MCF and LVEF (r = 0.43, P < 0.0001). MCF outperformed LVEF and LVMI in discriminating between different etiologies of LVH and between AL and other forms of LVH (AUC = 0.84, P < 0.0001). Moreover, cut-off values for MCF <50% and LVEF <60% allowed to identify patients with high probability for CA.

Conclusion

In patients with heart failure MCF discriminates CA from other forms of LVH. As it can easily be derived from standard, non-contrast cine images, it may be a very useful marker in the diagnostic workup of patients with LVH.

Fibrosis quantification in Hypertensive Heart Disease with LVH and Non-LVH: Findings from T1 mapping and Contrast-free Cardiac Diffusion-weighted imaging

This study assessed the extent of fibrosis and the relationship between the ADC value and systolic strain in hypertensive patients with left ventricular hypertrophy (HTN LVH) and hypertensive patients without LVH (HTN non-LVH) using cardiac diffusion-weighted imaging and T1 mapping. T1 mapping was performed in 13 HTN LVH (mean age, 56.23 ± 3.30 years), 17 HTN non-LVH (mean age, 56.41 ± 2.78 years), and 12 normal control subjects (mean age, 55.67 ± 3.08 years) with 3.0 T MRI using cardiac diffusion-weighted imaging and T1 mapping. HTN LVH subjects had higher native T1 (1233.12 ± 79.01) compared with controls (1133.88 ± 27.40) (p < 0.05). HTN LVH subjects had higher ECV (0.28 ± 0.03) compared with HTN non-LVH subjects (0.26 ± 0.02) or controls (0.24 ± 0.03) (p < 0.05). HTN LVH subjects had higher ADC (2.23 ± 0.34) compared with HTN non-LVH subjects (1.88 ± 0.27) or controls (1.61 ± 0.38), (p < 0.05). Positive associations were noted between LVMI and ADC (Spearman = 0.450, p < 0.05) and between LVMI and ECV (Spearman = 0.181, p < 0.05). ADC was also related to an increase in ECV (R² = 0.210). Increased levels of ADC were associated with reduced peak systolic and early diastolic circumferential strain rates across all subjects. Contrast-free DW-CMR is an alternative sequence to ECV for the evaluation of fibrosis extent in HTN LVH and HTN non-LVH, while native T1 has limited value.

Role of Cardiac MRI in the Assessment of Cardiomyopathy

OPINION STATEMENT

Combining the diagnostic utilities of cardiac structures, myocardial perfusion, and various tissue characterizing pulse sequence methods in matching scan planes within a single imaging session, cardiac magnetic resonance imaging (CMR) provides a novel interrogation of myocardial physiology and abnormal anatomy from various forms of cardiomyopathy. Establishment of technical imaging standards and clinical adaptation in the past years has helped recognize the distinguishing features of different cardiomyopathies, with CMR currently assuming a pivotal role in the diagnosis of cases of new-onset cardiomyopathy in experienced centers. Quantitative measurements such as ventricular volumes, myocardial iron content, and extent of late gadolinium enhancement can effectively monitor disease status, guide medical therapy, and impact patient outcomes in specific clinical settings. This chapter will aim to summarize these current CMR applications with case examples.

Role of multimodality cardiac imaging in the management of patients with hypertrophic cardiomyopathy: an expert consensus of the European Association of Cardiovascular Imaging Endorsed by the Saudi Heart Association

Taking into account the complexity and limitations of clinical assessment in hypertrophic cardiomyopathy (HCM), imaging techniques play an essential role in the evaluation of patients with this disease. Thus, in HCM patients, imaging provides solutions for most clinical needs, from diagnosis to prognosis and risk stratification, from anatomical and functional assessment to ischaemia detection, from metabolic evaluation to monitoring of treatment modalities, from staging and clinical profiles to follow-up, and from family screening and preclinical diagnosis to differential diagnosis. Accordingly, a multimodality imaging (MMI) approach (including echocardiography, cardiac magnetic resonance, cardiac computed tomography, and cardiac nuclear imaging) is encouraged in the assessment of these patients. The choice of which technique to use should be based on a broad perspective and expert knowledge of what each technique has to offer, including its specific advantages and disadvantages. Experts in different imaging techniques should collaborate and the different methods should be seen as complementary, not as competitors. Each test must be selected in an integrated and rational way in order to provide clear answers to specific clinical questions and problems, trying to avoid redundant and duplicated information, taking into account its availability, benefits, risks, and cost.

Atrial fibrosis: a risk stratifier for atrial fibrillation

Atrial fibrillation (AF), especially persistent and long-standing persistent AF, may result in electro-anatomical changes in the left atrium, resulting in remodeling and deposition of fibrous tissue. There are emerging data that atrial substrate modification may increase the risk of thromboembolic complications, including stroke. Several studies have reported that atrial fibrosis is due to complex interactions among several cellular and neurohumoral mediators. Late gadolinium enhancement MRI has been reported to allow quantitative assessment of myocardial fibrosis in patients at risk of developing a stroke. Current stroke risk stratification criteria for AF do not utilize atrial fibrosis as an independent risk factor despite its association with AF and stroke. Further research is required in developing adequate risk stratification tools for predicting the stroke risk and catheter ablation outcomes in AF.

Comparison of echocardiographic and cardiac magnetic resonance imaging in hypertrophic cardiomyopathy sarcomere mutation carriers without left ventricular hypertrophy

BACKGROUND

Left ventricular hypertrophy (LVH) typically manifests during or after adolescence in sarcomere mutation carriers at risk for developing hypertrophic cardiomyopathy. Guidelines recommend serial imaging of mutation carriers without LVH (G+/LVH-) to monitor for phenotypic evolution, but the optimal strategy is undefined. Compared with echocardiography (echo), cardiac MRI (CMR) offers improved endocardial visualization and potential to assess scar. However, the incremental advantage offered by CMR for early diagnosis of hypertrophic cardiomyopathy is unclear. Therefore, we systematically compared echo and CMR in G+/LVH- subjects.

METHODS AND RESULTS

A total of 40 sarcomere mutation carriers with normal echo wall thickness (<12 mm or z score <2.5 in children) underwent concurrent CMR. Mean age was 21.7±11.1 years, 55% were female. If left ventricular wall thickness seemed nonuniform, the size and location of relatively thickened segments were noted. Late gadolinium enhancement was assessed with CMR. Diagnostic agreement between echo and CMR was good (90%), although CMR measurements of left ventricular wall thickness were ≈19% lower than echo. Four subjects had mild hypertrophy (12.6-14 mm; ≤2 segments) appreciated by CMR but not echo. No subjects had late gadolinium enhancement. During median 35-month follow-up, 2 subjects developed overt hypertrophic cardiomyopathy, including 1 with mild LVH by CMR at baseline.

CONCLUSIONS

Echo is unlikely to miss substantial LVH; however, CMR identified mild hypertrophy in ≈10% of mutation carriers with normal echo wall thickness. CMR may be a useful adjunct in hypertrophic cardiomyopathy family screening, particularly in higher risk situations, or if echocardiographic images are suboptimal or suggest borderline LVH.

Hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is a fascinating disease of marked heterogeneity. Hypertrophic cardiomyopathy was originally characterized by massive myocardial hypertrophy in the absence of known etiology, a dynamic left ventricular outflow obstruction, and increased risk of sudden death. It is now well accepted that multiple mutations in genes encoding for the cardiac sarcomere are responsible for the disease. Complex morphologic and pathophysiologic differences, disparate natural history studies, and novel treatment strategies underscore the challenge to the practicing cardiologist when faced with the management of the hypertrophic cardiomyopathy patient.

Cardiac myosin binding protein C insufficiency leads to early onset of mechanical dysfunction

BACKGROUND

Decreased expression of cardiac myosin binding protein C (cMyBPC) as a result of genetic mutations may contribute to the development of hypertrophic cardiomyopathy (HCM); however, the mechanisms that link cMyBPC expression and HCM development, especially contractile dysfunction, remain unclear.

METHODS AND RESULTS

We evaluated cardiac mechanical function in vitro and in vivo in young mice (8-10 weeks of age) carrying no functional cMyBPC alleles (cMyBPC(-/-)) or 1 functional cMyBPC allele (cMyBPC(±)). Skinned myocardium isolated from cMyBPC(-/-) hearts displayed significant accelerations in stretch activation cross-bridge kinetics. Cardiac MRI studies revealed severely depressed in vivo left ventricular (LV) magnitude and rates of LV wall strain and torsion compared with wild-type (WT) mice. Heterozygous cMyBPC(±) hearts expressed 23±5% less cMyBPC than WT hearts but did not display overt hypertrophy. Skinned myocardium isolated from cMyBPC(±) hearts displayed small accelerations in the rate of stretch induced cross-bridge recruitment. MRI measurements revealed reductions in LV torsion and circumferential strain, as well reduced circumferential strain rates in early systole and diastole.

CONCLUSIONS

Modest decreases in cMyBPC expression in the mouse heart result in early-onset subtle changes in cross-bridge kinetics and in vivo LV mechanical function, which could contribute to the development of HCM later in life.

Cardiovascular magnetic resonance in heart failure

Imaging has a central role in the evaluation of patients with heart failure (HF). Cardiovascular magnetic resonance (CMR) is rapidly evolving as a versatile imaging modality that often provides additional information to echocardiography in patients with suspected or known HF. CMR is the only imaging modality that has the ability to assess, without exposure to ionizing radiation, cardiac function, structure (tissue characterization), perfusion, and viability. Moreover, magnetic resonance spectroscopy techniques can assess the pathophysiologic role of deranged cardiac energetics in HF. In this review we discuss the role of CMR in the evaluation of patients with HF giving particular emphasis to recent developments and the additional information that can be obtained with this imaging modality, over and above standard echocardiography.

Deadly proposal: a case of catecholaminergic polymorphic ventricular tachycardia

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a rare adrenergically mediated arrhythmogenic disorder classically induced by exercise or emotional stress and found in structurally normal hearts. It is an important cause of cardiac syncope and sudden death in childhood. Catecholaminergic polymorphic ventricular tachycardia is a genetic cardiac channelopathy with known mutations involving genes affecting intracellular calcium regulation. We present a case of a 14-year-old boy who had cardiopulmonary arrest after an emotionally induced episode of CPVT while attempting to invite a girl to the school dance. Review of his presenting cardiac rhythm, induction of concerning ventricular arrhythmias during an exercise stress test, and genetic testing confirmed the diagnosis of CPVT. He recovered fully and was treated with β-blocker therapy and placement of an implantable cardioverter-defibrillator. In this report, we discuss this rare but important entity, including its molecular foundation, clinical presentation, basics of diagnosis, therapeutic options, and implications of genetic testing for family members. We also compare CPVT to other notable cardiomyopathic and channelopathic causes of sudden death in youth including hypertrophic cardiomyopathy, arrhythmogenic right ventricular dysplasia, long QT syndrome, short QT syndrome, and Brugada syndrome.

"Speckled" ventricular septum in hypertrophic cardiomyopathy revisited after 30 years

We found a highly inconsistent relation between the granular and reflective ultrasound ("speckling") pattern frequently observed in the ventricular septum of patients with hypertrophic cardiomyopathy and evidence of myocardial fibrosis by contrast-enhanced cardiovascular magnetic resonance imaging. Therefore, this distinctive echocardiographic appearance of the myocardium does not accurately characterize left ventricular scarring and is most likely explained as an extraneous ultrasound signal pattern. In conclusion, myocardial fibrosis in patients with hypertrophic cardiomyopathy is most reliably identified using contrast-enhanced cardiovascular magnetic resonance imaging.

Emerging MRI methods in translational cardiovascular research

Cardiac magnetic resonance imaging (CMR) has become a reference standard modality for imaging of left ventricular (LV) structure and function and, using late gadolinium enhancement, for imaging myocardial infarction. Emerging CMR techniques enable a more comprehensive examination of the heart, making CMR an excellent tool for use in translational cardiovascular research. Specifically, emerging CMR methods have been developed to measure the extent of myocardial edema, changes in ventricular mechanics, changes in tissue composition as a result of fibrosis, and changes in myocardial perfusion as a function of both disease and infarct healing. New CMR techniques also enable the tracking of labeled cells, molecular imaging of biomarkers of disease, and changes in calcium flux in cardiomyocytes. In addition, MRI can quantify blood flow velocity and wall shear stress in large blood vessels. Almost all of these techniques can be applied in both pre-clinical and clinical settings, enabling both the techniques themselves and the knowledge gained using such techniques in pre-clinical research to be translated from the lab bench to the patient bedside.

Echocardiography in patients with hypertrophic cardiomyopathy: usefulness of old and new techniques in the diagnosis and pathophysiological assessment

Hypertrophic cardiomyopathy (HCM) is one of the most common inherited cardiomyopathy. The identification of patients with HCM is sometimes still a challenge. Moreover, the pathophysiology of the disease is complex because of left ventricular hyper-contractile state, diastolic dysfunction, ischemia and obstruction which can be coexistent in the same patient. In this review, we discuss the current and emerging echocardiographic methodology that can help physicians in the correct diagnostic and pathophysiological assessment of patients with HCM.