Septal Reduction Therapy (SRT)
Definition
Septal reduction therapy (SRT) encompasses invasive procedures to reduce the interventricular septal mass and relieve left ventricular outflow tract obstruction (LVOTO) in HCM. The two main modalities are surgical ventricular septal myectomy and percutaneous alcohol septal ablation (ASA). Both are Class I indications for patients with LVOTO ≥50 mmHg and severe (NYHA III–IV) symptoms refractory to maximal medical therapy.
Key Concepts
Indications
- LVOTO ≥50 mmHg + NYHA III–IV symptoms or recurrent exertional syncope, refractory to maximally tolerated pharmacological therapy (Class I). (sources/esc-cmp-2023)
- May be considered in milder symptoms (NYHA II) with LVOTO ≥50 mmHg + SAM-related MR + AF or left atrial dilatation in expert centres with low complication rates. (sources/esc-cmp-2023)
- No data support SRT in asymptomatic patients regardless of gradient severity. (sources/esc-cmp-2023)
- Delay in SRT (>5 years from first detection) may worsen long-term outcomes even after successful gradient reduction. (sources/esc-cmp-2023)
Surgical Septal Myectomy
- Rectangular trough created in basal septum below the aortic valve, extending beyond mitral leaflet–septal contact point. (sources/esc-cmp-2023)
- Abolishes/substantially reduces LVOT gradient in >90% of cases; long-term survival comparable to general population. (sources/esc-cmp-2023)
- Good long-term outcome predictors: age <50 years, LA size <46 mm, absence of AF, male sex. (sources/esc-cmp-2023)
- Main complications: AV block (uncommon in expert centres), LBBB, VSD, aortic regurgitation. (sources/esc-cmp-2023)
- Can be combined with mitral valve repair/replacement (for intrinsic MV disease) or Cox-Maze ablation (for AF). (sources/esc-cmp-2023)
Alcohol Septal Ablation (ASA)
- Selective alcohol injection into a septal perforator artery creates a localized septal scar. (sources/esc-cmp-2023)
- Outcomes similar to surgery for gradient reduction, symptom improvement, and exercise capacity including in younger adults. (sources/esc-cmp-2023)
- Main non-fatal complication: AV block requiring permanent pacing in 7–20%. (sources/esc-cmp-2023)
- Myocardial contrast echocardiography is mandatory before alcohol injection to confirm target vessel. (sources/esc-cmp-2023)
- NOT recommended in children with HCM outside experimental settings. (sources/esc-cmp-2023)
Myectomy vs. ASA
- No randomized trials exist; meta-analyses show similar procedural mortality and functional status improvement. (sources/esc-cmp-2023)
- ASA: higher risk of AV block and larger residual LVOT gradients. (sources/esc-cmp-2023)
- Choice depends on anatomy, center expertise, and patient preference; multidisciplinary team assessment required. (sources/esc-cmp-2023)
- Note: Mavacamten (VALOR-HCM trial) significantly reduced the proportion of patients meeting SRT criteria at 16 and 32 weeks — may serve as a bridge to or substitute for SRT in selected patients. (sources/esc-cmp-2023)
AHA 2024 — Additional Guidance and Outcome Benchmarks
- Required outcome targets at HCM centers (AHA 2024): 30-day mortality ≤1% (both procedures); 30-day complications ≤5%; symptomatic improvement ≥1 NYHA class >90%; rest/provoked LVOT gradient <50 mmHg >90%. Permanent pacemaker rate: ≤5% (myectomy), ≤10% (ASA). Repeat procedure: ≤3% (myectomy), ≤10% (ASA). (sources/HCM-AHA-2024)
- Myectomy vs ASA long-term: 5-year survival similar between ASA and myectomy; however at 10 years, survival is lower with ASA compared with extended septal myectomy (ESM). (sources/HCM-AHA-2024)
- ASA limitations: Less effective when LVOT gradient ≥100 mmHg or septal thickness ≥30 mm; associated with greater risk of permanent pacemaker and higher repeat intervention rates vs myectomy. (sources/HCM-AHA-2024)
- Early SRT (NYHA II) at comprehensive centers: May be reasonable with additional factors: severe pulmonary hypertension from LVOTO/MR, left atrial enlargement + AF, poor functional capacity on treadmill, or children/young adults with very high resting gradients (>100 mmHg) (Class IIb). (sources/HCM-AHA-2024)
- Concomitant AF ablation: Surgical maze/pulmonary vein isolation at time of myectomy is reasonable (Class IIa) and can be added to myectomy with minimal added risk. (sources/HCM-AHA-2024)
- Mitral valve replacement: Should NOT be performed for sole purpose of LVOTO relief (Class III: Harm); if mitral intervention needed at time of myectomy, valve repair preferred over replacement (lower mortality). (sources/HCM-AHA-2024)
- Volume-outcome relationship: Literature demonstrates clear relationship between procedural volume/experience and outcomes; referral to comprehensive centers strongly encouraged when SRT not readily available. (sources/HCM-AHA-2024)
Contradictions / Open Questions
- 10-year survival divergence — ASA vs. myectomy: ESC 2023 frames ASA and myectomy as having similar outcomes for gradient reduction and symptom improvement, framing them as equivalent for most patients. AHA 2024 explicitly reports that 10-year survival is lower with ASA vs. extended septal myectomy — a difference ESC 2023 does not prominently feature. No randomized trial exists; the divergence reflects interpretation of retrospective registry data. Younger patients may face meaningfully different long-term outcomes depending on which guideline their physician follows. (sources/HCM-AHA-2024, sources/esc-cmp-2023)
- No randomized trial — all evidence is observational: The choice between surgical myectomy and ASA is guided entirely by non-randomized evidence. Meta-analyses show similar procedural mortality and functional improvement, but selection bias in who receives each procedure limits the comparability of outcomes. Without an RCT, neither procedure can claim superiority. (sources/esc-cmp-2023)
- HCM Risk-SCD calculator not validated post-SRT: The SCD risk calculator was not developed in patients post-myectomy or post-ASA. The impact of gradient reduction and LV remodeling on subsequent SCD risk — and therefore on ICD candidacy — is unknown. Using the same pre-procedure risk thresholds post-SRT may overestimate or underestimate residual arrhythmic risk. (sources/esc-cmp-2023)
Connections
- Related to entities/HCM
- Related to entities/Mavacamten
- Related to concepts/LVOTO
- Related to concepts/HCM-Risk-SCD