The massive fibrosis of the endocardium encroaches on and diminishes the size of the ventricular cavities and causes a restrictive and obliterative hemodynamic pattern. In any given case, features of more than one type of cardiomyopathy may be present. For example, the thick, stiff left ventricle of hypertrophic cardiomyopathy causes impaired diastolic relaxation and ventricular filling, which are also features of restrictive cardiomyopathy. Furthermore, the massive hypertrophy that characterizes hypertrophic cardiomyopathy may reduce left ventricular chamber size, which is also a feature of obliterative cardiomyopathy. Unfortunately, the causes of cardiomyopathies are poorly understood, and in many cases, the cause is unknown and the disorder is considered idiopathic.
Dilated cardiomyopathy can either be idiopathic or have a known etiology.
It can be associated with pregnancy, excessive alcohol consumption, or several disease processes or can occur as a toxic effect of drugs. Although the cause of obliterative cardiomyopathies remains unknown, it is known that the vast majority of cases of hypertrophic cardiomyopathy result from specific defects in the genes regulating the formation of cardiac muscle. On rare occasions, however, cardiac involvement may precede other systemic manifestations.