Alcohol septal ablation for hypertrophic obstructive cardiomyopathy procedural technique and intraprocedural imaging

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

Procedural technique and intraprocedural imaging

Alcohol septal ablation (ASA) produces a controlled infarction of the hypertrophied basal septum by delivering ethanol through a selected septal perforator. Safe execution requires balloon isolation of the target vessel, myocardial contrast echocardiography (MCE) to verify its perfusion territory, continuous hemodynamic and electrocardiographic monitoring, and immediate pacing capability. ASA should be performed by experienced operators at comprehensive hypertrophic cardiomyopathy (HCM) centers.

This microchapter covers catheterization-laboratory setup, septal perforator selection, MCE-guided target confirmation, ethanol delivery, and immediate intraprocedural assessment. Pre-procedural selection, post-procedural monitoring, permanent pacemaker decisions, long-term outcomes, and delayed complications are addressed separately.

Catheterization-laboratory preparation

ASA is performed under continuous fluoroscopic, hemodynamic, and electrocardiographic monitoring. Required preparation includes:

• Arterial access suitable for coronary intervention and simultaneous LV-aortic pressure measurement.
• Venous access for temporary transvenous pacing.
• A guide catheter capable of stable left coronary engagement.
• A catheter positioned in the LV for simultaneous LV and aortic pressure recording.
• Continuous 12-lead ECG and invasive blood-pressure monitoring.
• Immediate availability of temporary pacing, resuscitation, and defibrillation.
• Real-time transthoracic echocardiography (TTE) with an experienced echocardiographer; transesophageal echocardiography (TEE) may be used when transthoracic image quality is inadequate.
• Systemic anticoagulation according to the institutional coronary-intervention protocol.

Moderate sedation and analgesia are generally used while preserving stable hemodynamics and adequate echocardiographic imaging. General anesthesia is not routinely required but may be used when TEE guidance or clinical circumstances require it.

Temporary pacing

A transvenous temporary pacing lead is generally positioned in the right ventricle before ethanol delivery because transient or persistent atrioventricular block may occur during septal infarction. Temporary lead placement may be omitted when reliable pacing is already available from a functioning permanent pacemaker or implantable cardioverter-defibrillator.

Pacing capture and sensing should be confirmed before septal perforator instrumentation. Continuous ECG monitoring should be maintained throughout balloon occlusion, contrast injection, ethanol delivery, and immediate post-injection assessment.

Baseline coronary angiography and hemodynamics

Diagnostic coronary angiography is performed before target-vessel cannulation to:

• Exclude clinically important epicardial coronary artery disease.
• Identify the number, origin, caliber, and course of septal perforator branches.
• Recognize variant septal arterial origins.
• Identify collateral connections between the candidate septal perforator and non-target coronary territories.
• Assess the LAD and other coronary segments for anatomy that could complicate guide or balloon positioning.

The target is usually a proximal septal perforator supplying the basal septum at the point of systolic anterior motion (SAM)-septal contact. The angiographic location of a branch does not reliably establish its myocardial perfusion territory; MCE confirmation is required before ethanol injection.

Simultaneous LV and aortic pressures are recorded before ablation. The left ventricular outflow tract (LVOT) gradient should be measured at rest and, when appropriate, with Valsalva or post-extrasystolic potentiation.

Septal perforator cannulation and balloon isolation

After identifying a candidate septal branch:

1. Advance a flexible 0.014-inch coronary guidewire into the target septal perforator.
2. Advance a short, low-profile over-the-wire balloon into the proximal portion of the branch. Balloons approximately 1.5–2.5 mm in diameter and 6–10 mm in length are commonly used, with sizing adapted to the vessel.
3. Inflate the balloon to completely occlude the branch while maintaining stable position.
4. Remove the guidewire, leaving the balloon's central lumen available for selective contrast and ethanol delivery.
5. Inject a small amount of radiographic contrast through the balloon lumen to confirm complete vessel isolation and exclude retrograde leakage into the LAD.
6. Perform selective angiography through the occluded branch to identify collateral filling of non-target coronary territories.

Any retrograde contrast leakage into the LAD requires balloon repositioning and repeat seal verification. Demonstrated collateral filling of another coronary territory generally precludes ethanol delivery through that branch. Balloon position and seal should be reconfirmed immediately before both MCE contrast and ethanol injection.

Myocardial contrast echocardiography

MCE is the decisive target-confirmation and safety step. Ethanol should not be administered on the basis of angiographic anatomy alone. MCE changes the interventional strategy—by changing the target vessel or prompting procedure termination—in approximately 15%–20% of cases.

Technique

With the balloon inflated and the guidewire removed:

1. Inject approximately 1–2 mL of appropriately diluted echocardiographic contrast through the balloon lumen, followed by a small saline flush.
2. Acquire simultaneous TTE images in multiple planes, including parasternal long-axis and short-axis views.
3. Identify the myocardial territory opacified by the candidate septal perforator.
4. Confirm that the perfused region corresponds to the basal septum responsible for SAM-septal contact.
5. Assess carefully for opacification of remote or non-target structures.

Agitated radiographic contrast or an appropriate ultrasound-enhancing agent may be used according to institutional experience and imaging protocol. Excessive contrast volume or concentration should be avoided because acoustic attenuation may obscure the distribution of myocardial enhancement.

Interpretation

MCE finding	Interpretation and action
Well-demarcated opacification of the basal septum at or immediately adjacent to the SAM-septal contact point	Acceptable target, provided no non-target perfusion or angiographic leak is present
No enhancement of the basal target region	The branch does not supply the obstructive septal segment; select another branch or terminate the procedure
Opacification of the LV free wall, papillary muscle, or another remote LV territory	Non-target perfusion; do not inject ethanol through that branch
Opacification of RV myocardium or an extensive RV insertion-point territory	Unacceptable non-target perfusion; reconsider branch selection
Enhancement extending substantially into the mid or apical septum	Excessive infarct territory; do not proceed through that branch without reassessment
Indeterminate territory because of inadequate echocardiographic visualization	Improve imaging, use TEE if necessary, or select another strategy; ethanol should not be injected without definitive confirmation

If the MCE distribution is unacceptable, the balloon should be deflated and removed from that branch. An alternative perforator may be assessed using the same angiographic, balloon-seal, collateral, and MCE confirmation steps. If no suitable branch is identified, ASA should be terminated.

Three-dimensional MCE may provide volumetric assessment of the anticipated infarct territory. In a 52-patient observational study, three-dimensional imaging reclassified two-dimensional MCE findings in 42% of cases and identified potentially hazardous non-target contrast distributions not recognized on two-dimensional imaging alone. These findings require external validation; three-dimensional MCE is not yet standard practice.

Ethanol selection and dose

In the United States, dehydrated alcohol 98% (Ablysinol) is approved to induce a controlled cardiac septal infarction in adults with symptomatic hypertrophic obstructive cardiomyopathy who are not candidates for surgical myectomy. The product label states that 1–2 mL is sufficient in most situations and establishes a maximum total dose of 5 mL during a single procedure.

The labeled population is narrower than the full 2024 AHA/ACC guideline framework for septal reduction therapy. The guideline recommends septal reduction therapy for appropriately selected patients with severely symptomatic obstructive HCM and specifically recommends ASA when surgery is contraindicated or surgical risk is unacceptable because of serious comorbidity or advanced age. Regulatory labeling and guideline-based procedural selection should therefore not be treated as identical.

The minimum volume necessary to ablate the MCE-confirmed target territory should be used. One operational approach used at an experienced center administers approximately 1 mL per 1 cm of target septal thickness, up to 3 mL per session. This is not a universally accepted dosing formula and should not supersede MCE-defined territory, vessel anatomy, or the product-label maximum.

Observational data support contemporary low-volume dosing, but no universally accepted formula based on septal thickness or acute gradient response has been established. Excessive dosing should not be used solely to obtain immediate abolition of the LVOT gradient because infarct maturation and ventricular remodeling continue after the procedure.

Ethanol injection technique

After acceptable MCE confirmation and repeat verification of balloon position:

1. Confirm that the temporary pacing system is functional.
2. Reconfirm absence of balloon leak into the LAD with selective radiographic contrast.
3. Confirm stable balloon position and complete septal branch occlusion.
4. Slowly inject the planned ethanol dose through the over-the-wire balloon lumen. The product label specifies delivery over approximately 1–2 minutes; some expert protocols use slower delivery over approximately 5–10 minutes. The injection rate should permit continuous assessment for hemodynamic changes, conduction disturbance, and balloon displacement.
5. Maintain continuous fluoroscopic, ECG, pacing, and invasive hemodynamic monitoring.
6. Observe for atrioventricular block, ventricular arrhythmia, hypotension, or balloon displacement.
7. Keep the balloon inflated for approximately 5–10 minutes after the final ethanol injection to minimize retrograde ethanol leakage into the LAD or other non-target vessels.

Chest discomfort is expected during ethanol-induced myocardial ischemia and should be treated with appropriately titrated analgesia and sedation. Pain alone does not establish procedural success; adequacy of ablation is determined by target confirmation, angiography, hemodynamics, and subsequent remodeling.

Recognized intraprocedural complications include coronary dissection, anterior wall infarction from non-target ethanol delivery, cardiac perforation, ventricular arrhythmias requiring cardioversion, and hemodynamic collapse. These events are uncommon at experienced centers but should be anticipated during procedural preparation and monitored for throughout ethanol delivery.

Intraprocedural hemodynamic and ECG assessment

The LVOT gradient is recorded before balloon occlusion, during target-branch occlusion when informative, and after ethanol delivery. Measurements should include:

• Simultaneous LV and aortic pressures.
• Resting peak-to-peak LVOT gradient.
• Provoked gradient using Valsalva or post-extrasystolic potentiation when clinically appropriate.
• Heart rate and rhythm at the time of each measurement.

An acute gradient reduction is expected but does not represent the final hemodynamic result. Published procedural endpoints include a resting gradient below 25 mm Hg or a reduction greater than 50%, but thresholds vary among operators and are not standardized. The operator should avoid escalating ethanol volume solely to eliminate the acute gradient.

Continuous ECG monitoring should identify:

• New right bundle branch block.
• Transient or persistent atrioventricular block.
• Ventricular arrhythmias.
• Requirement for temporary pacing.

Transient atrioventricular block during or shortly after ethanol delivery has been reported in approximately 15%–50% of patients and is the principal reason for immediate temporary pacing capability. In one cohort, 86% of complete heart block events occurred within the first 24 hours, although delayed events were also observed. Detailed surveillance duration and permanent pacemaker criteria belong in the post-procedural management microchapter.

Immediate post-injection assessment

After the balloon dwell period:

1. Deflate and remove the balloon while monitoring for hemodynamic or ECG change.
2. Repeat coronary angiography to confirm LAD patency and preserved flow in non-target branches.
3. Assess for coronary dissection, thrombus, distal embolization, or unintended vessel occlusion.
4. Document the angiographic status of the treated septal perforator.
5. Repeat resting and provoked LVOT gradient measurements.
6. Confirm stable hemodynamics and rhythm.
7. Secure the temporary pacing lead when continued backup pacing is required.

Additional septal branches

The decision to treat an additional septal perforator during the same session or to allow remodeling before reassessment is not standardized. No randomized evidence establishes a superior single-session or staged strategy.

When an additional branch is considered, it must undergo the complete target-selection process independently, including balloon-seal verification, collateral assessment, and MCE confirmation. Residual acute obstruction alone should not justify ethanol injection into an inadequately characterized or non-target vessel.

Procedural endpoint

The procedure is complete when:

• The ablated territory was confirmed by MCE before ethanol administration.
• The minimum effective ethanol dose was delivered through a securely isolated septal perforator.
• Repeat angiography confirms LAD patency and absence of major coronary injury.
• Immediate hemodynamic assessment documents the post-ablation gradient without prompting unsafe pursuit of complete acute abolition.
• The patient has stable hemodynamics and an acceptable intrinsic or paced rhythm.
• Temporary pacing remains available for subsequent monitored care when indicated.