Atrial Myopathy in HCM
Definition
Atrial myopathy in hypertrophic cardiomyopathy refers to intrinsic disease of the atrial myocardium — manifesting as fibrosis, low-voltage areas, and impaired conduction — that arises from the same sarcomeric gene defects causing ventricular hypertrophy, independently of hemodynamic effects such as elevated left atrial pressure.
Key Concepts
Mechanism
- In HCM, AF has historically been attributed to diastolic dysfunction → elevated LA pressure → secondary atrial remodeling and fibrosis
- Emerging evidence supports a primary atrial myopathy model: sarcomeric mutations (particularly MYBPC3, MYH7) may directly affect atrial cardiomyocytes, promoting fibrosis independent of LA pressure
- In patients with MYBPC3/MYH7-mediated HCM undergoing AF ablation, low-voltage LA areas were significantly more extensive than in gene-negative HCM controls despite similar LA pressures — implicating a genetically driven primary atrial process (sources/MYBPC3-MYH7-JACCEP-2024, rating: medium)
- Interval progression of LA fibrosis was observed in 5/7 gene-positive HCM patients at repeat ablation procedures, suggesting ongoing, progressive atrial disease (sources/MYBPC3-MYH7-JACCEP-2024)
Electroanatomical Substrate
- Gene-positive HCM patients have appreciably more LA abnormal voltage than gene-negative HCM patients:
- Normal voltage (>0.5 mV): 87.7% vs. 94.3% (P<0.001)
- Intermediate scar (0.1–0.5 mV): 6.33% vs. 3.07% (P<0.01)
- Dense scar (<0.1 mV): 5.93% vs. 2.61% (P<0.01) (sources/MYBPC3-MYH7-JACCEP-2024)
- MYH7 variant–positive patients show a predilection for dense scar in lateral LA regions; MYBPC3 variant–positive patients tend to have greater LV mass but similar atrial scar distribution overall (sources/MYBPC3-MYH7-JACCEP-2024)
- No correlation between LA volume index or LA pressure and degree of low-voltage areas in either cohort — argues against a purely hemodynamic explanation (sources/MYBPC3-MYH7-JACCEP-2024)
Clinical Implications for AF
- AF prevalence in HCM is ~20–30%, rising with age; MYH7 carriers have particularly high incident AF rates (sources/eoaf-jama-2021, rating: high)
- Thicker LA walls (expected in MYBPC3 carriers with greater LV mass) may result in non-transmural ablation lesions → increased pulmonary vein reconnection rates (sources/MYBPC3-MYH7-JACCEP-2024)
- Progressive atrial myopathy means fibrosis advances even after successful ablation, requiring repeat procedures over time (sources/MYBPC3-MYH7-JACCEP-2024)
Therapeutic Consequences
- Catheter ablation remains effective in gene-positive HCM; freedom from AF at 12 months ~75%, comparable to gene-negative HCM (~73%) — but significantly more procedures required (1.67 vs. 1.20; P=0.03) (sources/MYBPC3-MYH7-JACCEP-2024)
- All gene-positive patients required AADs post-ablation (sources/MYBPC3-MYH7-JACCEP-2024)
- Whether substrate-guided ablation targeting low-voltage areas (analogous to ERASE-AF in persistent AF) improves outcomes in HCM-genotype patients is unstudied (sources/MYBPC3-MYH7-JACCEP-2024)
Contradictions / Open Questions
- Hemodynamic vs. primary genetic mechanism — evidence is correlational, not causal: The absence of correlation between LA pressure and low-voltage areas supports primary atrial myopathy, but causality cannot be established in a retrospective observational study. Genotype-positive and genotype-negative HCM patients may differ in other unmeasured variables. (sources/MYBPC3-MYH7-JACCEP-2024)
- MYH7 → AF mechanism: secondary to hypertrophy vs. primary atrial involvement (pre-existing debate): The primary atrial myopathy model is supported by this study but conflicts with the dominant hypothesis that MYH7-associated ventricular hypertrophy and diastolic dysfunction drive atrial remodeling. If AF can precede overt hypertrophy in MYH7 carriers, this would strongly favor primary atrial involvement. (sources/eoaf-jama-2021, sources/MYBPC3-MYH7-JACCEP-2024)
- Whether mavacamten or other myosin inhibitors targeting sarcomere hypercontractility could prevent atrial myopathy is entirely unknown: If atrial fibrosis in HCM is sarcomere-driven (not pressure-driven), upstream therapy reducing sarcomere ATPase activity might theoretically reduce atrial fibrosis progression. No trial data exist.
Connections
- Related to entities/MYBPC3
- Related to entities/MYH7
- Related to entities/HCM
- Related to entities/Atrial-Fibrillation
- Related to concepts/Catheter-Ablation-AF
- Related to concepts/Late-Gadolinium-Enhancement
- Related to concepts/Early-Onset-Atrial-Fibrillation