Cardiomyopathies: classification, pathomorphology
Cardiomyopathies are cardiac muscle diseases, primary or secondary to other conditions (damage due to coronary atherosclerosis, hypertension or valvular heart disease is not included). Diseases under the umbrella of cardiomyopathies include:
- Myocarditis
- Immunological diseases such as sarcoidosis
- Systemic metabolic disorders such as hemochromatosis
- Muscular dystrophies
- And genetic disorders
Common pathomorphological classification is as follows:
- Dilated cardiomyopathy
- Hypertrophic cardiomyopathy
- Restrictive cardiomyopathy
Dilated cardiomyopathy
- Progressive cardiac dilation and contractile dysfunction with concurrent hypertrophy
- Morphologically, the heart is obviously enlarged, with flabby distention of all chambers.
- Ventricular thickness may be less than, equal to or greater than normal, depending on the extent of hypertrophy compared to distension
- Possible causes include
- Genetic
- Infections
- Toxic exposure
- Iron overload
- In these cases, hemosiderin is visible with Prussian blue staining
- Histologically, most myocytes exhibit hypertrophy with enlarged nuclei, as well as being stretched and irregular
- Symptom are really that of progressive CHF, with dyspnea, fatigue and poor exercise tolerance. We fundamentally see loss of myocardial contraction (reduced EF).
Hypertrophic Cardiomyopathy
- Myocardial hypertrophy with defective diastolic filling (and in ⅓ of cases, outflow obstruction)
- Effectively, the myocardium thickens, heart is thick-walled and heavy with hypercontractility (think the opposite to DCM). Failure of the myocardium to effectively relax means deficient diastolic filling.
- Most common cause is genetic, a disorder of sarcomeric proteins (most commonly beta myosin).
- Morphologically, we have massive myocardial hypertrophy without dilation. On longitudinal section the very narrow left ventricular cavity is visible (see below).
- Histologically, look at hypertrophy and haphazard myocyte organisation
- Symptoms are in line with expected, decreased preload means decreased CO, along with hypertrophy increased Ischemic risk (increased myocytes = increased demand), which can cause MI.
Remember: HCM is usually autosomal dominant and a leading cause of sudden cardiac death in young athletes (ventricular arrhythmia). Typical gross picture: asymmetric hypertrophy of the interventricular septum, a small banana-shaped left ventricular cavity and, in obstructive cases, a fibrous plaque on the septum where the anterior mitral leaflet touches it in systole.
Restrictive cardiomyopathy
- A primary decrease in ventricular compliance resulting in impaired ventricular filling during diastole
- Ventricles are of normal size, but there is no compliance so ventricles cannot fill. Microscopic examination shows interstitial fibrosis
- Etiology is generally idiopathic or as a result of a systemic disease (e.g. radiation fibrosis, amyloidosis, sarcoidosis or genetic metabolic deficiencies)
- Specific forms mentioned
- Amyloidosis - occurs with systemic amyloidosis, particularly in senile cases