Contribution of cardiac muscle cell disorganization to the clinical features of hypertrophic cardiomyopathy

Cardiac lipid metabolism, mitochondrial function, and heart failure

A fine balance between uptake, storage, and the use of high energy fuels, like lipids, is crucial in the homeostasis of different metabolic tissues. Nowhere is this balance more important and more precarious than in the heart. This highly energy-demanding muscle normally oxidizes almost all the available substrates to generate energy, with fatty acids being the preferred source under physiological conditions. In patients with cardiomyopathies and heart failure, changes in the main energetic substrate are observed; these hearts often prefer to utilize glucose rather than oxidizing fatty acids. An imbalance between uptake and oxidation of fatty acid can result in cellular lipid accumulation and cytotoxicity. In this review, we will focus on the sources and uptake pathways used to direct fatty acids to cardiomyocytes. We will then discuss the intracellular machinery used to either store or oxidize these lipids and explain how disruptions in homeostasis can lead to mitochondrial dysfunction and heart failure. Moreover, we will also discuss the role of cholesterol accumulation in cardiomyocytes. Our discussion will attempt to weave in vitro experiments and in vivo data from mice and humans and use several human diseases to illustrate metabolism gone haywire as a cause of or accomplice to cardiac dysfunction.

Cardiac transplantation in patients with hypertrophic cardiomyopathy

Cardiac transplantation is a treatment option for patients with hypertrophic cardiomyopathy (HC) who developed refractory heart failure and/or intractable arrhythmia. However, the pretransplant characteristics and post-transplant prognosis for patients with nondilated idiopathic HC has not yet fully elucidated. Therefore, we retrospectively reviewed 813 consecutive transplant recipients undergoing cardiac transplantation at Columbia University Medical Center from 1999 to 2010 and compared the clinical course of 41 patients with idiopathic HC with that of 373 patients with ischemic heart disease and 398 patients with other heart disease. The patients with HC were younger than those with ischemic heart disease (47.8 ± 14.0 vs 57.1 ± 9.4 years; p <0.0001). The proportion of patients undergoing ventricular assist devise surgery for bridge-to-transplant was lower in patients with HC than in those with ischemic heart disease or other heart disease (14.6% vs 31.1% vs 35.7%, all p <0.01). The post-transplant survival of those with HC was better than that for those with ischemic heart disease (90.1% vs 85.8% and 83.9% vs 67.1% at 1 and 5 years, respectively; p = 0.0359), although it was not significantly different from those with other heart disease. Proportional hazards analysis revealed that the subjects with HC had reduced post-transplant mortality (hazard ratio 0.4760, 95% confidential interval 0.1889 to 0.9762; p = 0.042) on univariate, but not multivariate, analysis. Most patients with HC had nondilated left ventricles (left ventricular end-diastolic dimension ≤ 55 mm; n = 27), and post-transplant survival did not differ from that for those with dilated left ventricles (left ventricular end-diastolic dimension >55 mm; n = 14). In conclusion, the post-transplant survival of those with HC did not differ from those of the subjects who underwent transplant for other non-HC indications.

Morphologic features of exertional versus nonexertional sudden death in patients with hypertrophic cardiomyopathy

Pathologic features that characterize hypertrophic cardiomyopathy (HC) in exertional versus nonexertional sudden deaths have not been extensively studied. We performed gross measurements and histologic analysis on 103 autopsy cases of HC and correlated these with clinical findings. Pathologic features of the 71 sudden deaths were compared between exertional and nonexertional deaths. Age at death was significantly younger in exertional (27 +/- 13 years) versus nonexertional sudden deaths (40 +/- 16 years, p = 0.0003). Exertional deaths were more likely in women (35 of 37) versus sudden deaths at rest (21 of 34, p = 0.0002). There was no significant difference in the incidence of syncope in the exertional sudden deaths (14%) compared to the nonexertional sudden deaths (9%, p = 0.5) or in the rate of a previous diagnosis of HC (21% vs 21%, respectively). Mean heart weight was significantly decreased in exertional sudden deaths versus nonexertional sudden deaths. There was no difference in the frequency of left ventricular outflow tract plaque (54% exertional vs 46% nonexertional, p = 0.06). By multivariate analysis, including all categories of HC, only decreased heart weight (p = 0.02) and male gender (p = 0.002) were significantly associated with exertional sudden death. In conclusion, there are no pathologic features that would identify patients with HC at risk for exertional death. Because relatively decreased heart weight is strongly associated with exertional death, and because a large proportion of exertional deaths with HC are not associated with significant asymmetry, cardiologists should be careful in excluding the diagnosis of HC in athletes with even mild degrees of cardiomegaly, especially young men.

Myocardial fibrosis in patients with symptomatic obstructive hypertrophic cardiomyopathy: correlation with echocardiographic measurements, sarcomeric genotypes, and pro-left ventricular hypertrophy polymorphisms involving the renin-angiotensin-aldosterone system

INTRODUCTION

Hypertrophic cardiomyopathy (HCM) is a heterogeneous disorder of the cardiac sarcomere, resulting in myocyte hypertrophy and disarray, interstitial fibrosis, and cardiac dysfunction. Our aim was to determine whether the amount of fibrosis in HCM correlates with echocardiographic measures of diastolic dysfunction, presence of HCM-susceptibility mutations, or polymorphisms in the renin-angiotensin-aldosterone system (RAAS).

METHODS

Surgical specimens from patients with obstructive HCM undergoing septal myectomy at the Mayo Clinic (2001-2004) were examined and compared with autopsy-derived tissues from age- and sex-matched normal controls. Digital image analysis was used to quantitate the fibrosis in representative microscopic sections. Genotyping was performed for myofilament-HCM using polymerase chain reaction, high-performance liquid chromatography, and direct DNA sequencing. RAAS polymorphism status was similarly established.

RESULTS

The study included 59 HCM cases and 44 controls. Patients with HCM exhibited more fibrosis (mean 17%, range 3-45%) than controls (mean 8%, range 3-17%) (P<.0001). A significant relationship existed between amount of fibrosis and maximum wall thickness (P=.02), left ventricular ejection fraction (P=.02), and peak early/late diastolic mitral annulus velocity (E/A ratio) (P=.002). Although there was no association between amount of fibrosis and myofilament-HCM genotype status or polymorphisms in the RAAS cascade, there was a trend toward more fibrosis in patients with > or =1 C-encoding allele in CYP11B2-encoded aldosterone synthase.

CONCLUSIONS

Patients with HCM undergoing septal myectomy had significantly more myocardial interstitial fibrosis than controls. The amount of fibrosis in HCM patients correlated with degree of septal hypertrophy and left ventricular systolic and diastolic function. Notably, neither mutations in cardiac myofilament proteins or polymorphisms in RAAS exhibited strong associations with severity of myocardial fibrosis.

Side-to-side linking of myocardial cells in hypertrophic cardiomyopathy: whole heart microscopic observation with tangential sections

By cross-section or longitudinal section, it is difficult to investigate longitudinal features of myocardial cells in the whole heart. Here, introducing the use of tangential sections to obtain longitudinal aspect of myocardial cells in any part of myocardium, the authors evaluated myocardium in the left ventricle in 10 normal hearts and four hearts with hypertrophic cardiomyopathy (HCM). Tangential sections were obtained by peeling the superficial layer of myocardium. After peeling the whole surface, secondary deep layer was peeled. These procedures were repeated more than five times through the wall. Intercalated discs (ICD) were observed immunohistochemically with anti-N-cadherin and antidesmoplakin. In normal hearts, myocardial cells were cut longitudinally and ran parallel in tangential sections. They linked end-to-end with simple and regular ICD with average lengths of 120-130 microm and average sarcomere numbers of 56-65. In HCM hearts, many myocardial cells were cut almost longitudinally running approximately parallel in tangential sections. Myocardial cells frequently showed side-to-side linking characterized by skewed ICD, indistinct ICD counterparts, and longitudinally arranged ICD. Two young HCM hearts had circle-shaped ICD and vacuole-like structures highlighted by immunostaining for N-cadherin, which were actually extracellular structures comparable with irregular side-to-side linking. It is considered that side-to-side linking of myocardial cells is a characteristic microscopic feature in HCM rather than myocardial disarray.

Cardiac muscle cell disorganization in apical hypertrophic cardiomyopathy: a cardiac biopsy study

Apical hypertrophic cardiomyopathy has been divided into two entities: apical asymmetric septal hypertrophy (apical ASH) and apical symmetric hypertrophy (AH). The latter differs clinically from hypertrophic cardiomyopathy (HCM) with ASH, and it is unclear whether AH represents a distinct subtype of HCM. In the present study, the presence or absence and the extent of cardiac muscle cell disorganization, a histologic characteristic of HCM, were compared in patients with AH (n = 10) and ASH (n = 29) in whom cardiac biopsy specimens were obtained from the left ventricular apex and interventricular septum. Disorganization was graded as (1+) in only 1 patient in the AH group and (-) in the remaining 9. In contrast, in the ASH group disorganization was graded as (1+) in 15 patients, (2+) in 7, (3+) in 3, and (-) in only 4 (P < 0.0001). Thus, it was observed that in AH disorganization is virtually absent or at most limited to a very narrow area. It is concluded from a histological stand point as well that the type of apical hypertrophic cardiomyopathy showing apical symmetric hypertrophy differs from usual HCM.

Surgical pathology of subaortic septal myectomy associated with hypertrophic cardiomyopathy. A study of 204 cases (1996-2000)

BACKGROUND

No large surgical series have qualitatively examined all histopathologic features of hypertrophic cardiomyopathy (HCM).

METHODS

Medical records and microscopic slides were reviewed from 204 patients undergoing septal myectomy for HCM at Mayo Clinic Rochester.

RESULTS

The 108 females and 96 males (1-86 years old; mean, 48) included 133 patients <60 years old (Group 1) and 71 patients > or =60 years (Group 2). Clinical features more prevalent in Group 2 than in Group 1 included female gender (68% vs. 45%; P=.003), aortic valve disease (31% vs. 12%; P=.01) and severe coronary atherosclerosis (43% vs. 9%; P=.001). Overall, microscopic abnormalities included myocyte hypertrophy (100%), endocardial (96%) and myocardial (93%) fibrosis, myocyte disarray (79%) and vacuolization (60%), endocardial inflammation (48%), arterial thickening (46%), dilated venules (28%), arterial dysplasia (16%), left bundle branch tissue (12%), infarction (2%), endocardial (1%) and myocardial (<1%) calcium, and amyloid (1%; senile type in all three). Lesions more prevalent in Group 1 than Group 2 were vacuolization (68% vs. 45%; P=.002), disarray (87% vs. 65%; P=.0003) and dilated venules (33% vs. 18%; P=.02). In contrast, lesions more frequent in Group 2 than in Group 1 included left bundle branch (20% vs. 8%; P=.02) and amyloid and endocardial calcium (4% vs. 0%; P=.04, each).

CONCLUSIONS

Among patients undergoing septal myectomy for HCM, 53% were women and 35% were >/=60 years old. The most common microscopic features were hypertrophy, disarray, fibrosis, inflammation and vascular alterations. Disarray cannot be used as a morphologic hallmark for HCM in small surgical myectomy specimens because it was absent in 21% of the patients. Because amyloid unexpectedly affected three elderly patients, routine amyloid staining is recommended for patients >/=65 years old.