Alcohol septal ablation for hypertrophic obstructive cardiomyopathy patient and anatomic selection

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Nehal Eid, M.D.[2]

Patient and Anatomic Selection

Candidacy for alcohol septal ablation (ASA) in obstructive hypertrophic cardiomyopathy (HCM) requires concordant clinical, hemodynamic, and anatomic eligibility. Selection should occur at an experienced HCM center after confirmation that symptoms are attributable to dynamic left ventricular outflow tract (LVOT) obstruction and remain limiting despite guideline-directed medical therapy (GDMT).

Eligibility for septal reduction therapy (SRT) also applies when optimal medical therapy is limited by intolerable adverse effects. Contemporary GDMT before SRT may include cardiac myosin inhibitors such as mavacamten or aficamten when appropriate and available.

Guideline-based eligibility

Eligibility domain	Required findings	Clinical interpretation
Clinical	Severe dyspnea or chest pain, usually NYHA functional class III–IV, or exertional syncope or near-syncope attributable to LVOT obstruction and interfering with everyday activity or quality of life despite GDMT, or when GDMT causes intolerable adverse effects.	Symptoms must be attributable to obstruction rather than another cardiac or noncardiac condition.
Hemodynamic	Dynamic LVOT peak gradient ≥50 mmHg at rest or with physiologic provocation, associated with septal hypertrophy and systolic anterior motion of the mitral valve.	A gradient alone is insufficient in the absence of clinically important symptoms.
Anatomic	Target anterior septal thickness sufficient for safe and effective ablation in the judgment of the operator, together with a suitable septal perforator supplying the basal septum at the systolic anterior motion–septal contact point.	Anatomic suitability must be confirmed before ethanol injection; an unsuitable target territory precludes ASA.

For patients who remain symptomatic despite GDMT or cannot tolerate its adverse effects, SRT with myectomy or ASA at an experienced HCM center is a Class 1 recommendation (LOE B-NR). ASA is specifically a Class 1 recommendation (LOE C-LD) in severely symptomatic adults for whom surgery is contraindicated or considered unacceptably risky because of serious comorbidities or advanced age.

SRT may be considered instead of further escalation of medical therapy after shared decision-making (Class 2b, LOE C-LD). It is not recommended (Class 3: Harm) in asymptomatic patients with normal exercise capacity.

Anatomic suitability

Anatomic feature	Favorable finding	Selection implication
Location of obstruction	Dynamic basal subaortic obstruction caused by systolic anterior motion–septal contact	Midventricular, apical, multilevel, or fixed subaortic obstruction is unlikely to be adequately treated by ASA.
Septal thickness	Localized basal septal hypertrophy of sufficient thickness; a range of approximately 17–25 mm is commonly considered favorable in candidate descriptions, although registry data demonstrate that ASA may also be effective with septal thickness ≤16 mm.	The guideline does not define a universal minimum or a formal 25-mm upper cutoff and defers suitability to operator judgment. Mild hypertrophy may provide limited target tissue, whereas thickness ≥30 mm predicts reduced efficacy and generally favors extended surgical myectomy.
Septal perforator	A suitable perforator, usually arising from the left anterior descending coronary artery, that selectively supplies the basal anterior septum at the systolic anterior motion–septal contact point	Absence of an appropriate perforator makes ASA technically infeasible. Up to 20% of referred patients may lack a vessel supplying the required target territory.
Myocardial contrast distribution	Selective opacification of the intended basal septal target	Opacification of the anterolateral wall, right ventricular free wall, papillary muscles, or another nontarget structure makes that perforator unsuitable. Ethanol must not be injected unless an alternative suitable branch is identified.
Mitral and subvalvular apparatus	Obstruction predominantly caused by basal septal hypertrophy, without intrinsic mitral or papillary muscle pathology requiring repair	Markedly elongated mitral leaflets, anomalous papillary muscles, accessory muscle bundles, or abnormal chordal attachments generally favor surgical correction.

Final target-vessel validation requires intraprocedural myocardial contrast echocardiography. Angiographic appearance alone does not establish that the candidate perforator supplies the intended myocardium.

Features influencing procedure choice

Selection factor	Favors ASA	Favors myectomy or argues against ASA
Age and operative risk	Advanced age, frailty, severe comorbidity, prior sternotomy, or otherwise unacceptable surgical risk	Younger patient with acceptable operative risk
Concomitant cardiac disease	No additional lesion requiring surgical treatment	Intrinsic mitral valve disease, anomalous papillary muscles, multivessel coronary artery disease requiring coronary artery bypass grafting, valvular aortic stenosis, or a subaortic membrane
Septal morphology	Localized, moderate basal septal hypertrophy	Septal thickness ≥30 mm, extensive hypertrophy, or midventricular or multilevel obstruction
LVOT gradient	Symptomatic resting or provocable gradient ≥50 mmHg	Resting gradient ≥100 mmHg is associated with reduced ASA efficacy and may favor myectomy.
Perforator anatomy	Selective vessel supplying the intended basal septal target	Absent suitable perforator or unavoidable nontarget myocardial perfusion
Baseline conduction	No major conduction abnormality that substantially increases the risk of complete heart block	Pre-existing left bundle branch block is unfavorable because ASA commonly produces right bundle branch block, observed in approximately 50–60% of cases, and the combination may precipitate complete heart block.
Patient preference	Informed preference to avoid sternotomy after discussion of the limitations and risks of ASA	Preference for surgical correction or for a single operation capable of addressing associated structural disease

Children and young adults should generally not undergo ASA because of limited lifetime follow-up and concern regarding the long-term consequences of an alcohol-induced myocardial scar. Age alone should not determine treatment; anatomy, operative risk, associated disease, center expertise, comparative long-term outcomes, and informed patient preference must be considered together.

Contraindications and evidence-limited features

An absent suitable perforator, fixed non-dynamic obstruction, or anatomy requiring surgical correction makes ASA inappropriate or technically infeasible. Other findings are relative or context-dependent rather than universal contraindications.

• Pre-existing septal late gadolinium enhancement: This is not an established absolute contraindication. A limited observational study found that ASA remained effective in patients with baseline late gadolinium enhancement, although residual LVOT obstruction >30 mmHg occurred more often than in patients without enhancement (13% versus 2%). The role of scar burden in selecting ASA remains uncertain.
• Mild septal hypertrophy: No universally accepted minimum septal thickness is specified in the guideline. Suitability depends on the location of the systolic anterior motion–septal contact point, expected ablation territory, and operator assessment.
• Marked hypertrophy or very high gradients: Septal thickness ≥30 mm or resting LVOT gradient ≥100 mmHg predicts less reliable relief with ASA and generally shifts selection toward myectomy.

Selection-focused imaging and testing

Study	Selection question addressed	Findings that may change procedure choice
Transthoracic echocardiography	Are symptoms associated with dynamic obstruction, and is the anatomy suitable for focal basal septal reduction?	Defines resting and provocable LVOT gradients, septal thickness and distribution, systolic anterior motion, mitral regurgitation, and mitral valve or papillary muscle abnormalities.
Cardiac magnetic resonance imaging	Is the mechanism of obstruction or distribution of hypertrophy incompletely defined by echocardiography?	Better identifies multilevel hypertrophy, anomalous papillary muscles, accessory muscle bundles, abnormal chordal connections, and pre-existing septal scar. CMR is recommended when the anatomic mechanism of obstruction is inconclusive on echocardiography (Class 1, LOE B-NR).
Coronary angiography	Is there an accessible septal perforator supplying the intended basal septal target?	Absence of a suitable branch, unfavorable vessel geometry, or supply to an inappropriate myocardial territory may preclude ASA.
Myocardial contrast echocardiography	Does the selected perforator exclusively perfuse the intended ablation zone?	Nontarget opacification requires selection of another perforator or abandonment of ASA.
Baseline electrocardiogram	Is pre-existing conduction disease likely to increase the risk of complete heart block?	Pre-existing left bundle branch block is an important unfavorable feature and may shift the decision toward myectomy.

Shared decision-making and center experience

The choice between ASA and septal myectomy should be made by an experienced multidisciplinary HCM team after discussion of:

• The probability of symptom and gradient improvement with the patient's specific anatomy
• The operative risk and presence of comorbidities or prior sternotomy
• Whether mitral, subvalvular, coronary, or valvular pathology requires surgical correction
• The risk of conduction disturbance and permanent pacemaker implantation
• The possibility of residual obstruction or repeat septal reduction after ASA
• Recovery time, procedural preferences, comparative long-term survival, and the patient's values and goals

ASA avoids sternotomy and generally provides a shorter recovery, but it has higher risks of permanent pacing and repeat intervention than myectomy. The 2024 AHA/ACC guideline notes that survival at 10 years is lower after ASA than after surgical myectomy, which is an important consideration in younger patients with acceptable operative risk.

These tradeoffs should be discussed without treating ASA as a substitute for surgery when the target anatomy is unsuitable. Both procedures should be undertaken at experienced HCM centers. Referral to a comprehensive HCM center is encouraged when the required expertise or procedural option is unavailable locally.