Cardiomyopathy, literally “a disease of the heart,” includes a large variety of myocardial disorders involving structural and functional abnormalities. Cardiomyopathy may be thought of as the etiologic classification of heart disease and usually results in heart failure. Other classifications, of course, include the New York Heart Association functional classes I through IV, the American College of Cardiology/American Heart Association structural stages A to D, and the pathophysiological classification of systolic and diastolic heart failure.
Technically, the World Health Organization and professional societies define cardiomyopathy as a myocardial disorder in which the heart muscle is structurally and functionally abnormal in the absence of coronary artery disease, hypertension, valvular disease, and congenital heart disease to explain the condition. In practice, clinicians most commonly use the term in reference to hypertensive and ischemic cardiomyopathies.
Primary cardiomyopathy generally refers to cases without a specific identifiable underlying cause, mainly idiopathic and hereditary. Secondary cardiomyopathy is a general, nonspecific term that refers to any cardiomyopathy with an identifiable underlying cause. Hypertensive and ischemic cardiomyopathy are by far the most common types encountered.
Dilated cardiomyopathy is characterized by dilation and impaired contraction of one or both ventricles causing systolic heart failure and associated with conduction abnormalities and dysrhythmias. Hypertrophic cardiomyopathy is characterized by ventricular hypertrophy and is commonly due to severe aortic valve stenosis.
Restrictive (constrictive) cardiomyopathy is characterized by nondilated ventricles with impaired ventricular filling, usually without hypertrophy. Systolic function usually remains normal, at least initially. Takotsubo cardiomyopathy is a syndrome characterized by transient regional systolic dysfunction of the left ventricle causing ballooning of the ventricular apex, mimicking myocardial infarction, but in the absence of obstructive coronary artery disease.
Cardiomyopathy codes (see Table) are scattered throughout ICD-10-CM, but many are grouped together under categories I42 and I43. Infectious and parasitic diseases typically have unique codes for the cardiac conditions they cause, including cardiomyopathy. Ischemic cardiomyopathy is grouped under ischemic heart disease. Hypertensive cardiomyopathy is assigned one of two codes: I11.0 (hypertensive heart disease with heart failure) or I11.9 (hypertensive heart disease without heart failure). Some conditions causing cardiomyopathy, like amyloidosis, are coded and sequenced first, followed by the cardiomyopathy code.
Primary and secondary are both coded as unspecified cardiomyopathy. The specific cause, when known, should always be documented and coded. From a clinical perspective, primary usually refers to genetic or unknown causes. Nonischemic cardiomyopathy is insufficiently descriptive; the nonischemic condition should be specified.
In summary, cardiomyopathy encompasses a large variety of myocardial disorders involving structural and functional abnormalities, of which hypertensive and ischemic cardiomyopathy are by far the most common. Avoid vague terms like unspecified or nonischemic cardiomyopathy, and specify the cause whenever possible. Cardiomyopathy codes are scattered throughout ICD-10-CM but many are grouped together under categories I42 and I43.