Roselle Abraham

Matrix Rigidity Controls Endothelial Differentiation and Morphogenesis of Cardiac Precursors

Culturing cardiac precursors on a surface with the rigidity of heart tissue increases the yield of endothelial cells. The Heart of the Matrix Cardiosphere-derived cells (CDCs) are adult stem cells with the potential to differentiate into endothelial cells and cardiomyocytes, which are the major cell types of the heart. Their potential to induce cardiac regeneration after myocardial infarct is currently being clinically tested. Kshitiz et al. showed that CDCs cultured on a substrate with a rigidity matching that of normal myocardium yielded higher proportions of cells with the adhesion molecule CD31 (a marker of differentiated endothelial cells) than did those cultured on less or more rigid substrata. CDCs cultured on substratum equivalent in rigidity to the myocardium developed into organized cellular networks reminiscent of blood vessels and appeared to integrate more efficiently into the vasculature of ischemic rat myocardium. The process of sensing substratum rigidity occurred throughout the in vitro culture period, and the signaling pathway involved required the guanosine triphosphatase (GTPase)–activating protein p190RhoGAP acting through various downstream effectors, including the GTPase RhoA. These results could potentially increase the efficacy of regenerative therapies that use CDCs to repair hearts after myocardial infarction. Tissue development and regeneration involve tightly coordinated and integrated processes: selective proliferation of resident stem and precursor cells, differentiation into target somatic cell type, and spatial morphological organization. The role of the mechanical environment in the coordination of these processes is poorly understood. We show that multipotent cells derived from native cardiac tissue continually monitored cell substratum rigidity and showed enhanced proliferation, endothelial differentiation, and morphogenesis when the cell substratum rigidity closely matched that of myocardium. Mechanoregulation of these diverse processes required p190RhoGAP, a guanosine triphosphatase–activating protein for RhoA, acting through RhoA-dependent and -independent mechanisms. Natural or induced decreases in the abundance of p190RhoGAP triggered a series of developmental events by coupling cell-cell and cell-substratum interactions to genetic circuits controlling differentiation.

In hypertrophic cardiomyopathy reduction of relative resting myocardial blood flow is related to late enhancement, T2-signal and LV wall thickness

Objectives To quantify resting myocardial blood flow (MBF) in the left ventricular (LV) wall of HCM patients and to determine the relationship to important parameters of disease: LV wall thickness, late gadolinium enhancement (LGE), T2-signal abnormalities (dark and bright signal), LV outflow tract obstruction and age. Materials and Methods Seventy patients with proven HCM underwent cardiac MRI. Absolute and relative resting MBF were calculated from cardiac perfusion MRI by using the Fermi function model. The relationship between relative MBF and LV wall thickness, T2-signal abnormalities (T2 dark and T2 bright signal), LGE, age and LV outflow gradient as determined by echocardiography was determined using simple and multiple linear regression analysis. Categories of reduced and elevated perfusion in relation to non- or mildly affected reference segments were defined, and T2-signal characteristics and extent as well as pattern of LGE were examined. Statistical testing included linear and logistic regression analysis, unpaired t-test, odds ratios, and Fisher’s exact test. Results 804 segments in 70 patients were included in the analysis. In a simple linear regression model LV wall thickness (p<0.001), extent of LGE (p<0.001), presence of edema, defined as focal T2 bright signal (p<0.001), T2 dark signal (p<0.001) and age (p = 0.032) correlated inversely with relative resting MBF. The LV outflow gradient did not show any effect on resting perfusion (p = 0.901). Multiple linear regression analysis revealed that LGE (p<0.001), edema (p = 0.026) and T2 dark signal (p = 0.019) were independent predictors of relative resting MBF. Segments with reduced resting perfusion demonstrated different LGE patterns compared to segments with elevated resting perfusion. Conclusion In HCM resting MBF is significantly reduced depending on LV wall thickness, extent of LGE, focal T2 signal abnormalities and age. Furthermore, different patterns of perfusion in HCM patients have been defined, which may represent different stages of disease.

Cardiac MRI evaluation of hypertrophic cardiomyopathy: Left ventricular outflow tract/aortic valve diameter ratio predicts severity of LVOT obstruction

To evaluate if left ventricular outflow tract/aortic valve (LVOT/AO) diameter ratio measured by cardiac magnetic resonance (CMR) imaging is an accurate marker for LVOT obstruction in patients with hypertrophic cardiomyopathy (HCM) compared to Doppler echocardiography.

Age-related changes in familial hypertrophic cardiomyopathy phenotype in transgenic mice and humans

Summaryβ-myosin heavy chain mutations are the most frequently identified basis for hypertrophic cardiomyopathy (HCM). A transgenic mouse model (αMHC403) has been extensively used to study various mechanistic aspects of HCM. There is general skepticism whether mouse and human disease features are similar. Herein we compare morphologic and functional characteristics, and disease evolution, in a transgenic mouse and a single family with a MHC mutation. Ten male αMHC403 transgenic mice (at t-5 weeks, −12 weeks, and −24 weeks) and 10 HCM patients from the same family with a β-myosin heavy chain mutation were enrolled. Morphometric, conventional echocardiographic, tissue Doppler and strain analytic characteristics of transgenic mice and HCM patients were assessed. Ten male transgenic mice (αMHC403) were examined at ages −5 weeks, −12 weeks, and −24 weeks. In the transgenic mice, aging was associated with a significant increase in septal (0.59±0.06 vs. 0.64±0.05 vs. 0.69±0.11 mm, P<0.01) and anterior wall thickness (0.58±0.1 vs. 0.62±0.07 vs. 0.80±0.16 mm, P<0.001), which was coincident with a significant decrease in circumferential strain (−22%±4% vs. −20%±3% vs. −19%±3%, P=0.03), global longitudinal strain (−19%±3% vs. −17%±2% vs. −16%±3%, P=0.001) and E/A ratio (1.9±0.3 vs. 1.7±0.3 vs. 1.4±0.3, P=0.01). The HCM patients were classified into 1st generation (n=6; mean age 53±6 years), and 2nd generation (n=4; mean age 32±8 years). Septal thickness (2.2±0.9 vs. 1.4±0.1 cm, P<0.05), left atrial (LA) volume (62±16 vs. 41±5 mL, P=0.03), E/A ratio (0.77±0.21 vs. 1.1±0.1, P=0.01), E/e’ ratio (25±10 vs. 12±2, P=0.03), global left ventricular (LV) strain (−14%±3% vs. −20%±3%, P=0.01) and global LV early diastolic strain rate (0.76±0.17 s−1vs. 1.3±0.2 s-1, P=0.01) were significantly worse in the older generation. In β-myosin heavy chain mutations, transgenic mice and humans have similar progression in morphologic and functional abnormalities. The αMHC403 transgenic mouse model closely recapitulates human disease.

LEFT ATRIAL STRAIN RATE AS A PREDICTOR OF LOW EXERCISE CAPACITY IN HYPERTROPHIC CARDIOMYOPATHY PATIENTS

Methods/Results: We included 151 patients, being 100(66%) men, 76(50%) with the obstructive HCM, age 55±17yrs. Left ventricular (LV) ejection fraction (EF) was 69±9%, LV mass index was 139±47g/m2, basal and mid septum thickness were 2.0±0.5cm and 1.9±0.6cm, respectively and gradient was 31±34mmHg. Regarding diastolic function, HCM patients had 247±76ms of deceleration time, E/A ratio of 1.3±0.6 and E/e’ ratio of 23±11. Pulmonary pressure by tricuspid regurgitation gradient was 33±13mmHg. On univariate analysis, LAST and LASR showed significant association with LEC, and LASR showed the highest odds ratio when compared to all other variables. After multivariate regression, LASR was also significantly associated with LEC after adjusting by age and E/e’ ratio (OR=9.6, 95%CI=1.1-91, p=0.04) (Table 1).

Safety profile and utility of treadmill exercise in patients with high-gradient hypertrophic cardiomyopathy

Background Exercise echocardiography in the evaluation of hypertrophic cardiomyopathy (HCM) provides valuable information for risk stratification, selection of optimal treatment, and prognostication. However, HCM patients with left ventricular outflow tract gradients ≥30 mm Hg are often excluded from exercise testing because of safety considerations. We examined the safety and utility of exercise testing in patients with high‐gradient HCM. Methods We evaluated clinical characteristics, hemodynamics, and imaging variables in 499 consecutive patients with HCM who performed 959 exercise tests. Patients were divided based on peak left ventricular outflow tract gradients using a 30‐mm Hg threshold into the following: obstructive (n = 152), labile‐obstructive (n = 178), and nonobstructive (n = 169) groups. Results There were no deaths during exercise testing. We noted 20 complications (2.1% of tests) including 3 serious ventricular arrhythmias (0.3% of tests). There was no difference in complication rate between groups. Patients with obstructive HCM had a higher frequency of abnormal blood pressure response (obstructive: 53% vs labile: obstructive: 41% and nonobstructive: 37%; P = .008). Obstructive patients also displayed a lower work capacity (obstructive: 8.4 ± 3.4 vs labile obstructive: 10.9 ± 4.2 and nonobstructive: 10.2 ± 4.0, metabolic equivalent; P < .001). Exercise testing provided incremental information regarding sudden cardiac death risk in 19% of patients with high‐gradient HCM, and we found a poor correlation between patient‐reported functional class and work capacity. Conclusion Our results suggest that exercise testing in HCM is safe, and serious adverse events are rare. Although numbers are limited, exercise testing in high‐gradient HCM appears to confer no significant additional safety hazard in our selected cohort and could potentially provide valuable information.

Native T1 is predictive of abnormal myocardial strain in hypertrophic cardiomyopathy

Background Hypertrophic cardiomyopathy (HCM) is an autosomal dominant inherited disease, characterized by myocardial wall thickening in the absence of other etiologies of hypertrophy. Histologically, HCM is characterized by myocyte hypertrophy and disarray with collagen deposition. Native T1 time of the myocardium is increased in the presence of myocardial fibrosis. The purpose of this study was to determine if greater T1 time was associated with abnormal myocardial wall strain.

Regional evolution of mechanical dyssynchrony in a closed-chest porcine model of myocardial infarction as assessed by cardiac magnetic resonance

Methods In six pigs, cine, late gadolinium enhancement, and tagged cardiac magnetic resonance imaging were performed at baseline (before MI) and early (10 ± 2 days) and late (34 ± 10 days) after balloon induced occlusionreperfusion myocardial injury. Infarct, peri-infarct, and remote normal regions were defined as previously described. Cardiac morphology, function, location and extent of MI, and regional mechanics (circumferential strain (eC)) were measured.