What interventricular septal diastolic thickness predicts a good outcome with alcohol septal ablation?

Interventricular Septal Thickness for Alcohol Septal Ablation Success

Alcohol septal ablation should not be performed if the interventricular septal thickness is less than 15 mm due to risk of ventricular septal defect, and patients with septal thickness approaching or exceeding 30 mm may experience little or no benefit from the procedure. 1

Minimum Septal Thickness Threshold

• The absolute contraindication is IVS(d) <15 mm because of the potential for creating a ventricular septal defect during alcohol injection 1
• This 15 mm cutoff represents a critical safety threshold below which the septum is too thin to safely ablate 1

Optimal Range for Good Outcomes

• Patients with IVS thickness between 16-30 mm represent the ideal candidates for alcohol septal ablation based on ACC/AHA guidelines 1
• Recent research demonstrates that patients with IVS ≤16 mm can achieve successful outcomes, though they have higher rates of pacemaker implantation (13% vs 8%) compared to those with thicker septa 2
• The European guidelines specifically recommend ASA only for patients with IVS >16 mm, though this threshold has been challenged by recent data 2

Upper Limit Considerations

• Patients with massive septal thickness approaching or exceeding 30 mm may experience little or no benefit from alcohol septal ablation 1
• Research from the Euro-ASA registry confirms that while ASA is technically feasible in patients with IVS ≥30 mm, these patients have worse long-term all-cause mortality (2.94 vs 2.57 deaths per 100 person-years) compared to those with IVS <30 mm 3
• Despite higher mortality, patients with IVS ≥30 mm achieve similar symptomatic relief and gradient reduction as those with thinner septa 3

Clinical Algorithm for Patient Selection

For IVS <15 mm:

• Absolute contraindication to ASA 1
• Consider surgical myectomy if septal reduction needed 1

For IVS 15-16 mm:

• Proceed with caution; higher risk of complete heart block requiring pacemaker 2
• Ensure optimal septal perforator anatomy before proceeding 4

For IVS 16-30 mm:

• Ideal range for ASA with best risk-benefit profile 1, 2
• Expected success rate of 85-90% for gradient reduction >50% 5

For IVS ≥30 mm:

• ASA remains technically feasible but surgical myectomy is strongly preferred 1
• If surgery is contraindicated, ASA can still provide symptomatic relief despite higher long-term mortality 3
• The surgeon can directly visualize and tailor myectomy for massive hypertrophy, whereas alcohol ablation is limited by septal perforator distribution 1

Important Caveats

• The success of ASA depends critically on the ability to cannulate a septal perforator artery that supplies the area of SAM-septal contact, regardless of septal thickness 1
• Myocardial contrast echocardiography should be performed prior to alcohol injection to ensure proper localization 4
• Patients with extensive septal scarring on CMR may have reduced effectiveness regardless of thickness 4
• The 4-5 fold higher risk of permanent pacemaker implantation with ASA compared to myectomy applies across all septal thickness ranges 1