Alcohol septal ablation for hypertrophic obstructive cardiomyopathy pre-procedural imaging and assessment

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

Pre-procedural imaging and assessment

Pre-procedural assessment for alcohol septal ablation (ASA) should confirm physiologically significant left ventricular outflow tract obstruction (LVOTO), define the anatomic substrate responsible for obstruction, establish whether an appropriate septal territory can be targeted, and identify structural or conduction-system findings that favor septal myectomy. Assessment should be integrated by an experienced multidisciplinary hypertrophic cardiomyopathy (HCM) team.

This assessment is ASA-specific and does not replace the general diagnostic evaluation or sudden cardiac death risk stratification required for HCM. Intraprocedural myocardial contrast echocardiography and post-procedural surveillance are addressed separately.

Core assessment

Assessment	Principal role	Findings that affect the procedural plan
Transthoracic echocardiography (TTE)	Measure resting and provoked LVOT gradients; define septal morphology, systolic anterior motion (SAM), and the mechanism of mitral regurgitation	Basal target-septum thickness and SAM-septal contact; mid-ventricular obstruction; intrinsic mitral or subvalvular disease
Transesophageal echocardiography (TEE)	Selected use when TTE does not adequately define mitral, subvalvular, or LVOT anatomy	Mitral valve or papillary muscle pathology requiring surgical correction
Cardiac magnetic resonance imaging (CMR)	Define the distribution of hypertrophy, LVOT geometry, papillary muscle anatomy, and myocardial fibrosis	Mid-ventricular extension, accessory muscle bundles, anomalous papillary muscle insertion, apical aneurysm, or extensive scar
Coronary angiography	Define epicardial coronary disease and septal perforator anatomy	Absence of a suitable target perforator, non-target perfusion, or coronary disease requiring surgical revascularization
Cardiac computed tomography angiography (CCTA)	Selective adjunct for coronary and structural mapping	Complex or variant septal arterial anatomy; anomalous coronary origin; subaortic membrane
Baseline electrocardiography	Document rhythm, atrioventricular conduction, and bundle branch status	Pre-existing left bundle branch block or other conduction disease increasing post-ASA pacing risk
Invasive hemodynamics	Selected use when noninvasive gradient assessment is equivocal or discordant	Confirmation of dynamic LVOTO and exclusion of fixed or mid-ventricular obstruction

Echocardiographic assessment

Comprehensive TTE is the primary imaging examination before ASA. The examination should document:

• Maximal LV wall thickness and the distribution of hypertrophy.
• Subaortic septal thickness at the site of SAM-septal contact.
• Resting peak LVOT gradient by continuous-wave Doppler.
• Presence, duration, and location of SAM-septal contact.
• Severity and mechanism of mitral regurgitation.
• Mitral leaflet morphology and papillary muscle position, insertion, and number.
• Basal versus mid-ventricular obstruction.
• LV systolic and diastolic function and left atrial size.

A precisely defined minimum septal thickness for safe ASA has not been established; target suitability therefore requires integration of wall thickness, perfusion territory, and operator experience.

If the resting LVOT gradient is less than 50 mm Hg, physiologic provocation should be performed. Bedside maneuvers such as Valsalva may demonstrate latent obstruction; exercise stress echocardiography is preferred when symptoms and obstruction cannot be adequately reproduced at rest. Hemodynamic eligibility for septal reduction therapy generally requires a peak gradient of at least 50 mm Hg at rest or with physiologic provocation, together with symptoms attributable to LVOTO despite appropriate medical therapy.

TEE is not routinely required when TTE and CMR adequately define the anatomy. It is useful when acoustic windows are limited or when the mechanism of mitral regurgitation, leaflet abnormalities, or subvalvular anatomy remains uncertain.

Cardiac magnetic resonance imaging

CMR complements echocardiography during septal reduction therapy planning, particularly when the extent or distribution of hypertrophy and mitral-subvalvular anatomy are incompletely characterized by TTE. CMR should assess:

• Maximal wall thickness and basal versus mid-ventricular extension of hypertrophy.
• LVOT geometry and the relationship between the basal septum and mitral apparatus.
• Anomalous papillary muscle insertion, accessory muscle bundles, and abnormal chordal attachments.
• LV apical aneurysm or regional wall-motion abnormality.
• Myocardial fibrosis by late gadolinium enhancement (LGE).

LGE contributes to HCM sudden cardiac death risk assessment and documents pre-existing scar before ASA. Observational evidence suggests that ASA may remain effective in patients with baseline LGE, although residual obstruction may be more frequent; LGE alone is not an established absolute contraindication.

Coronary and septal perforator assessment

Coronary angiography is required as part of the ASA procedure before ethanol delivery. It should:

• Identify the candidate septal perforator and assess its caliber, course, and branching pattern.
• Evaluate variant septal arterial origins and collateral connections.
• Identify obstructive epicardial coronary disease that may require surgical revascularization.
• Exclude anatomy in which a candidate branch supplies a substantial non-target territory.

A septal perforator must perfuse the basal septal region corresponding to SAM-septal contact. Angiographic appearance alone is insufficient for final target selection; perfusion territory must be confirmed with intraprocedural myocardial contrast echocardiography before ethanol is administered. Absence of an appropriate septal perforator or demonstration of clinically important non-target perfusion precludes ethanol injection through that branch.

Cardiac computed tomography angiography

CCTA is not routinely required before ASA. It may be considered when septal coronary anatomy is complex, noninvasive imaging is inconclusive, or CMR is contraindicated or unavailable. CCTA can delineate septal perforators, variant coronary origins, wall thickness, LV morphology, and fixed subaortic abnormalities.

Evidence supporting CT-guided ASA planning is observational and limited; routine use is not established. Limitations include ionizing radiation, iodinated contrast exposure, and lower temporal resolution than echocardiography.

ECG and conduction-system assessment

A baseline 12-lead ECG should document:

• Cardiac rhythm.
• PR interval and atrioventricular conduction.
• QRS duration and axis.
• Pre-existing right or left bundle branch block.
• Existing pacemaker or implantable cardioverter-defibrillator function, when applicable.

ASA commonly injures the right bundle. Pre-existing left bundle branch block therefore increases the risk of complete atrioventricular block and permanent pacing after ASA and may favor surgical myectomy or require an explicit pacing strategy. Pre-existing bundle branch block of any type is associated with increased permanent pacemaker risk after ASA. These abnormalities increase risk but are not uniformly treated as absolute contraindications; management should be individualized by the HCM team.

Prior ambulatory rhythm monitoring and HCM sudden cardiac death risk assessment should be reviewed so that any ICD indication is addressed independently of the anticipated reduction in LVOT obstruction.

Invasive hemodynamic assessment

When Doppler findings are equivocal or discordant with symptoms, simultaneous LV and aortic pressure measurement may be used to confirm the gradient and distinguish dynamic LVOTO from fixed subaortic or mid-ventricular obstruction. This assessment is usually performed during catheterization immediately before ASA rather than as a separate procedure.

Findings that may redirect treatment toward surgery

The following findings identified during pre-procedural assessment commonly favor surgical evaluation rather than ASA; they should not be treated as isolated absolute rules without multidisciplinary review.

Finding	Procedural implication
Intrinsic mitral valve disease requiring repair or replacement	ASA does not correct the primary mitral lesion; myectomy with concomitant mitral surgery may be required
Anomalous papillary muscle insertion, accessory muscle bundles, or other surgically correctable subvalvular abnormalities	Persistent obstruction may remain after isolated basal septal infarction
Hypertrophy extending into the mid-ventricle	May require an extended surgical myectomy
Massive septal hypertrophy (approximately 30 mm or greater) or resting gradient of 100 mm Hg or greater	Associated with less favorable ASA response and often favors myectomy; decisions remain individualized
Fixed subaortic membrane or concomitant aortic valve disease requiring surgery	Requires direct surgical correction
Coronary artery disease requiring bypass surgery	Favors combined coronary revascularization and surgical myectomy
No suitable septal perforator or unavoidable non-target myocardial perfusion	ASA is not technically feasible through the assessed branch
Pre-existing left bundle branch block	Increased risk of complete heart block after ASA-associated right bundle injury; may favor myectomy or require a planned pacing strategy

Pre-procedural completion checklist

Before proceeding with ASA, the HCM team should confirm that:

• The resting or physiologically provoked LVOT gradient is at least 50 mm Hg and is attributable to SAM-septal contact.
• The basal septal target is anatomically suitable and sufficiently thick for controlled ablation.
• Mitral, papillary muscle, chordal, or fixed subaortic abnormalities do not require surgical correction.
• A potentially suitable septal perforator is present, with final territory confirmation planned using myocardial contrast echocardiography.
• Concomitant coronary or valvular disease does not create an independent surgical indication.
• Baseline conduction disease and anticipated temporary or permanent pacing requirements have been reviewed.
• HCM sudden cardiac death risk assessment and ICD decisions have been addressed independently.