Effect of Mavacamten on Echocardiographic Features in Symptomatic Patients With Obstructive Hypertrophic Cardiomyopathy

Stress Echocardiography for Assessment of Diastolic Function

PURPOSE OF REVIEW

Diastolic dysfunction is an important, though often underappreciated, cause for exertional dyspnea. Echocardiography enables noninvasive evaluation of diastolic function and filling pressure, but images acquired at rest may be insensitive for detection of exertional abnormalities. This review focuses on stress echocardiography to assess diastolic function, including traditional and novel techniques, with emphasis on specific patient sub-groups in whom this testing may be valuable.

RECENT FINDINGS

Emerging data informs patient selection for diastolic stress testing. Further, increasing literature provides considerations for performance and interpretation of diastolic metrics relevant to patients with heart failure with preserved ejection fraction, hypertrophic cardiomyopathy, athletes, and those with microvascular coronary dysfunction. Methods, such as speckle-tracking and multi-modality imaging, provide additional and complementary information for non-invasive diastolic assessment. This review serves as a guide to optimally utilize existing and novel techniques of stress echocardiography for diastolic assessment across a broad range of patients.

Advancements in the Diagnosis and Treatment of Hypertrophic Cardiomyopathy: A Comprehensive Review

Hypertrophic cardiomyopathy (HCM) is characterized by excessive growth of myocardial tissue, most commonly due to genetic mutations in sarcomere proteins. This can lead to complications such as heart failure, mitral regurgitation, syncope, arrhythmias, sudden cardiac death, and myocardial ischemia. While we have come a long way in our understanding of the pathophysiology, genetics, and epidemiology of HCM, the past 10 years have seen significant advancements in diagnosis and treatment. As the body of evidence on hypertrophic cardiomyopathy continues to grow, a comprehensive review of the current literature is an invaluable resource in organizing this knowledge. By doing so, the vast progress that has been made thus far will be widely available to all experts in the field. This review provides a comprehensive analysis of the scientific literature, exploring both well-established and cutting-edge diagnostic and therapeutic options. It also presents a unique perspective by incorporating topics such as exercise testing, genetic testing, radiofrequency ablation, risk stratification, and symptomatic management in non-obstructive HCM. Lastly, this review highlights areas where current and future research is at the forefront of innovation in hypertrophic cardiomyopathy.

Mavacamten-Associated Temporal Changes in Left Atrial Function in Obstructive HCM: Insights From the VALOR-HCM Trial

BACKGROUND

In severely symptomatic patients with obstructive hypertrophic cardiomyopathy (HCM), the VALOR-HCM (A Study to Evaluate Mavacamten in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy Who Are Eligible for Septal Reduction Therapy) trial showed that mavacamten reduced the eligibility for septal reduction therapy with sustained improvement in left ventricular outflow tract gradients. Mavacamten also resulted in favorable cardiac remodeling, including improvement in biomarkers (eg, N-terminal pro-B-type natriuretic peptide and troponin T). However, the impact of mavacamten on left atrial (LA) function is unknown.

OBJECTIVES

The aim of this study was to assess serial changes in LA strain measures in patients enrolled in the VALOR-HCM trial.

METHODS

VALOR-HCM included 112 symptomatic patients with obstructive HCM (mean age 60 years; 51% male). Patients assigned to receive mavacamten at baseline (n = 56) continued therapy for 56 weeks and those assigned to placebo transitioned to mavacamten (n = 52) from week 16 to week 56. Echocardiographic LA strain (reservoir, conduit, and contraction) was measured by using a vendor-neutral postprocessing software.

RESULTS

At baseline, the mean LA volume index (LAVI) and LA strain values (conduit, contraction, and reservoir) were 41.3 ± 16.5 mL/m2, -11.8% ± 6.5%, -8.7% ± 5.0%, and 20.5% ± 8.7%, respectively (all worse than reported normal). LAVI significantly improved by -5.6 ± 9.7 mL/m2 from baseline to week 56 (P < 0.001). There was a significant (P < 0.05) improvement in absolute LA strain values from baseline to week 56 (conduit [-1.7% ± 6%], contraction [-1.2% ± 4.5%], and reservoir [2.8% ± 7.7%]). Patients originally receiving placebo had no differences in LA measurements up to week 16. There was no significant improvement in LA strain values (conduit [-0.9% ± 3.8%], contraction [-0.4% ± 3.4%], and reservoir [1.4% ± 6.1%]; all; P = NS) from baseline to week 56 in patients with history of atrial fibrillation.

CONCLUSIONS

In VALOR-HCM, mavacamten resulted in an improvement in LAVI and LA strain at week 56, suggesting sustained favorable LA remodeling and improved function, except in the atrial fibrillation subgroup. Whether the advantageous LA remodeling associated with long-term treatment with mavacamten results in a favorable impact on the observed high burden of atrial tachyarrhythmias in HCM remains to be proven. (A Study to Evaluate Mavacamten in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy Who Are Eligible for Septal Reduction Therapy [VALOR-HCM]; NCT04349072).

Serial Changes in Ventricular Strain in Symptomatic Obstructive Hypertrophic Cardiomyopathy Treated With Mavacamten: Insights From the VALOR-HCM Trial

BACKGROUND

In severely symptomatic patients with obstructive hypertrophic cardiomyopathy, VALOR-HCM (A Study to Evaluate Mavacamten in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy Who Are Eligible for Septal Reduction Therapy) demonstrated that mavacamten reduces the need for septal reduction therapy with sustained improvement in left ventricular (LV) outflow tract gradients and symptoms. Global longitudinal strain (GLS), a measure of regional myocardial function, is a more sensitive marker of systolic function. In VALOR-HCM, we assessed serial changes in LV and right ventricular (RV) strain.

METHODS

VALOR-HCM included 112 patients with symptomatic obstructive hypertrophic cardiomyopathy (mean, 60 years; 51% male; LV ejection fraction, 68%). Patients assigned to mavacamten at baseline continued the drug for 56 weeks (n=56) and those assigned to placebo (n=52) transitioned to mavacamten from weeks 16 to 56 (40-week exposure). LV-GLS and RV-GLS assessment was performed using a vendor-neutral software. Non-foreshortened apical (4-, 3-, and 2-chamber) views were used to obtain peak LV-GLS. RV focused 4-chamber view was used to calculate RV 4-chamber and free wall strain. A more negative strain value is favorable.

RESULTS

At baseline, the mean LV-GLS, RV 4-chamber, and free wall strain values were -14.7%, -22.2%, and -16.8%, respectively (all worse than reported normal means). In the total study sample, LV-GLS significantly improved from baseline to week 56 (P=0.02). Twelve patients had transient reduction in LV ejection fraction (<50%) requiring temporary drug interruption (including 3 permanent discontinuations). The LV-GLS in this subgroup was worse at baseline versus total study population (-11.4%), with no significant worsening from baseline through week 56 (P=0.64). Both free wall and 4-chamber RV-GLS remained unchanged from baseline to week 56 (P=0.62 and P=0.56, respectively).

CONCLUSIONS

In VALOR-HCM, treatment with mavacamten improved LV-GLS from baseline through week 56 (with no significant worsening of LV-GLS in patients with a reduction in LV ejection fraction ≤50%), suggesting a favorable long-term impact on regional LV systolic function. Additionally, there was no detrimental impact on RV systolic function.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT04349072.

Accelerated hypertension following mavacamten introduction in severe obstructive hypertrophic cardiomyopathy with hypertension: a case report

Background

Mavacamten in Phase 2 and 3 clinical trials was well tolerated, reduced left ventricular outflow tract obstruction (LVOTO), and improved exercise capacity and symptoms. However, due to its recent introduction in the market, there is limited evidence from real-world patients with severe/multiple comorbidities and/or who are exposed to potential treatment interactions. Hypertension is common in patients with hypertrophic cardiomyopathy (HCM), but its impact on the treatment of LVOTO is undefined.

Case summary

A 55-year-old man with severely obstructive symptomatic HCM and Grade I arterial hypertension underwent treatment with mavacamten 5 mg. He presented an accelerated hypertension from Day 10 of treatment. On admission, he reported improvement of his dyspnoea [New York Heart Association (NYHA) Class II] and NT-pro BNP decreased to 1646 ng/L. Echocardiography showed a left ventricular ejection fraction of 60% with reduced systolic anterior motion and LVOTO (max 21 mmHg). Causes of secondary hypertension were excluded, and blood pressure (BP) was controlled by eplerenone and amlodipine introduction. Accelerated hypertension was concluded as a final diagnosis, and a potential causal link with the introduction of mavacamten was made. Evolution up to Day 135 proved a stabilization of the BP profile and of the LVOT gradient (max 36 mmHg) as well as improvement in functional capacity (NYHA Class I).

Discussion

We hypothesize that rapid relief of excess afterload may induce alterations potentially leading to high BP in patients with impaired peripheral vascular resistances. Patients with severe obstructive HCM and hypertension should be given special attention during mavacamten titration and should self-monitor the BP during this phase.

Comparison of Drug Therapy Efficacy in Patients With Hypertrophic Cardiomyopathy: A Network Meta-Analysis

The aim of this network meta-analysis was to compare the efficacy of various commonly used drugs in treating patients with hypertrophic cardiomyopathy (HCM). Randomized controlled trials on drugs for HCM treatment were retrieved from PubMed, Embase, Cochrane Library, and Web of Science (search cutoff: January 10, 2024). Quality assessment was performed using the risk of bias tool, and data analysis used R software. Seventeen studies (1,133 patients with HCM) were included. The network meta-analysis indicated that mavacamten and perhexiline improved peak oxygen consumption compared with placebo. Mavacamten reduced N-terminal pro-B-type natriuretic peptide, left ventricular mass index, left atrial volume index, and septal E/e' ratio. Losartan decreased systolic blood pressure, whereas candesartan, mavacamten, and valsartan reduced maximum wall thickness. Perhexiline had better efficacy in increasing peak oxygen consumption, and candesartan in reducing maximum wall thickness. No drug significantly improved left ventricular ejection fraction compared with placebo. In conclusion, on the basis of current studies, commonly used drugs may effectively improve some of the outcome measures in patients with HCM, whereas the novel drug mavacamten showed significant therapeutic effects in most of the remaining outcome measures except for left ventricular ejection fraction.

Novel Cardiac Myosin Inhibitor Therapy for Hypertrophic Cardiomyopathy in Adults: A Contemporary Review

Hypertrophic cardiomyopathy (HCM) affects as many as 1 in 200 people in the adult population globally. Patients may present with exertional dyspnea, presyncope or syncope, atrial and ventricular arrhythmias, heart failure, and even sudden cardiac death. Current guideline-based therapy involves medical therapy for treatment of symptoms in milder forms of the disease and surgical or catheter-based septal reduction therapies in obstructive HCM. Until recently, there has existed a gap between these two approaches that is now being filled by a new class of drugs, cardiac myosin inhibitors, which directly target the underlying disease process in HCM. Current investigations examine the effects of two cardiac myosin inhibitors on reported symptoms, echocardiographic evidence of disease, and the associated need for septal reduction. This paper reviews the contemporary evidence for the use of cardiac myosin inhibitors in HCM in adults and highlights future directions for this exciting field of cardiovascular medicine.

Evolving Strategies for the Management of Obstructive Hypertrophic Cardiomyopathy

For many years, treatment of hypertrophic cardiomyopathy (HCM) has focused on non-disease-specific therapies. Cardiac myosin modulators (ie, mavacamten and aficamten) reduce the pathologic actin-myosin interactions that are characteristic of HCM, leading to improved cardiac energetics and reduction in hypercontractility. Several recently published randomized clinical trials have demonstrated that mavacamten improves exercise capacity, left ventricular outflow tract obstruction and symptoms in patients with obstructive HCM and may delay the need for septal-reduction therapy. Long-term data in real-world populations will be needed to fully assess the safety and efficacy of mavacamten. Importantly, HCM is a complex and heterogeneous disease, and not all patients will respond to mavacamten; therefore, careful patient selection and shared decision making will be necessary in guiding the use of mavacamten in obstructive HCM.

Impact of Aficamten on Echocardiographic Cardiac Structure and Function in Symptomatic Obstructive Hypertrophic Cardiomyopathy

BACKGROUND

Aficamten, a next-in-class cardiac myosin inhibitor, improved peak oxygen uptake (pVO2) and lowered resting and Valsalva left ventricular outflow (LVOT) gradients in adults with symptomatic obstructive hypertrophic cardiomyopathy (oHCM) in SEQUOIA-HCM (Phase 3 Trial to Evaluate the Efficacy and Safety of Aficamten Compared to Placebo in Adults With Symptomatic oHCM), a phase 3, multicenter, randomized, double-blinded, placebo-controlled study.

OBJECTIVES

The authors sought to evaluate the effect of aficamten on echocardiographic measures of cardiac structure and function in SEQUOIA-HCM.

METHODS

Serial echocardiograms were performed over 28 weeks in patients randomized to receive placebo or aficamten in up to 4 individually titrated escalating doses (5-20 mg daily) over 24 weeks based on Valsalva LVOT gradients and left ventricular ejection fraction (LVEF).

RESULTS

Among 282 patients (mean age 59 ± 13 years; 41% female, 79% White, 19% Asian), mean LVEF was 75% ± 6% with resting and Valsalva LVOT gradients of 55 ± 30 mm Hg and 83 ± 32 mm Hg, respectively. Over 24 weeks, aficamten significantly lowered resting and Valsalva LVOT gradients, and improved left atrial volume index, lateral and septal e' velocities, and lateral and septal E/e' (all P ≤ 0.001). LV end-systolic volume increased and wall thickness decreased (all P ≤ 0.003). Aficamten resulted in a mild reversible decrease in LVEF (-4.8% [95% CI: -6.4 to -3.3]; P < 0.001) and absolute LV global circumferential strain (-3.7% [95% CI: 1.8-5.6]; P < 0.0010), whereas LV global longitudinal strain was unchanged. Several measures, including LVEF, LVOT gradients, and E/e' returned to baseline following washout. Among those treated with aficamten, improved pVO2 and reduction in N-terminal pro-B-type natriuretic peptide (NT-proBNP) were associated with improvement in lateral e' velocity and septal and lateral E/e' (all P < 0.03), whereas improvement in Kansas City Cardiomyopathy Questionnaire Clinical Summary Scores (KCCQ-CSS) was associated with a decrease in both LVOT gradients (all P < 0.001).

CONCLUSIONS

Compared with placebo, patients receiving aficamten demonstrated significant improvement in LVOT gradients and measures of LV diastolic function, and several of these measures were associated with improvements in pVO2, KCCQ-CSS, and NT-proBNP. A modest decrease in LVEF occurred yet remained within normal range. These findings suggest aficamten improved multiple structural and physiological parameters in oHCM without significant adverse changes in LV systolic function. (Phase 3 Trial to Evaluate the Efficacy and Safety of Aficamten Compared to Placebo in Adults With Symptomatic oHCM [SEQUOIA-HCM]; NCT05186818).

Comparison Between Heart Failure Without Left Ventricular Systolic Dysfunction and Progression to End-Stage in Hypertrophic Cardiomyopathy

BACKGROUND

The incidence and prognostic predictors of heart failure (HF) without left ventricular systolic dysfunction (LVSD) in hypertrophic cardiomyopathy (HCM), particularly their differences in terms of developing LVSD (progression to end-stage) or sudden cardiac death (SCD), are not fully elucidated.

METHODS AND RESULTS

This study included 330 consecutive HCM patients with left ventricular ejection fraction (LVEF) ≥50%. HF hospitalization without LVSD and development of LVSD were evaluated as main outcomes. During a median follow-up of 7.3 years, the incidence of HF hospitalization without LVSD was 18.8%, which was higher than the incidence of developing LVSD (10.9%) or SCD (8.8%). Among patients who developed LVSD, only 19.4% experienced HF hospitalization without LVSD before developing LVSD. Multivariable analysis showed that predictors for HF hospitalization without LVSD (higher age, atrial fibrillation, history of HF hospitalization, and higher B-type natriuretic peptide concentrations) were different from those of developing LVSD (male sex, lower LVEF, lower left ventricular outflow tract gradient, and higher tricuspid regurgitation pressure gradient). Known risk factors for SCD did not predict either HF without LVSD or developing LVSD.

CONCLUSIONS

In HCM with LVEF ≥50%, HF hospitalization without LVSD was more frequently observed than development of LVSD or SCD during mid-term follow-up. The overlap between HF without LVSD and developing LVSD was small (19.4%), and these 2 HF events had different predictors.

Early left atrial reverse remodelling in patients with hypertrophic obstructive cardiomyopathy receiving transapical beating-heart septal myectomy

OBJECTIVES

This study aims to investigate the short-term effects of transapical beating-heart septal myectomy (TA-BSM) on left atrial (LA) anatomy and function and its association with clinical indicators in patients with hypertrophic obstructive cardiomyopathy (HOCM).

METHODS

A total of 105 HOCM patients who received TA-BSM were included. Clinical and comprehensive echocardiographic data were obtained before surgery, at discharge, and 3 months after myectomy. LA reverse remodelling was defined as LA maximum volume index (LAVI) ≤34 ml/m2 and a change of ≥10%.

RESULTS

At 3 months after TA-BSM, New York Heart Association (NYHA) functional class and 6-min walking test were significantly improved, N-terminal pro-B-type natriuretic peptide (NT-proBNP) decreased, left ventricular outflow tract (LVOT) peak gradient and mitral regurgitation were significantly reduced. LAVI decreased in 76%, with a median change of 20%, and the criteria for LA reverse remodelling were met in 48%. LA strain parameters were improved at 3 months after TA-BSM. Moreover, left ventricular (LV) diastolic function was significantly improved, but LV global longitudinal strain was not significantly changed at 3 months after operation. Improvement in LVOT peak gradient, LAVI, LA reservoir strain (LASr) and conduit strain (LAScd) were associated with reduction in NT-proBNP.

CONCLUSIONS

Along with effectively relieving the obstruction of the LVOT and mitral regurgitation, TA-BSM could significantly improve LA size and function during the short-term follow-up for HOCM patients. The indicators of LA reverse remodelling were associated with reduction in a biomarker of myocardial wall stress, indicating the early recovery of LV relaxation and clinical status for patients.

Pharmacokinetics and safety of mavacamten in healthy Chinese participants with different CYP2C19 phenotypes

Obstructive hypertrophic cardiomyopathy (oHCM) is a subtype of HCM characterized by left ventricular outflow tract obstruction resulting from cardiac muscle hypertrophy and anatomic alterations in the mitral valve and apparatus. Mavacamten, a cardiac myosin inhibitor metabolized primarily by CYP2C19 in the liver, is the first and only targeted medication approved for the treatment of symptomatic New York Heart Association (NYHA) class II-III oHCM. Previous pharmacokinetic (PK) results of mavacamten in healthy Caucasian, Japanese, and Asian participants demonstrated that mavacamten exposure was affected by CYP2C19 metabolism status. This open-label, parallel-group, phase I trial aimed to determine the PK and safety of mavacamten in healthy Chinese participants with different CYP2C19 genotypes. The primary outcome was to define the PK of mavacamten in healthy Chinese participants; the secondary outcome was to examine safety and tolerability. After a single oral dose of 15 or 25 mg mavacamten in fasted healthy adult Chinese individuals, Cmax was reached within a median Tmax of 0.6-1.5 h, indicating rapid absorption. Inter-individual variability was moderate, and individuals carrying non-functional CYP2C19 alleles (*2/*2, *3/*3, or *2/*3) exhibited longer half-life and increased total exposure. After stratification of CYP2C19 genotypes, total mavacamten exposures were similar among different ethnic groups when compared with prior PK studies. No significant adverse events were observed in this study. Single oral administration of mavacamten at 15 mg was well tolerated across all CYP2C19 genotypes, and 25 mg dose was well tolerated in healthy participants with CYP2C19 genotypes UM/RM/NM. The PK profile of mavacamten in the healthy Chinese population was consistent with that in other healthy populations.

An overview of the treatments for hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a very prevalent inherited disease with a wide global distribution and a prevalence rate of approximately 0.2% in the general population. Left ventricular hypertrophy (LVH) caused by sarcomere mutation is the primary reason of HCM. The histopathology feature is that cardiomyocyte hypertrophy, myocyte disorder and myocardial fibrosis lead to diminished diastolic function, left ventricular outflow tract obstruction (LVOTO) and arrhythmia, all of which result in serious cardiac complications. Previously, HCM was considered a malignant disease that was almost untreatable. With the improvement of medical standards and increasing awareness of HCM, it has become a highly treatable disease in contemporary times, with a significant decrease in mortality rates. However, there are still significant unmet requirements in the therapy of HCM. This paper draws on more than 100 references from the past four decades and summarizes current advances in the treatment of HCM. The article will review the pathogenesis and types, recent development in pharmacotherapy, invasive treatments and gene therapies, as well as dilemma and future development of HCM.

Management of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is an important cause of heart failure and arrhythmias, including sudden death, with a major impact on the healthcare system. Genetic causes and different phenotypes are now increasingly being identified for this condition. In addition, specific medications, such as myosin inhibitors, have been recently shown as potentially able to modify its symptoms, hemodynamic abnormalities and clinical course. Our article aims to provide a comprehensive outline of the epidemiology, diagnosis and treatment of hypertrophic cardiomyopathy in the current era.

Prediction of cardiac death in patients with hypertrophic cardiomyopathy using plasma adipokine levels

BACKGROUNDS AND AIMS

Hypertrophic cardiomyopathy (HCM) causes cardiac death through both sudden cardiac death (SCD) and death due to heart failure (HF). Although adipokines lead to adverse cardiac remodeling in HCM, the prognostic value of plasma adipokines in HCM remains unknown. We aimed to predict cardiac death in patients with HCM using plasma adipokines.

METHODS AND RESULTS

We performed a multicenter prospective cohort study of patients with HCM. The outcome was cardiac death including heart transplant, death due to HF, and SCD. With data from 1 institution (training set), a prediction model was developed using random forest classification algorithm based on 10 plasma adipokines. The performance of the prediction model adjusted for 8 clinical parameters was examined in samples from another institution (test set). Time-to-event analysis was performed in the test set to compare the rate of outcome events between the low-risk and high-risk groups determined by the prediction model. In total, 389 (267 in the training set; 122 in the test set) patients with HCM were included. During the median follow-up of 2.7 years, 21 patients experienced the outcome event. The area under the covariates-adjusted receiver-operating characteristics curve was 0.89 (95 % confidence interval [CI] 0.71-0.99) in the test set. revealed the high-risk group had a significantly higher risk of cardiac death (hazard ratio 17.8, 95 % CI 2.1-148.3, P = 0.008).

CONCLUSION

The present multicenter prospective study demonstrated that a panel of plasma adipokines predicts cardiac death in patients with HCM.

Cardiac myosin inhibitor, CK-586, minimally reduces systolic function and ameliorates obstruction in feline hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) remains the most common cardiomyopathy in humans and cats with few preclinical pharmacologic interventional studies. Small-molecule sarcomere inhibitors are promising novel therapeutics for the management of obstructive HCM (oHCM) patients and have shown efficacy in left ventricular outflow tract obstruction (LVOTO) relief. The objective of this study was to explore the 6-, 24-, and 48-hour (h) pharmacodynamic effects of the cardiac myosin inhibitor, CK-586, in six purpose-bred cats with naturally occurring oHCM. A blinded, randomized, five-treatment group, crossover preclinical trial was conducted to assess the pharmacodynamic effects of CK-586 in this oHCM model. Dose assessments and select echocardiographic variables were assessed five times over a 48-h period. Treatment with oral CK-586 safely ameliorated LVOTO in oHCM cats. CK-586 treatment dose-dependently eliminated obstruction (reduced LVOTOmaxPG), increased measures of systolic chamber size (LVIDs Sx), and decreased select measures of heart function (LV FS% and LV EF%) in the absence of impact on heart rate. At all tested doses, a single oral CK-586 dose resulted in improved or resolved LVOTO with well-tolerated, dose-dependent, reductions in LV systolic function. The results from this study pave the way for the potential use of CK-586 in both the veterinary and human clinical setting.

Myosin inhibitor reverses hypertrophic cardiomyopathy in genotypically diverse pediatric iPSC-cardiomyocytes to mirror variant correction

Pathogenic variants in MYH7 and MYBPC3 account for the majority of hypertrophic cardiomyopathy (HCM). Targeted drugs like myosin ATPase inhibitors have not been evaluated in children. We generate patient and variant-corrected iPSC-cardiomyocytes (CMs) from pediatric HCM patients harboring single variants in MYH7 (V606M; R453C), MYBPC3 (G148R) or digenic variants (MYBPC3 P955fs, TNNI3 A157V). We also generate CMs harboring MYBPC3 mono- and biallelic variants using CRISPR editing of a healthy control. Compared with isogenic and healthy controls, variant-positive CMs show sarcomere disorganization, higher contractility, calcium transients, and ATPase activity. However, only MYH7 and biallelic MYBPC3 variant-positive CMs show stronger myosin-actin binding. Targeted myosin ATPase inhibitors show complete rescue of the phenotype in variant-positive CMs and in cardiac Biowires to mirror isogenic controls. The response is superior to verapamil or metoprolol. Myosin inhibitors can be effective in genotypically diverse HCM highlighting the need for myosin inhibitor drug trials in pediatric HCM.

Retrofitting the Heart: Explaining the Enigmatic Septal Thickening in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy is the most common genetic cardiac disease and is characterized by left ventricular hypertrophy. Although this hypertrophy often associates with sarcomeric gene mutations, nongenetic factors also contribute to the disease, leading to diastolic dysfunction. Notably, this dysfunction manifests before hypertrophy and is linked to hypercontractility, as well as nonuniform contraction and relaxation (myofibril asynchrony) of the myocardium. Although the distribution of hypertrophy in hypertrophic cardiomyopathy can vary both between and within individuals, in most cases, it is primarily confined to the interventricular septum. The reasons for septal thickening remain largely unknown. In this article, we propose that alterations in muscle fiber geometry, present from birth, dictate the septal shape. When combined with hypercontractility and exacerbated by left ventricular outflow tract obstruction, these factors predispose the septum to an isometric type of contraction during systole, consequently constraining its mobility. This contraction, or more accurately, this focal increase in biomechanical stress, prompts the septum to adapt and undergo remodeling. Drawing a parallel, this is reminiscent of how earthquake-resistant buildings are retrofitted with vibration dampers to absorb the majority of the shock motion and load. Similarly, the heart adapts by synthesizing viscoelastic elements such as microtubules, titin, desmin, collagen, and intercalated disc components. This pronounced remodeling in the cytoskeletal structure leads to noticeable septal hypertrophy. This structural adaptation acts as a protective measure against damage by attenuating myofibril shortening while reducing cavity tension according to Laplace Law. By examining these events, we provide a coherent explanation for the septum's predisposition toward hypertrophy.

From Atrial Fibrillation Management to Atrial Myopathy Assessment: The Evolving Concept of Left Atrium Disease in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most prevalent genetically inherited cardiovascular disorder in adults and a significant cause of heart failure and sudden cardiac death. Historically, atrial fibrillation (AF) has been considered as a critical aspect in HCM patients as it is considered to be a marker of disease progression, escalates the frequency of heart failure hospitalisations, increases the risk of thromboembolic events, and worsens quality of life and outcome. Increasing evidence suggests that AF is the result of a subtle long-standing process that starts early in the history of HCM. The process of left atrial dilation accompanied by morphologic and functional remodelling is the quintessential prerequisite for the onset of AF. This review aims to describe the current understanding of AF pathophysiology in HCM, emphasising the role of left atrial myopathy in its development. In addition, we discuss risk factors and management strategies specific to AF in the context of HCM, providing insights into the complexities and challenges of treating this specific patient population.

The Revolution of Cardiac Myosin Inhibitors in Patients With Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common genetic cardiomyopathy worldwide and causes significant morbidity and mortality. For decades, medical treatment options have been limited and untargeted, with frequent need for invasive interventions not readily accessible to many HCM patients. More recently, our understanding of the genetic basis and pathophysiologic mechanism of HCM has grown significantly, leading to the discovery of a new class of medications, cardiac myosin inhibitors (CMIs), that shift myosin into the super-relaxed state to counteract the hypercontractility in HCM. Subsequent clinical trials have proven the mechanism and efficacy of CMIs in humans with obstructive HCM, and additional trials are under way in patients with nonobstructive HCM. With favourable results in the completed clinical trials and ongoing research on the horizon, CMIs represent a bright new era in the targeted management of HCM. This review is focused on the discovery of CMIs, provides a summary of the results of clinical trials to date, provides clinicians with a roadmap for implementing CMIs into practice, and identifies gaps in our current understanding as well as areas of ongoing investigation.

Evaluating the efficacy and safety of mavacamten in hypertrophic cardiomyopathy: A systematic review and meta-analysis focusing on qualitative assessment, biomarkers, and cardiac imaging

BACKGROUND

Hypertrophic Cardiomyopathy (HCM) is a complex cardiac condition characterized by hypercontractility of cardiac muscle leading to a dynamic obstruction of left ventricular outlet tract (LVOT). Mavacamten, a first-in-class cardiac myosin inhibitor, is increasingly being studied in randomized controlled trials. In this meta-analysis, we aimed to analyse the efficacy and safety profile of Mavacamten compared to placebo in patients of HCM.

METHOD

We carried out a comprehensive search in PubMed, Cochrane, and clinicaltrials.gov to analyze the efficacy and safety of mavacamten compared to placebo from 2010 to 2023. To calculate pooled odds ratio (OR) or risk ratio (RR) at 95% confidence interval (CI), the Mantel-Haenszel formula with random effect was used and Generic Inverse Variance method assessed pooled mean difference value at a 95% CI. RevMan was used for analysis. P<0.05 was considered significant.

RESULTS

We analyzed five phase 3 RCTs including 609 patients to compare mavacamten with a placebo. New York Heart Association (NYHA) grade improvement and KCCQ score showed the odds ratio as 4.94 and 7.93 with p<0.00001 at random effect, respectively. Cardiac imaging which included LAVI, LVOT at rest, LVOT post valsalva, LVOT post-exercise, and reduction in LVEF showed the pooled mean differences for change as -5.29, -49.72, -57.45, -36.11, and -3.00 respectively. Changes in LVEDV and LVMI were not statistically significant. The pooled mean difference for change in NT-proBNP and Cardiac troponin-I showed 0.20 and 0.57 with p<0.00001. The efficacy was evaluated in 1) A composite score, which was defined as either 1·5 mL/kg per min or greater increase in peak oxygen consumption (pVO2) and at least one NYHA class reduction, or a 3·0 mL/kg per min or greater pVO2 increase without NYHA class worsening and 2) changes in pVO2, which was not statistically significant. Similarly, any treatment-associated emergent adverse effects (TEAE), treatment-associated serious adverse effects (TSAE), and cardiac-related adverse effects were not statistically significant.

CONCLUSION

Mavacamten influences diverse facets of HCM comprehensively. Notably, our study delved into the drug's impact on the heart's structural and functional aspects, providing insights that complement prior findings. Further large-scale trials are needed to evaluate the safety profile of Mavacamten.

Long-Term Safety and Efficacy of Mavacamten in Symptomatic Obstructive Hypertrophic Cardiomyopathy: Interim Results of the PIONEER-OLE Study

BACKGROUND

The phase 2 PIONEER-HCM (Phase 2 Open-label Pilot Study Evaluating Mavacamten in Subjects With Symptomatic Hypertrophic Cardiomyopathy and Left Ventricular Outflow Tract Obstruction) study showed that mavacamten improved left ventricular outflow tract gradients, exercise capacity, and symptoms in patients with obstructive hypertrophic cardiomyopathy (HCM), but the results of longer-term treatment are less well described. We report interim results from the PIONEER-OLE (PIONEER Open-Label Extension) study, the longest-term study of mavacamten in patients with symptomatic obstructive HCM.

METHODS AND RESULTS

Patients who previously completed PIONEER-HCM (n=20) were eligible to enroll in PIONEER-OLE. Patients received oral mavacamten, 5 mg once daily (starting dose), with individualized dose titration at week 6. Evaluations included serial monitoring of safety, echocardiography, Kansas City Cardiomyopathy Questionnaire-Overall Summary Score, and serum NT-proBNP (N-terminal pro-B-type natriuretic peptide) levels. Thirteen patients enrolled and received mavacamten (median study duration at data cutoff, 201 weeks). Most patients (92.3%) received β-blockers concomitantly. Treatment-emergent adverse events were predominantly mild/moderate. One patient had an isolated reduction in left ventricular ejection fraction to 47%, which recovered and remained normal with continued treatment at a reduced dose. At week 180, mavacamten was associated with New York Heart Association class improvements from baseline (class II to I, n=9; class III to II, n=1; and unchanged, n=2), sustained reductions in left ventricular outflow tract gradients (mean [SD] change from baseline: resting, -50 [55] mm Hg; Valsalva, -70 [41] mm Hg), and serum NT-proBNP levels (median [interquartile range] change from baseline: -498 [-2184 to -76] ng/L), and improved Kansas City Cardiomyopathy Questionnaire-Overall Summary Score (mean [SD] change from baseline: +17 [16]).

CONCLUSIONS

This long-term analysis supports the continued safety and effectiveness of mavacamten for >3 years in obstructive HCM.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT03496168.

The Expansion of Genetic Testing in Cardiovascular Medicine: Preparing the Cardiology Community for the Changing Landscape

PURPOSE OF REVIEW

Pathogenic DNA variants underlie many cardiovascular disease phenotypes. The most well-recognized of these include familial dyslipidemias, cardiomyopathies, arrhythmias, and aortopathies. The clinical presentations of monogenic forms of cardiovascular disease are often indistinguishable from those with complex genetic and non-genetic etiologies, making genetic testing an essential aid to precision diagnosis.

RECENT FINDINGS

Precision diagnosis enables efficient management, appropriate use of emerging targeted therapies, and follow-up of at-risk family members. Genetic testing for these conditions is widely available but under-utilized. In this review, we summarize the potential benefits of genetic testing, highlighting the specific cardiovascular disease phenotypes in which genetic testing should be considered, and how clinicians can integrate guideline-directed genetic testing into their practice.

Mavacamten for Obstructive Hypertrophic Cardiomyopathy With or Without Hypertension: Post-Hoc Analysis of the EXPLORER-HCM Trial

BACKGROUND

Hypertension (HTN) is common in patients with hypertrophic cardiomyopathy (HCM), but its effect on the treatment of left ventricular outflow tract (LVOT) obstruction is undefined. Although elevated systolic blood pressure (SBP) may impact dynamic LVOT gradients, its response to cardiac myosin inhibition is unknown.

OBJECTIVES

In a post hoc exploratory analysis of the EXPLORER-HCM trial (Clinical Study to Evaluate Mavacamten [MYK-461] in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy), the authors examined the characteristics of patients with obstructive HCM and HTN and the associations between HTN, SBP, and the response to mavacamten treatment of LVOT obstruction.

METHODS

Patients were stratified by baseline history of HTN and mean SBP during 30-week treatment with mavacamten or placebo. The study estimated treatment differences and evaluated HTN and SBP groups by treatment interaction. Analysis of covariance was used to model changes in continuous endpoints, and a generalized linear model was used for binary endpoints.

RESULTS

HTN was present in 119 of 251 patients (47.4%), including 60 receiving mavacamten and 59 receiving placebo. Patients with HTN vs no HTN were older (63.4 vs 54.0 years; P < 0.001), had higher SBP (134 ± 15.1 mm Hg vs 123 ± 13.8 mm Hg; P < 0.001), more comorbidities, and lower peak oxygen consumption (19 ± 3 vs 20 ± 4 mL/kg/min; P = 0.021). Patients with HTN had similar NYHA functional class (NYHA functional class II, 72% vs 73%), Valsalva LVOT gradients (72 ± 34 mm Hg vs 74 ± 30 mm Hg), Kansas City Cardiomyopathy Questionnaire-Clinical Summary Scores (70.6 ± 18.8 vs 68.9 ± 23.1), and NT pro-B-type natriuretic peptide levels (geometric mean 632 ± 129 pg/mL vs 745 ± 130 pg/mL). Mavacamten-treated patients had improvement in all primary, secondary, and exploratory endpoints regardless of HTN status or mean SBP.

CONCLUSIONS

The clinical benefits of mavacamten in symptomatic, obstructive HCM were similar in patients with and without HTN, despite differences in baseline characteristics. (Clinical Study to Evaluate Mavacamten [MYK-461] in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy [EXPLORER-HCM]; NCT03470545).

Current perspectives of sudden cardiac death management in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is an autosomal dominant disorder characterized by left ventricular hypertrophy. Sudden cardiac death (SCD) is a rare but the most catastrophic complication in patients with HCM. Implantable cardioverter-defibrillators (ICDs) are widely recognized as effective preventive measures for SCD. Individualized risk stratification and early intervention in HCM can significantly improve patient prognosis. In this study, we review the latest findings regarding pathogenesis, risk stratification, and prevention of SCD in HCM patients, highlighting the clinic practice of cardiovascular magnetic resonance imaging for SCD management.

Effect of Mavacamten in Women Compared With Men With Obstructive Hypertrophic Cardiomyopathy: Insights From EXPLORER-HCM

BACKGROUND

Compared with men, women with hypertrophic cardiomyopathy (HCM) have a higher incidence of heart failure and worse outcomes. We investigated baseline clinical and echocardiographic characteristics and response to mavacamten among women compared with men in the EXPLORER-HCM study (Clinical Study to Evaluate Mavacamten [MYK-461] in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy).

METHODS

A prespecified post hoc analysis of sex from the blinded, randomized EXPLORER-HCM trial of mavacamten versus placebo in symptomatic patients with obstructive HCM was performed. Baseline characteristics were compared with t tests for continuous variables (expressed as mean values) and χ2 tests for categorical variables. Prespecified primary, secondary, and exploratory end points and echocardiographic measurements from baseline to end of treatment (week 30) were analyzed with ANCOVA for continuous end points and a generalized linear model with binomial distribution for binary end points, with adjustment for each outcome's baseline value, New York Heart Association class, β-blocker use, and ergometer type.

RESULTS

At baseline, women (n=102) were older (62 years versus 56 years; P<0.0001), had lower peak oxygen consumption (16.7 mL·kg-1·min-1 versus 21.3 mL·kg-1·min-1; P<0.0001), were more likely to be assigned New York Heart Association class III (42% versus 17%; P<0.0001), had worse health status (Kansas City Cardiomyopathy Questionnaire-Clinical Summary Score 64 versus 75; P<0.0001), and had higher baseline plasma NT-proBNP (N-terminal pro-B-type natriuretic peptide) levels (1704 ng/L versus 990 ng/L; P=0.004) than men (n=149). After 30 weeks of mavacamten treatment, similar improvements were observed in women and men in the primary composite end point (percentage difference on mavacamten versus placebo, 22% versus 19%, respectively; P=0.759) and in the secondary end points of change in postexercise left ventricular outflow tract gradient (-42.4 mm Hg versus -33.6 mm Hg; P=0.348), change in peak oxygen consumption (1.2 mL·kg-1·min-1 versus 1.6 mL·kg-1·min-1; P=0.633), and percentage achieving ≥1 New York Heart Association class improvement (41% versus 28%; P=0.254). However, women had greater improvement in health status (Kansas City Cardiomyopathy Questionnaire-Clinical Summary Score 14.8 versus 6.1; P=0.026) and in the exploratory end point of NT-proBNP levels (-1322 ng/L versus -649 ng/L; P=0.0008).

CONCLUSIONS

Although at baseline women with symptomatic obstructive HCM enrolled in EXPLORER-HCM were older and had worse heart failure and health status than men, treatment with mavacamten resulted in similar improvements in the primary and most secondary EXPLORER-HCM end points and greater improvements in health status and NT-proBNP.

REGISTRATION

URL: https://www.clinicaltrials.gov; Unique identifier: NCT03470545.

Short time effects of two radiofrequency ablation methods on hypertrophic obstructive cardiomyopathy

BACKGROUND

Radiofrequency ablation has been applied for the treatment of hypertrophic obstructive cardiomyopathy (HOCM). The two known procedures are percutaneous intramyocardial septal radiofrequency ablation (PIMSRA) and endocardial radiofrequency septal ablation (ERSA).

METHODS

This study presents a retrospective analysis of the PIMSRA and ERSA procedures in patients with drug-refractory HOCM. A total of 28 patients participated in the study, with 12 receiving PIMSRA and 16 receiving ERSA. The objective of our study was to compare the short-term effects of these two radiofrequency ablation procedures.

RESULTS

At the 30-day follow-up, the PIMSRA group demonstrated a greater reduction in left ventricular outflow tract peak gradient at rest compared to the ERSA group (22.25 [16.72] mmHg versus 47.75 [21.94] mmHg) (p < .01). The values for the PIMSRA group decreased from 99.33 (32.00) mmHg to 22.25 (16.72) mmHg (p < .01), while the ERSA group decreased from 97.75 (30.24) mmHg to 47.75 (21.94) mmHg (p < .01). Only the PIMSRA group exhibited a decrease in mitral regurgitation (MR). The area of MR decreased from 10.13 (4.12) mm2 to 3.65 (2.80) mm2 in the PIMSRA group (p < .01). Additionally, the PIMSRA group experienced reductions in left atrial diameter (LAD) and left ventricular ejection fraction (LVEF)%. The values for LAD changed from 43.58 (7.53) mm to 37.08 (6.92) mm (p = .03), and the values for LVEF% decreased from 65.75 (6.12) pg/mL to 60.83 (4.06) pg/mL (p = .03).

CONCLUSION

In terms of the two types of radiofrequency ablation methods used in HOCM, it has been observed that PIMSRA demonstrates a more favorable early treatment effect compared to ERSA.

Exploring the Connection Between Relaxed Myosin States and the Anrep Effect

The Anrep effect is an adaptive response that increases left ventricular contractility following an acute rise in afterload. Although the mechanistic origin remains undefined, recent findings suggest a two-phase activation of resting myosin for contraction, involving strain-sensitive and posttranslational phases. We propose that this mobilization represents a transition among the relaxed states of myosin-specifically, from the super-relaxed (SRX) to the disordered-relaxed (DRX)-with DRX myosin ready to participate in force generation. This hypothesis offers a unified explanation that connects myosin's SRX-DRX equilibrium and the Anrep effect as parts of a singular phenomenon. We underscore the significance of this equilibrium in modulating contractility, primarily studied in the context of hypertrophic cardiomyopathy, the most common inherited cardiomyopathy associated with diastolic dysfunction, hypercontractility, and left ventricular hypertrophy. As we posit that the cellular basis of the Anrep effect relies on a two-phased transition of myosin from the SRX to the contraction-ready DRX configuration, any dysregulation in this equilibrium may result in the pathological manifestation of the Anrep phenomenon. For instance, in hypertrophic cardiomyopathy, hypercontractility is linked to a considerable shift of myosin to the DRX state, implying a persistent activation of the Anrep effect. These valuable insights call for additional research to uncover a clinical Anrep fingerprint in pathological states. Here, we demonstrate through noninvasive echocardiographic pressure-volume measurements that this fingerprint is evident in 12 patients with hypertrophic obstructive cardiomyopathy before septal myocardial ablation. This unique signature is characterized by enhanced contractility, indicated by a leftward shift and steepening of the end-systolic pressure-volume relationship, and a prolonged systolic ejection time adjusted for heart rate, which reverses post-procedure. The clinical application of this concept has potential implications beyond hypertrophic cardiomyopathy, extending to other genetic cardiomyopathies and even noncongenital heart diseases with complex etiologies across a broad spectrum of left ventricular ejection fractions.

Mavacamten Treatment for Symptomatic Obstructive Hypertrophic Cardiomyopathy: Interim Results From the MAVA-LTE Study, EXPLORER-LTE Cohort

BACKGROUND

Data assessing the long-term safety and efficacy of mavacamten treatment for symptomatic obstructive hypertrophic cardiomyopathy are needed.

OBJECTIVES

The authors sought to evaluate interim results from the EXPLORER-Long Term Extension (LTE) cohort of MAVA-LTE (A Long-Term Safety Extension Study of Mavacamten in Adults Who Have Completed EXPLORER-HCM; NCT03723655).

METHODS

After mavacamten or placebo withdrawal at the end of the parent EXPLORER-HCM (Clinical Study to Evaluate Mavacamten [MYK-461] in Adults With Symptomatic Obstructive Hypertrophic Cardiomyopathy; NCT03470545), patients could enroll in MAVA-LTE. Patients received mavacamten 5 mg once daily; adjustments were made based on site-read echocardiograms.

RESULTS

Between April 9, 2019, and March 5, 2021, 231 of 244 eligible patients (94.7%) enrolled in MAVA-LTE (mean age: 60 years; 39% female). At data cutoff (August 31, 2021) 217 (93.9%) remained on treatment (median time in study: 62.3 weeks; range: 0.3-123.9 weeks). At 48 weeks, patients showed improvements in left ventricular outflow tract (LVOT) gradients (mean change ± SD from baseline: resting: -35.6 ± 32.6 mm Hg; Valsalva: -45.3 ± 35.9 mm Hg), N-terminal pro-B-type natriuretic peptide (NT-proBNP) levels (median: -480 ng/L; Q1-Q3: -1,104 to -179 ng/L), and NYHA functional class (67.5% improved by ≥1 class). LVOT gradients and NT-proBNP reductions were sustained through 84 weeks in patients who reached this timepoint. Over 315 patient-years of exposure, 8 patients experienced an adverse event of cardiac failure, and 21 patients had an adverse event of atrial fibrillation, including 11 with no prior history of atrial fibrillation. Twelve patients (5.2%) developed transient reductions in site-read echocardiogram left ventricular ejection fraction of <50%, resulting in temporary treatment interruption; all recovered. Ten patients discontinued treatment due to treatment-emergent adverse events.

CONCLUSIONS

Mavacamten treatment showed clinically important and durable improvements in LVOT gradients, NT-proBNP levels, and NYHA functional class, consistent with EXPLORER-HCM. Mavacamten treatment was well tolerated over a median 62-week follow-up.

Biomechanical response of ultrathin slices of hypertrophic cardiomyopathy tissue to myosin modulator mavacamten

Hypertrophic cardiomyopathy (HCM) is the most common inherited myocardial disorder of the heart, but effective treatment options remain limited. Mavacamten, a direct myosin modulator, has been presented as novel pharmacological therapy for HCM. The aim of this study was to analyze the biomechanical response of HCM tissue to Mavacamten using living myocardial slices (LMS). LMS (n = 58) from patients with HCM (n = 10) were cultured under electromechanical stimulation, and Verapamil and Mavacamten were administered on consecutive days to evaluate their effects on cardiac biomechanics. Mavacamten and Verapamil reduced contractile force and dF/dt and increased time-to-relaxation in a similar manner. Yet, the time-to-peak of the cardiac contraction was prolonged after administration of Mavacamten (221.0 ms (208.8 - 236.3) vs. 237.7 (221.0 - 254.7), p = 0.004). In addition, Mavacamten prolonged the functional refractory period (FRP) (330 ms (304 - 351) vs. 355 ms (313 - 370), p = 0.023) and better preserved twitch force with increasing stimulation frequencies, compared to Verapamil. As such, Mavacamten reduced (hyper-)contractility and prolonged contraction duration of HCM LMS, suggesting a reduction in cardiac wall stress. Also, Mavacamten might protect against the development of ventricular tachyarrhythmias due to prolongation of the FRP, and improve toleration of tachycardia due to better preservation of twitch force at tachycardiac stimulation frequencies.

Incidence, risk assessment and prevention of sudden cardiac death in cardiomyopathies

Cardiomyopathies are a significant contributor to cardiovascular morbidity and mortality, mainly due to the development of heart failure and increased risk of sudden cardiac death (SCD). Despite improvement in survival with contemporary treatment, SCD remains an important cause of mortality in cardiomyopathies. It occurs at a rate ranging between 0.15% and 0.7% per year (depending on the cardiomyopathy), which significantly surpasses SCD incidence in the age- and sex-matched general population. The risk of SCD is affected by multiple factors including the aetiology, genetic basis, age, sex, physical exertion, the extent of myocardial disease severity, conduction system abnormalities, and electrical instability, as measured by various metrics. Over the past decades, the knowledge on the mechanisms and risk factors for SCD has substantially improved, allowing for a better-informed risk stratification. However, unresolved issues still challenge the guidance of SCD prevention in patients with cardiomyopathies. In this review, we aim to provide an in-depth discussion of the contemporary concepts pertinent to understanding the burden, risk assessment and prevention of SCD in cardiomyopathies (dilated, non-dilated left ventricular, hypertrophic, arrhythmogenic right ventricular, and restrictive). The review first focuses on SCD incidence in cardiomyopathies and then summarizes established and emerging risk factors for life-threatening arrhythmias/SCD. Finally, it discusses validated approaches to the risk assessment and evidence-based measures for SCD prevention in cardiomyopathies, pointing to the gaps in evidence and areas of uncertainties that merit future clarification.

Prediction of worsening heart failure in hypertrophic cardiomyopathy using plasma proteomics

OBJECTIVE

Heart failure (HF) is one of the most common and lifestyle-limiting complications of hypertrophic cardiomyopathy (HCM). Prediction of worsening HF using clinical measures alone remains limited. Moreover, the mechanisms by which patients with HCM develop worsening HF have not been elucidated. Therefore, the aim of this study was to develop a plasma proteomics-based model to predict worsening HF among patients with HCM and to identify signalling pathways that are differentially regulated in those who subsequently develop worsening HF.

METHODS

In this multi-centre, prospective cohort study of 389 patients with HCM, plasma proteomics profiling of 4986 proteins was performed at enrolment. A proteomics-based random forest model was developed to predict worsening HF using data from one institution (training set, n=268). This model was externally validated in patients from a different institution (test set, n=121). Pathway analysis of proteins significantly dysregulated in patients who subsequently developed worsening HF compared with those who did not was executed, using a false discovery rate (FDR) threshold of <0.001.

RESULTS

Using the 11-protein proteomics-based model derived from the training set, the area under the receiver-operating characteristic curve to predict worsening HF was 0.87 (95% CI: 0.76 to 0.98) in the test set. Pathway analysis revealed that the Ras-MAPK pathway (FDR<0.00001) and related pathways were dysregulated in patients who subsequently developed worsening HF.

CONCLUSIONS

The present study with comprehensive plasma proteomics profiling demonstrated a high accuracy to predict worsening HF in patients with HCM and identified the Ras-MAPK and related signalling pathways as potential underlying mechanisms.

Mavacamten: a first-in-class myosin inhibitor for obstructive hypertrophic cardiomyopathy

Mavacamten is a first-in-class, targeted, cardiac-specific myosin inhibitor approved by the US Food and Drug Administration for the treatment of adults with symptomatic New York Heart Association Classes II and III obstructive hypertrophic cardiomyopathy (oHCM). Mavacamten was developed to target the hyper-contractile phenotype, which plays a critical role in the pathophysiology of the disease. In Phase 2 and 3 clinical trials, mavacamten was well tolerated, reduced left ventricular outflow tract gradients, improved exercise capacity and symptoms, and was associated with improvements in other clinically relevant parameters, such as patient-reported outcomes and circulating biomarkers. In addition, treatment with mavacamten was associated with evidence of favourable cardiac remodelling in multi-modality imaging studies. Mavacamten substantially reduced guideline eligibility for septal reduction therapy candidates with oHCM and drug-refractory symptoms. In this article, the available efficacy and safety data from completed and ongoing clinical studies of mavacamten in patients with symptomatic oHCM are reviewed. Longer term extension studies may help address questions related to the positioning of mavacamten in current oHCM management algorithms, interactions with background therapy, as well as the potential for disease modification beyond symptomatic relief of left ventricular outflow tract obstruction.

Novel Therapeutic Avenues for Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a complicated, heterogeneous genetic condition that causes left ventricular hypertrophy, fibrosis, hypercontractility, and decreased compliance. Despite the advances made over the past 3 decades in understanding the molecular and cellular mechanisms aggravating HCM, the relationship between pathophysiological stress stimuli and distinctive myocyte growth profiles is still imprecise. Currently, mavacamten, a selective and reversible inhibitor of cardiac myosin ATPase, is the only drug approved by the US FDA for the treatment of HCM. Thus, there is an unmet need for developing novel disease-specific therapeutic approaches. This article provides an overview of emerging therapeutic targets for the treatment of HCM based on various molecular pathways and novel developments that are hopefully soon to enter the clinical study. These newly discovered targets include the dual specificity tyrosine-phosphorylation-regulated kinase 1B, the absence of the melanoma 1 inflammasome, the leucine-rich repeat kinase 2 enzyme, and the cluster of differentiation 147.

State-of-the-art document on optimal contemporary management of cardiomyopathies

Cardiomyopathies represent significant contributors to cardiovascular morbidity and mortality. Over the past decades, a progress has occurred in characterization of the genetic background and major pathophysiological mechanisms, which has been incorporated into a more nuanced diagnostic approach and risk stratification. Furthermore, medications targeting core disease processes and/or their downstream adverse effects have been introduced for several cardiomyopathies. Combined with standard care and prevention of sudden cardiac death, these novel and emerging targeted therapies offer a possibility of improving the outcomes in several cardiomyopathies. Therefore, the aim of this document is to summarize practical approaches to the treatment of cardiomyopathies, which includes the evidence-based novel therapeutic concepts and established principles of care, tailored to the individual patient aetiology and clinical presentation of the cardiomyopathy. The scope of the document encompasses contemporary treatment of dilated, hypertrophic, restrictive and arrhythmogenic cardiomyopathy. It was based on an expert consensus reached at the Heart Failure Association online Workshop, held on 18 March 2021.

Alcohol Septal Ablation or Mavacamten for Obstructive Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic disease characterized by an increased left ventricular wall thickness in the absence of increased afterload conditions. In addition to diastolic dysfunction, obstruction of the left ventricular outflow tract is common in HCM and has an important influence on symptoms and outcome. Over the last five decades or two decades, respectively, surgical myectomy and alcohol septal ablation were the only therapeutic options if standard medical care was not sufficient. Recently, a new option has become available that has the potential to revolutionize the therapeutic strategies for patients with HCM. Mavacamten is a myosin inhibitor that belongs to a completely new drug class and targets the excessive actin-myosin cross-bridging that is the underlying pathology of HCM. By reducing the actin-myosin interactions, mavacamten not only reduces the left ventricular outflow tract (LVOT) obstruction but also seems to have positive effects on the diastolic function, microcirculation, and cardiac structure. This article summarizes the current evidence on alcohol septal ablation and reviews the preclinical and clinical data on mavacamten for the treatment of patients with obstructive HCM.

Multi-Omic, Histopathologic, and Clinicopathologic Effects of Once-Weekly Oral Rapamycin in a Naturally Occurring Feline Model of Hypertrophic Cardiomyopathy: A Pilot Study

Hypertrophic cardiomyopathy (HCM) remains the single most common cardiomyopathy in cats, with a staggering prevalence as high as 15%. To date, little to no direct therapeutical intervention for HCM exists for veterinary patients. A previous study aimed to evaluate the effects of delayed-release (DR) rapamycin dosing in a client-owned population of subclinical, non-obstructive, HCM-affected cats and reported that the drug was well tolerated and resulted in beneficial LV remodeling. However, the precise effects of rapamycin in the hypertrophied myocardium remain unknown. Using a feline research colony with naturally occurring hereditary HCM (n = 9), we embarked on the first-ever pilot study to examine the tissue-, urine-, and plasma-level proteomic and tissue-level transcriptomic effects of an intermittent low dose (0.15 mg/kg) and high dose (0.30 mg/kg) of DR oral rapamycin once weekly. Rapamycin remained safe and well tolerated in cats receiving both doses for eight weeks. Following repeated weekly dosing, transcriptomic differences between the low- and high-dose groups support dose-responsive suppressive effects on myocardial hypertrophy and stimulatory effects on autophagy. Differences in the myocardial proteome between treated and control cats suggest potential anti-coagulant/-thrombotic, cellular remodeling, and metabolic effects of the drug. The results of this study closely recapitulate what is observed in the human literature, and the use of rapamycin in the clinical setting as the first therapeutic agent with disease-modifying effects on HCM remains promising. The results of this study establish the need for future validation efforts that investigate the fine-scale relationship between rapamycin treatment and the most compelling gene expression and protein abundance differences reported here.

Effects of septal myectomy on left atrial and left ventricular function in obstructive hypertrophic cardiomyopathy

AIMS

Mechanical function of the left atrium (LA) and the left ventricle (LV) has been demonstrated to be a prognostic factor in patients with hypertrophic cardiomyopathy (HCM). We explore whether myocardial mechanical function can be improved by septal reduction therapy in symptomatic obstructive HCM.

METHODS AND RESULTS

Among 65 patients who underwent septal myectomy for symptomatic obstructive HCM from 2006 to 2022, 44 were analysed after excluding those who underwent simultaneous valve repair or replacement or maze operation. LA and LV functional variables including LA strain and LV global longitudinal strain were evaluated by two-dimensional and speckle-tracking echocardiography and compared before and 1 year after surgery. After septal myectomy, LA volume index (58.1 ± 18.3 vs. 45.3 ± 14.6 mL/m2 , P = 0.001) decreased significantly. As LV end-systolic dimension increased after surgery, the LV ejection fraction decreased (73.8 ± 6.7 vs. 62.9 ± 8.3%, P < 0.001). LA strain (24.4 ± 9.3 vs. 30.5 ± 13.6%, P = 0.004) improved after septal myectomy, but LV global longitudinal strain deteriorated (-12.6 ± 3.6 vs. -11.6 ± 4.3%, P = 0.033), mainly related to worsening non-septal longitudinal strain (-14.4 ± 4.3 vs. -10.9 ± 8.4%, P = 0.005).

CONCLUSIONS

As haemodynamic loads due to LV outflow tract obstruction was relieved through surgical septal reduction therapy in patients with symptomatic obstructive HCM, there was a significant reduction in LA volume and restoration of LA mechanical dysfunction. However, LV mechanical dysfunction deteriorated even after surgical septal reduction therapy.

Medical Therapies to Improve Left Ventricular Outflow Obstruction and Diastolic Function in Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy-both obstructive hypertrophic cardiomyopathy (oHCM) and nonobstructive hypertrophic cardiomyopathy (nHCM) subtypes-is the most common monogenic cardiomyopathy. Its structural hallmarks are abnormal thickening of the myocardium and hyperdynamic contractility, while its hemodynamic consequences are left ventricular outflow tract or intracavitary obstruction (in oHCM) and diastolic dysfunction (in both oHCM and nHCM). Several medical therapies are routinely used to improve these abnormalities with the goal to decrease symptom burden in patients with HCM. Current guidelines recommend nonvasodilating beta blockers as first-line and nondihydropyridine calcium channel blockers followed by disopyramide as second- and third-line medical therapies for symptomatic oHCM and give weaker recommendations for beta blockers and calcium channel blockers in nHCM. These recommendations are based on small studies-mostly nonrandomized-and expert opinion. Our review will summarize the available data on the effectiveness of commonly prescribed medications used in oHCM and nHCM to uncover knowledge gaps, but also new data on cardiac myosin inhibitors.

Imaging in Hypertrophic Cardiomyopathy: Beyond Risk Stratification

A multimodality imaging evaluation in hypertrophic cardiomyopathy is often used for risk stratification. Recent developments in imaging have allowed for better diagnosis, prognosis, and decision-making for a variety of therapies from medical to interventional. Echocardiography and magnetic resonance have been integral in evaluating subtype, left ventricular function, tissue characterization, left atrial measurements, valvular function, and presence of left ventricular aneurysm and outflow tract obstruction. These factors have helped to quantify risk of atrial fibrillation and determine the likely usefulness of pharmacologic therapy and septal reduction therapy. This review covers these in detail.

The role of imaging in the selection of patients for HFpEF therapy

Heart failure with preserved ejection fraction (HFpEF) traditionally has been characterized as a form of heart failure without therapeutic options, in particular with a lack of response to the established therapies of heart failure with reduced ejection fraction (HFrEF). However, this is no longer true. Besides physical exercise, risk factor modification, aldosterone blocking agents, and sodium-glucose cotransporter 2 inhibitors, specific therapies are emerging for specific HFpEF etiologies, such as hypertrophic cardiomyopathy or cardiac amyloidosis. This development justifies increased efforts to arrive at specific diagnoses within the umbrella of HFpEF. Cardiac imaging plays by far the largest role in this effort and is discussed in the following review.

A Practical Approach to Echocardiographic Imaging in Patients With Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is frequently unrecognized or misdiagnosed. The recently published consensus recommendations from the American Society of Echocardiography provided recommendations for the utilization of multimodality imaging in the care of patients with HCM. This document provides an additional practical framework for optimal image and measurement acquisition and guidance on how to tailor the echocardiography examination for individuals with HCM. It also provides resources for physicians and sonographers to use to develop HCM imaging protocols.

Long-Term Prevalence of Systolic Dysfunction in MYBPC3 Versus MYH7-Related Hypertrophic Cardiomyopathy

BACKGROUND

The 2 sarcomere genes most commonly associated with hypertrophic cardiomyopathy (HCM), MYBPC3 (myosin-binding protein C3) and MYH7 (β-myosin heavy chain), are indistinguishable at presentation, and genotype-phenotype correlations have been elusive. Based on molecular and pathophysiological differences, however, it is plausible to hypothesize a different behavior in myocardial performance, impacting lifetime changes in left ventricular (LV) function.

METHODS

We reviewed the initial and final echocardiograms of 402 consecutive HCM patients with pathogenic or likely pathogenic MYBPC3 (n=251) or MYH7 (n=151) mutations, followed over 9±8 years.

RESULTS

At presentation, MYBPC3 patients were less frequently obstructive (15% versus 26%; P=0.005) and had lower LV ejection fraction compared with MYH7 (66±8% versus 68±8%, respectively; P=0.03). Both HCM patients harboring MYBPC3 and MYH7 mutations exhibited a small but significant decline in LV systolic function during follow-up; however, new onset of severe LV systolic dysfunction (LV ejection fraction, <50%) was greater among MYBPC3 patients (15% versus 5% among MYH7; P=0.013). Prevalence of grade II/III diastolic dysfunction at final evaluation was comparable between MYBPC3 and MYH7 patients (P=0.509). In a Cox multivariable analysis, MYBPC3-positive status (hazard ratio, 2.53 [95% CI, 1.09-5.82]; P=0.029), age (hazard ratio, 1.03 [95% CI, 1.00-1.06]; P=0.027), and atrial fibrillation (hazard ratio, 2.39 [95% CI, 1.14-5.05]; P=0.020) were independent predictors of severe systolic dysfunction. No statistically significant differences occurred with regard to incidence of atrial fibrillation, heart failure, appropriate implanted cardioverter defibrillator shock, or cardiovascular death.

CONCLUSIONS

MYBPC3-related HCM showed increased long-term prevalence of systolic dysfunction compared with MYH7, in spite of similar outcome. Such observations suggest different pathophysiology of clinical progression in the 2 subsets and may prove relevant for understanding of genotype-phenotype correlations in HCM.

Mavacamten, a precision medicine for hypertrophic cardiomyopathy: From a motor protein to patients

Hypertrophic cardiomyopathy (HCM) is a primary myocardial disorder characterized by left ventricular hypertrophy, hyperdynamic contraction, and impaired relaxation of the heart. These functional derangements arise directly from altered sarcomeric function due to either mutations in genes encoding sarcomere proteins, or other defects such as abnormal energetics. Current treatment options do not directly address this causal biology but focus on surgical and extra-sarcomeric (sarcolemmal) pharmacological symptomatic relief. Mavacamten (formerly known as MYK-461), is a small molecule designed to regulate cardiac function at the sarcomere level by selectively but reversibly inhibiting the enzymatic activity of myosin, the fundamental motor of the sarcomere. This review summarizes the mechanism and translational progress of mavacamten from proteins to patients, describing how the mechanism of action and pharmacological characteristics, involving both systolic and diastolic effects, can directly target pathophysiological derangements within the cardiac sarcomere to improve cardiac structure and function in HCM. Mavacamten was approved by the Food and Drug Administration in April 2022 for the treatment of obstructive HCM and now goes by the commercial name of Camzyos. Full information about the risks, limitations, and side effects can be found at www.accessdata.fda.gov/drugsatfda_docs/label/2022/214998s000lbl.pdf.

Cardiac Myosin Inhibitors for Managing Obstructive Hypertrophic Cardiomyopathy: JACC: Heart Failure State-of-the-Art Review

Hypertrophic cardiomyopathy (HCM) is frequently caused by pathogenic variants in genes encoding sarcomere proteins and is characterized by left ventricular (LV) hypertrophy, hypercontractility, and-in many cases-left ventricular outflow tract (LVOT) obstruction. Despite standard management, obstructive HCM (oHCM) can still cause substantial morbidity, highlighting the critical need for more effective disease-specific therapeutic approaches. Over the past decade, improved understanding of the molecular pathobiology of HCM has culminated in development of cardiac myosin inhibitors (CMIs), a novel drug class that in recent randomized clinical trials has been shown to decrease LVOT obstruction, improve exercise capacity, and ameliorate symptom burden in patients with oHCM. Although promising, areas of uncertainty remain, including the long-term safety and efficacy of CMIs and whether they have the potential to modify progression of disease. Herein, we review key milestones in the clinical development of CMIs, contextualize CMIs with established oHCM therapies, and discuss future challenges and opportunities for the use of CMIs across the HCM spectrum.

Stage-specific therapy for hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is the most common inherited myocardial disease and is defined by otherwise unexplained left ventricular hypertrophy. The main complications include heart failure and arrhythmias such as atrial fibrillation and ventricular arrhythmias. Current treatment rests on septal reduction therapies, prevention of sudden cardiac death through implantable cardioverter defibrillator, and use of drugs such as beta-blockers, calcium antagonists, or amiodarone. In the last years, new pharmacological agents specifically targeting the pathophysiology of the disease have been developed with encouraging results in terms of functional capacity and symptoms improvement from clinical trials. In this review, we summarize the possible treatment approaches for each phase of the natural history of the disease: pre-phenotype expression, classic phenotype, adverse remodelling, and overt dysfunction.

Old and new therapeutic solutions in the treatment of hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic disease of the myocardium that is relatively common in the general population, with an autosomal dominant inheritance as a genetic basis. Clinical and natural history pathways can be very different among patients with HCM. Treatment strategies have made very important advances in the last two decades, especially reducing cases of sudden death through effective risk stratification and the use of implantable defibrillators. Heart failure has become the predominant cause of morbidity and mortality in patients with HCM, being responsible for as many as 60% of disease-related deaths. HCM is most often characterized by the presence of left ventricular outflow tract (LVOT) obstruction, and this obstruction is the most frequent cause of impaired exercise tolerance in HCM and a strong independent predictor of heart failure progression and mortality. The different treatment strategies of LVOT obstruction in HCM are discussed below: surgical, invasive, and the more recent pharmacological.

Effects of Mavacamten on Measures of Cardiopulmonary Exercise Testing Beyond Peak Oxygen Consumption: A Secondary Analysis of the EXPLORER-HCM Randomized Trial

Importance

Mavacamten, a cardiac myosin inhibitor, improved peak oxygen uptake (pVO2) in patients with symptomatic obstructive hypertrophic cardiomyopathy (HCM) in the EXPLORER-HCM study. However, the full extent of mavacamten's effects on exercise performance remains unclear.

Objective

To investigate the effect of mavacamten on exercise physiology using cardiopulmonary exercise testing (CPET).

Design, Setting, and Participants

Exploratory analyses of the data from the EXPLORER-HCM study, a randomized, double-blind, placebo-controlled, phase 3 trial that was conducted in 68 cardiovascular centers in 13 countries. In total, 251 patients with symptomatic obstructive HCM were enrolled.

Interventions

Patients were randomly assigned in a 1:1 ratio to mavacamten or placebo.

Main Outcomes and Measures

The following prespecified exploratory cardiovascular and performance parameters were assessed with a standardized treadmill or bicycle ergometer test protocol at baseline and week 30: carbon dioxide output (VCO2), minute ventilation (VE), peak VE/VCO2 ratio, ventilatory efficiency (VE/VCO2 slope), peak respiratory exchange ratio (RER), peak circulatory power, ventilatory power, ventilatory threshold, peak metabolic equivalents (METs), peak exercise time, partial pressure of end-tidal carbon dioxide (PETCO2), and VO2/workload slope.

Results

Two hundred fifty-one patients were enrolled. The mean (SD) age was 58.5 (11.9) years and 59% of patients were male. There were significant improvements with mavacamten vs placebo in the following peak-exercise CPET parameters: peak VE/VCO2 ratio (least squares [LS] mean difference, -2.2; 95% CI, -3.05 to -1.26; P < .001), peak METs (LS mean difference, 0.4; 95% CI, 0.17-0.60; P < .001), peak circulatory power (LS mean difference, 372.9 mL/kg/min × mm Hg; 95% CI, 153.12-592.61; P = .001), and peak PETCO2 (LS mean difference, 2.0 mm Hg; 95% CI, 1.12-2.79; P < .001). Mavacamten also improved peak exercise time compared with placebo (LS mean difference, 0.7 minutes; 95% CI, 0.13-1.24; P = .02). There was a significant improvement in nonpeak-exercise CPET parameters, such as VE/VCO2 slope (LS mean difference, -2.6; 95% CI, -3.58 to -1.52; P < .001) and ventilatory power (LS mean difference, 0.6 mm Hg; 95% CI, 0.29-0.90; P < .001) favoring mavacamten vs placebo.

Conclusions and Relevance

Mavacamten improved a range of CPET parameters beyond pVO2, indicating consistent and broad benefits on maximal exercise capacity. Although improvements in peak-exercise CPET parameters are clinically meaningful, the favorable effects of mavacamten on submaximal exertional tolerance provide further insights into the beneficial impact of mavacamten in patients with obstructive HCM.

Trial Registration

ClinicalTrials.gov Identifier: NCT03470545.