Coronary microvascular dysfunction in hypertrophic cardiomyopathy: Pathophysiology, assessment, and clinical impact

A pilot study investigating serum carnitine profile of cats with preclinical hypertrophic cardiomyopathy

This study aimed to prospectively investigate the hypothesis that myocardial energy metabolism changes in the early stages of feline hypertrophic cardiomyopathy (HCM) by evaluating the blood carnitine profiles. Fourteen client owned cats with HCM stage B1 and 22 clinically healthy cats were included in this study. Total-carnitine, free-carnitine, acylcarnitine, and acylcarnitine/free-carnitine ratio (AF ratio) in serum were measured in both groups. No significant differences were observed in total-carnitine, free-carnitine, and acylcarnitine concentrations between the groups. However, the AF ratio in the HCM group was significantly lower than that of the control group (P=0.02). The lower serum AF ratio in cats with early-stage HCM, may suggest an alteration in their myocardial energy metabolism.

Relationship of Subendocardial Perfusion to Myocardial Injury, Cardiac Structure, and Clinical Outcomes Among Patients With Hypertension

BACKGROUND

Coronary microvascular dysfunction has been implicated in the development of hypertensive heart disease and heart failure, with subendocardial ischemia identified as a driver of sustained myocardial injury and fibrosis. We aimed to evaluate the relationships of subendocardial perfusion with cardiac injury, structure, and a composite of major adverse cardiac and cerebrovascular events consisting of death, heart failure hospitalization, myocardial infarction, and stroke.

METHODS

Layer-specific blood flow and myocardial flow reserve (MFR; stress/rest myocardial blood flow) were assessed by 13N-ammonia perfusion positron emission tomography in consecutive patients with hypertension without flow-limiting coronary artery disease (summed stress score <3) imaged at Brigham and Women's Hospital (Boston, MA) from 2015 to 2021. In this post hoc observational study, biomarkers, echocardiographic parameters, and longitudinal clinical outcomes were compared by tertiles of subendocardial MFR (MFRsubendo).

RESULTS

Among 358 patients, the mean age was 70.6±12.0 years, and 53.4% were male. The median MFRsubendo was 2.57 (interquartile range, 2.08-3.10), and lower MFRsubendo was associated with older age, diabetes, lower renal function, greater coronary calcium burden, and higher systolic blood pressure (P<0.05 for all). In cross-sectional multivariable regression analyses, the lowest tertile of MFRsubendo was associated with myocardial injury and with greater left ventricular wall thickness and volumes compared with the highest tertile. Relative to the highest tertile, low MFRsubendo was independently associated with an increased rate of major adverse cardiac and cerebrovascular events (adjusted hazard ratio, 2.99 [95% CI, 1.39-6.44]; P=0.005) and heart failure hospitalization (adjusted hazard ratio, 2.76 [95% CI, 1.04-7.32; P=0.042) over 1.1 (interquartile range, 0.6-2.8) years median follow-up.

CONCLUSIONS

Among patients with hypertension without flow-limiting coronary artery disease, impaired MFRsubendo was associated with cardiovascular risk factors, elevated cardiac biomarkers, cardiac structure, and clinical events.

Obstructive - Nonobstructive hypertrophic cardiomyopathy: differences and predictors

INTRODUCTION

Hypertrophic cardiomyopathy(HCM) is a genetic cardiomyopathy with a prevalence of 1/500 and causes adverse outcomes, usually due to left ventricular outflow tract obstruction.

AIM

In this study, we aimed to determine the possible differences and predictors of obstructive hypertrophic cardiomyopathy HCM (Obs-HCM) and nonobstructive HCM (Nonobs-HCM) by electrocardiographic (ECG) and echocardiographic (ECHO) evaluations with clinical, demographic, and biochemical characteristics.

METHODS

This study is a subgroup analysis of a multicentre, national, and observational 'LVH-TR study' that included 886 left ventricular hypertrophy(LVH) patients in 22 centres between February 2020 and August 2021. After excluding six patients with atrial fibrillation, pace rhythm, bundle branch blocks, and second, and third-degree atrioventricular(AV) block, 60 HCM patients were included, 23 of whom were obstructive, and 37 were nonobstructive.

RESULTS

Body surface area(BSA) (2.01 ± 0.17, 1.89 ± 0.19; p = .01), ST-segment depression (%82.6, %54.1; p = .02), QT and QTc durations (436.3 ± 58.3, 398.0 ± 65.5; p = .02/470.6 ± 58.7, 432.8 ± 74.7; p = .04), left ventricular mass index(LVMI) (176.4 ± 47.0, 152.7 ± 10.2; p = .004), and systolic anterior motion(SAM) rates (%82.6, %18.9; p < 0.001) were significantly higher in the obstructive HCM compared to nonobstructive HCM. Furthermore, the significance of ST-segment depression, QT duration, LVMI, and SAM continued in the univariate analyses to assess obstruction prediction (all p values < .05).

CONCLUSION

In multivariate and correlation analyses, ST segment depression (rho = 0.29), QT prolongation (rho = 0.34), and SAM (rho = 0.62) are found as predictors for obstruction (all p values < .05). Our study will guide future studies since it has detailed ECG and ECHO comparisons of Obs-HCM and Nonobs-HCM patients over 18 are made.

Tissue-level evidence of fibroblast activation protein inhibitor imaging in hypertrophic obstructive cardiomyopathy: a case series

Background

Myocardial fibrosis is a key pathological factor for the occurrence of ventricular arrhythmias in hypertrophic obstructive cardiomyopathy (HOCM).

Case summary

This case series reports on two patients diagnosed with HOCM who underwent 18F-fibroblast activation protein inhibitor (FAPI) positron-emission tomography/computed tomography imaging and Morrow myotomy procedure. The collected myocardial tissue was examined histopathologically. Both patients exhibited intense and heterogeneous 18F-FAPI uptake in the septum, with significant number of activated fibroblasts.

Discussion

Enhanced 18F-FAPI uptake was observed before irreversible fibrosis, and the degree of 18F-FAPI uptake was higher in tissue with greater fibrosis. 18F-FAPI imaging may provide a promising tool for guiding surgical strategy in HOCM, and further research is needed to fully explore its potential in clinical practice.

Coronary microvascular dysfunction, arrythmias, and sudden cardiac death: A literature review

The coronary vascular system has a unique structure and function that is adaptive to myocardial demand. It is composed of a continuous network of vessels receding in size from epicardial arteries to the microvascular circulation. Failure to meet myocardial demand results in ischemia, angina, and adverse myocardial outcomes. It is evident that 50 % of patients with angina have a non-obstructive coronary disease and 66 % of these patients have coronary microvascular dysfunction (CMD). The impact of CMD on the atria and ventricles is exhibited through its association with atrial fibrillation and distortion of ventricular repolarization. Ultimately, this influence increases the risk of mortality, morbidity, and sudden cardiac arrest. CMD serves as an independent risk for atrial fibrillation, increases ventricular electrical inhomogeneity, and contributes to the progression of cardiac disease. The underlying pathogenesis may be attributed to oxidative stress evident through reactive oxygen species, impaired vasoactive function, and structural disorders such as fibrotic changes. Myocardial ischemia, brought about by a demand-supply mismatch in CMD, may create a milieu for ventricular arrythmia and sudden cardiac arrest through distortion of ventricular repolarization parameters such as QT dispersion and corrected QT dispersion.

Chinese expert consensus on the diagnosis and treatment of coronary microvascular diseases (2023 Edition)

Since the four working groups of the Chinese Society of Cardiology issued first expert consensus on coronary microvascular diseases (CMVD) in 2017, international consensus documents on CMVD have increased rapidly. Although some of these documents made preliminary recommendations for the diagnosis and treatment of CMVD, they did not provide classification of recommendations and levels of evidence. In order to summarize recent progress in the field of CMVD, standardize the methods and procedures of diagnosis and treatment, and identify the scientific questions for future research, the four working groups of the Chinese Society of Cardiology updated the 2017 version of the Chinese expert consensus on CMVD and adopted a series of measures to ensure the quality of this document. The current consensus has raised a new classification of CMVD, summarized new epidemiological findings for different types of CMVD, analyzed key pathological and molecular mechanisms, evaluated classical and novel diagnostic technologies, recommended diagnostic pathways and criteria, and therapeutic strategies and medications, for patients with CMVD. In view of the current progress and knowledge gaps of CMVD, future directions were proposed. It is hoped that this expert consensus will further expedite the research progress of CMVD in both basic and clinical scenarios.

The weight of obesity in hypertrophic cardiomyopathy

Hypertrophic cardiomyopathy is one of the most frequently diagnosed primary conditions of the heart muscle. It is considered to be inherited, caused by genetic mutations encoding for sarcomere proteins. The marked heterogeneity in clinical manifestations and natural course of the disease, even among family members sharing the same genetic mutation, has raised the question of non-genetic environmental factors contributing to the phenotype. Obesity has been associated with worse cardiovascular outcomes in the general population. Its prevalence is increased in hypertrophic cardiomyopathy, and the two conditions share some similar pathophysiological and clinical characteristics. In this review, we aim to summarise the effects of obesity in the cardiac phenotype, the symptoms and management in patients with hypertrophic cardiomyopathy.

The Value of the Cardiac Magnetic Resonance Intravoxel Incoherent Motion Technique in Evaluating Microcirculatory Dysfunction in Hypertrophic Cardiomyopathy

Objective

To evaluate the value of the cardiac magnetic resonance intravoxel incoherent motion (IVIM) technique in microcirculatory dysfunction in patients with hypertrophic cardiomyopathy (HCM).

Methods

The medical records of 19 patients with HCM in our hospital from January 2020 to May 2021 were collected retrospectively, and 23 healthy people with a similar age and gender distribution to the patients with HCM were included as controls. All the included subjects underwent clinical assessment and cardiac magnetic resonance imaging. The original IVIM images were analysed, and the imaging parameters of each segment were measured. The HCM group was divided into non-hypertrophic myocardium and hypertrophic myocardium groups. The differences in imaging parameters between the normal and HCM groups were compared. A Spearman correlation analysis was used to explore the correlation between end-diastolic thickness (EDTH) and each IVIM parameter.

Results

The D^∗ and f values in the HCM group were lower than those in the normal group (p < 0.0001 and p = 0.004, respectively). The f, D, D^∗, and EDTH values of the hypertrophic segment, non-hypertrophic segment, and normal groups were statistically significant (p < 0.05). The difference in D^∗ values among the mild, moderate, severe, and very severe HCM groups was statistically significant (p < 0.05). There was a statistically significant difference in EDTH among the mild, moderate, severe, and very severe groups (p < 0.001). There were significant differences in the values of D, D^∗, and f between the non-delayed enhancement group and the delayed enhancement group (p < 0.05). The EDTH values of 304 segments in the HCM group were negatively correlated with f (r = -0.219, p = 0.028) and D^∗ values (r = -0.310, p < 0.001).

Conclusion

The use of IVIM technology can achieve a non-invasive early quantitative assessment of microvascular disease in HCM without the injection of a contrast agent and provide a reference for the early diagnosis of and intervention in myocardial ischemia in patients with HCM.

Altered coronary artery function, arteriogenesis and endothelial YAP signaling in postnatal hypertrophic cardiomyopathy

Introduction: Hypertrophic cardiomyopathy (HCM) is a cardiovascular genetic disease caused largely by sarcomere protein mutations. Gaps in our understanding exist as to how maladaptive sarcomeric biophysical signals are transduced to intra- and extracellular compartments leading to HCM progression. To investigate early HCM progression, we focused on the onset of myofilament dysfunction during neonatal development and examined cardiac dynamics, coronary vascular structure and function, and mechano-transduction signaling in mice harboring a thin-filament HCM mutation. Methods: We studied postnatal days 7-28 (P7-P28) in transgenic (TG) TG-cTnT-R92Q and non-transgenic (NTG) mice using skinned fiber mechanics, echocardiography, biochemistry, histology, and immunohistochemistry. Results: At P7, skinned myofiber bundles exhibited an increased Ca2+-sensitivity (pCa50 TG: 5.97 ± 0.04, NTG: 5.84 ± 0.01) resulting from cTnT-R92Q expression on a background of slow skeletal (fetal) troponin I and α/β myosin heavy chain isoform expression. Despite the transition to adult isoform expressions between P7-P14, the increased Ca2+- sensitivity persisted through P28 with no apparent differences in gross morphology among TG and NTG hearts. At P7 significant diastolic dysfunction was accompanied by coronary flow perturbation (mean diastolic velocity, TG: 222.5 ± 18.81 mm/s, NTG: 338.7 ± 28.07 mm/s) along with localized fibrosis (TG: 4.36% ± 0.44%, NTG: 2.53% ± 0.47%). Increased phosphorylation of phospholamban (PLN) was also evident indicating abnormalities in Ca2+ homeostasis. By P14 there was a decline in arteriolar cross-sectional area along with an expansion of fibrosis (TG: 9.72% ± 0.73%, NTG: 2.72% ± 0.2%). In comparing mechano-transduction signaling in the coronary arteries, we uncovered an increase in endothelial YAP expression with a decrease in its nuclear to cytosolic ratio at P14 in TG hearts, which was reversed by P28. Conclusion: We conclude that those early mechanisms that presage hypertrophic remodeling in HCM include defective biophysical signals within the sarcomere that drive diastolic dysfunction, impacting coronary flow dynamics, defective arteriogenesis and fibrosis. Changes in mechano-transduction signaling between the different cellular compartments contribute to the pathogenesis of HCM.

Safety and efficacy of ranolazine in hypertrophic cardiomyopathy: Real-world experience in a National Referral Center

OBJECTIVES

We assessed the efficacy and safety of ranolazine in real-world patients with hypertrophic cardiomyopathy (HCM).

BACKGROUND

Ranolazine is an anti-anginal drug that inhibits the late phase of the inward sodium current. In a small prospective trial, ranolazine reduced the arrhythmic burden and improved biomarker profile in HCM patients. However, systematic reports reflecting real-world use in this setting are lacking.

METHODS

Changes in clinical and instrumental features, symptoms and arrhythmic burden were evaluated in 119 patients with HCM before and during treatment with ranolazine at a national referral centre for HCM.

RESULTS

Patients were treated with ranolazine for 2 [1-4] years; 83 (70%) achieved a dosage ≥1000 mg per day. Treatment interruption was necessary in 24 patients (20%) due to side effects (n = 10, 8%) or disopyramide initiation (n = 8, 7%). Seventy patients (59%) were treated with ranolazine for relief of angina. Among them, 51 (73%) had total symptomatic relief and 47 patients (67%) showed ≥2 Canadian Cardiovascular society (CCS) angina grade improvement. Sixteen patients (13%) were treated for recurrent ventricular arrhythmias, including 4 with a clear ischemic trigger, who experienced no further arrhythmic episodes while on ranolazine. Finally, 33 patients (28%) were treated for heart failure associated with severe diastolic dysfunction: no symptomatic benefit could be observed in this group.

CONCLUSION

Ranolazine was safe and well tolerated in patients with HCM. The use of ranolazine may be considered in patients with HCM and microvascular angina.

Microvascular Dysfunction in Hypertrophic Cardiomyopathy

Myocardial ischemia is an established pathophysiological feature of hypertrophic cardiomyopathy (HCM) that impacts various clinical features, including heart failure (HF) and sudden cardiac death (SCD). The major determinant of myocardial ischemia in HCM is coronary microvascular dysfunction (CMD) in the absence of epicardial coronary artery abnormalities. Despite the impossibility to directly visualize microcirculation in vivo, a multimodality approach can allow a detailed assessment of microvascular dysfunction and ischemia. Accordingly, the non-invasive assessment of CMD using transthoracic Doppler echocardiography, positron emission tomography, and cardiac magnetic resonance should now be considered mandatory in any HCM patient. Noteworthy, a complete diagnostic work-up for myocardial ischemia plays a major role in the approach of the patients with HCM and their risk stratification. Chronic and recurrent episodes of ischemia can contribute to fibrosis, culminating in LV remodeling and HF. Ischemia can potentially constitute an arrhythmic substrate and might prove to have an added value in risk stratification for SCD. Accordingly, strategies for the early diagnosis of CMD should now be considered an important challenge for the scientific community.

Demographic and Regional Trends of Hypertrophic Cardiomyopathy-Related Mortality in the United States, 1999 to 2019

BACKGROUND

Hypertrophic cardiomyopathy (HCM)-related mortality has been decreasing within the United States; however, persistent disparities in demographic subsets may exist. In this study, we assessed nationwide trends in mortality related to HCM among people ≥15 years of age in the United States from 1999 to 2019.

METHODS

Trends in mortality related to HCM were assessed through a cross-sectional analysis of the Centers for Disease Control and Prevention Wide-Ranging Online Data for Epidemiological Research database. Age-adjusted mortality rates per 1 000 000 people and associated annual percent changes with 95% CIs were determined. Joinpoint regression was used to assess the trends in the overall, demographic (sex, race and ethnicity, age), and regional groups.

RESULTS

Between 1999 and 2019, 39 200 HCM-related deaths occurred. In the overall population, age-adjusted mortality rate decreased from 11.2 in 1999 to 5.4 in 2019. Higher mortality rates were observed for males, Black patients, and patients ≥75 years of age. Large metropolitan counties experienced pronounced declines in age-adjusted mortality rate over the study period. In addition, California had the highest overall age-adjusted mortality rate.

CONCLUSIONS

Over the past 2 decades, HCM-related mortality has decreased overall in the United States. However, demographic and geographic disparities in HCM-related mortality have persisted over time and require further investigation.

Nuclear Imaging in Pediatric Cardiology: Principles and Applications

Nuclear imaging plays a unique role within diagnostic imaging since it focuses on cellular and molecular processes. Using different radiotracers and detection techniques such as the single photon emission scintigraphy or the positron emission tomography, specific parameters can be assessed: myocardial perfusion and viability, pulmonary perfusion, ventricular function, flow and shunt quantification, and detection of inflammatory processes. In pediatric and congenital cardiology, nuclear imaging can add complementary information compared to other imaging modalities such as echocardiography or magnetic resonance imaging. In this state-of-the-art paper, we appraise the different techniques in pediatric nuclear imaging, evaluate their advantages and disadvantages, and discuss the current clinical applications.

Acute coronary syndrome with non-obstructive coronary arteries (ACS-NOCA) in patients with hypertrophic cardiomyopathy

OBJECTIVES

Our study aimed to determine the prevalence and prognosis of acute coronary syndrome with non-obstructive coronary artery (ACS-NOCA) in patients with hypertrophic cardiomyopathy (HCM).

METHODS AND RESULTS

We enrolled a total of 200 consecutive patients with HCM over a 139-month period from 2002 to 2013. The study found that 28 patients (14% of overall patients, 51% of patients with ACS) had ACS-NOCA, and 18 patients (9% of overall patients, 86% of patients with acute MI) had MINOCA as initial clinical presentations. The highest prevalence of non-obstructive coronary artery disease (NOCA) in patients with HCM was found in acute ST-elevation myocardial infarction (STEMI) (100%), followed by non-STEMI (82%), and unstable angina (29%). Patients with ACS-NOCA had more frequent ventricular tachycardia and lower resting left ventricular (LV) outflow tract gradients than those with no ACS-NOCA (p < 0.05 for all). The ACS-NOCA group had a lower probability of HCM-related death compared with the no ACS-NOCA group and the significant coronary artery disease (CAD) group (p-log-rank = 0.0018).

CONCLUSIONS

MINOCA or ACS-NOCA is not an uncommon initial presentation (prevalence rate 9-14%) in patients with HCM. NOCA was highly prevalent (51-86%) in patients with HCM presenting with ACS and had a favorable prognosis. Our findings highlight as a reminder that in an era of rapid reperfusion therapy, ACS in patients with HCM is not only a result of obstructive epicardial CAD, but also stems from the complex cellular mechanisms of myocardial necrosis.

Shared Molecular Mechanisms of Hypertrophic Cardiomyopathy and Its Clinical Presentations: Automated Molecular Mechanisms Extraction Approach

Hypertrophic cardiomyopathy (HCM) is the most common inherited cardiovascular disease with a prevalence of 1 in 500 people and varying clinical presentations. Although there is much research on HCM, underlying molecular mechanisms are poorly understood, and research on the molecular mechanisms of its specific clinical presentations is scarce. Our aim was to explore the molecular mechanisms shared by HCM and its clinical presentations through the automated extraction of molecular mechanisms. Molecular mechanisms were congregated by a query of the INDRA database, which aggregates knowledge from pathway databases and combines it with molecular mechanisms extracted from abstracts and open-access full articles by multiple machine-reading systems. The molecular mechanisms were extracted from 230,072 articles on HCM and 19 HCM clinical presentations, and their intersections were found. Shared molecular mechanisms of HCM and its clinical presentations were represented as networks; the most important elements in the intersections’ networks were found, centrality scores for each element of each network calculated, networks with reduced level of noise generated, and cooperatively working elements detected in each intersection network. The identified shared molecular mechanisms represent possible mechanisms underlying different HCM clinical presentations. Applied methodology produced results consistent with the information in the scientific literature.