Differences in global and regional left ventricular myocardial mechanics in various morphologic subtypes of patients with obstructive hypertrophic cardiomyopathy referred for ventricular septal myotomy/myectomy

Tailored Planning of Surgical Myectomy in Obstructive Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is a genetic myocardial disease characterized by abnormal thickening of the myocardium caused by myocardial disarray and interstitial fibrosis. HCM is associated with sudden cardiac-related events, such as ventricular fibrillation, tachycardia, and syncope. Moreover, left ventricular or midcavity obstruction due to the thickened myocardium can result in severe heart failure and mortality in patients with HCM. Surgical myectomy is a standard treatment option for patients with symptomatic obstructive HCM; however, it is a complex procedure that requires careful planning and execution to avoid complications, such as residual flow obstruction, persistent obliteration of the left ventricular cavity in systole, or iatrogenic ventricular septal defects. Therefore, a thorough understanding of the mechanics of HCM and precise evaluation of the location and extent of the hypertrophic myocardium to be removed are crucial for preoperative planning. Multiphase cardiac CT postprocessing is important for preoperative evaluation and planning of surgical myectomy in patients with HCM. In this review, the authors highlight use of multiphase cardiac CT with step-by-step postprocessing methods to simulate successful surgical myectomy. The transaortic surgeon's view on end-diastolic phase images accurately represents the surgical field. Moreover, myocardial segmentation can be used to generate volume-rendered images and three-dimensional printing. CT evaluation can also assist in identifying concurrent abnormalities, such as mitral valve or papillary muscle abnormalities. In addition to CT, other imaging modalities for preoperative evaluation of HCM and postmyectomy evaluation methods are presented. ©RSNA, 2023 Test Your Knowledge questions in the supplemental material and the slide presentation from the RSNA Annual Meeting are available for this article.

Etiology-Discriminative Multimodal Imaging of Left Ventricular Hypertrophy and Synchrotron-Based Assessment of Microstructural Tissue Remodeling

Background: Distinguishing the etiology of left ventricular hypertrophy (LVH) is clinically relevant due to patient outcomes and management. Easily obtained, echocardiography-based myocardial deformation patterns may improve standard non-invasive phenotyping, however, the relationship between deformation phenotypes and etiology-related, microstructural cardiac remodeling has not been reported. Synchrotron radiation-based X-ray phase-contrast imaging (X-PCI) can provide high resolution, three-dimensional (3D) information on myocardial microstructure. The aim of this pilot study is to apply a multiscale, multimodality protocol in LVH patients undergoing septal myectomy to visualize in vivo and ex vivo myocardial tissue and relate non-invasive LVH imaging phenotypes to the underlying synchrotron-assessed microstructure.

Methods and findings: Three patients (P1-3) undergoing septal myectomy were comprehensively studied. Medical history was collected, and patients were imaged with echocardiography/cardiac magnetic resonance prior to the procedure. Myocardial tissue samples obtained during the myectomy were imaged with X-PCI generating high spatial resolution images (0.65 μm) to assess myocyte organization, 3D connective tissue distribution and vasculature remodeling. Etiology-centered non-invasive imaging phenotypes, based on findings of hypertrophy and late gadolinium enhancement (LGE) distribution, and enriched by speckle-tracking and tissue Doppler echocardiography deformation patterns, identified a clear phenotype of hypertensive heart disease (HTN) in P1, and hypertrophic cardiomyopathy (HCM) in P2/P3. X-PCI showed extensive interstitial fibrosis with normal 3D myocyte and collagen organization in P1. In comparison, in P2/P3, X-PCI showed 3D myocyte and collagen disarray, as well as arterial wall hypertrophy with increased perivascular collagen, compatible with sarcomere-mutation HCM in both patients. The results of this pilot study suggest the association of non-invasive deformation phenotypes with etiology-related myocyte and connective tissue matrix disorganization. A larger patient cohort could enable statistical analysis of group characteristics and the assessment of deformation pattern reproducibility.

Conclusion: High-resolution, 3D X-PCI provides novel ways to visualize myocardial remodeling in LVH, and illustrates the correspondence of macrostructural and functional non-invasive phenotypes with invasive microstructural phenotypes, suggesting the potential clinical utility of non-invasive myocardial deformation patterns in phenotyping LVH in everyday clinical practice.

Osteomodulin is a Potential Genetic Target for Hypertrophic Cardiomyopathy

Hypertrophic cardiomyopathy (HCM) is one of the most common genetic heart diseases. Its features include abnormal cardiomyocyte hypertrophy, microvascular dysfunction, and increased accumulation of intercellular matrix. We aim to unravel genes associated with the pathogenesis of HCM and provide a potential target for diagnosis and treatment. Key modules were identified by weighted gene co-expression network analysis (WGCNA). A miRNA-mRNA network was constructed with the predicted miRNA and the most likely hub gene was screened out for gene set enrichment analysis (GSEA). The diagnostic capacity of hub gene was verified by receiver operating characteristic (ROC) curves. Single-cell sequencing (sc-RNA seq) data of normal adult hearts were used to further predict the specific cell types expressing the hub gene. WGCNA assigned genes into different modules and found that the genes contained in the red module had the strongest positive correlation with HCM disease. 2.5% of the genes were common between DEG and hub genes. With the miRNA-mRNA network, osteomodulin (OMD) was identified as the most potential hub gene. GSEA showed that OMD was mainly involved in the synthesis of extracellular matrix and had a certain inhibitory effect on the immune system. The expression of OMD in HCM was validated and ROC curve analysis showed that OMD could distinguish HCM from controls with the area under the curve (AUC) > 0.7. The sc-RNA seq revealed that OMD was mainly expressed in the later stages of cardiac fibroblasts, suggesting that OMD may have an effect on fibroblasts, participating in the pathogenesis of HCM. OMD may serve as a biomarker and therapeutic target for HCM in the future.

Late Gadolinium Enhancement in Patients With Hypertrophic Cardiomyopathy and Preserved Systolic Function

BACKGROUND

A high proportion of patients with hypertrophic cardiomyopathy (HCM) have evidence of late gadolinium enhancement (LGE) on cardiac magnetic resonance (CMR).

OBJECTIVES

This study sought to assess the incremental prognostic utility of LGE in patients with HCM.

METHODS

We studied 1,423 consecutive low-/intermediate-risk patients with HCM (age ≥18 years) with preserved left ventricular (LV) ejection fraction (mean age 66 ± 14 years, 60% men) who underwent transthoracic echocardiography (TTE) (including dimensions and LV outflow tract gradients) and CMR (including LGE as a % of LV mass) at our center between January 2008 and December 2015. The primary composite endpoint was sudden cardiac death (SCD) and appropriate implantable cardioverter-defibrillator discharge. The percent 5-year SCD risk score was calculated.

RESULTS

The mean 5-year SCD risk score was 2.3 ± 2.0. Mean maximal LV outflow tract gradient (TTE) was 70 ± 55 mm Hg (median 74 mm Hg [interquartile range (IQR): 10 to 67 mm Hg]); indexed LV mass and LGE (both on CMR) were 91 ± 10 g/m² and 8.4 ± 12% (IQR: 0% to 19%); 50% had LGE on CMR. Of these, 458 were nonobstructive and 965 were obstructive (of which 686 were underwent myectomy). At 4.7 ± 2.0 years of follow-up, 60 (4%) met the composite endpoint. On quadratic spline analysis, LGE ≥15% was associated with increased risk of composite events. In the obstructive subgroup, on competing risk regression analysis, ≥15% LGE (subhazard ratio: 3.04 [95% confidence interval: 1.48 to 6.10]) was associated with a higher rate and myectomy (subhazard ratio: 0.44 [95% confidence interval: 0.20 to 0.76]) was associated with a lower rate of composite endpoints (both p < 0.01). Similarly, sequential addition of LGE ≥15% and myectomy to % 5-year SCD risk score improved the log likelihood ratios from -227.85 to -219.14 (chi-square 17) and to -215.14 (chi-square 8; both p < 0.01). Association of %LGE with composite events was similar even in myectomy and nonobstructive subgroups.

CONCLUSIONS

In low-/intermediate-risk adult patients with HCM (obstructive, myectomy, and nonobstructive subgroups) with preserved systolic function, %LGE was significantly associated with a higher rate of composite endpoint, providing incremental prognostic utility.

Left Ventricular Wall Stress Is Sensitive Marker of Hypertrophic Cardiomyopathy With Preserved Ejection Fraction

Hypertrophic cardiomyopathy (HCM) patients present altered myocardial mechanics due to the hypertrophied ventricular wall and are typically diagnosed by the increase in myocardium wall thickness. This study aimed to quantify regional left ventricular (LV) shape, wall stress and deformation from cardiac magnetic resonance (MR) images in HCM patients and controls, in order to establish superior measures to differentiate HCM from controls. A total of 19 HCM patients and 19 controls underwent cardiac MR scans. The acquired MR images were used to reconstruct 3D LV geometrical models and compute the regional parameters (i.e., wall thickness, curvedness, wall stress, area strain and ejection fraction) based on the standard 16 segment model using our in-house software. HCM patients were further classified into four quartiles based on wall thickness at end diastole (ED) to assess the impact of wall thickness on these regional parameters. There was a significant difference between the HCM patients and controls for all regional parameters (P < 0.001). Wall thickness was greater in HCM patients at the end-diastolic and end-systolic phases, and thickness was most pronounced in segments at the septal regions. A multivariate stepwise selection algorithm identified wall stress index at ED (σ_i,ED) as the single best independent predictor of HCM (AUC = 0.947). At the cutoff value σ_i,ED < 1.64, both sensitivity and specificity were 94.7%. This suggests that the end-diastolic wall stress index incorporating regional wall curvature—an index based on mechanical principle—is a sensitive biomarker for HCM diagnosis with potential utility in diagnostic and therapeutic assessment.

Incremental Prognostic Utility of Left Ventricular Global Longitudinal Strain in Hypertrophic Obstructive Cardiomyopathy Patients and Preserved Left Ventricular Ejection Fraction

BACKGROUND

In obstructive hypertrophic cardiomyopathy patients with preserved left ventricular (LV) ejection fraction, we sought to determine whether LV global longitudinal strain (LV-GLS) provided incremental prognostic utility.

METHODS AND RESULTS

We studied 1019 patients with documented hypertrophic cardiomyopathy (mean age, 50±12 years; 63% men) evaluated at our center between 2001 and 2011. We excluded age <18 years, maximal LV outflow tract gradient <30 mm Hg, bundle branch block or atrial fibrillation, past pacemaker/cardiac surgery, including myectomy/alcohol ablation, and obstructive coronary artery disease. Average resting LV-GLS was measured offline on 2-, 3-, 4-chamber views using Velocity Vector Imaging (Siemens, Malvern, PA). Outcome was a composite of cardiac death and appropriate internal defibrillator (implantable cardioverter defibrillator) discharge. Maximal LV thickness, LV ejection fraction, indexed left atrial dimension, rest and maximal LV outflow tract gradient, and LV-GLS were 2.0±0.2 cm, 62±4%, 2.2±4 cm/m2, 52±42 mm Hg, 103±36 mm Hg, and -13.6±4%. During 9.4±3 years of follow-up, 668 (66%), 166 (16%), and 122 (20%), respectively, had myectomy, atrial fibrillation, and implantable cardioverter defibrillator implantation, whereas 69 (7%) had composite events (62 cardiac deaths). Multivariable competing risk regression analysis revealed that higher age (subhazard ratio, 1.04 [1.02-1.07]), AF during follow-up (subhazard ratio, 1.39 [1.11-1.69]), and worsening LV-GLS (subhazard ratio, 1.11 [1.05-1.22]) were associated with worse outcomes, whereas myectomy (subhazard ratio, 0.44 [0.25-0.72]) was associated with improved outcomes (all P<0.01). Sixty-one percent of events occurred in patients with LV-GLS worse than median (-13.7%).

CONCLUSIONS

In obstructive hypertrophic cardiomyopathy patients with preserved LV ejection fraction, abnormal LV-GLS was independently associated with higher events, whereas myectomy was associated with improved outcomes.

Systolic and diastolic myocardial mechanics in hypertrophic cardiomyopathy and their link to the extent of hypertrophy, replacement fibrosis and interstitial fibrosis

Aim of the present study was to investigate the relations between myocardial mechanics and the extent of hypertrophy and fibrosis in hypertrophic cardiomyopathy (HCM). Forty-five consecutive patients with HCM and 15 subjects without structural heart disease were included. Cardiac magnetic resonance with late gadolinium enhancement (LGE) imaging was performed to evaluate biventricular function, LV mass index and presence/extent of LGE, expression of replacement fibrosis. Myocardial T1 relaxation, a surrogate of interstitial fibrosis, was measured from Look-Locker sequence. Feature-tracking analysis was applied to LV basal, mid and apical short-axis images to assess systolic and diastolic global LV circumferential strain (CS) and strain rate (CSr). Peak systolic CS and CSr were significantly higher among HCM patients as compared to control subjects (p = 0.015 and p = 0.007, respectively). The ratio of peak CSr during early filling to peak systolic CSr was significantly lower among HCM patients (p = 0.002). At multivariate linear regression analysis, LV mass index (p < 0.001) and %LV LGE (p = 0.011) were significantly and independently related to peak systolic CS; LV mass index (p < 0.001) and %LV LGE (p = 0.023) were significantly and independently related to peak systolic CSr; %LV LGE (p = 0.021) and T1 ratio (p = 0.006) were significantly and independently related to the ratio of peak CSr during early filling to peak systolic CSr. LV systolic mechanics are enhanced and LV diastolic mechanics are impaired in HCM. Extent of hypertrophy and replacement fibrosis influence the LV systolic mechanics while extent of replacement fibrosis and interstitial fibrosis influence the LV diastolic mechanics.