Arrhythmogenic Cardiomyopathy (ACM)
Definition
Arrhythmogenic cardiomyopathy (ACM) is an arrhythmogenic heart muscle disorder not explained by ischemic, hypertensive, or valvular heart disease, in which arrhythmia (conduction disease, atrial arrhythmia, or ventricular arrhythmia) is a defining clinical feature. ACM incorporates a broad spectrum of genetic, systemic, infectious, and inflammatory disorders. If arrhythmia is absent, ACM is excluded by definition.
Key Concepts
Spectrum and Classification
- ACM is an umbrella term encompassing: ARVC (right-dominant, desmosomal), ALVC (left-dominant, associated with LMNA, DSP, PLN, FLNC, SCN5A), biventricular forms, and acquired causes including cardiac amyloidosis, sarcoidosis, Chagas disease, and LVNC. (sources/acm-hrs-2019)
- The defining distinction from DCM is the arrhythmia-first presentation: in ACM, the proband and/or family member typically presents with arrhythmia rather than heart failure, though both may coexist in advanced disease. (sources/acm-hrs-2019)
- ACM can overlap with HCM (sarcomeric variants — troponin T → SCD without significant hypertrophy; troponin I → RCM with AF), RCM, and LVNC. (sources/acm-hrs-2019)
Genetic Architecture
- Causative genes span multiple protein classes: desmosomal (PKP2, DSP, DSG2, DSC2, JUP), nuclear envelope (LMNA), sodium channel (SCN5A), cytoskeletal (FLNC, DES, LDB3/ZASP), calcium handling (PLN), RNA splicing (RBM20), transmembrane (TMEM43), and chaperone (BAG3). (sources/acm-hrs-2019)
- Autosomal dominant inheritance predominates; 3–6% of patients carry multiple pathogenic variants — associated with earlier onset (<20 vs. 35 years for single-variant patients) and higher lifetime arrhythmia/SCD risk. (sources/acm-hrs-2019)
- Penetrance is incomplete and age-related; disease expression is highest between 20–50 years of age (40%). Expression under age 14 is almost exclusively seen in probands, not at-risk relatives. (sources/acm-hrs-2019)
Final Common Pathway
- The "final common pathway" hypothesis holds that ACM subtypes converge on dysfunction of key protein complexes at the intercalated disc — primarily the desmosome in ARVC, with broader involvement of the area composita (desmosome + adherens junction hybrid) in all ACMs. (sources/acm-hrs-2019)
- See: concepts/Final-Common-Pathway
Evaluation Framework
- Initial evaluation includes: clinical history, 3-generation family history, physical exam, 12-lead ECG, 2D echocardiography, ambulatory ECG monitoring, and CMR.
- Genetic testing of all established ACM-susceptibility genes is recommended (COR I, LOE C-EO) in individuals with clinical or necropsy diagnosis. (sources/acm-hrs-2019)
- Cascade family screening is recommended every 1–3 years starting at age 10–12 in first-degree relatives. (sources/acm-hrs-2019)
- See: concepts/Cascade-Family-Screening
ICD and Management
- ICD decisions should be shared between patient and physician. Primary prevention indications vary by genotype; secondary prevention (cardiac arrest, hemodynamically intolerated sustained VT) warrants ICD in all ACM subtypes. (sources/acm-hrs-2019)
- Exercise restriction is a major modifiable risk factor — competitive and high-intensity endurance exercise is contraindicated in ARVC (COR III: Harm). (sources/acm-hrs-2019)
- See: concepts/Exercise-Restriction-in-ARVC
ESC 2023 Position on ACM Terminology
- The 2023 ESC Guidelines explicitly reject "arrhythmogenic cardiomyopathy (ACM)" as a distinct cardiomyopathy subtype, arguing that it lacks a morphological or functional definition consistent with the existing classification scheme. (sources/esc-cmp-2023)
- ESC 2023 position: ARVC remains a defined phenotype (RV-dominant disease); predominantly LV disease is now classified as NDLVC. The umbrella term ACM is not recommended as a clinical diagnostic category.
- This creates a direct conflict with the HRS 2019 Consensus Statement (sources/acm-hrs-2019) which embraces ACM as an umbrella term encompassing ARVC, ALVC, and biventricular forms — two major society guidelines use incompatible nomenclature frameworks.
- ESC 2023 acknowledges the arrhythmic dimension of multiple phenotypes but concludes that highlighting arrhythmia as a diagnostic red flag across phenotypes is preferable to creating a new morphologically-undefined entity. (sources/esc-cmp-2023)
Contradictions / Open Questions
- Nomenclature conflict — ACM vs. phenotype-based classification: HRS 2019 promotes ACM as a clinically useful umbrella term that captures the arrhythmia-first presentation across RV-dominant, LV-dominant, biventricular, and acquired forms. ESC 2023 explicitly rejects ACM as a diagnostic category, arguing it lacks morphological specificity, and instead categorizes patients under ARVC, NDLVC, or DCM. Two major society guidelines published 4 years apart use incompatible classification systems — a clinician attending an HRS conference and an ESC conference would receive different categorical frameworks for the same patients. (sources/acm-hrs-2019, sources/esc-cmp-2023)
- "Arrhythmia-first" criterion excludes late presentations: ACM as defined by HRS 2019 requires arrhythmia as a defining clinical feature — if arrhythmia is absent, ACM is excluded by definition. But late-stage DCM-phenotype disease originating from a PKP2 or DSP variant may present with HF without prior arrhythmia recognition. These patients may be mis-categorized as DCM and miss ACM-specific counseling (exercise restriction, gene-specific ICD thresholds). (sources/acm-hrs-2019)
Connections
- Related to entities/ARVC
- Related to entities/ALVC
- Related to concepts/Final-Common-Pathway
- Related to concepts/Desmosome
- Related to concepts/ARVC-Task-Force-Criteria
- Related to concepts/Cascade-Family-Screening
- Related to concepts/Sudden-Cardiac-Death
- Related to concepts/Ion-Channel-Mutations
- Related to entities/PKP2
- Related to entities/DSP
- Related to entities/PLN
- Related to entities/DSG2
- Related to entities/DSC2
- Related to entities/JUP
- Related to entities/TMEM43
- Related to entities/DES
- Related to concepts/Exercise-Restriction-in-ARVC
- Related to sources/ACM-Genotype-Mx-JCE-2024