Primary Cardiomyopathies (Diagnosis of Exclusion)

PRIMARY CARDIOMYOPATHIES (DIAGNOSIS OF EXCLUSION)

Dilated cardiomyopathy (most common form) is cardiac enlargement with dilatationof all 4 chambers, resulting in progressive congestive heart failure (typical mode of presentation). The cause is genetic in 20–50% of cases, but some cases are related to alcohol, medications (Adriamycin [doxorubicin]), cocaine, viral myocarditis (Cox-sackievirus B and enteroviruses), parasitic infections (Chagas disease), iron overload or pregnancy.

In cases of all types, the underlying etiology leads to destruction of myocardial con-tractility, which affects systolic function. Echocardiogram typically shows decreased ejection fraction. Complications include mural thrombi and cardiac arrhythmias; prognosis is poor with 5-year survival of 25%. Treatment is heart transplantation. There is myocyte hypertrophy with interstitial fibrosis on microscopy, and eccentric hypertrophy seen on gross examination.

Hypertrophic cardiomyopathy (also called asymmetrical septal hypertrophy, andidiopathic hypertrophic subaortic stenosis [IHSS]) is a common cause of sudden cardiac death in young athletes. The condition is an asymmetrical hypertrophy of cardiac muscle that causes decreased compliance affecting diastolic function. Hypertrophic cardiomyopathy can be an autosomal dominant disorder (>50% of cases) or idiopathic. The muscle hypertrophy is due to the increased synthesis of actin and myosin, and on microscopic examination, the cardiac muscle fibers are hypertrophied and in disarray. Hypertrophic cardiomyopathy is most prominent in the ventricular septum, where it can obstruct the ventricular outflow tract. This can potentially lead to death during severe exercise when the cardiac outflow tract collapses, preventing blood from exiting the heart.

Restrictive cardiomyopathy (uncommon form) is caused by diseases which producerestriction of cardiac filling during diastole; etiologies include amyloidosis, sarcoid-osis, endomyocardial fibroelastosis, and Loeffler endomyocarditis. In all of these diseases, increased deposition of material leads to decreased compliance, affecting diastolic function. On gross examination, the ventricles are not enlarged and the cavities are not dilated. Microscopy will reflect the underlying cause.

Arrhythmogenic right ventricular cardiomyopathy causes thinning of the right ven-tricle due to autosomal dominant mutations that encode desmosomal junctional proteins. On microscopy, there is fatty infiltration of the myocardium.