Alcohol septal ablation for hypertrophic obstructive cardiomyopathy periprocedural complications

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

Periprocedural complications

Periprocedural complications of alcohol septal ablation (ASA) include events occurring during the procedure, hospitalization, or within 30 days. Conduction disturbances are most frequent; less common but potentially fatal complications include ventricular arrhythmias, non-target myocardial infarction, coronary injury, cardiac tamponade, ventricular septal defect, stroke, and death. Complication rates vary with patient selection, procedural technique, ethanol volume, pacing thresholds, and institutional experience.

This microchapter describes complication incidence, mechanisms, risk factors, and prevention. Detailed post-procedural monitoring, temporary pacing management, permanent pacemaker timing, and long-term arrhythmic outcomes are addressed separately.

Contemporary complication profile

Reported rates differ among registries because of differences in case selection, operator experience, event definitions, and pacemaker practices.

Complication	Contemporary reported frequency	Clinical context
New right bundle branch block (RBBB)	Approximately 60%	Common consequence of target-septal injury; clinically important when baseline left-sided conduction disease is present
Transient atrioventricular block	Approximately 15%–50%	Usually begins during or shortly after ethanol injection
Permanent pacemaker implantation	Approximately 8%–11% in contemporary large registries	Usually results from persistent high-grade atrioventricular block
Sustained ventricular tachycardia or ventricular fibrillation	Approximately 1%–4%, depending on definition and registry	May occur during ethanol injection or within the first several days
LAD dissection	Approximately 0.9% in the North American Registry	Related to guide-catheter, wire, balloon, or injection injury
Cardiac perforation or tamponade	Approximately 0.5% in the North American Registry	May arise from temporary pacing, catheter, or coronary instrumentation
Ventricular septal defect	Approximately 0%–0.1% in contemporary series	Rare with contemporary low-volume, MCE-guided ablation
Stroke	Approximately 0.2% in the North American Registry	Related to catheterization, embolism, or peri-interventional arrhythmia
Periprocedural death	Approximately 0.2%–1.0% in contemporary registries	Strongly influenced by institutional and operator experience

Conduction disturbances

Conduction injury results from the proximity of the basal septal infarct to the atrioventricular conduction system and right bundle branch. New RBBB is common after ASA and is usually an expected ECG consequence rather than an isolated adverse clinical event. In patients with pre-existing left bundle branch block (LBBB), however, new right bundle injury can produce complete heart block.

Transient atrioventricular block occurs in approximately 15%–50% of patients, most often during ethanol injection or shortly afterward. In a 243-patient temporal analysis, 86% of complete heart block events occurred within 24 hours and 3.4% presented after 72 hours. A multinational study found that 97% of atrioventricular block events requiring permanent pacing occurred within five days.

Permanent pacemaker implantation is required in approximately 8%–11% of patients in contemporary large registries, although published rates vary because of differences in baseline conduction disease and institutional pacing thresholds. For context, a meta-analysis cited by the 2018 ACC/AHA/HRS bradycardia guideline estimated permanent pacemaker rates of approximately 10% after ASA compared with 4.4% after surgical myectomy.

Risk factors for permanent pacing

The Ablysinol product label identifies the following markers of permanent pacemaker dependency:

Timing	Risk marker
Baseline	PR/PQ interval greater than 160 ms
Baseline	Minimum heart rate less than 50 beats/min
Baseline	LVOT gradient greater than 70 mm Hg
Intraprocedural	Third-degree atrioventricular block during ASA
First 48 hours	Maximum QRS duration greater than 155 ms
First 48 hours	No clinical recovery of conduction between 12 and 48 hours

Additional risk factors reported in registry analyses include:

• Pre-existing bundle branch block, particularly LBBB.
• Older age, with progressively higher pacemaker rates across age groups.
• Higher ethanol volume.
• Lower basal septal thickness.
• More severe baseline functional limitation.
• Female sex in the Japanese J-SHD registry; this finding requires confirmation in other populations.

These factors support careful selection, use of the minimum effective ethanol volume, temporary pacing capability, and extended surveillance when conduction recovery is incomplete. Specific permanent pacemaker timing and monitoring protocols belong in the post-procedural management microchapter.

Ventricular arrhythmias

Sustained ventricular tachycardia or ventricular fibrillation may be triggered by acute ischemia, myocardial necrosis, conduction injury, or non-target ethanol delivery. The FDA label reports VT/VF requiring cardioversion in approximately 1% of patients. The North American Registry reported ventricular fibrillation in 1.6% and ventricular tachycardia in 3.9%; all reported events were successfully cardioverted.

The Japanese J-SHD registry reported ventricular arrhythmia in 0.63%. In a Chinese registry, higher ethanol volume and age 40 years or younger were independent predictors of lethal periprocedural ventricular arrhythmia; whether these associations are generalizable to other populations remains uncertain.

Immediate pacing and defibrillation capability should be available throughout the procedure. Long-term arrhythmic significance of the iatrogenic septal scar is outside the scope of this microchapter.

Non-target infarction and excessive myocardial necrosis

Retrograde ethanol leakage into the LAD or perfusion of an unrecognized collateral or remote myocardial territory may produce anterior wall, papillary muscle, right ventricular, or other non-target infarction.

Risk-reduction measures include:

• Myocardial contrast echocardiography confirmation of the target perfusion territory before ethanol administration.
• Verification of complete balloon occlusion and absence of retrograde leakage into the LAD.
• Selective angiography to exclude septal collateral filling of non-target coronary territories.
• Use of the minimum effective ethanol volume.
• Avoidance of ethanol injection when myocardial contrast distribution is indeterminate or extends beyond the intended basal septum.

The FDA label warns that higher ethanol volume and injection of a greater number of septal branches increase the risk of excessive myocardial necrosis. Infarct size increases with ethanol volume, whereas gradient reduction is not proportionally dose-dependent, supporting a low-volume, territory-guided approach.

Coronary and structural complications

Coronary or structural injury may result from guide-catheter manipulation, septal perforator wiring, balloon instrumentation, temporary pacing, or unintended ethanol delivery.

Complication	Typical mechanism or finding	Contemporary evidence
LAD dissection	Guide-catheter, wire, balloon, or injection injury	0.9% in the North American Registry
Acute LAD or non-target infarction	Retrograde ethanol leakage, balloon displacement, collateral flow, thrombosis, or coronary occlusion	Uncommon; risk reduced by balloon-seal verification and MCE guidance
Cardiac perforation or tamponade	Temporary pacing lead, coronary wire, or catheter-related perforation	0.5% in the North American Registry
Ventricular septal defect	Excessive septal necrosis	0.1% in the North American Registry and absent in a large contemporary Euro-ASA cohort
Acute pulmonary edema	Acute hemodynamic deterioration, ischemia, or mitral regurgitation	0.2% in the North American Registry

Repeat angiography after ethanol delivery should confirm LAD patency and exclude dissection, thrombosis, unintended occlusion, or impaired non-target coronary flow. Sudden hypotension, chest-pain severity disproportionate to the expected septal infarction, new pericardial effusion, or extensive ST-segment change should prompt immediate evaluation for coronary or structural injury.

Cerebrovascular and vascular-access complications

Stroke is uncommon; the North American Registry reported stroke in 2 of 874 patients (0.2%). A French nationwide observational comparison found a lower risk of all-cause stroke with ASA than with surgical myectomy (adjusted incidence rate ratio 0.18, 95% CI 0.06–0.55). This administrative-database comparison does not establish causal superiority of ASA. Potential stroke mechanisms include catheter-related embolism, thrombus, air embolism, and peri-interventional atrial arrhythmia.

Reported access-site complications in the North American Registry included:

• Arteriovenous fistula: 2 of 874 patients.
• Femoral pseudoaneurysm: 2 of 874 patients.
• Groin hematoma: 2 of 874 patients.
• Retroperitoneal hemorrhage: 1 of 874 patients.

Prevention and management follow standard principles for coronary catheterization and percutaneous coronary intervention.

Periprocedural mortality

Contemporary high-volume cohorts generally report periprocedural mortality below 1%, although estimates vary by population and definition:

• Euro-ASA Registry: 1% 30-day mortality among 1,275 patients.
• Batzner single-center registry: 0.21% periprocedural mortality among 952 patients.
• Japanese J-SHD registry: 0.16% in-hospital mortality among 634 patients.
• SHARE international registry: 0.4% 30-day mortality across the septal reduction therapy cohort at 13 international HCM centers; the registry included 455 ASA-treated patients.

Potential fatal mechanisms include complete heart block, ventricular arrhythmia, non-target myocardial infarction, coronary dissection, tamponade, stroke, and hemodynamic collapse.

Volume-outcome relationship

Institutional and operator experience are important modifiable determinants of periprocedural risk. In a Euro-ASA analysis, procedures performed within a center's first 50 ASA cases were associated with higher 30-day major cardiovascular adverse events (21% versus 12%), cardiovascular mortality (2.1% versus 0.4%), and permanent pacemaker implantation (15% versus 9%).

A US database analysis found nearly threefold higher adjusted 30-day mortality with low-volume compared with high-volume operators. Among patients 65 years or older, a CMS analysis found 30-day mortality ranging from 3.1% at the lowest-volume centers to 1.4% at the highest-volume centers.

A 2025 Euro-ASA follow-up found that patients treated during a center's first 50 procedures had lower odds of achieving a complete clinical and hemodynamic response (OR 0.49, 95% CI 0.34–0.71). Although this was an effectiveness rather than a complication endpoint, it further supports a meaningful institutional learning curve.

Current guidelines recommend that septal reduction therapy be performed by experienced operators at comprehensive HCM centers.

Risk-reduction principles

• Perform ASA at a comprehensive HCM center with experienced operators.
• Review baseline conduction disease, particularly LBBB and prolonged atrioventricular conduction.
• Establish reliable temporary pacing before ethanol administration unless dependable permanent pacing is already present.
• Confirm target perfusion with myocardial contrast echocardiography before every ethanol injection.
• Verify complete balloon seal and exclude non-target collateral filling.
• Use the minimum effective ethanol volume and avoid pursuing complete acute gradient abolition with additional ethanol.
• Maintain immediate defibrillation and resuscitation capability.
• Perform repeat coronary angiography and hemodynamic assessment before concluding the procedure.
• Continue rhythm surveillance according to conduction findings and the post-procedural monitoring protocol.