<B>hypertrophy of the heart </B>

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hypertrophy of the heart

Etiology:

• Hypertension of any cause, any type of aortic stenosis or regurgitation, mitral regurgitation, and congenital heart diseases.
• Familial dilated and hypertrophic CM.
• Idiopathic DCM, HCM, and restrictive CM.
• Some secondary CM's due to infectious, vascular, metabolic, toxic, immune,and neoplastic causes.
• Alcoholic CM most common secondary form but anatomically same as idiopathic DCM.

Pathogenesis:

• Pressure and/or volume overload stimulate stretched myocytes to enlarge. Mechanism for this mechanogrowth coupling unknown.
• Gene expression changes with reappearence of fetal isoforms of contractile proteins requiring less energy and having a slower more sustained contraction than adult forms.
• Proto-oncogenes are expressed encoding growth factors, which also result in increased interstitial fibrous tissue.

Epidemiology:

• Known causes of hypertrophy, i.e., HHD, AS, and MR each have unique epidemiologies.
• Cardiomyopathies with big hearts, and non-specific histopathology, and by definition of unknown cause, make up a minority among cases of big hearts.

General Gross Description:

• Varies with cause: hypertension - a concentric predominantly LV hypertrophy > 2X normal wt.
• Aortic stenosis = hypertension > 3X normal wt.
• Mitral regurgitation (MR)- hypertrophied and dilated heart involving all chambers.
• Hypertrophic CM - similar to hypertension, but not uniformly concentric. Asymmetric septal hypertrophy (ASH) a variant.
• Restrictive CM - moderate hypertrophy.

General Microscopic Description:

• Muscle fibers uniformly thickened in proportion to increased weight.
• Nuclei larger, some with pleomorphic shapes.
• Hypertrophic cardiomyopathy (HCM): loss of normal structure of formed bundles of parallel fibers cut transversely or lengthwise. Total disorder of fiber grouping with interstial fibrosis.
• Restrictive CM - focal or diffuse interstitial fibrosis.

Clinical Correlations:

• Hypertrophy alone without CAD causes coronary insufficiency, i.e. angina pectoris, SCD, etc.
• Arrhythmias and CHF.
• Prognosis of all forms of idiopathic, familial, and secondary CM's poor with death < 2 years after symptoms begin (IHD, CHF, SCD).
• Hypertension curable medically .
• Valvular lesions and some congenital lesions amenable to surgical management with increased life expectancy.

References:
1. Robbins Pathological Basis of Disease, 5th Edition pp. 45-47, 520-523, 540-547, and 558-562. 2. Harrison's Principles of Internal Medicine, 13th Edition, pp. 941-942 and 1088-1094.