I42.8 — Other cardiomyopathies

Clinical Definition

Other cardiomyopathies encompasses a group of myocardial diseases that do not fall into the primary classified categories of dilated (I42.0), hypertrophic obstructive (I42.1), other hypertrophic (I42.2), endomyocardial (I42.3), endocardial fibroelastosis (I42.4), other restrictive (I42.5), or alcoholic (I42.6) cardiomyopathy. This residual category includes several clinically important conditions: arrhythmogenic right ventricular cardiomyopathy (ARVC/ARVD), left ventricular noncompaction cardiomyopathy, peripartum cardiomyopathy, stress-induced (takotsubo) cardiomyopathy, and other specified forms of myocardial disease not classified elsewhere.

ICD-10-CM code I42.8 is the "other specified" cardiomyopathy code, used when the provider documents a specific type of cardiomyopathy that does not have its own unique ICD-10-CM code within the I42 category. Notably, takotsubo cardiomyopathy (stress cardiomyopathy, broken heart syndrome) is coded to I51.81 (takotsubo syndrome) rather than I42.8 in the current ICD-10-CM edition, though it was previously classified here. Providers should be aware that I42.8 captures the cardiomyopathy types that fall between the specifically enumerated codes (I42.0-I42.7) and the unspecified code (I42.9). It is a nonischemic cardiomyopathy code — ischemic cardiomyopathy should be coded to I25.5 (ischemic cardiomyopathy).

Diagnosis of cardiomyopathies classified under I42.8 typically requires advanced cardiac imaging (echocardiography, cardiac MRI with late gadolinium enhancement), and in some cases genetic testing or endomyocardial biopsy. ARVC is characterized by fibrofatty replacement of the right ventricular myocardium and diagnosed using the revised Task Force Criteria. Left ventricular noncompaction features prominent trabeculations with deep intertrabecular recesses on imaging. Peripartum cardiomyopathy develops in the last month of pregnancy or within five months postpartum in the absence of prior heart disease. Each subtype has distinct management considerations, prognosis, and genetic counseling implications.

When to Use I42.8

• ✓The provider documents a specific cardiomyopathy subtype that does not have its own dedicated ICD-10-CM code, such as ARVC, left ventricular noncompaction, or peripartum cardiomyopathy.
• ✓Cardiac imaging (echocardiography or MRI) identifies a cardiomyopathy that does not fit the criteria for dilated (I42.0), hypertrophic (I42.1/I42.2), or restrictive (I42.5) cardiomyopathy.
• ✓The provider documents 'nonischemic cardiomyopathy, other specified' and the specific subtype falls within the I42.8 classification.
• ✓Genetic testing or family screening identifies a cardiomyopathy variant (such as ARVC or noncompaction) that is classified under the 'other' category.
• ✓The patient has a documented peripartum cardiomyopathy diagnosed during the postpartum period.

Common Coding Mistakes

Related & Differential Codes

Documentation Requirements

• 1Cardiomyopathy subtype: clearly specify the type of cardiomyopathy (ARVC, noncompaction, peripartum, infiltrative, or other specified type) to distinguish from dilated, hypertrophic, and restrictive forms that have their own codes.
• 2Cardiac imaging findings: document echocardiographic or cardiac MRI findings including ejection fraction, chamber dimensions, wall motion abnormalities, trabeculation pattern, fibrofatty infiltration, or late gadolinium enhancement.
• 3Functional status: document NYHA functional class (I-IV) and the patient's exercise capacity and symptom burden.
• 4Etiology and associated conditions: document any identified triggers (pregnancy for peripartum, emotional stress for takotsubo), genetic mutations (ARVC-related desmosomal gene variants), or associated systemic diseases.
• 5Arrhythmia history: document any associated arrhythmias (ventricular tachycardia, atrial fibrillation) as many cardiomyopathies in the I42.8 category carry significant arrhythmic risk.
• 6Device therapy: document the presence of implantable cardioverter-defibrillators (ICDs), cardiac resynchronization therapy (CRT), or ventricular assist devices if applicable.
• 7Genetic testing and family screening: document genetic test results and family history of cardiomyopathy or sudden cardiac death, particularly for ARVC and noncompaction.

Reimbursement & Billing Notes

ICD-10-CM code I42.8 is a valid, billable code accepted by Medicare, Medicaid, and commercial payers for encounters related to other specified cardiomyopathies. It supports medical necessity for advanced cardiac imaging (echocardiography, cardiac MRI), electrophysiology studies, genetic testing, and specialized heart failure management. Cardiomyopathy codes are commonly used to justify referrals to advanced heart failure specialists, cardiac transplant evaluation, and device implantation.

Cardiomyopathy codes in the I42 range map to HCC 85 (Heart Failure) in the CMS-HCC V28 risk adjustment model when associated with heart failure. Accurate documentation and coding of the specific cardiomyopathy type impacts risk adjustment factor (RAF) scores, capitated payment calculations, and quality measure reporting. For peripartum cardiomyopathy during the obstetric period, O90.3 may be used instead of I42.8 depending on the timing and clinical context. Providers should document the cardiomyopathy subtype as specifically as possible to support accurate code assignment and avoid defaulting to I42.9 (unspecified).

Frequently Asked Questions